TY - JOUR A1 - Peter, Daniel A1 - Dalmer, Michael A1 - Lechner, Alfred A1 - Gigler, Alexander M. A1 - Stark, Robert W. A1 - Bensch, Wolfgang T1 - The influence of liquid media on the fracture strength of polysilicon nanostructures JF - Solid State Phenomena N2 - The mechanical stability of nanostructures depends on the surrounding medium. Their stability was probed by lateral force microscopy in liquid media. Previously reported data on water and isopropanol showed an increase in the fracture strength for the latter. Further tests with other alcohols (ethanol, 1-butanol) also showed an increasing strength. The interface between the liquid and the surface is the decisive factor for the influence of the media. When altering the interface with a cationic surfactant or a self-assembled monolayer, an increase of the fracture force by 100 % compared to de-ionized water could be measured. KW - pattern collapse KW - fracture strength KW - damage KW - atomic force microscopy Y1 - 2012 U6 - https://doi.org/10.4028/www.scientific.net/SSP.187.127 VL - 187 SP - 127 EP - 130 PB - Trans Tech Publications ER - TY - JOUR A1 - Pangerl, Jonas A1 - Sukul, Pritam A1 - Rück, Thomas A1 - Escher, Lukas A1 - Miekisch, Wolfram A1 - Bierl, Rudolf A1 - Matysik, Frank-Michael T1 - Photoacoustic trace-analysis of breath isoprene and acetone via interband- and Quantum Cascade Lasers JF - Sensors and Actuators: B. Chemical N2 - This research presents two laser-based photoacoustic approaches for analyzing exhaled breath isoprene and acetone. The integration of a PTR-ToF-MS as a reference device ensured the reliability and accuracy of the photoacoustic systems that is based on an ICL for isoprene and a QCL for acetone detection. The calibration yielded limits of detection of 26.9 ppbV and 1.7 ppbV, respectively, and corresponding normalized noise equivalent absorption coefficients (NNEAs) of 5.0E-9 Wcm 1Hz 0.5 and 4.9E-9 Wcm 1Hz 0.5. Laboratory as well as real breath sample measurements from alveolar breath revealed a robust system performance, with only one outlier within the static isoprene measurements. However, discrepancies emerged under dynamic breath sampling conditions, emphasizing the need for further optimization. Especially by knowing the dynamic nature and endogenous origin of exhaled isoprene our findings highlight the potential of breath analysis for non-invasive physio-metabolic and pathophysiological monitoring towards point-of-care devices KW - Photoacoustic spectroscopy KW - Breath analysis/profiling KW - Real-time mass spectrometry KW - Isoprene KW - Acetone Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-77024 N1 - Corresponding author der OTH Regensburg: Jonas Pangerl VL - 424 PB - Elsevier ER - TY - JOUR A1 - Rück, Thomas A1 - Pangerl, Jonas A1 - Escher, Lukas A1 - Jobst, Simon A1 - Müller, Max A1 - Bierl, Rudolf A1 - Matysik, Frank-Michael T1 - Kinetic cooling in mid-infrared methane photoacoustic spectroscopy: A quantitative analysis via digital twin verification JF - Photoacoustics N2 - This study presents a detailed quantitative analysis of kinetic cooling in methane photoacoustic spectroscopy, leveraging the capabilities of a digital twin model. Using a quantum cascade laser tuned to 1210.01 cm⁻¹, we investigated the effects of varying nitrogen-oxygen matrix compositions on the photoacoustic signals of 15 ppmV methane. Notably, the photoacoustic signal amplitude decreased with increasing oxygen concentration, even falling below the background signal at oxygen levels higher than approximately 6 %V. This phenomenon was attributed to kinetic cooling, where thermal energy is extracted from the surrounding gas molecules rather than added, as validated by complex vector analysis using a previously published digital twin model. The model accurately reproduced complex signal patterns through simulations, providing insights into the underlying molecular mechanisms by quantifying individual collision contributions. These findings underscore the importance of digital twins in understanding the fundamentals of photoacoustic signal generation at the molecular level. Y1 - 2024 U6 - https://doi.org/10.1016/j.pacs.2024.100652 VL - 40 PB - Elsevier ER - TY - JOUR A1 - Leonhardt, Carina A1 - Guertler, Katherine T1 - Unearthing Corporate Greenwashing: A Content Analysis of Sustainability Reporting in the Mining Sector JF - Tripodos N2 - Greenwashing is a common form of corporate disinformation that is often challenging for the general public to detect. Companies engage in greenwashing in their reporting to mislead shareholders and stakeholders about their environmental efforts, seeking to enhance legitimacy and gain competitive advantages. While systems for identifying greenwashing exist, they typically focus on advertising, leaving greenwashing in corporate reports underexamined. This study aims to address this gap by conducting a qualitative content analysis of a climate report from a mining and commodity trading company, considering the company’s profile, the report’s target audience, and current research. The findings reveal that the company employs numerous subtle greenwashing strategies to project a more sustainable image through strategic omissions, hedging and vague long-term goals. Moreover, this research broadens the scope of greenwashing analysis to include corporate reporting, which targets a more informed audience, such as shareholders and experts, rather than the general public. The results underscore the need for stricter regulation of sustainability reports and highlight the importance of fostering greater scrutiny among shareholders. KW - climate communication KW - corporate communication KW - greenwashing KW - sustainability reporting Y1 - 2025 U6 - https://doi.org/10.51698/tripodos.2025.57.06 SN - 1138-3305 VL - 2025 IS - 57 SP - 78 EP - 97 PB - Blanquerna School of Communication and International Relations CY - Barcelona ER - TY - JOUR A1 - Jobst, Simon A1 - Recum, Patrick A1 - Écija-Arenas, Ángela A1 - Moser, Elisabeth A1 - Bierl, Rudolf A1 - Hirsch, Thomas T1 - Semi-Selective Array for the Classification of Purines with Surface Plasmon Resonance Imaging and Deep Learning Data Analysis JF - ACS sensors N2 - In process analytics or environmental monitoring, the real-time recording of the composition of complex samples over a long period of time presents a great challenge. Promising solutions are label-free techniques such as surface plasmon resonance (SPR) spectroscopy. They are, however, often limited due to poor reversibility of analyte binding. In this work, we introduce how SPR imaging in combination with a semi-selective functional surface and smart data analysis can identify small and chemically similar molecules. Our sensor uses individual functional spots made from different ratios of graphene oxide and reduced graphene oxide, which generate a unique signal pattern depending on the analyte due to different binding affinities. These patterns allow four purine bases to be distinguished after classification using a convolutional neural network (CNN) at concentrations as low as 50 μM. The validation and test set classification accuracies were constant across multiple measurements on multiple sensors using a standard CNN, which promises to serve as a future method for developing online sensors in complex mixtures. KW - surface plasmon resonance imaging KW - functional surface KW - graphene oxide KW - reduced graphene oxide KW - 2D materials KW - pattern recognition KW - small-molecule sensing Y1 - 2023 U6 - https://doi.org/10.1021/acssensors.3c01114 VL - 8 IS - 9 SP - 3530 EP - 3537 PB - American Chemical Society ER - TY - JOUR A1 - Genslein, Christa A1 - Hausler, Peter A1 - Kirchner, Eva-Maria A1 - Bierl, Rudolf A1 - Baeumner, Antje J. A1 - Hirsch, Thomas T1 - Graphene-enhanced plasmonic nanohole arrays for environmental sensing in aqueous samples JF - Beilstein Journal of Nanotechnology N2 - The label-free nature of surface plasmon resonance techniques (SPR) enables a fast, specific, and sensitive analysis of molecular interactions. However, detection of highly diluted concentrations and small molecules is still challenging. It is shown here that in contrast to continuous gold films, gold nanohole arrays can significantly improve the performance of SPR devices in angle-dependent measurement mode, as a signal amplification arises from localized surface plasmons at the nanostructures. This leads consequently to an increased sensing capability of molecules bound to the nanohole array surface. Furthermore, a reduced graphene oxide (rGO) sensor surface was layered over the nanohole array. Reduced graphene oxide is a 2D nanomaterial consisting of sp2-hybridized carbon atoms and is an attractive receptor surface for SPR as it omits any bulk phase and therefore allows fast response times. In fact, it was found that nanohole arrays demonstrated a higher shift in the resonance angle of 250–380% compared to a continuous gold film. At the same time the nanohole array structure as characterized by its diameter-to-periodicity ratio had minimal influence on the binding capacity of the sensor surface. As a simple and environmentally highly relevant model, binding of the plasticizer diethyl phthalate (DEP) via π-stacking was monitored on the rGO gold nanohole array realizing a limit of detection of as low as 20 nM. The concentration-dependent signal change was studied with the best performing rGO-modified nanohole arrays. Compared to continuous gold films a diameter-to-periodicity ratio (D/P) of 0.43 lead to a 12-fold signal enhancement. Finally, the effect of environmental waters on the sensor was evaluated using samples from sea, lake and river waters spiked with analytically relevant amounts of DEP during which significant changes in the SPR signal are observed. It is expected that this concept can be successfully transferred to enhance the sensitivity in SPR sensors. KW - diethyl phthalate KW - environmental sensing KW - nanohole array KW - nanosphere lithography KW - surface plasmon resonance Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:355-epub-398623 IS - 7 SP - 1564 EP - 1573 ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Blome, Christian A1 - Blums, Juris A1 - Dietrich, Clemens A1 - Tarsevitch, Alexander A1 - Horn-von Hoegen, Michael A1 - von der Linde, Dietrich A1 - Cavalleri, Andrea A1 - Kammler, Martin A1 - Uschmann, Ingo A1 - Foerster, Eckhart T1 - Femtosecond X-ray Diffraction Study of Large Amplitude Coherent Optical Phonons in Laser-Excited Bismuth JF - Conference on Lasers and Electro-Optics, 1–6 June 2003, Baltimore, Maryland N2 - Femtosecond time-resolved X-ray diffraction was used to directly study optical phonons in laser-excited Bismuth. A periodic modulation of the diffraction efficiency reveals initially coherent lattice distortions with atomic displacements of nearly 10% of the nearest- neighbor-distance. Y1 - 2003 UR - https://opg.optica.org/abstract.cfm?uri=cleo-2003-CMZ6 PB - Optical Society of America ER - TY - JOUR A1 - Lindner, Matthias A1 - Pipa, Andrei V. A1 - Karpen, Norbert A1 - Hink, Rüdiger A1 - Berndt, Dominik A1 - Foest, Rüdiger A1 - Bonaccurso, Elmar A1 - Weichwald, Robert A1 - Friedberger, Alois A1 - Caspari, Ralf A1 - Brandenburg, Ronny A1 - Schreiner, Rupert T1 - Icing Mitigation by MEMS-Fabricated Surface Dielectric Barrier Discharge JF - Applied Sciences N2 - Avoiding ice accumulation on aerodynamic components is of enormous importance to flight safety. Novel approaches utilizing surface dielectric barrier discharges (SDBDs) are expected to be more efficient and effective than conventional solutions for preventing ice accretion on aerodynamic components. In this work, the realization of SDBDs based on thin-film substrates by means of micro-electro-mechanical-systems (MEMS) technology is presented. The anti-icing performance of the MEMS SDBDs is presented and compared to SDBDs manufactured by printed circuit board (PCB) technology. It was observed that the 35 mu m thick electrodes of the PCB SDBDs favor surface icing with an initial accumulation of supercooled water droplets at the electrode impact edges. This effect was not observed for 0.3 mu m thick MEMS-fabricated electrodes indicating a clear advantage for MEMS-technology SDBDs for anti-icing applications. Titanium was identified as the most suitable material for MEMS electrodes. In addition, an optimization of the MEMS-SDBDs with respect to the dielectric materials as well as SDBD design is discussed. KW - aerospace engineering KW - anti-icing KW - DBD PLASMA ACTUATORS KW - EXCITATION KW - FLOW-CONTROL KW - low-temperature plasma KW - MEMS KW - SEPARATION CONTROL KW - SDBD Y1 - 2021 U6 - https://doi.org/10.3390/app112311106 N1 - Corresponding author: Matthias Lindner VL - 11 IS - 23 SP - 1 EP - 17 PB - MDPI CY - Basel ER - TY - JOUR A1 - Wall, Simone A1 - Krenzer, Boris A1 - Wippermann, Stefan A1 - Sanna, Simone A1 - Klasing, Friedrich A1 - Hanisch-Blicharski, Anja A1 - Kammler, Martin A1 - Schmidt, Wolf Gero A1 - Horn-von Hoegen, Michael T1 - Atomistic picture of charge density wave formation at surfaces JF - Physical review letters N2 - We used ultrafast electron diffraction and density-functional theory calculations to gain insight into the charge density wave (CDW) formation on In/Si(111). Weak excitation by a femtosecond-laser pulse results in the melting of the CDW. The immediate freezing is hindered by a barrier for the motion of atoms during the phase transition: The melted CDW constitutes a long-lived, supercooled phase and is strong evidence for a first-order transition. The freezing into the CDW is triggered by preexisting adsorbates. Starting at these condensation nuclei, the CDW expands one dimensionally on the In/Si(111) surface, with a constant velocity of more than 80 m/s. Y1 - 2012 U6 - https://doi.org/10.1103/PhysRevLett.109.186101 VL - 109 IS - 18 PB - APS ER - TY - JOUR A1 - Frigge, Tim A1 - Kalus, Annika A1 - Klasing, Friedrich A1 - Kammler, Martin A1 - Hanisch-Blicharski, Anja A1 - Horn-von Hoegen, Michael T1 - Nanoscale Heat Transport in Self-Organized Ge Clusters on Si(001) JF - MRS Online Proceedings Library N2 - Ultrafast time resolved transmission electron diffraction (TED) in a reflection geometry was used to study the cooling behavior of self-organized, well defined nanoscale germanium hut and dome clusters on Si(001). The clusters were heated in a pump-probe scheme by fs-laser pulses. The resulting transient temperature rise was then determined from the drop in diffraction intensity caused by the Debye-Waller effect. From a cooling time of τ=177 ps we estimated a strongly reduced heat transfer compared with homogeneous films of equivalent thickness. Y1 - 2012 U6 - https://doi.org/10.1557/opl.2013.148 SP - 45 EP - 50 PB - Springer ER - TY - JOUR A1 - Möllenbeck, Simone A1 - Hanisch-Blicharski, Anja A1 - Schneider, Paul A1 - Ligges, Manuel A1 - Zhou, Ping A1 - Kammler, Martin A1 - Krenzer, Boris A1 - Horn-von Hoegen, Michael T1 - Ultra-fast Time-Resolved Electron Diffraction of Strongly Driven Phase Transitions on Silicon Surfaces JF - MRS Online Proceedings Library N2 - The dynamics of strongly driven phase transitions at surfaces are studied by ultra-fast time-resolved reflection high energy electron diffraction. The surfaces are excited by an intense fs-laser pulse (pump) and probed by an ultra-short electron pulse with variable time delay. The order-disorder phase transition from a c(4 × 2) to a(2 × 1) of the bare Si(001) surface shows a transient decrease of the intensity of the c(4 × 2) spots which recovers on a time scale of a few hundred picoseconds indicating the excitation of the phase transition. On Si(111) a monolayer of Indium induces a (4 × 1) reconstruction which undergoes a Peierls like phase transition to a (8 × "2") reconstruction below 100 K. Upon laser excitation with a fluence of 3.4 mJ/cm 2 at a temperature of 72 K the phase transition was strongly driven. The (8 × "2")-diffraction spots instantaneously disappears, while the intensity of the (4 × 1)-spots increases. This increase of the (4 × 1) spot intensity excludes an explanation by the Debye-Waller-Effect and is evidence for a true structural phase transition at a surface. © 2010 Materials Research Society. Y1 - 2009 U6 - https://doi.org/10.1557/PROC-1230-MM03-09 PB - Springer ER - TY - JOUR A1 - Lu, Wei A1 - Nicoul, Matthieu A1 - Shymanovich, Uladzimir A1 - Tarsevitch, Alexander A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael A1 - von der Linde, Dietrich A1 - Sokolowski-Tinten, Klaus T1 - Extreme Phonon Softening in Laser-excited Bismuth - Towards an Inverse Peierls-transition JF - MRS Online Proceedings Library N2 - Large amplitude coherent optical phonons have been investigated in laser-excited Bismuth by means of femtosecond time-resolved X-ray diffraction. For absorbed laser fluences above 2 mJ/cm2, the experimental data reveal an extreme softening of the excited A1g-mode down to frequencies of about 1 THz, only 1/3 of the unperturbed A1g-frequency. At even stronger excitation the measured diffraction signals no longer exhibit an oscillatory behavior presenting strong indication that upon intense laser-excitation the Peierls-distortion, which defines the equilibrium structure of Bismuth, can be transiently reversed. Y1 - 2009 U6 - https://doi.org/10.1557/PROC-1230-MM03-05 VL - 1230 PB - Springer ER - TY - JOUR A1 - Hanisch-Blicharski, Anja A1 - Krenzer, Boris A1 - Möllenbeck, Simone A1 - Ligges, Manuel A1 - Zhou, Ping A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael T1 - Transient Cooling of Ultrathin Epitaxial Bi(111)-Films on Si(111) Upon Femtosecond Laser Excitation Studied by Ultrafast Reflection High Energy Electron Diffraction JF - MRS Online Proceedings Library N2 - With time resolved ultrafast electron diffraction the cooling process across the interface between a thin film and the underlying substrate was studied after excitation with short laser pulses. From the exponential decay of the surface temperature evolution a thermal boundary conductance of 1430 W/(cm2K) is determined for a 9.7 nm thin Bi(111) film on Si(111). A linear dependence between laser fluence and initial temperature rise was measured for film-thicknesses between 2.5 nm and 34.5 nm. The ratio of initial temperature rise and laser fluence for different film-thicknesses is compared to a model taking multilayer optics into account. The data agree well with this model. Y1 - 2009 U6 - https://doi.org/10.1557/PROC-1172-T04-08 SP - 1 EP - 6 PB - Springer ER - TY - JOUR A1 - Al-Falou, A. A. A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael T1 - Strain state analysis of hetero-epitaxial systems JF - Europhysics Letters N2 - We present a new method to analyze the strain state of epitaxial hetero structures by high-resolution spot profile analysis low-energy electron diffraction. From the variation of the spot profiles with the vertical scattering vector we determine the hetero film roughness, the change of interlayer spacing due to tetragonal distortion, and the variation of the interlayer distance due to partial relaxation of the strained rough film. The practical implementation of this method is simple and can be used to determine the onset of strain-relieving defects during the growth process. Y1 - 2005 U6 - https://doi.org/10.1209/epl/i2004-10399-6 VL - 69 IS - 4 SP - 570 EP - 576 PB - IOP ER - TY - JOUR A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael T1 - Low energy electron diffraction of epitaxial growth of bismuth on Si(111) JF - Surface Science N2 - The epitaxial growth of Bi on Si(1 1 1) studied by spot profile analyzing low energy electron diffraction shows for low coverage rotationally disordered Bi cluster with preferred orientations following the threefold symmetry of the Si substrate. With further deposition the Bi cluster coalesces and the surface orientation changes from the pseudo cubic Bi(1 1 0) surface orientation of the Bi cluster into the hexagonal Bi(1 1 1) surface of the resulting Bi film. KW - Bismuth KW - Epitaxial growth KW - LEED KW - low energy electron diffraction KW - Silicon KW - Structural transition Y1 - 2005 U6 - https://doi.org/10.1016/j.susc.2004.11.033 VL - 576 IS - 1-3 SP - 56 EP - 60 PB - Elsevier ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Blome, Christian A1 - Blums, Juris A1 - Cavalleri, Andrea A1 - Dietrich, Clemens A1 - Tarasevitch, Alexander A1 - Uschmann, Ingo A1 - Förster, Eckhard A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael A1 - von der Linde, Dietrich T1 - Femtosecond X-ray measurement of coherent lattice vibrations near the Lindemann stability limit JF - Nature N2 - The study of phase-transition dynamics in solids beyond a time-averaged kinetic description requires direct measurement of the changes in the atomic configuration along the physical pathways leading to the new phase. The timescale of interest is in the range 10(-14) to 10(-12) s. Until recently, only optical techniques were capable of providing adequate time resolution, albeit with indirect sensitivity to structural arrangement. Ultrafast laser-induced changes of long-range order have recently been directly established for some materials using time-resolved X-ray diffraction. However, the measurement of the atomic displacements within the unit cell, as well as their relationship with the stability limit of a structural phase, has to date remained obscure. Here we report time-resolved X-ray diffraction measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition. Excitation of large-amplitude coherent optical phonons gives rise to a periodic modulation of the X-ray diffraction efficiency. Stronger excitation corresponding to atomic displacements exceeding 10 per cent of the nearest-neighbour distance-near the Lindemann limit-leads to a subsequent loss of long-range order, which is most probably due to melting of the material. Y1 - 2003 U6 - https://doi.org/10.1038/nature01490 VL - 422 IS - 6929 SP - 287 EP - 289 PB - Springer ER - TY - JOUR A1 - Hild, R. A1 - Seifert, C. A1 - Kammler, Martin A1 - Meyer zu Heringdorf, Frank-Joachim A1 - Horn-von Hoegen, Michael A1 - Zhachuk, R.A A1 - Olshanetsky, B.Z T1 - Kinetics of Au induced faceting of vicinal Si(111) JF - Surface Science N2 - Au induced faceting of vicinal Si(1 1 1) has been studied during adsorption at elevated temperature by spot profile analyzing of low energy electron diffraction and after quenching to room temperature by scanning tunneling microscopy. On the surfaces inclined towards five different types of facets form with increasing Au coverage at adsorption temperatures Tads below 800 °C. They are (4 4 3), (7 7 5), (5 5 3), a stepped (2 2 1), and the (3 3 1) facets. Atomic models for the (5 5 3) and (7 7 5) facet planes are proposed on the basis of high resolution STM images. At C we found the formation of an ordered step train which covers the entire surface. With further increasing Au coverage the stepped surface decomposes again into (1 1 1) terraces and step bunches. Driving force is the formation of the Si(1 1 1)-(5×2)–Au reconstruction. KW - Low energy electron diffraction (LEED) KW - Scanning tunneling microscopy KW - Silicon KW - Gold KW - Faceting KW - Adsorption kinetics KW - Step formation and bunching Y1 - 2002 U6 - https://doi.org/10.1016/S0039-6028(02)01666-7 VL - 512 IS - 1-2 SP - 117 EP - 127 PB - Elsevier ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Leitner, D. M. A1 - Tóth, Csaba A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. A1 - Kammler, Martin T1 - Transient lattice dynamics in fs-laser-excited semiconductors probed by ultrafast X-ray diffraction JF - Journal de Physique IV N2 - A study of lattice dynamics in fs-laser-excited crystalline bulk Ge and Ge/Si-heterostructures, using time-resolved x-ray diffraction, was presented. Fast energy transport deep into the bulk of the material, coherent acoustic phonon dynamics, lattice anharmonicity, and vibrational transport across a buried interfaces were observed. Graphs showing time-dependent shifts of the centroid of the measured rocking curves in the Ge-overlayer and in the Si-substrate for different fluences, were presented. Y1 - 2001 U6 - https://doi.org/10.1051/jp4:2001290 VL - 11 IS - Pr2 SP - 473 EP - 477 PB - EDP ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Leitner, D. M. A1 - Tóth, Csaba A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. T1 - Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures JF - Chemical Physics N2 - Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed. Y1 - 2001 U6 - https://doi.org/10.1007/978-3-642-56546-5_81 VL - 66 SP - 281 EP - 283 PB - Springer ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Blome, Christian A1 - Dietrich, Clemens A1 - Tarasevitch, A. A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Cavalleri, Andrea A1 - Squier, Jeff A. A1 - Kammler, Martin T1 - Femtosecond x-ray measurement of ultrafast melting and large acoustic transients JF - Physical review letters N2 - Time-resolved x-ray diffraction with ultrashort ( approximately 300 fs), multi-keV x-ray pulses has been used to study the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germanium. Nonthermal melting is observed to take place within 300-500 fs. Following ultrafast melting we observe strong acoustic perturbations evolving on a picosecond time scale. Y1 - 2001 U6 - https://doi.org/10.1103/PhysRevLett.87.225701 VL - 87 PB - APS ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Blome, Christian A1 - Dietrich, Clemens A1 - Tarasevitch, A. A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Cavalleri, Andrea A1 - Squier, Jeff A. A1 - Kammler, Martin T1 - Femtosecond time-resolved X-ray diffraction study of ultrafast structural dynamics in laser-excited solids JF - International Conference on Ultrafast Phenomena, 12 May 2002, Vancouver Canada N2 - Time-resolved x-ray diffraction with sub-300 fs, multi-keV x-ray pulses was used to study ultrafast lattice dynamics in laser-irradiated germanium and bismuth. In bismuth strong excitation of optical phonons is observed prior to disordering of the material. Y1 - 2002 U6 - https://doi.org/10.1007/978-3-642-59319-2_10 VL - 71 SP - 36 EP - 38 PB - Optica Publishing Grou ER - TY - JOUR A1 - Horn-von Hoegen, Michael A1 - Meyer zu Heringdorf, Frank-Joachim A1 - Kammler, Martin A1 - Schaeffer, C. A1 - Reinking, D. A1 - Hofmann, K. R. T1 - Bi surfactant mediated epitaxy of Ge on Si(111) JF - Thin Solid Films N2 - We have tested Bi for the surfactant mediated epitaxy of Ge on Si(111). Islanding of Ge is prevented and a 2D layer growth of smooth and continuous Ge films is observed. The lattice mismatch is accommodated by a periodic array of dislocations confined to the Si/Ge interface. The large covalent radius of Bi reduces the binding energy, allowing Very efficient segregation and low doping levels even at low growth temperatures. Unfortunately, this results also in a high Bi desorption flux limiting the possible growth temperatures below 600 degrees C. Consequently the Ge films show a high defect density in the order of 10(8) cm(-2) for stacking faults and 10(9) cm(-2) for dislocations which limit electron Hall mobility to values below 700 cm(2)/V s at room temperature. KW - Hall mobility KW - Heteroepitaxial growth KW - Surfactants KW - Doping KW - Molecular beam epitaxy KW - Silicon KW - Germanium KW - Bismuth KW - Low energy electron diffraction KW - Scanning electron microscopy Y1 - 1999 U6 - https://doi.org/10.1016/S0040-6090(98)01659-9 VL - 343-344 SP - 579 EP - 582 PB - Elsevier ER - TY - JOUR A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Leitner, D. M. A1 - Tóth, Csaba A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. A1 - Sokolowski-Tinten, Klaus A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Kammler, Martin T1 - Anharmonic lattice dynamics in germanium measured with ultrafast x-ray diffraction JF - Physical review letters N2 - Damping of impulsively generated coherent acoustic oscillations in a femtosecond laser-heated thin germanium film is measured as a function of fluence by means of ultrafast x-ray diffraction. By simultaneously measuring picosecond strain dynamics in the film and in the unexcited silicon substrate, we separate anharmonic damping from acoustic transmission through the buried interface. The measured damping rate and its dependence on the calculated temperature of the thermal bath is consistent with estimated four-body, elastic dephasing times (T2) for 7-GHz longitudinal acoustic phonons in germanium. Y1 - 2000 U6 - https://doi.org/10.1103/PhysRevLett.85.586 VL - 85 IS - 3 SP - 586 EP - 589 PB - APS ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. A1 - Cavalleri, Andrea A1 - Siders, C. W. A1 - Brown, F. L. H. A1 - Tóth, Csaba A1 - Squier, Jeff A. A1 - Barty, C. P. J. A1 - Wilson, K. R. A1 - Kammler, Martin T1 - Time-resolved x-ray diffraction study of ultrafast acoustic phonon dynamics in Ge/Si-heterostructures JF - International Conference on Ultrafast Phenomena , 9 July 2000, Charleston N2 - Using time-resolved x-ray diffraction the ultafast strain dynamics in fs-laserexcited Ge/Si-heterostructures has been studied. A fluence dependent, anharmonic damping of the impulsively generated acoustic phonons and vibrational transport across the buried Ge/Si-interface are observed. KW - Acoustic Phonon KW - Acoustic Transmission KW - Carrier Diffusion KW - Homogenous Expansion KW - Lattice Anharmonicity Y1 - 2000 UR - https://opg.optica.org/abstract.cfm?uri=UP-2000-MF43 PB - Optica ER - TY - JOUR A1 - Siders, C. W. A1 - Cavalleri, Andrea A1 - Sokolowski-Tinten, Klaus A1 - Tóth, Csaba A1 - Guo, T. A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael A1 - Wilson, K. R. A1 - von der Linde, D. A1 - Barty, C. P. J. T1 - Detection of nonthermal melting by ultrafast X-ray diffraction JF - Science N2 - Using ultrafast, time-resolved, 1.54 angstrom x-ray diffraction, thermal and ultrafast nonthermal melting of germanium, involving passage through nonequilibrium extreme states of matter, was observed. Such ultrafast, optical-pump, x-ray diffraction probe measurements provide a way to study many other transient processes in physics, chemistry, and biology, including direct observation of the atomic motion by which many solid-state processes and chemical and biochemical reactions take place. Y1 - 1999 U6 - https://doi.org/10.1126/science.286.5443.1340 VL - 286 IS - 5443 SP - 1340 EP - 1342 ER - TY - JOUR A1 - Reinking, D. A1 - Kammler, Martin A1 - Hoffmann, N. A1 - Horn-von Hoegen, Michael A1 - Hofmann, K. R. T1 - Fabrication of high-mobility Ge p-channel MOSFETs on Si substrates JF - Electronics Letters N2 - The first fabrication of Ge p-channel MOSFETs (p-MOSFETs) on Si substrates is reported. A CMOS compatible process based on relaxed Ge layers grown on Si(111) substrates by surfactant mediated epitaxy (SME) was used. The non-optimised low temperature process yielded normally-off Ge p-MOSFETs with record channel drift mobilities of 430 cm2/Vs KW - silicon KW - CMOS integrated circuits KW - germanium KW - carrier mobility KW - epitaxial growth KW - integrated circuit technology KW - elemental semiconductors KW - semiconductor growth KW - MOSFET KW - Insulated gate field effect transistors KW - Thin film growth and epitaxy Y1 - 1999 U6 - https://doi.org/10.1049/el:19990349 VL - 35 IS - 6 SP - 503 EP - 504 PB - IET ER - TY - JOUR A1 - Siders, C. W. A1 - Cavalleri, Andrea A1 - Sokolowski-Tinten, Klaus A1 - Tóth, Csaba A1 - Guo, T. A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael A1 - Wilson, K. R. A1 - von der Linde, D. A1 - Barty, C. P. J. T1 - Direct Observation of Ultrafast Non-thermal Melting by Ultrafast X-ray Diffraction JF - Ultrafast Phenomena XII N2 - Ultrafast nonthermal melting of femtosecond laser-irradiated germanium was observed directly for the first time using sub-picosecond, 1.54-angstrom x-ray diffraction. Such measurements allow the study of transient atomic motion fundamental to many processes in physics, chemistry, and biology. Y1 - 2000 U6 - https://doi.org/10.1007/978-3-642-56546-5_80 VL - 66 SP - 276 EP - 280 PB - Springer ER - TY - JOUR A1 - Schmidt, Thomas A1 - Kröger, Roland A1 - Flege, Jan Ingo A1 - Horn-von Hoegen, Michael A1 - Clausen, T. A1 - Falta, J. A1 - Janzen, Andreas A1 - Zahl, P. A1 - Kury, P. A1 - Kammler, Martin T1 - Less strain energy despite fewer misfit dislocations: the impact of ordering JF - Physical review letters N2 - The average strain state of Ge films grown on Si(111) by surfactant mediated epitaxy has been compared to the ordering of the interfacial misfit dislocation network. Surprisingly, a smaller degree of average lattice relaxation was found in films grown at higher temperature. On the other hand, these films exhibit a better ordered dislocation network. This effect energetically compensates the higher strain at higher growth temperature, leading to the conclusion that, apart from the formation of misfit dislocations, their ordering represents an important channel for lattice-strain energy relaxation. Y1 - 2006 U6 - https://doi.org/10.1103/PhysRevLett.96.066101 VL - 96 IS - 6 PB - APS ER - TY - JOUR A1 - Hull, Robert A1 - Gray, J. L. A1 - Kammler, Martin A1 - Vandervelde, T. A1 - Kobayashi, Takeshi A1 - Kumar, P. A1 - Pernell, T. A1 - Bean, J. C. A1 - Floro, J. A. A1 - Ross, Frances M. T1 - Precision placement of heteroepitaxial semiconductor quantum dots JF - Materials Science and Engineering: B N2 - We describe two new approaches to the patterning of Si(1 0 0) surfaces for controlled nucleation of heteroepitaxial Ge semiconductor clusters. In the first method, a Ga ' -focused ion beam in situ to the growth chamber is used to create local regions of enhanced Ga ' concentration and surface topography. It is shown that at low ion doses (Â/10 14 cm (2), implanted Ga causes local nucleation of Ge clusters upon the implanted region. At higher doses (]/10 15 cm (2), a complex surface topography localizes nucleation of Ge clusters. This approach can be used to seed complex patterns of Ge clusters with diameters of tens of nanometers and positional accuracy of sub-100 nm. The second method employs self-assembly of complex strain-stabilized ''quantum quadruplet'' and ''quantum fortress'' structures, whereby cooperative island nucleation around shallow strain-relieving pits is identified during Ge x Si 1(x /Si(1 0 0) heteroepitaxy. These configurations are kinetically limited structures that exist over a range of compositions, growth temperatures, and growth rates, but which are destabilized by strain relaxation (e.g. by the introduction of misfit dislocations) and by growth conditions which provide high adatom surface mobilities. Both methods have broad potential application to nanoelectronic device architectures. 2003 Elsevier Science B.V. All rights reserved. KW - Strained layer epitaxy KW - Strain relaxation KW - Quantum fortress KW - Molecular beam epitaxy KW - Controlled nucleation Y1 - 2003 U6 - https://doi.org/10.1016/S0921-5107(02)00680-3 VL - 101 IS - 1-3 SP - 1 EP - 8 PB - Elsevier ER - TY - JOUR A1 - Koenig, Eric A1 - Guertler, Katherine T1 - Parlaying students´ work experience into practice-oriented esp JF - Journal of teaching english for specific and academic purposes N2 - Instructors of English for Special Purposes often describe the challenge of determining which specific content and competencies to address in their courses. After all, it is the focus on technical subject matter which students expect to differentiate engineering ESP from standard EFL. Yet ESP instructors, who frequently have a background in fields such as applied linguistics or education, often receive little input from technical specialists as to which specialist topics are most relevant to their target domain. Our research indicates that ESP instructors in higher education can leverage a valuable resource to enrich teaching effectiveness: students who have already gained professional experience. As part of a longitudinal study at two universities of applied sciences (UAS) in southern Germany, engineering students at the beginning of their first semester of compulsory technical English participate in an online survey. The course participants provide relevant biographical information such as work experience and evaluate the perceived importance of a selection of skills and applications for a Technical English course. The surveys, administered in October 2016 and October 2017 and encompassing nearly 1000 respondents, provide compelling insights. Analysis reveals conclusive correlations between the perceived importance of course components and students' declared level of previous work experience. Listening comprehension, reading comprehension, process description, and test and measurement are topics whose importance correlates positively with work experience level. In addition, there are clear trends relating work experience level with the importance of the reading and writing of technical documents as well as communication and interaction. This data provides empirically-founded criteria for selecting the topics to include in the scope of a Technical English course for engineers, informed by the judgment of students with occupational experience. Additionally, recognizing that students with work experience have legitimate practitioner credibility allows instructors to identify and select relevant subject matter in concordance with experienced students' learning objectives. ESP learners will profit greatly from cultivating skills with proven practical applicability. KW - ESP curricula KW - ESP practitioners KW - Technical English KW - work experience Y1 - 2018 U6 - https://doi.org/10.22190/JTESAP1802277K VL - 6 IS - 2, Special issue SP - 277 EP - 284 PB - Universität Nis ER - TY - JOUR A1 - Hanisch-Blicharski, Anja A1 - Janzen, Andreas A1 - Krenzer, Boris A1 - Wall, S. A1 - Klasing, Friedrich A1 - Kalus, Annika A1 - Frigge, Tim A1 - Kammler, Martin A1 - Horn-von Hoegen, Michael T1 - Ultra-fast electron diffraction at surfaces: from nanoscale heat transport to driven phase transitions JF - Ultramicroscopy N2 - Many fundamental processes of structural changes at surfaces occur on a pico- or femtosecond time scale. In order to study such ultra-fast processes, we have combined modern surface science techniques with fs-laser pulses in a pump-probe scheme. Reflection high energy electron diffraction (RHEED) with grazing incident electrons ensures surface sensitivity for the probing electron pulses. Utilizing the Debye-Waller effect, we studied the cooling of vibrational excitations in monolayer adsorbate systems or the nanoscale heat transport from an ultra-thin film through a hetero-interface on the lower ps-time scale. The relaxation dynamics of a driven phase transition far away from thermal equilibrium is demonstrated with the In-induced (8×2) reconstruction on Si(111). This surface exhibits a Peierls-like phase transition at 100K from a (8×2) ground state to (4×1) excited state. Upon excitation by a fs-laser pulse, this structural phase transition is driven into an excited (4×1) state at a sample temperature of 20K. Relaxation into the (8×2) ground state occurs after more than 150 ps. Y1 - 2013 U6 - https://doi.org/10.1016/j.ultramic.2012.07.017 VL - 127 SP - 2 EP - 8 PB - Elsevier ER - TY - JOUR A1 - Prommesberger, Christian A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Hofmann, Martin A1 - Pahlke, Andreas A1 - Schreiner, Rupert T1 - Regulation of the Transmitted Electron Flux in a Field-Emission Electron Source Demonstrated on Si Nanowhisker Cathodes JF - IEEE Transactions on Electron Devices N2 - We report on a method to stabilize the transmitted electron flux in a field-emission electron source using an external regulation circuit. The electron source was realized with an array of silicon (Si) nanowhiskers on the top of elongated pillar structures, a mica spacer, and an extraction grid made of Si. As for most applications, the emitted electron current from the cathode is not as crucial as the transmitted electron flux through the extraction grid toward the anode. We investigated a method which allows the regulation directly by the emitted electron flux and not merely on the cathode current. By using this method, we were able to stabilize the emitted electron flux of our electron source down to values below 1%. Simultaneously, it was shown that there is the possibility to stabilize the influencing value in the real application as well. The effectiveness of this method was demonstrated successfully with an X-ray source setup. The measured X-ray photon count rate was stabilized to a standard deviation of 0.30% at a pressure of 1 × 10 -7 mbar. Even in harsh environment of 2 × 10 -5 mbar, a stabilization of the X-ray photon count rate down to a value of 0.63% was achieved. KW - Cathodes KW - Nanostructured devices KW - Current measurement KW - Photonics KW - Electron sources KW - Emissions KW - Voltage measurement Y1 - 2017 U6 - https://doi.org/10.1109/TED.2017.2763239 SN - 5128-5133 VL - 64 IS - 12 PB - IEEE ER - TY - JOUR A1 - Langer, Christoph A1 - Bomke, Vitali A1 - Hausladen, Matthias A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Bachmann, Michael A1 - Schreiner, Rupert T1 - Silicon Chip Field Emission Electron Source Fabricated by Laser Micromachining JF - Journal of Vacuum Science & Technology B N2 - The components for a silicon chip electron source were fabricated by laser micromachining using pulsed laser ablation and wet chemical cleaning and etching dips. The field emission electron source consists of a silicon field emission cathode with 4 × 4 conical shaped emitters with a height of 250 μm and a tip radius of about 50 nm, a 50 μm thick laser-structured mica spacer, and a silicon grid electrode with a grid periodicity of 200 μm and a bar width of 50 μm. These three components are combined to a single chip with the size of 14 × 10 mm2 and the thickness of 1 mm to form the electron source. Several of these devices were characterized in ultrahigh vacuum. Onset voltages of about 165 V and cathode currents of about 15 μA for voltages lower than 350 V were observed. Operating the electron source with an anode voltage of 500 V and an extraction grid voltage of 300 V yielded a cathode current of 4.5 μA ± 8.9%, an anode current of 4.0 μA ± 9.6%, and a corresponding grid transmittance of 89%. Regulating the anode current by the extraction grid voltage, an extremely stable anode current of 5.0 μA ± 0.017% was observed. A long-term measurement over 120 h was performed, and no significant degradation or failure was observed. KW - Ultra-high vacuum KW - Field emitter arrays KW - Etching KW - Electrical properties and parameters KW - Electron sources KW - Laser ablation KW - Laser micromachining KW - Silicon chip KW - Triodes Y1 - 2020 U6 - https://doi.org/10.1116/1.5134872 VL - 38 IS - 1 PB - AIP Publishing ER - TY - JOUR A1 - Breuer, Janis A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert A1 - Serbun, Pavel A1 - Lützenkirchen-Hecht, Dirk T1 - Extraction of the current distribution out of saturated integral measurement data of p-type silicon field emitter arrays JF - Journal of Vacuum Science and Technology B N2 - At the moment, only complicated techniques are known for the determination of array properties of field emitter arrays such as the number of active tips, the current distribution, or the individual tip radii. In this work, a method for extracting these parameters from integral measurement data is presented. A model describing the characteristics of a single emitter, including the saturation as a function of the applied voltage and the emitter radius, is developed. It is shown that experimental data of field emitter arrays can be represented as the sum of these functions and the characteristic parameters can be fitted to field emission data of an array. Using this method, the values of the radii as well as the parameters of distribution models can be determined directly. Analysis of experimental data from p-type Si emitter arrays shows that only 1–2% of the tips contribute significantly. Y1 - 2018 U6 - https://doi.org/10.1116/1.5035189 VL - 36 IS - 5 PB - AIP Publishing ER - TY - JOUR A1 - Edler, Simon A1 - Bachmann, Michael A1 - Breuer, Janis A1 - Dams, Florian A1 - Düsberg, Felix A1 - Hofmann, Martin A1 - Jakšič, Jasna A1 - Pahlke, Andreas A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Schreiner, Rupert T1 - Influence of adsorbates on the performance of a field emitter array in a high voltage triode setup JF - Journal of Applied Physics N2 - In the present work, black-silicon field emitter arrays (FEAs) are investigated regarding the influence of residual gas pressure on the characteristics and lifetime in the high voltage triode setup. Current-voltage-characteristics at different pressure levels are recorded and show a decreasing emission current with rising pressure. This decrease can be explained by an increase of the work function and charging of the emitter surface caused by adsorbates. The emission current can be restored to its initial value by heating of the FEA up to 110 °C during active emission. With this regeneration procedure, an extended lifetime from about 20 h to 440 h at a residual gas pressure of 10−5 mbar is achieved. Y1 - 2017 U6 - https://doi.org/10.1063/1.4987134 VL - 122 ER - TY - JOUR A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert A1 - Serbun, Pavel A1 - Müller, Günter A1 - Düsberg, Felix A1 - Hofmann, Martin A1 - Bachmann, Michael A1 - Pahlke, Andreas T1 - Field emission properties of p-type black silicon on pillar structures JF - Journal of Vacuum Science & Technology B N2 - Arrays of black silicon field emission pillar structures were fabricated on p-type silicon substrates. Two types of samples with the same number of pillars (arrays of 10 × 10) but different pillar heights (8 and 20 μm) were prepared as well as a black silicon reference sample without pillars. The field emission properties of these cathodes were investigated both by means of integral current-voltage measurements and by field emission scanning microscopy. Samples with a pillar height of 20 μm revealed onset fields as low as 6.4 V/μm, field enhancement factors up to 800, and emission currents up to 8 μA at an applied field of 20 V/μm. Due to the p-type material, a saturation of the emission current for fields above 11 V/μm was observed. This saturation leads to a stable operation with a current fluctuation of less than ±8%. It was found that samples with a pillar height of 20 μm showed improved emission characteristics compared to samples with a pillar height of 8 μm or without pillars. The voltage maps revealed an increased emission homogeneity after a “burn-in” sequence of the sample. The current map showed that a few of the pillars dominate the emission. Integral current stability measurements were performed under different vacuum pressures, in order to investigate altered emission behavior and a potential degradation of the emitters. At pressures above 10−6 mbar, the sample starts to degrade irreversibly. Nevertheless, even after a harsh treatment over 30 min at 5 × 10−5 mbar and at an applied field of 23 V/μm, the cathode was still operating, and did not fail during further operation over 20 h at 5 × 10−8 mbar and at an applied field of 28 V/μm. Y1 - 2016 U6 - https://doi.org/10.1116/1.4943919 VL - 34 IS - 2 ER - TY - JOUR A1 - Bachmann, Michael A1 - Dams, Florian A1 - Düsberg, Felix A1 - Hofmann, Martin A1 - Pahlke, Andreas A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Schreiner, Rupert A1 - Serbun, Pavel A1 - Lützenkirchen-Hecht, Dirk A1 - Müller, Günter T1 - Extraction of the characteristics of current-limiting elements from field emission measurement data JF - Journal of Vacuum Science & Technology B N2 - In this contribution, the authors will present an algorithm to extract the characteristics of nonideal field emission circuit elements from saturation-limited field emission measurement data. The method for calculating the voltage drop on current-limiting circuit elements is based on circuit theory as well as Newton's method. Since the only assumption the authors make on the current-limiting circuit is a connection in series, this method is applicable to most field emission data showing saturation. To be able to determine the significance of any parameter output, the uncertainties of data and extracted parameters as well as the parameter correlations are fully taken into account throughout the algorithm. N-type silicon samples with varying external serial resistors are analyzed. All results show a good agreement to the nominal resistor values. Additionally, several p-type samples are analyzed, showing a diodelike behavior. The extracted current-limiting characteristics of the p-type samples are in good agreement with a pn-junction model. The stability of the emission current of the p-type samples is measured by constant voltage measurements and compared to the extracted current-limiting characteristics. The application of the algorithm to measurement data shows that the given algorithm is a valuable tool to analyze field emission measurement data influenced by nonemissive processes. Y1 - 2017 U6 - https://doi.org/10.1116/1.4971768 VL - 35 IS - 2 ER - TY - JOUR A1 - Prommesberger, Christian A1 - Langer, Christoph A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert T1 - Investigations on the long-term performance of gated p-type silicon tip arrays with reproducible and stable field emission behavior JF - Journal of Vacuum Science & Technology B N2 - The authors report on the fabrication and characterization of p-type Si tip arrays with an integrated gate electrode for applications as field emission electron sources. After the reactive ion etching of the emitters, the combined thermal dry and wet oxidation was used for both the sharpening of the emitters and for the realization of an enhanced insulation layer. Au was evaporated in a self-aligned process as gate electrode. Arrays of 16 Si tips were fabricated with tip heights of about 3 μm and tip radii of about 20 nm with integrated gate electrode concentrically positioned ≈2 μm below the tip apex. Integral measurements with an additional anode showed improved field emission properties with a reproducible and stable emission behavior. A fast activation of the tips, low onset voltages of about 30 V, and moderate field emission currents up to 0.55 μA were noticed. The field emission parameters were calculated using the Fowler–Nordheim characteristics. A pronounced saturation regime was observed, and current fluctuations of less than ±1% were investigated for 30 min. Long-term measurements were carried out for a period of more than 8 h. In the first 6 h of operation, the authors observed a drift of the emission current from 0.35 to 0.55 μA caused by an increased emission surface. Y1 - 2017 U6 - https://doi.org/10.1116/1.4972519 VL - 35 IS - 1 ER - TY - JOUR A1 - Ławrowski, Robert Damian A1 - Hausladen, Matthias A1 - Buchner, Philipp A1 - Schreiner, Rupert T1 - Silicon Field Emission Electron Source With Individually Controllable Single Emitters JF - IEEE Transactions on Electron Devices N2 - An electron source with an array of individually controllable single tips allows the observation of each emitter current simultaneously as well as the measurement of the integral current. Furthermore, the initial activation process of the individual tips and current distribution of the source can be examined. The Si cathode consists of an array of 2 x 2 conically shaped emitter structures on a borosilicate glass substrate. The emitters were fabricated by laser micromachining and wet etching. Integral field emission (FE) measurements were performed in a diode configuration in a vacuum chamber at pressures of about 10(-9) mbar with a self-aligned Si extraction grid, due to adjustment pins. The total emission current was regulated to a predefined value (4.0, 10, 20, 40, and 50 mu A) by an external regulating circuit and recorded individually during the measurement. The onset voltage for a current of 1 nA varied between 320 and 430 V. The voltage conversion factor is in the range of 7.6 x 10(4) cm(-1) to 1.3 x 10(5) cm(-1). Constant currentmeasurementsover a longer periodof time (1800 values with a sample rate of 0.5 Hz) were performed and show a total current fluctuation less than 0.6% due to the regulation circuit. Despite the stable total current in regulated operation, it was observed that the individual emitters fluctuate up to 75% for low (similar to 10(-8) A) and 5% for high (similar to 10(-5) A) currents. KW - Current distribution KW - current limiters KW - electron emission KW - electron sources KW - silicon-on-insulator Y1 - 2021 U6 - https://doi.org/10.1109/TED.2021.3093374 VL - 68 IS - 8 SP - 4116 EP - 4122 PB - IEEE ER - TY - JOUR A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Schels, Andreas A1 - Herdl, Florian A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert T1 - High current silicon nanowire field emitter arrays JF - Journal of Vacuum Science & Technology B N2 - Arrays of n-doped silicon nanowire field emitters with a high aspect ratio are realized by a novel dry etching technique. Compared to the high current silicon emitters in the literature, the manufacturing process is much simpler and requires only a single photolithography step and two dry etching steps. The cathodes realized with this method exhibit a total current of 20 mA from an active area of 4×4 mm2, which is significantly higher than that for most known structures made from silicon and also represents good performance in comparison with other emitter types, e.g., carbon nanotubes. In addition to characterization in ultrahigh vacuum, measurements at 10−5 mbar are performed and compared with our recent silicon emitters. Compared to these cathodes, the structures with the nanowires exhibit at least two orders of magnitude higher current-carrying capability. Y1 - 2022 U6 - https://doi.org/10.1116/6.0001639 VL - 40 IS - 1 PB - AIP Publishing ER - TY - JOUR A1 - Remskar, Maja A1 - Hüttel, Andreas K. A1 - Shubina, Tatiana V. A1 - Seabaugh, Alan A1 - Fathipour, Sara A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert T1 - Confinement Related Phenomena in MoS2 Tubular Structures Grown from Vapour Phase JF - Israel Journal of Chemistry N2 - We review recently discovered phenomena observed in the MoS2 tubular structures, which were synthesized by a lasting chemical transport reaction nearly at chemical equilibrium. Such MoS2 nanotubes are distinguished by low density of structural defects, thin walls and a high aspect ratio, which intrinsically provide a confined, edge-free geometry. Quantum confinement with single electron conductance was recorded and a bright exciton photoluminescence with appearance of whispering gallery modes was observed. In addition, the field-effect transistors and field emitters based on single MoS2 nanotubes were demonstrated. These discoveries revitalize research of MoS2 curved structures grown from vapour phase, which were reported several decades ago. Y1 - 2021 U6 - https://doi.org/10.1002/ijch.202100100 SN - 1869-5868 VL - 62 IS - 3-4 SP - 1 EP - 11 PB - Wiley ER - TY - JOUR A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Langer, Christoph A1 - Herdl, Florian A1 - Bergbreiter, Lukas A1 - Dams, Florian A1 - Miyakawa, Natuski A1 - Eggert, Tobias A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Hausladen, Matthias A1 - Schreiner, Rupert T1 - Vacuum-sealed field emission electron gun JF - Journal of Vacuum Science & Technology B N2 - A compact vacuum-sealed field emission electron gun with an operation voltage below 5 kV is presented. With a 150 nm thick pyrolytic carbon membrane, a transmission of 40% at 5 kV is obtained. For more than 2500 h of continuous operation at an emission current of 100 nA, no significant increase (<50V ) and almost no degradation were found. From this measurement, a lifetime of more than 10 000 h at continuous operation with approximately a linear increase of the extraction voltage from about 545 V to about 730 V is predicted. This electron source enables application of field emitter arrays in poor vacuum or even ambient pressure. ACKNOWLEDGMENT This work was supported by the German Federal Ministry for Economic Affairs and Energy under Project No. ZF4081502GM8. C.P., R.L., M.H., and R.S. were supported by Grant No. ZF4562901GM8. Y1 - 2020 U6 - https://doi.org/10.1116/1.5139316 VL - 38 IS - 2 PB - AIP Publishing ER - TY - JOUR A1 - Langer, Christoph A1 - Prommesberger, Christian A1 - Ławrowski, Robert Damian A1 - Dams, Florian A1 - Schreiner, Rupert T1 - Simulation and Fabrication of Silicon Field Emission Cathodes for Cold Electron Sources JF - Advanced Materials Research N2 - We report on the simulation and fabrication of nanostructured silicon surfaces for field emission (FE) applications, e.g. ionization sensors and x-ray tubes. For the design and optimization of field-emitting silicon structures, the influence of the geometric parameters like tip height, apex radius, aperture angle and curvature shape on the field enhancement factor was investigated by simulation using finite element method. A universal geometric model which describes the real geometry of our silicon structures sufficiently accurate was taken for modeling a variety of different silicon tip structures as well as ridge structures. While a high dependency of the field enhancement on the aspect ratio and the aperture angle was found, the simulations show that the elliptic curvature affects the field enhancement only marginally. Finally, an improved process for fabrication of such silicon structures on n-type as well as p-type substrate is described, using reactive ion etching with adjustable anisotropy, wet thermal oxidation and wet etching. KW - field emission cathodes KW - field enhancement factor KW - silicon field emitter Y1 - 2014 U6 - https://doi.org/10.4028/www.scientific.net/amr.1024.48 VL - 1024 SP - 48 EP - 51 ER - TY - JOUR A1 - Ławrowski, Robert Damian A1 - Bachmann, Michael A1 - Schreiner, Rupert T1 - Field emission arrays from graphite fabricated by laser micromachining JF - Journal of Vacuum Science & Technology B N2 - Laser micro structuring allows the manufacturing of conical shaped emitters on a graphitized carbon substrate without any additional treatment. Integral field emission measurements were performed in a diode configuration with a 50 µm mica spacer and a metalized Si-grid in a vacuum chamber at pressures of about 10-9 mbar. Emission currents up to 10 µA at a voltage of 1000 V (11 MV/m) with a positive current drift were observed for an array of 16 emitters. A strong modification of the emitter tip is noticeable after individual measurements. A comparable alteration of the surface is also achieved by an electrochemical treatment of the samples with a potassium hydroxide solution. However, the IV-measurements of such samples show higher onset voltages, but also higher integral emission currents. For all arrays an ideal FN behaviour is only noticeable at applied voltages below 625 V (7 MV/m). Numerical calculations indicate that the deviation in the FN-plot for higher voltage values is caused by the change of the effective work function. Y1 - 2022 U6 - https://doi.org/10.1116/6.0001547 VL - 40 IS - 2 PB - AIP Publishing ER - TY - JOUR A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Langer, Christoph A1 - Dams, Florian A1 - Schreiner, Rupert T1 - Improvement of Homogenity and Aspect Ratio of Silicon Tips for Field Emission by Reactive-Ion Etching JF - Advances in materials science and engineering N2 - The homogeneity of emitters is very important for the performance of field emission (FE) devices. Reactive-ion etching (RIE) and oxidation have significant influences on the geometry of silicon tips. The RIE influences mainly the anisotropy of the emitters. Pressure has a strong impact on the anisotropic factor. Reducing the pressure results in a higher anisotropy, but the etch rate is also lower. A longer time of etching compensates this effect. Furthermore an improvement of homogeneity was observed. The impact of uprating is quite low for the anisotropic factor, but significant for the homogeneity. At low power the height and undercut of the emitters are more constant over the whole wafer. The oxidation itself is very homogeneous and has no observable effect on further variation of the homogeneity. This modified fabrication process allows solving the problem of inhomogeneity of previous field emission arrays. Y1 - 2014 U6 - https://doi.org/10.1155/2014/948708 VL - 2014 PB - Hindawi ER - TY - JOUR A1 - Ławrowski, Robert Damian A1 - Prommesberger, Christian A1 - Langer, Christoph A1 - Dams, Florian A1 - Schreiner, Rupert T1 - Improvement of Homogeneity and Aspect Ratio of Silicon Tips for Field Emission by Reactive-Ion Etching JF - Advances in Materials Science and Engineering. Special issue: Advances in Smart Materials and Applications N2 - The homogeneity of emitters is very important for the performance of field emission (FE) devices. Reactive-ion etching (RIE) and oxidation have significant influences on the geometry of silicon tips. The RIE influences mainly the anisotropy of the emitters. Pressure has a strong impact on the anisotropic factor. Reducing the pressure results in a higher anisotropy, but the etch rate is also lower. A longer time of etching compensates this effect. Furthermore an improvement of homogeneity was observed. The impact of uprating is quite low for the anisotropic factor, but significant for the homogeneity. At low power the height and undercut of the emitters are more constant over the whole wafer. The oxidation itself is very homogeneous and has no observable effect on further variation of the homogeneity. This modified fabrication process allows solving the problem of inhomogeneity of previous field emission arrays. Y1 - 2014 U6 - https://doi.org/10.1155/2014/948708 SN - 1687-8442 SN - 1687-8434 VL - 2014 SP - 1 EP - 6 PB - Hindawi ER - TY - JOUR A1 - Lindner, Matthias A1 - Pipa, Andrei V. A1 - Brandenburg, Ronny A1 - Schreiner, Rupert T1 - Expansion of surface barrier discharge scrutinized JF - Plasma Sources Science and Technology N2 - Developing the fundamentals for the electrical diagnostics of surface dielectric barrier discharges (SDBDs) is of enormous importance for several applications, for example, flow control and gas cleaning. The main challenge is to account for the discharge expansion along the dielectric surface. Typically, a linear expansion with the amplitude of the applied voltage is observed. In this work, we report on a step-wise SDBD expansion along the Al 2 O 3 dielectric surface. More specific, the discharge occupied a certain area after ignition, which remained constant until the voltage exceeded the critical amplitude V L . This absence of expansion is seen as a linear dependence of the discharge power on the applied voltage and it was additionally confirmed by photographs with long exposure times. This novel phenomenon is more pronounced for thicker dielectrics. It is suggested that the derivative of the charge-voltage characteristics can be used for the determination of all essential parameters of the simplest equivalent circuit of SDBDs. Moreover, it was shown that the derivative of the charge-voltage characteristics for the positive half-cycle of the discharge agrees numerically with the voltage dependence of the reactor capacitance derived from photographs. This agreement between both measurement methods indicates a similar step-wise expansion of the SDBD even if a voltage amplitude above V L is applied. … Y1 - 2022 U6 - https://doi.org/10.1088/1361-6595/ac95bf VL - 31 IS - 10 PB - IOP Publishing ER - TY - JOUR A1 - Bornmann, Benjamin A1 - Mingels, Stephan A1 - Dams, Florian A1 - Prommesberger, Christian A1 - Schreiner, Rupert A1 - Lützenkirchen-Hecht, Dirk A1 - Müller, Günter T1 - Electron spectrometer in adjustable triode configuration for photo-induced field emission measurements JF - The Review of scientific instruments N2 - We have constructed a new ultrahigh vacuum apparatus with a triode configuration for the systematic investigation of photo-induced field emission (PFE) from metallic or semiconducting cathodes. These are exposed to electric fields up to 400 MV∕m and laser irradiation by means of hole or mesh gates. Cathodes and gates are in situ exchangeable and adjustable with high precision to ensure a homogeneous extraction of electrons which are partially transmitted to the fixed electron spectrometer. Its hemispherical sector analyzer provides an energy resolution limit of 8 meV. The commissioning of the measurement system has been performed with a tungsten needle. Its temperature showed up in the high-energy tail of the electron spectrum, while its work function was derived from the spectral low-energy part combined with the integral current-voltage curve. First PFE measurements on B-doped Si-tip arrays yielded a small field emission current increase under green laser illumination. A shift and splitting of the energy spectra was observed which revealed different emission regimes as well as the photosensitivity of the cathode due to carrier excitation into the conduction band. For the full exploitation of the PFE system, a tunable laser over a wide eV-range is required. Y1 - 2012 U6 - https://doi.org/10.1063/1.3673475 VL - 83 IS - 1 PB - American Institute of Physics CY - Melville, NY ER - TY - JOUR A1 - Pangerl, Jonas A1 - Moser, Elisabeth A1 - Müller, Max A1 - Weigl, Stefan A1 - Jobst, Simon A1 - Rück, Thomas A1 - Bierl, Rudolf A1 - Matysik, Frank-Michael T1 - A sub-ppbv-level Acetone and Ethanol Quantum Cascade Laser Based Photoacoustic Sensor– Characterization and Multi-Component Spectra Recording in Synthetic Breath JF - Photoacoustics N2 - Trace gas analysis in breath is challenging due to the vast number of different components. We present a highly sensitive quantum cascade laser based photoacoustic setup for breath analysis. Scanning the range between 8263 and 8270 nm with a spectral resolution of 48 pm, we are able to quantify acetone and ethanol within a typical breath matrix containing water and CO2. We photoacoustically acquired spectra within this region of mid-infra-red light and prove that those spectra do not suffer from non-spectral interferences. The purely additive behavior of a breath sample spectrum was verified by comparing it with the independently acquired single component spectra using Pearson and Spearman correlation coefficients. A previously presented simulation approach is improved and an error attribution study is presented. With a 3σ detection limit of 6.5 ppbv in terms of ethanol and 250 pptv regarding acetone, our system is among the best performing presented so far. KW - Acetone KW - Breath analysis KW - Photoacoustic spectroscopy KW - Quantum cascade laser KW - Spectral simulation Y1 - 2023 U6 - https://doi.org/10.1016/j.pacs.2023.100473 SN - 2213-5979 N1 - Corresponding author: Jonas Pangerl VL - 30 SP - 1 EP - 12 PB - Elsevier ER - TY - JOUR A1 - Menzel, Andreas A1 - Kammler, Martin A1 - Conrad, E. H. A1 - Yeh, V. A1 - Hupalo, Myron A1 - Tringides, Michael C. T1 - Kinetics measurements of Pb island growth on Si(111) JF - Physical Review B N2 - We present the results of kinetics experiments on quantum-size-effects (QSE) Pb islands formed on Si(111). We have looked at the evolution of seven-layer Pb islands from five-layer Pb islands due to the transport of Pb atoms from the interisland region, overcoming a barrier at the island edges, and moving to the island tops. By analyzing low-energy electron-diffraction and scanning-tunneling microscopy data, we have estimated the barrier for layer formation in this system to be ∼0.32eV. This energy is much larger than that expected from QSE electronic contributions alone. Y1 - 2003 U6 - https://doi.org/10.1103/PhysRevB.67.165314 VL - 67 IS - 16 PB - American Physical Society ER - TY - JOUR A1 - Streubühr, C. A1 - Kalus, Annika A1 - Zhou, Ping A1 - Ligges, Manuel A1 - Hanisch-Blicharski, Anja A1 - Kammler, Martin A1 - Bovensiepen, U. A1 - Horn-von Hoegen, Michael A1 - von der Linde, D. T1 - Comparing ultrafast surface and bulk heating using time-resolved electron diffraction JF - Applied Physics Letters N2 - From measurements of the transient Debye-Waller effect in Bismuth, we determine the buildup time of the random atomic motion resulting from the electronic relaxation after short pulse laser excitation. The surface sensitive reflection high energy electron diffraction and transmission electron diffraction yield a time constant of about 12 ps and 3 ps, respectively. The different energy transfer rates indicate relatively weak coupling between bulk and surface vibrational modes. (C) 2014 AIP Publishing LLC. Y1 - 2014 U6 - https://doi.org/10.1063/1.4872055 VL - 104 SP - 1 EP - 3 PB - American Institute of Physics ER - TY - JOUR A1 - Ławrowski, Robert Damian A1 - Pirker, Luka A1 - Kaneko, Keita A1 - Kokubo, Hiroki A1 - Bachmann, Michael A1 - Ikuno, Takashi A1 - Remskar, Maja A1 - Schreiner, Rupert T1 - Field emission from nanotubes and flakes of transition metal dichalcogenides JF - Journal of Vacuum Science and Technology B N2 - Transition metal dichalcogenides such as MoS2 and WS2 are low-dimensional semiconductor materials. MoS2 and WS2 nanotubes and flakes were grown by a chemical transport reaction under a temperature gradient. I2 was used as a transport agent for previously synthesized MoS2 and WS2, respectively. These multilayered nanotubes are indirect bandgap semiconductors with a bandgap depending on their diameter. WS2 flakes were prepared by the sulfurization of thin WOx flakes. To increase the field enhancement of such low-dimensional structures by a higher aspect ratio, two approaches were examined: (a) the MoS2 and WS2 nanotubes were attached individually by a focused ion beam with Pt on dry etched n-type Si pillars and (b) the WS2 flakes were grown directly on the surface of the (n-type and p-type) Si pillars. Integral field emission measurements were performed in a diode configuration with a 50 μm mica spacer in a vacuum chamber at pressures of about 10−9 mbar. At a voltage of 900 V (18 MV/m), the integral emission current from the nanotubes is up to 11 μA for the lateral mounted MoS2 and about 1.3 μA (1.0 μA) for the upright mounted WS2 (MoS2). The onset voltage for a current of 1 nA is about 550 V for MoS2 and 500 V for WS2, respectively. The voltage conversion factor is in the range of 6 × 104–8 × 104 cm−1 for the nanotubes. The mounted MoS2 flakes show a field emission current of about 6 μA at 18 MV/m in contrast to the directly grown WS2 flakes, which show a pronounced saturation regime and, therefore, a lower emission current of about 0.5 μA is reached at 1500 V (25 MV/m). The WS2 flakes show a two times higher (1 × 105 cm−1) voltage conversion factor in comparison to the MoS2 flakes (5 × 104 cm−1). The extracted characteristics of the current-limiting part show a difference in the behavior of the extracted current-limiting characteristics between the lateral (linear) and upright mounted (exponential) nanotubes and the MoS2 flakes. In contrast, the WS2 flakes show charge carrier depletion effects. Y1 - 2020 U6 - https://doi.org/10.1116/1.5140474 VL - 38 IS - 3 SP - 032801 PB - AIP Publishing ER - TY - JOUR A1 - Kleshch, Victor I. A1 - Serbun, Pavel A1 - Lützenkirchen-Hecht, Dirk A1 - Orekhov, Anton A1 - Ivanov, Victor E. A1 - Prommesberger, Christian A1 - Langer, Christoph A1 - Schreiner, Rupert A1 - Obraztsov, Alexander N. T1 - A Comparative Study of Field Emission from Pristine, Ion-treated and Tungsten Nanoparticle-decorated p-type Silicon Tips JF - Physica Status Solidi B N2 - The field electron emission characteristics of individual tips of a silicon field emitter array are analyzed. The array of conical‐shaped tips is fabricated on a p‐type silicon wafer by using reactive ion etching and sharpening oxidation. The tips are decorated with single tungsten nanoparticles at their apexes. Furthermore, the focused ion beam is also used to increase surface conductivity of some of the tips. Comparative measurements of field emission are performed by using the scanning anode probe field emission microscopy technique. All types of tips demonstrated emission activation consisting of a sudden current increase at a certain value of the applied voltage. Compared to the pristine tips, a noticeable reduction of the saturation effect in the current–voltage characteristics and a smaller light sensitivity for the decorated tips is found. For ion‐treated tips, saturation effects and light sensitivity are completely suppressed. Scanning electron microscopy observations reveal the formation of single nanoscale protrusions extending from the metal particles and from the apexes of bare ion‐treated tips after exposure under strong electric fields during the field emission measurements. The influence of protrusions growth on characteristics of silicon field emitter arrays is discussed. Y1 - 2019 U6 - https://doi.org/10.1002/pssb.201800646 VL - 256 IS - 9 PB - Wiley ER - TY - JOUR A1 - Mingels, Stephan A1 - Porshyn, Vitali A1 - Prommesberger, Christian A1 - Langer, Christoph A1 - Schreiner, Rupert A1 - Lützenkirchen-Hecht, Dirk A1 - Müller, Günter T1 - Photosensitivity of p-type black Si field emitter arrays JF - Journal of Applied Physics N2 - We have investigated the properties of black Si field emitter arrays under strong electric fields and laser illumination. A low onset field of 1.8 MV/m for an emission current of 1 nA was obtained. A pronounced saturation region of the dark and photo-enhanced current was observed, which provided a short-term stability of 0.1% at 0.4 μA and 0.7% at 1.0 μA, respectively. As maximum value for the photosensitivity, an on-off current switching ratio of 43 reaching about 13 μA was achieved at a laser power of 15 mW. Electron spectra in the dark and under laser illumination are presented, showing a current and light-sensitive voltage drop across the emitters as well as hints for hot electron emission. Y1 - 2016 U6 - https://doi.org/10.1063/1.4948328 VL - 119 IS - 16 ER - TY - JOUR A1 - Payer, Thomas A1 - Klein, C. A1 - Acet, M. A1 - Ney, V. A1 - Kammler, Martin A1 - Meyer zu Heringdorf, Frank-Joachim A1 - Horn-von Hoegen, Michael T1 - High-quality epitaxial Bi(111) films on Si(111) by isochronal annealing JF - Thin Solid Films N2 - Bi(111) films grown on Si(111) at room temperature show a significantly higher roughness compared to Bi films grown on Si(100) utilizing a kinetic pathway based on a low-temperature process. Isochronal annealing steps of 3 min duration each with temperatures up to 200 °C cause a relaxation of the Bi films' lattice parameter toward the Bi bulk value and yield an atomically flat Bi surface. Driving force for the relaxation and surface reordering is the magic mismatch of 11 Bi atoms to 13 Si atoms that emerges at annealing temperatures above 150 °C and reduces the remaining strain to less than 0.2%. KW - Epitaxy KW - Strain KW - Annealing KW - Bismuth KW - Silicon Y1 - 2012 U6 - https://doi.org/10.1016/j.tsf.2012.06.004 VL - 520 IS - 23 SP - 6905 EP - 6908 PB - Elsevier ER - TY - JOUR A1 - Portavoce, A. A1 - Kammler, Martin A1 - Hull, Robert A1 - Reuter, Mark C. A1 - Copel, M. A1 - Ross, Frances M. T1 - Growth of nanostructures by locally modified surface reactivity JF - Materials Science in Semiconductor Processing N2 - The chemical vapor deposition (CVD) of Si and Ge on Si(0 0 1) substrates covered by 1 monolayer of Ga has been studied. Ga modifies surface reactivity and surface atom mobility. We show that islanding occurs during Ga-mediated CVD even in the absence of strain, allowing for the formation of islands without a wetting layer or with a thinner wetting layer. The morphology of the grown layer is highly dependent on kinetic parameters, i.e. growth temperature and growth pressure, that control Si and Ge deposition and Ga desorption. Si Ga-mediated CVD promotes the formation of self-assembled epitaxial Si islands exhibiting {1 1 3} facets. Ge islands grown by Ga-mediated CVD present reduced lateral sizes and an increased surface density compared to non Ga-mediated CVD. The growth morphology (particularly island size and density) can be understood by considering a qualitative model in which atoms are deposited only on sites whose dangling bonds are not passivated by Ga. We suggest that modification of surface reactivity during surfactant-mediated CVD can thus provide a new degree of freedom for quantum dot fabrication. KW - UHV TEM KW - UHV CVD KW - Epitaxial growth KW - Si KW - Ge KW - Surfactant Ga Y1 - 2009 U6 - https://doi.org/10.1016/j.mssp.2009.07.001 VL - 12 IS - 1-2 SP - 25 EP - 30 PB - Elsevier ER - TY - JOUR A1 - Portavoce, A. A1 - Kammler, Martin A1 - Hull, Robert A1 - Reuter, Mark C. A1 - Ross, Frances M. T1 - Mechanism of the nanoscale localization of Ge quantum dot nucleation on focused ion beam templated Si(001) surfaces JF - Nanotechnology N2 - We investigate the fundamental mechanism by which self-assembled Ge islands can be nucleated at specific sites on Si(001) using ultra-low-dose focused ion beam (FIB) pre-patterning. Island nucleation is controlled by a nanotopography that forms after the implantation of Ga ions during subsequent thermal annealing of the substrate. This nanotopography evolves during the annealing stage, changing from a nanoscale annular depression associated with each focused ion beam spot to a nanoscale pit, and eventually disappearing (planarizing). The correspondence of Ge quantum dot nucleation sites to the focused ion beam features requires a growth surface upon which the nanotopography is preserved. A further key observation is that the Ge wetting layer thickness is reduced in patterned regions, allowing the formation of islands on the templated regions without nucleation elsewhere. These results provide routes to the greatly enhanced design and control of quantum dot distributions and dimensions. Y1 - 2006 U6 - https://doi.org/10.1088/0957-4484/17/17/028 VL - 17 IS - 17 SP - 4451 EP - 4455 PB - IOP ER - TY - JOUR A1 - Ross, Frances M. A1 - Kammler, Martin A1 - Reuter, Mark C. A1 - Hull, Robert T1 - In-situ observations of self-assembled island nucleation on patterned substrates JF - Philosophical Magazine N2 - We compare in-situ electron microscopy observations of Ge island growth on Si surfaces modulated by different techniques. Si(001) substrates were patterned either using a focused Ga ion beam or lithographically to produce similar feature sizes. In the case of the focused-ion-beam patterned substrates, chemical or strain effects caused by low Ga doses control the positions at which islands nucleate. Nucleation on topographically modulated substrates, with the pattern produced either by high-dose sputtering or lithographically, is controlled by the nature of the side walls of topographic features. The two patterning approaches have different benefits in creating arrays of islands for device applications. Y1 - 2004 U6 - https://doi.org/10.1080/14786430410001671430 VL - 84 IS - 25-26 SP - 2687 EP - 2702 PB - Taylor & Francis ER - TY - JOUR A1 - Menzel, Andreas A1 - Conrad, E. H. A1 - Tringides, Michael C. A1 - Kammler, Martin A1 - Horn- von Hoegen, Michael T1 - Finite collection time effects in autocovariance function measurements JF - Journal of Applied Physics N2 - In this paper we discuss how finite data sets influence experimental measurements of the autocovariance function. Autocovariance estimators are biased, meaning that the expectation value for any measured autocovariance function is not identical to the actual autocovariance function. In this work we show that the measured autocovariance function for a finite length time series must become negative for some lag times. We derive analytic corrections to these finite time errors for different types of correlated random sequences. Our results explain the apparent anticorrelated noise observed in experimental observations. Y1 - 2003 U6 - https://doi.org/10.1063/1.1537466 VL - 93 IS - 4 SP - 2229 EP - 2235 PB - AIP Publishing ER - TY - JOUR A1 - Kammler, Martin A1 - Hull, Robert A1 - Reuter, Mark C. A1 - Ross, Frances M. T1 - Lateral control of self-assembled island nucleation by focused-ion-beam micropatterning JF - Applied Physics Letters N2 - We demonstrate that the nucleation sites of nanoscale, self-assembled Ge islands on Si(001) can be controlled by patterning the Si surface in situ with a focused ion beam. At low doses of 6000 Ga+ ions per <100 nm spot, the selective growth is achieved without modifying the initial surface topography. At larger doses, topographic effects produced by sputtering and redeposition control the selective nucleation sites. Islands grown on irradiated spots are smaller with higher aspect ratio than islands grown on clean Si(001), suggesting a strong surfactant effect of Ga. Y1 - 2003 U6 - https://doi.org/10.1063/1.1542680 VL - 82 IS - 7 SP - 1093 EP - 1095 ER - TY - JOUR A1 - Sokolowski-Tinten, Klaus A1 - Blome, Christian A1 - Blums, Juris A1 - Shymanovich, Uladzimir A1 - Nicoul, Matthieu A1 - Cavalleri, Andrea A1 - Tarasevitch, A. A1 - Horn-von Hoegen, Michael A1 - Kammler, Martin A1 - von der Linde, D. T1 - Ultrafast X-ray diffraction JF - Ultrafast Phenomena XIV N2 - In the last few years the generation of femtosecond pulses in the X-ray regime has become possible. These ultrashort X-ray pulses have enabled femtosecond time- resolution to be extended to X-rays. Y1 - 2005 U6 - https://doi.org/10.1007/3-540-27213-5_53 VL - 79 SP - 170 EP - 174 PB - Springer ER - TY - JOUR A1 - Kammler, Martin A1 - Hull, Robert A1 - Portavoce, A. A1 - Reuter, Mark C. A1 - Ross, Frances M. T1 - In-Situ Focused Ion Beam Micropatterning of Ge Islands JF - Microscopy and Microanalysis Y1 - 2003 U6 - https://doi.org/10.1017/S1431927603441214 VL - 9 IS - S02 SP - 132 EP - 134 PB - Microscopy Society of America ER - TY - JOUR A1 - Moser, Elisabeth A1 - Jobst, Simon A1 - Bierl, Rudolf A1 - Jenko, Frank T1 - A Deep Learning System to Transform Cross-Section Spectra to Varying Environmental Conditions JF - Vibrational Spectroscopy N2 - Absorption cross-sections provide a basis for many gas sensing applications. Therefore, any error in molecular cross-sections caused by varying environmental conditions propagates to spectroscopic applications. Original molecular cross-sections in varying environmental conditions can only be simulated for some molecules, whereas for most multi-atom molecules, one must rely on high-precision measurements at certain environmental configurations. In this study, a deep learning system trained with simulated absorption cross-sections for predicting cross-sections at a different pressure configuration is presented. The system’s capability to transfer to measured, multi-atom cross-sections is demonstrated. Thus, it provides an alternative to (pseudo-) line lists whenever the required information for simulation is unavailable. The predictive performance of the system was evaluated on validation data via simulation, and its transfer learning capabilities were demonstrated on actual measurement chlorine nitrate data. From the comparison between the system and line lists, the system shows slightly worse performance than pseudo-line lists but its predictive quality is still deemed acceptable with less than 5% relative integral change with a highly localized error around the peak center. This opens a promising way for further research to use deep learning to simulate the effect of varying environmental conditions on absorption cross-sections. KW - Spectroscopy KW - Deep learning KW - Simulation KW - Pressure broadening KW - Pseudo-line lists KW - Transfer learning Y1 - 2022 U6 - https://doi.org/10.1016/j.vibspec.2022.103410 SN - 0924-2031 VL - 122 IS - September PB - Elsevier ER - TY - JOUR A1 - Goldschmidt, Jens A1 - Moser, Elisabeth A1 - Nitzsche, Leonard A1 - Bierl, Rudolf A1 - Wöllenstein, Jürgen T1 - Improving the performance of artificial neural networks trained on synthetic data in gas spectroscopy – a study on two sensing approaches JF - tm - Technisches Messen N2 - Artificial neural networks (ANNs) are used in quantitative infrared gas spectroscopy to predict concentrations on multi-component absorption spectra. Training of ANNs requires vast amounts of labelled training data which may be elaborate and time consuming to obtain. Additional data can be gained by the utilization of synthetically generated spectra, but at the cost of systematic deviations to measured data. Here, we present two approaches to train ANNs with a combination of comparatively small, measured data sets and synthetically generated data. For the first approach a neural network is trained hybridly with synthetically generated infrared absorption spectra of mixtures of N2O and CO and measured zero-gas spectra, taken with a mid-infrared dual comb spectrometer. This improves the mean absolute error (MAE) of the network predictions from 0.46 to 0.01 ppmV and 0.24 to 0.01 ppmV for the concentration predictions of N2O and CO respectively for zero-gas measurements which was previously observed for training with purely synthetic data. At the same time a similar performance on spectra from gas mixtures of 0–100 ppmV N2O and 0 to 60 ppmV CO was achieved. For the second approach an ANN pre-trained on synthetic infrared spectra of mixtures of acetone and ethanol is retrained on a small dataset consisting of 26 spectra taken with a mid-infrared photoacoustic spectrometer. In this case the MAE for the concentration predictions of ethanol and acetone are improved by 45 % and 20 % in comparison to purely synthetic training. This shows the capability of using synthetically generated data to train ANNs in combination with small amounts of measured data to further improve neural networks for gas sensing and the transferability between different sensing approaches. N2 - Künstliche neuronale Netze werden in der quantitativen Infrarot-Gasspektroskopie eingesetzt, um Gaskonzentrationen in Multi-Komponenten-Absorptionsspektren vorherzusagen. Das Training von künstlichen neuronalen Netzen benötigt große Mengen an Trainingsdaten, was mit einem hohen Arbeits- und Zeitaufwand verbunden ist. Zusätzliche Trainingsdaten können durch synthetisch generierte Spektren gewonnen werden, sind jedoch mit systematischen Abweichungen zu tatsächlich gemessenen Daten verbunden. In dieser Arbeit werden zwei Ansätze präsentiert, um künstliche neuronale Netze mit einer Kombination aus vergleichsweise kleinen, gemessenen Datensätzen und synthetisch erzeugten Daten zu trainieren. Für den ersten Ansatz wird das neuronale Netz hybrid mit synthetisch erzeugten Infrarot-Absorptionsspektren von Mischungen aus N2O und CO und gemessenen Null-Gas-Spektren trainiert, welche mit einem Doppel-Kamm-Spektrometer im Mittelinfraroten aufgenommen wurden. Dieses Vorgehen verbessert den mittleren, absoluten Fehler der Netzvorhersagen von 0,46 auf 0,01 ppmV und 0,24 auf 0,01 ppmV für N2O bzw. für CO für Null-Gas-Messungen, im Vergleich zu den Vorhersagen des neuronalen Netzes, welches nur mit synthetisch erzeugten Daten trainiert wurde. Gleichzeitig zeigte das hybrid trainierte Netz eine gleichbleibende Performance für Konzentrationsvorhersagen für Spektren aus Gasmischungen von 0 bis 100 ppmV N2O und 0 bis 60 ppmV CO. Für den zweiten Ansatz wird ein neuronales Netz, welches bereits mit synthetischen erzeugten Infrarotspektren von Mischungen aus Aceton und Ethanol trainiert wurde, erneut auf einem kleinen gemessenen Datensatz bestehend aus 26 Spektren trainiert, welche mit einem photoakustischen Spektrometer im mittleren Infrarot aufgenommen wurden. In diesem Fall hat sich der mittlere absolute Fehler der Konzentrationsvorhersage für Ethanol und Aceton um 45 % bzw. 20 % im Vergleich zu einem rein synthetischen Training verbessert. Das zeigt das Potential synthetisch erzeugte Daten für das Training von künstlichen neuronalen Netzen in Kombination mit kleinen gemessenen Datensätzen zu nutzen, um neuronale Netze für den Einsatz im Bereich der Gassensorik zu verbessern und gleichzeitig die Übertragbarkeit der Methodik auf verschiedene Messansätze. Y1 - 2023 U6 - https://doi.org/10.1515/teme-2023-0051 PB - Oldenbourg Wissenschaftsverlag ET - Online veröffentlicht ER - TY - JOUR A1 - Müller, Max A1 - Weigl, Stefan A1 - Müller-Williams, Jennifer A1 - Lindauer, Matthias A1 - Rück, Thomas A1 - Jobst, Simon A1 - Bierl, Rudolf A1 - Matysik, Frank-Michael T1 - Comparison of photoacoustic spectroscopy and cavity ring-down spectroscopy for ambient methane monitoring at Hohenpeißenberg JF - Atmospheric Measurement Techniques N2 - With an atmospheric concentration of approximately 2000 parts per billion (ppbV, 10−9), methane (CH4) is the second most abundant greenhouse gas (GHG) in the atmosphere after carbon dioxide (CO2). The task of long-term and spatially resolved GHG monitoring to verify whether climate policy actions are effective is becoming more crucial as climate change progresses. In this paper we report the CH4 concentration readings of our photoacoustic (PA) sensor over a 5 d period at Hohenpeißenberg, Germany. As a reference device, a calibrated cavity ring-down spectrometer, Picarro G2301, from the meteorological observatory of the German Weather Service (DWD) was employed. Trace gas measurements with photoacoustic instruments promise to provide low detection limits at comparably low costs. However, PA devices are often susceptible to cross-sensitivities related to fluctuating environmental conditions, e.g. ambient humidity. The obtained results show that for PA sensor systems non-radiative relaxation effects induced by varying humidity are a non-negligible factor. Applying algorithm compensation techniques, which are capable of calculating the influence of non-radiative relaxation effects on the photoacoustic signal, increase the accuracy of the photoacoustic sensor significantly. With an average relative deviation of 1.11 % from the G2301, the photoacoustic sensor shows good agreement with the reference instrument. Y1 - 2023 U6 - https://doi.org/10.5194/amt-16-4263-2023 SN - 1867-8548 VL - 16 IS - 18 SP - 4263 EP - 4270 PB - Copernicus Publications ER - TY - JOUR A1 - Fritz, D. M. A1 - Reis, D. A. A1 - Adams, B. A1 - Akre, R. A. A1 - Arthur, J. A1 - Blome, Christian A1 - Bucksbaum, P. H. A1 - Cavalieri, A. L. A1 - Engemann, S. A1 - Fahy, S. A1 - Falcone, R. W. A1 - Fuoss, P. H. A1 - Gaffney, K. J. A1 - George, M. J. A1 - Hajdu, J. A1 - Hertlein, M. P. A1 - Hillyard, P. B. A1 - Horn-von Hoegen, Michael A1 - Kammler, Martin A1 - Kaspar, J. A1 - Kienberger, R. A1 - Krejcik, P. A1 - Lee, S. H. A1 - Lindenberg, A. M. A1 - McFarland, B. A1 - Meyer, D. A1 - Montagne, T. A1 - Murray, E. D. A1 - Nelson, A. J. A1 - Nicoul, Matthieu A1 - Pahl, R. A1 - Rudati, J. A1 - Schlarb, H. A1 - Siddons, D. P. A1 - Sokolowski-Tinten, Klaus A1 - Tschentscher, Th A1 - von der Linde, D. A1 - Hastings, J. B. T1 - Ultrafast bond softening in bismuth: mapping a solid's interatomic potential with X-rays JF - Science N2 - Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be substantially altered. Here, we present the detailed mapping of the carrier density-dependent interatomic potential of bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques that use a high-brightness linear electron accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution, allowing quantitative characterization of the interatomic potential energy surface of the highly excited solid. Y1 - 2007 U6 - https://doi.org/10.1126/science.1135009 VL - 315 IS - 5812 SP - 633 EP - 636 PB - AAAS ER - TY - JOUR A1 - Kammler, Martin A1 - Horn- von Hoegen, Michael A1 - Voss, N. A1 - Tringides, Michael C. A1 - Menzel, Andreas A1 - Conrad, E. H. T1 - Si(001) step dynamics: A temporal low-energy electron diffraction study JF - Physical Review B N2 - We present equilibrium measurements of the dynamics of steps on Si(001) using temporal electron-diffraction spectroscopy. Activation energies and the rate limiting kinetics are identified for 950K<~T<~1130K. Unlike previous studies at higher temperatures, we can exclude evaporation and condensation of atoms or dimers from the step edges as the rate limiting process in this temperature regime. The possible reason for this difference is discussed in terms of a crossover from different rate-limiting kinetics. Y1 - 2002 U6 - https://doi.org/10.1103/PhysRevB.65.075312 VL - 65 IS - 7 PB - APS ER - TY - JOUR A1 - Pirker, Luka A1 - Ławrowski, Robert Damian A1 - Schreiner, Rupert A1 - Remškar, Maja A1 - Višić, Bojana T1 - MoₓWₓ₋₁S₂ Nanotubes for Advanced Field Emission Application JF - Advanced Functional Materials N2 - Transition metal dichalcogenide (TMDC) nanotubes complement the field of low-dimensional materials with their quasi-1D morphology and a wide set of intriguing properties. By introducing different transition metals into the crystal structure, their properties can be tailored for specific purpose and applications. Herein, the characterization and a subsequent preparation of single-nanotube field emission devices of MoxWx-1S2 nanotubes prepared via the chemical vapor transport reaction is presented. Energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction indicate that the molybdenum and tungsten atoms are randomly distributed within the crystal structure and that the material is highly crystalline. High resolution transmission electron microscopy and electron diffraction (ED) patterns further corroborate these findings. A detailed analysis of the ED patterns from an eight-layer nanotube reveal that the nanotubes grow in the 2H structure, with each shell consists of one bilayer. The work function of the nanotubes is comparable to that of pure MoS2 and lower of pure WS2 NTs, making them ideal candidates for field emission applications. Two devices with different geometrical setup are prepared and tested as field emitters, showing promising results for single nanotube field emission applications. Y1 - 2023 U6 - https://doi.org/10.1002/adfm.202213869 SN - 1616-3028 N1 - Early View. Online Version of Record before inclusion in an issue SP - 1 EP - 8 PB - Wiley ER - TY - JOUR A1 - Krenzer, Boris A1 - Hanisch-Blicharski, Anja A1 - Schneider, Paul A1 - Payer, Thomas A1 - Möllenbeck, Simone A1 - Osmani, O. A1 - Kammler, Martin A1 - Meyer, R. A1 - Horn-von Hoegen, Michael T1 - Phonon confinement effects in ultrathin epitaxial bismuth films on silicon studied by time-resolved electron diffraction JF - Physical Review B N2 - The transient temperature evolution of ultrathin bismuth films, epitaxially grown on a silicon single crystal, upon femtosecond laser excitation is studied by time-resolved electron diffraction. The exponential decay of the film temperature is explained by phonon reflection at the interface, which results in a strongly reduced thermal conduction in the cross plane of the layered system. The thermal boundary conductance is found to be as low as 1273 W/(K cm2). Model calculations, including phonon confinement effects, explain the linear relationship between the observed film-temperature decay constant and the film thickness. Even for 2.5 nm thin films the phonon transmission probability across the interface is given by bulk properties. Our simulations show that phonon confinement effects are negligible for bismuth-film thicknesses larger than 1 nm. Y1 - 2009 U6 - https://doi.org/10.1103/PhysRevB.80.024307 VL - 80 IS - 2 PB - APS ER - TY - JOUR A1 - Klein, C. A1 - Nabbefeld, T. A1 - Hattab, H. A1 - Meyer, D. A1 - Jnawali, G. A1 - Kammler, Martin A1 - Meyer zu Heringdorf, Frank-Joachim A1 - Golla-Franz, A. A1 - Müller, B. H. A1 - Schmidt, Thomas A1 - Henzler, M. A1 - Horn-von Hoegen, Michael T1 - Lost in reciprocal space? Determination of the scattering condition in spot profile analysis low-energy electron diffraction JF - Review of scientific instruments N2 - The precise knowledge of the diffraction condition, i.e., the angle of incidence and electron energy, is crucial for the study of surface morphology through spot profile analysis low-energy electron diffraction (LEED). We demonstrate four different procedures to determine the diffraction condition: employing the distortion of the LEED pattern under large angles of incidence, the layer-by-layer growth oscillations during homoepitaxial growth, a G(S) analysis of a rough surface, and the intersection of facet rods with 3D Bragg conditions. Y1 - 2011 U6 - https://doi.org/10.1063/1.3554305 VL - 82 IS - 3 PB - American Institute of Physics ER - TY - JOUR A1 - Schmidt, Thomas A1 - Kröger, Roland A1 - Clausen, T. A1 - Falta, J. A1 - Janzen, Andreas A1 - Kammler, Martin A1 - Kury, P. A1 - Zahl, P. A1 - Horn-von Hoegen, Michael T1 - Surfactant-mediated epitaxy of Ge on Si(111): Beyond the surface JF - Applied Physics Letters N2 - For a characterization of interface and “bulk” properties of Ge films grown on Si(111) by Sb surfactant-mediated epitaxy, grazing incidence x-ray diffraction and transmission electron microscopy have been used. The interface roughness, defect structure, and strain state have been investigated in dependence of film thickness and growth temperature. For all growth parameters, atomically smooth interfaces are observed. For thin Ge layers, about 75% of the strain induced by the lattice mismatch is relaxed by misfit dislocations at the Ge/Si interface. Only a slight increase of the degree of relaxation is found for thicker films. At growth temperatures below about 600 °C, the formation of twins is observed, which can be avoided at higher temperatures. Y1 - 2005 U6 - https://doi.org/10.1063/1.1882760 VL - 86 IS - 11 PB - AIP ER - TY - JOUR A1 - Frigge, Tim A1 - Wall, S. A1 - Krenzer, Boris A1 - Wippermann, St. A1 - Sanna, Simone A1 - Klasing, Friedrich A1 - Hanisch-Blicharski, Anja A1 - Kammler, Martin A1 - Schmidt, Wolf Gero A1 - Horn-von Hoegen, Michael T1 - Abstract - A Reply to the Comment by H. Shim et al. JF - Physical review letters Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevLett.111.149602 VL - 111 IS - 14 PB - American Physical Society ER - TY - JOUR A1 - Chee, See Wee A1 - Kammler, Martin A1 - Graham, Jeremy A1 - Ross, Frances M. A1 - Hull, Robert T1 - Direct Imaging of Microstructural Changes in Si Induced by FIB-Patterning with Si ++ and Ga + Ions JF - Microscopy and Microanalysis Y1 - 2011 U6 - https://doi.org/10.1017/S1431927611004156 VL - 17 IS - S2 SP - 656 EP - 657 PB - Cambridge University Press ER - TY - JOUR A1 - Schels, Andreas A1 - Herdl, Florian A1 - Hausladen, Matthias A1 - Wohlfartsstätter, Dominik A1 - Edler, Simon A1 - Bachmann, Michael A1 - Pahlke, Andreas A1 - Schreiner, Rupert A1 - Hansch, Walter T1 - Quantitative Field Emission Imaging for Studying the Doping-Dependent Emission Behavior of Silicon Field Emitter Arrays JF - Micromachines N2 - Field emitter arrays (FEAs) are a promising component for novel vacuum micro- and nanoelectronic devices, such as microwave power amplifiers or fast-switching X-ray sources. However, the interrelated mechanisms responsible for FEA degradation and failure are not fully understood. Therefore, we present a measurement method for quantitative observation of individual emission sites during integral operation using a low-cost, commercially available CMOS imaging sensor. The emission and degradation behavior of three differently doped FEAs is investigated in current-regulated operation. The measurements reveal that the limited current of the p-doped emitters leads to an activation of up to 55% of the individual tips in the array, while the activation of the n-type FEA stopped at around 30%. This enhanced activation results in a more continuous and uniform current distribution for the p-type FEA. An analysis of the individual emitter characteristics before and after a constant current measurement provides novel perspectives on degradation behavior. A burn-in process that trims the emitting tips to an integral current-specific ideal field enhancement factor is observed. In this process, blunt tips are sharpened while sharp tips are dulled, resulting in homogenization within the FEA. The methodology is described in detail, making it easily adaptable for other groups to apply in the further development of promising FEAs. Y1 - 2023 U6 - https://doi.org/10.3390/mi14112008 VL - 14 IS - 11 PB - MDPI ER - TY - JOUR A1 - Bachmann, Michael A1 - Düsberg, Felix A1 - Pahlke, Andreas A1 - Edler, Simon A1 - Schels, Andreas A1 - Herdl, Florian A1 - Hausladen, Matthias A1 - Buchner, Philipp A1 - Schreiner, Rupert T1 - The “LED‐version” of the electron gun: An electron source for operation in ambient pressure environments based on silicon field emitter arrays JF - Vakuum in Forschung und Praxis N2 - We report on our progress to develop and optimize electron sources for practical applications. A simple fabrication process is introduced based on a wafer dicing saw and a wet chemical etch step without the need for a clean room. Due to the formation of crystal facets the samples show a homogeneous geometry throughout the array. Characterization techniques are developed to systematically compare various arrays. A very defined measurement procedure based on current controlled IV-sweeps as well as lifetime measurements at various currents is proposed. To investigate the current distribution in the array a commercial CMOS detector is used and shows the potential for in depth analysis of the arrays. Finally, a compact hermetically sealed housing is presented enabling electron generation in atmospheric pressure environments. Y1 - 2023 U6 - https://doi.org/10.1002/vipr.202300801 VL - 35 IS - 3 SP - 32 EP - 37 PB - Wiley ER - TY - JOUR A1 - Hausladen, Matthias A1 - Schels, Andreas A1 - Buchner, Philipp A1 - Bartl, Mathias A1 - Asgharzade, Ali A1 - Edler, Simon A1 - Wohlfartsstätter, Dominik A1 - Bachmann, Michael A1 - Schreiner, Rupert T1 - Measurement of field emission array current distributions by metal-coated CMOS image sensors JF - Journal of Vacuum Science & Technology B N2 - A CMOS image sensor is utilized to determine the time- and spatially resolved distribution of the total electron emission current of a silicon field emission array. The sensor measures electron emission without the need for phosphorus screens or scintillators as converters. However, in initial experiments, rather low field emission currents of several hundreds of nanoamperes per emitter already damaged the sensor surface, which altered the systems’ signal response over the measurement time. In consequence, we coated the CMOS sensor surface with a Cu layer for surface protection. In contrast to the original insulating surface, Cu is an excellent current- and heat-conductor, which avoids lens charging by providing a conductive path for incident electrons and has an improved heat dissipation capability. Measurements using a segmented field emission cathode with four individually addressable tips demonstrate a consistent correlation between the emission current and the sensor signal of the metal-coated image sensor. Furthermore, the characterization of a field emission array showed that single tip emission currents of up to 12 μA per tip are measurable without discernible damage effects of the sensor’s surface. KW - Bremsstrahlung KW - Laser micromachining KW - Image sensors KW - Field emitter arrays Y1 - 2024 U6 - https://doi.org/10.1116/6.0004074 VL - 42 IS - 6 PB - AIP Publishing ER - TY - JOUR A1 - Schreiner, Rupert A1 - Wiedmann, J. A1 - Coenning, W. A1 - Porsche, J. A1 - Gentner, Jean-Louis A1 - Berroth, Manfred A1 - Scholz, Ferdinand A1 - Schweizer, H. T1 - Fabrication approach for antiphase narrow linewidth complex coupled 1.55 μm DFB lasers JF - Electronics Letters N2 - A new method for fabricating narrow linewidth antiphase complex coupled MQW DFB lasers by periodically etching the active layer and quartemary InGaAsP overgrowth is reported. The minimum linewidth for a 375 µm long ridge waveguide laser is only 250 kHz at an optical output power of 4 mW. KW - etching KW - optical fabrication KW - quantum well lasers KW - ridge waveguides KW - distributed feedback lasers Y1 - 1999 U6 - https://doi.org/10.1049/el:19990132 SN - 0013-5194 VL - 35 IS - 2 SP - 146 EP - 148 PB - The Institution of Engineering and Technology IET ER - TY - JOUR A1 - Hausladen, Matthias A1 - Schels, Andreas A1 - Asgharzade, Ali A1 - Buchner, Philipp A1 - Bartl, Mathias A1 - Wohlfartsstätter, Dominik A1 - Edler, Simon A1 - Bachmann, Michael A1 - Schreiner, Rupert T1 - Investigation of Influencing Factors on the Measurement Signal of a CMOS Image Sensor for Measuring Field Emission Currents JF - Sensors Y1 - 2025 U6 - https://doi.org/10.3390/s25051529 N1 - Corresponding author der OTH Regensburg: Matthias Hausladen VL - 25 IS - 5 PB - MDPI ER - TY - JOUR A1 - Schwarz, Tobias A1 - Pastötter, Angelina A1 - Tran, T. H. A1 - Schlosser, Marc A1 - Kaulen, Corinna A1 - Lechner, Alfred A1 - Slabon, A. A1 - Kammler, Martin T1 - Effect of temperature on the growth of Cupric and Cuprous Nanoparticles in a wet chemical synthesis JF - Materials Letters N2 - Cuprous oxide (Cu2O) and cupric oxide (CuO) particles were synthesized using a wet chemical surfactant free method at different synthesis temperatures from 25 °C to 60 °C. Morphology, size, and chemical composition of the prepared Cu2O particles were analyzed by FESEM, PXRD, and UV-vis. We discovered that the chemical composition of the Cu2O particles remained unaffected by the synthesis temperature. However, morphology and size of the particles showed a strong temperature dependency. This could be attributed to the temperature induced formation of CuO species from the copper hydroxide (Cu(OH)2) precursor which also functions as copper precursor for the Cu2O particle growth. The cupric oxide species was determined to be the main cause for the formation of micrometer sized particles, whereas with the Cu(OH)2 precursor species for the Cu2O particles nanocubes with smaller edge lengths as well as octahedrons were obtained. KW - Crystal structure KW - Crystal growth KW - Nanoparticle KW - Copper oxide Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-79279 VL - 381 PB - Springer Nature ER - TY - JOUR A1 - Bresinsky, Markus A1 - Fillenberg, Barbara T1 - Krisen, Katastrophen und Konflikte JF - Hebammen Wissen N2 - Hebammen als Akteurinnen im Bevölkerungsschutz In Deutschland folgt der Bevölkerungsschutz einer komplexen Struktur, die sich größtenteils auch auf das Rettungswesen stützt. Doch die wertvolle Ressource Hebammentätigkeit wurde dabei bisher nicht mitgedacht. Y1 - 2025 U6 - https://doi.org/10.1007/s43877-025-1335-x VL - 6 IS - 4 SP - 24 EP - 27 ER - TY - JOUR A1 - Diachkova, Yana A1 - Nikolaeva, Sofiya A1 - Guertler, Katherine T1 - Communication in International Humanitarian Relief: Profiling Ukrainian Boundary Spanners JF - Journal of Intercultural Communication N2 - Boundary spanning—the actions and roles individuals or organizations undertake to bridge differences and facilitate communication, collaboration, and understanding across diverse cultural, organizational, or geographical divisions—is an essential element of international cooperation. Set against the backdrop of the Russia-Ukraine war, The purpose of this study is to explore the type of boundary spanning in this uncertain context, the linguistic characteristics of boundary spanners, the necessary skills and competencies required to navigate the complex socio-political landscape, and the role of boundary spanners in humanitarian assistance. This study employs a qualitative research approach, using semi-structured interviews with informants actively engaged in relief efforts and cross-cultural collaboration. The findings emphasized the significance of English as the primary language of communication, the importance of cultural sensitivity and awareness, and the need for intercultural competence in effective boundary spanning. The study concludes with insights from the ongoing Ukrainian experience of bridging geodemographic boundaries and the role of boundary spanners in this process, highlighting key aspects of boundary spanning. Overall, the study contributes to the theoretical background of boundary spanning and enhances the understanding of how linguistic and cultural boundary spanning can drive positive change and improve outcomes in humanitarian aid. The implications of this study suggest that underscore the critical need for collaboration with experienced boundary spanners in educational settings. Y1 - 2025 U6 - https://doi.org/10.36923/jicc.v25i1.1019 SN - 1404-1634 N1 - Corresponding author der Partnerhochschule aus Kiew: Yana Diachkova VL - 25 IS - 1 SP - 98 EP - 106 PB - ICR Publications ER - TY - JOUR A1 - Eiler, Julian A1 - Weber, Stefan A1 - Gerlesberger, Peter A1 - Plöchinger, Heinz A1 - Schreiner, Rupert T1 - Active heat-loss compensated miniaturized pirani sensor chip JF - IEEE Sensors Letters N2 - Due to the limited measuring range of commercial Pirani sensors in lower pressure regimes, attempts are being made to extend the measuring range of the sensors. Our approach to extend the measuring range toward lower pressures is a micro-electromechanical systems (MEMS) Pirani sensor with active heat compensation on the suspensions. The sensor element has the shape of a microhotplate and consists of a nickel heating meander embedded in two silicon nitride layers. The whole structure is built on a silicon wafer. The sensor element is suspended on all four corners of the substrate. On each of the suspensions, there is an additional heating structure that minimizes the heat flux from the hot sensor element toward the substrate. The sensor is driven at a constant temperature through a self-balancing Wheatstone bridge. A constant voltage is applied to the heating structures on the suspensions. It has been demonstrated that with these additional heaters, the sensitivity of the sensor can be increased in the high-vacuum regime. This enables reliable vacuum measurements down to 10−6 mbar. KW - Temperature measurement KW - Heating systems KW - Temperature sensors KW - Sensitivity KW - Pressure measurement KW - Voltage measurement KW - Heat sinks KW - Semiconductor device measurement KW - Noise measurement KW - Bridge circuits Y1 - 2025 U6 - https://doi.org/10.1109/LSENS.2025.3605747 SN - 2475-1472 VL - 9 IS - 10 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - JOUR A1 - Pierobon, Chiara A1 - Sharshenova, Aijan T1 - German and Russian Public Diplomacy Efforts in Kyrgyzstan: A Comparative Study of Norm Entrepreneurship JF - Europe-Asia Studies N2 - This article explores Russian and German public diplomacy efforts in Central Asia through the example of Kyrgyzstan. Due to a difficult economic and socio-political situation, Kyrgyzstan remains open to externally funded programmes and projects, including initiatives funded by foreign governments, and thus offers a unique environment for the study of public diplomacy. The article looks at transnational public diplomacy actors such as German political foundations and Russian-sponsored organisations active in the country. Overall, the article offers interesting insights into the nature and substance of the soft power policies pursued by Germany and Russia that are relevant for Kyrgyzstan and beyond. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-87380 VL - 75 IS - 8 SP - 1384 EP - 1407 PB - Taylor & Francis ER - TY - JOUR A1 - Pierobon, Chiara T1 - European Union, civil society and local ownership in Kyrgyzstan: analysing patterns of adaptation, reinterpretation and contestation in the prevention of violent extremism (PVE) JF - Central Asian Survey N2 - In the last decade, a growing body of literature has investigated the promotion of good governance, rule of law, democracy and human rights in Central Asia through funding from the European Union (EU). Most of this research has taken an EU-centric approach and is concerned with the supply side of external democratization. As a result, little is known about how EU projects are implemented on the ground and what EU-funded civil society organizations consider to be their priorities. This article investigates the agency of such organizations in Kyrgyzstan by focusing on their contribution to one particular EU instrument: the Instrument contributing to Stability and Peace (IcSP), and its programme: Strengthening Resilience to Violence and Extremism (STRIVE). The findings offer new insights into the processes of adaptation, reinterpretation and contestation through which EU-funded organizations exercise ownership while engaging in the prevention of violent extremism (PVE). Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-87378 VL - 41 IS - 4 SP - 752 EP - 769 PB - Taylor & Francis ER - TY - JOUR A1 - Pierobon, Chiara T1 - EU’s support to civil society in Kazakhstan: A pilot evaluation of the social capital generated JF - Evaluation N2 - In the last decade, several studies have been devoted to the analysis of the EU’s support to civil society abroad, but only recently has scholarly attention turned to Central Asia. Most of the research in this field has adopted a macro-level perspective, concerned with the supply side of external democratization, and has examined external assistance to civil society in terms of democratization ideal types and typologies. The main contribution of this study consists of a meso-level analysis of the outcomes of the EU’s support to civil society in terms of production of social capital, conceived as the raw material of civil society itself. More precisely, the article evaluates the first wave of grants awarded to civil society organizations in Kazakhstan as part of two EU funding schemes—the European Instrument for Democracy and Human Rights and the Non-State Actors and Local Authorities in Development. The article sheds new light on the use of social capital and its two dimensions-structural and cognitive-as heuristic tools for evaluating civil society support programs. Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-87394 VL - 25 IS - 2 SP - 207 EP - 223 PB - Sage ER - TY - JOUR A1 - Wolfgramm, Alex A1 - Abb, Valerius A1 - Samp, Artur A1 - Samp, Rafal A1 - Hoffmann, Jens Christoph A1 - Müller, Rainer A1 - Kammler, Martin T1 - Structural and functional evolution of HKUST-1 nanoparticles induced by ball milling JF - Next Materials N2 - In this study, the effect of post-synthetic ball milling on the structural and functional properties of as-synthesized nanoparticles of the copper-based metal-organic framework (MOF) HKUST-1 was investigated for the first time. Nanoparticles were synthesized using sodium formate as a capping agent. The crystalline particles were subjected to a controlled ball milling process, which induced significant structural changes. Powder X-ray diffraction (PXRD) revealed a reduction in crystallite size from 91 nm to 21 nm and the introduction of microstrain, partially disrupting the MOF's long-range crystalline order, as evidenced by peak broadening and the diminished intensity of high-angle reflections. Particle morphology pre- and post-milling was further studied with scanning electron microscopy (SEM) imaging, verifying a narrow particle size distribution of ± 22 nm after milling. Fourier-transform infrared spectroscopy (FTIR) indicated protonation of carboxylate groups in the larger pores of the framework, likely due to moisture incorporation during milling. Brunauer-Emmett-Teller (BET) surface area analysis showed a substantial decrease in specific surface area from 521 m²/g to 226 m²/g, suggesting a partial collapse of the porous framework. We discuss the applicability of ball milling as a versatile means of post-synthetic approach to reduce MOF particle sizes, a key element in the preparation of MOF-based thin films using inks or polymers. KW - Ball milling KW - Copper-based metal-organic framework KW - HKUST-1 KW - Nitrogen adsorption Y1 - 2026 U6 - https://doi.org/10.1016/j.nxmate.2025.101544 N1 - Corresponding author der OTH Regensburg: Alex Wolfgramm VL - 10 PB - Elsevier ER - TY - JOUR A1 - Buchner, Philipp A1 - Hausladen, Matthias A1 - Bartl, Mathias A1 - Bachmann, Michael A1 - Schreiner, Rupert T1 - High current field emission from Si nanowires on pillar structures JF - Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics N2 - We investigate the influence of the geometry and doping level on the performance of n-type silicon nanowire field emitters on silicon pillar structures. Therefore, multiple cathodes with 50 by 50 pillar arrays (diameter: 5 μm, height: 30 μm, spacing: 50 μm) were fabricated and measured in diode configuration. In the first experiment, we compared two geometry types using the same material. Geometry 1 is black silicon, which is a highly dense surface covering a forest of tightly spaced silicon needles resulting from self-masking during a plasma etching process of single crystal silicon. Geometry 2 are silicon nanowires, which are individual spaced-out nanowires in a crownlike shape resulting from a plasma etching process of single crystal silicon. In the second experiment, we compared two different silicon doping levels [n-type (P), 1–10 and <0.005 Ω cm] for the same geometry. The best performance was achieved with lower doped silicon nanowire samples, emitting 2 mA at an extraction voltage of 1 kV. The geometry/material combination with the best performance was used to assemble an integrated electron source. These electron sources were measured in a triode configuration and reached onset voltages of about 125 V and emission currents of 2.5 mA at extraction voltages of 400 V, while achieving electron transmission rates as high as 85.0%. KW - Doping KW - Electron sources KW - Nanowires KW - Plasma processing KW - Field emitter arrays KW - Triodes KW - Semiconductors Y1 - 2024 U6 - https://doi.org/10.1116/6.0003384 SN - 2166-2754 VL - 42 IS - 2 PB - AIP ER - TY - JOUR A1 - Tan, Jing Jie A1 - Schreiner, Rupert A1 - Hausladen, Matthias A1 - Asgharzade, Ali A1 - Edler, Simon A1 - Bartsch, Julian A1 - Bachmann, Michael A1 - Schels, Andreas A1 - Kwan, Ban-Hoe A1 - Ng, Danny Wee-Kiat A1 - Hum, Yan-Chai T1 - SiMiC: Context-aware silicon microstructure characterization using attention-based convolutional neural networks for field-emission tip analysis JF - Journal of Vacuum Science & Technology B N2 - Accurate characterization of silicon microstructures is essential for advancing microscale fabrication, quality control, and device performance. Traditional analysis using scanning electron microscopy (SEM) often requires labor-intensive, manual evaluation of feature geometry, limiting throughput and reproducibility. In this study, we propose SiMiC: Context-aware Silicon Microstructure Characterization Using Attention-based Convolutional Neural Networks for Field-Emission Tip Analysis. By leveraging deep learning, our approach efficiently extracts morphological features—such as size, shape, and apex curvature—from SEM images, significantly reducing human intervention while improving measurement consistency. A specialized dataset of silicon-based field-emitter tips was developed, and a customized convolutional neural network architecture incorporating attention mechanisms was trained for multiclass microstructure classification and dimensional prediction. Comparative analysis with classical image processing techniques demonstrates that SiMiC achieves high accuracy while maintaining interpretability. The proposed framework establishes a foundation for data-driven microstructure analysis directly linked to field-emission performance, opening avenues for correlating emitter geometry with emission behavior and guiding the design of optimized cold-cathode and SEM electron sources. The related dataset and algorithm repository that could serve as a baseline in this area can be found at https://research.jingjietan.com/?q=SIMIC. KW - Field emitter arrays KW - Quality assurance KW - Convolutional neural network KW - Deep learning KW - Image processing KW - Machine learning KW - Cold cathodes KW - Scanning electron microscopy KW - Electron sources KW - Chemical elements Y1 - 2025 U6 - https://doi.org/10.1116/6.0005068 VL - 43 IS - 6 PB - AVS ER -