@inproceedings{MelekhovAbbLechneretal., author = {Melekhov, Evgeny and Abb, Valerius and Lechner, Alfred and Kammler, Martin}, title = {Development of a glass-fiber-based spectrometer for the determination of drug residues in groundwater}, series = {Tagungsband 2. Symposium Elektronik und Systemintegration ESI 2020 "Intelligente Systeme und ihre Komponenten: Forschung und industrielle Anwendung"}, booktitle = {Tagungsband 2. Symposium Elektronik und Systemintegration ESI 2020 "Intelligente Systeme und ihre Komponenten: Forschung und industrielle Anwendung"}, editor = {Ivanov, Artem and Bicker, Marc and Patzelt, Peter}, isbn = {978-3-9818439-4-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:860-opus4-2174}, pages = {101 -- 109}, abstract = {Within the scope of this project, a portable measuring device has been developed which enables a cost-effective analysis of organic substances from ppm to sub-ppm range, such as drug residues in groundwater. The measurement is carried out by means of a surface-enhanced Raman scattering effect (SERS effect) and an exchangeable sensor head. The sensor head used is a nanostructured optical glass fiber glued into a fiber cannula. The tip of the fiber has been processed to act as a SERS cell. The fiber cannula is connected to a freely movable patch cable by using an adapter. Para-thiocresol is used to characterize the SERS cells.}, language = {en} } @misc{MelekhovAbbWeidaueretal., author = {Melekhov, Evgeny and Abb, Valerius and Weidauer, Tobias and Kammler, Martin and Lechner, Alfred}, title = {Tunable Nanopillars as Surface Enhanced Raman Scattering (SERS) Active Structure for Optical Quartz Glass Fiber}, series = {SMSI 2021 - Sensors and Instrumentation}, journal = {SMSI 2021 - Sensors and Instrumentation}, publisher = {AMA Association for Sensors and Measurement}, isbn = {978-3-9819376-4-0}, doi = {10.5162/SMSI2021/B8.2}, pages = {153 -- 154}, abstract = {In this work, a simple cost effective method to create tunable self-assembled three-dimensional nanostructure array-like nanoantennas on a tip of an optical quartz glass fiber is described. The structures are prepared using lithography-less dry etching. Gold nanoparticles are used as an etching mask using a thin metal-film thermal dewetting technique. The structures are applied as sensor for label-free analysis of organic substances in ppb range, such as drug residues in groundwater. The measurements are carried out by means of a Surface-enhanced Raman scattering (SERS) effect, an exchangeable sensor head, and a portable Raman device. This method allows in situ applications. Parathiocresol is used as a model substance to characterize the SERS cells. For metallization, gold and silver are compared. Reproducible SERS enhancement factors up to 10 7 are evaluated.}, language = {en} } @unpublished{MenzelYehKammleretal., author = {Menzel, Andreas and Yeh, Wang-Chi Vincent and Kammler, Martin and Hupalo, Myron and Conrad, E. H. and Tringides, Michael C.}, title = {Measurements of the kinetic barriers controlling the formation of the uniform height islands in Pb/Si(111)}, abstract = {As demonstrated with SPA-LEED and STM uniform height islands of preferred thickness form during the growth of Pb on Si(111). The islands form at temperatures T<250K and for fluxes F 1/60ML/sec which requires fast kinetics and balance between several atomic processes: diffusion towards the islands , diffusion to higher layers and preference for the atoms to remain on top of the preferred height islands. We have carried out SPA-LEED experiments to measure the barriers of the processes: we prepare an initial predominantly 5-step island height distribution and we deposit an additional 0.5ML Pb at different growth temperatures Tg to determine the transition to the next preferred height of 7-step islands (i.e. 2-step islands on top of the 5-step islands) with Spot Profile Analysis(SPA-LEED). We observe that 7-step island formation is possible above a minimum temperature Tg*=175K which indicates that the transfer of atoms from the surrounding region to the top of the islands is the main controlling process.}, language = {en} } @unpublished{CavalleriSidersTothetal., author = {Cavalleri, Andrea and Siders, Craig and Toth, Csaba and Squier, Jeff A. and Barty, C. P. J. and Wilson, K. R. and Sokolowski-Tinten, Klaus and von der Linde, Dietrich and Kammler, Martin and Horn- von Hoegen, Michael}, title = {Measurement of harmonic and anharmonic semi-conductor-lattice dynamics with ultrafast x-ray diffraction}, abstract = {Many fundamental processes in solids, such as heat transport and phase transitions involve atomic movement on ultrafast time-scales, but cannot be directly measured with visible light. Using ultrafast x-ray diffraction, atomic motion can be measured on its natural time-scale. Photo-excitation of bulk and layered semiconductors was achieved with 800-nm wavelength femtosecond laser pulses. Optical excitation triggers a chain of relaxation processes, causing rapid lattice heating, generation and propagation of stress/strain waves into the bulk and eventual anharmonic decay of coherent acoustic phonons into the thermal bath of the solid. While the first steps of carrier relaxation, excitation and decay of Raman-active optical phonons have been in the past characterized optically at surfaces, the bulk acoustic dynamics at longer times has not. We measure length scales of lattice excitation, thereby detecting ultrafast heat diffusion via fast electrons, coherent acoustic pulse propagation into the bulk or across buried interfaces and anharmonic damping of non-equilibrium acoustic phonons. The measurement is performed with sensitivity on lattice spacing of 10 femtometers (i.e., 3 nuclear diameters).}, language = {en} } @unpublished{SidersCavalleriTothetal., author = {Siders, Craig and Cavalleri, Andrea and Toth, Csaba and Squier Jeff A., and Barty, C. P. J. and Wilson, K. R. and Sokolowski-Tinten, Klaus and von der Linde, Dietrich and Kammler, Martin and Horn- von Hoegen, Michael}, title = {Ultrafast Nonthermal Melting of Femtosecond-laser-irradiated Germanium Measured by Ultrafast X-ray Diffraction}, abstract = {Many fundamental processes in nature, such as chemical reactions and phase transitions involve rearrangement of the constituent atoms. Such changes cannot be directly measured with visible light and occur transiently on time-scales comparable with the natural oscillation periods of atoms (femtoseconds to picoseconds). We present experiments on Ge-111 films irradiated with 100-fs 800-nm light pulses and probed by a time-delayed sub-ps x-ray pulse at 8 keV. After excitation of a dense electron-hole plasma within the 160-nm film, the ultrafast pathway of lattice disordering is measured as a function laser fluence. For close-to-threshold irradiation, inhomogeneous thermal melting, occurring via surface nucleation of the liquid phase and growth into the bulk determines the dynamics of the solid-to-liquid phase transition. For excitation at about twice the melting threshold, a nonthermal pathway, starting from a highly excited cold solid and relaxing into a hot liquid causes ultrafast melting. At long time delays, nearly perfect recrystallization of a (111) crystal is observed.}, language = {en} } @article{CheeKammlerGrahametal., author = {Chee, See Wee and Kammler, Martin and Graham, Jeremy and Gignac, Lynne and Reuter, Mark C. and Hull, Robert and Ross, Frances M.}, title = {Directed Self-Assembly of Ge Quantum Dots Using Focused Si2+ Ion Beam Patterning}, series = {scientific reports}, volume = {8}, journal = {scientific reports}, publisher = {Nature}, doi = {10.1038/s41598-018-27512-z}, pages = {1 -- 10}, abstract = {We show that templating a Si surface with a focused beam of Si2+ or Si+ ions can create suitable nucleation sites for the subsequent growth of self-assembled Ge quantum dots by chemical vapor deposition. To determine the mechanism of patterning we use atomic force microscopy to show that, similar to Ga+ patterning, the formation of a surface pit is required to enable control over Ge quantum dot locations. We find that relatively high implantation doses are required to achieve patterning, and these doses lead to amorphization of the substrate. We assess the degree to which the substrate crystallinity can be recovered by subsequent processing. Using in situ transmission electron microscopy heating experiments we find that recrystallization is possible at the growth temperature of the Ge quantum dots, but defects remain that follow the pattern of the initial implantation. We discuss the formation mechanism of the defects and the benefits of using Si ions for patterning both defects and quantum dots on Si substrates.}, language = {en} } @article{MelekhovPennWeidaueretal., author = {Melekhov, Evgeny and Penn, Tatjana and Weidauer, Tobias and Abb, Valerius and Kammler, Martin and Lechner, Alfred}, title = {Tunable nanopillar array on a quartz-fiber tip for surface enhanced Raman scattering (SERS) detection}, series = {tm - Technisches Messen}, volume = {89}, journal = {tm - Technisches Messen}, number = {1}, publisher = {de Gruyter}, doi = {10.1515/teme-2021-0093}, pages = {70 -- 81}, abstract = {In this work, a simple two-step method to create tunable self-assembled three-dimensional nanostructure array-like nanoantennas directly on the tip of an optical quartz glass fiber is described. The structures are prepared by using dry etching of the fiber tip. For the etching process, gold nanoparticles fabricated by thermal dewetting technique were used as template. The structures are applied as sensors for label-free analysis of organic substances in ppb range, such as drug residues in liquid solutions. The measurements are carried out by a portable Raman device with an exchangeable sensor head utilizing the SERS-effect. This method allows in situ applications. In order to characterize the SERS cells, para-thiocresol and diclofenac sodium are used as model substances. For optimization of the substrate performance, different thicknesses of the dewetting-layer (6, 9, 12 nm), different etching times for formation of the pillars (6, 8, 10 and 12 min), and different thicknesses of SERS-metallization (25, 50, 75 nm) of gold and silver are compared. In order to show the applicability of the structure on the tip of a fiber, measurements from the upper side and from the underside of the substrate on quartz plates are compared. Reproducible SERS enhancement factors up to 10 7 {10^{7}} were achieved.}, language = {en} } @article{KammlerChidambarraoSchwarzetal., author = {Kammler, Martin and Chidambarrao, D. and Schwarz, K. W. and Black, C. T. and Ross, Frances M.}, title = {Controlled nucleation of dislocations by a spatially localized stress field}, series = {Applied Physics Letters}, volume = {87}, journal = {Applied Physics Letters}, number = {13}, publisher = {AIP}, doi = {10.1063/1.2061862}, abstract = {We analyze the nucleation of dislocations in silicon at spatially localized stress fields generated by silicon nitride pads having a high intrinsic stress. The nucleation and final configuration of the dislocations were studied using hot-stage transmission electron microscopy and were compared with dislocation simulations based on calculations of the stress fields around the pads. We find that the simulated configurations match well with the experimental data, and we show that the dislocation configuration can be controlled by the pad size.}, language = {en} } @article{KammlerHornvonHoegen, author = {Kammler, Martin and Horn-von Hoegen, Michael}, title = {Transition in growth mode by competing strain relaxation mechanisms}, series = {Applied Physics Letters}, volume = {85}, journal = {Applied Physics Letters}, number = {15}, publisher = {American Institute of Physics}, doi = {10.1063/1.1803914}, pages = {3056 -- 3058}, abstract = {Surfactant mediated epitaxy of Si(1-x)Gex alloys on Si(111) can, besides technological importance, clarify the influence of the lattice mismatch during surfactant mediated heteroepitaxial growth. For low Ge concentration we find an immediate layer-by-layer growth, whereas at high Ge concentration a roughening transition followed by relaxation of the lattice mismatch in a periodic dislocation network is preferred. This behavior can be explained by comparing the dislocation nucleation rate on a smooth surface with the island nucleation rate on a pseudomorphic film.}, language = {en} } @article{CheeKammlerBalasubramanianetal., author = {Chee, See Wee and Kammler, Martin and Balasubramanian, Prabhu and Reuter, Mark C. and Hull, Robert and Ross, Frances M.}, title = {Microstructural changes in silicon induced by patterning with focused ion beams of Ga, Si and Au}, series = {Ultramicroscopy}, volume = {127}, journal = {Ultramicroscopy}, publisher = {Elsevier}, doi = {10.1016/j.ultramic.2012.07.004}, pages = {126 -- 131}, abstract = {We use focused beams of Ga(+), Au(+) and Si(++) ions to induce local microstructural changes in single crystal silicon. The ions were delivered as single spot pulses into thin Si membranes that could subsequently be imaged and annealed in situ in a transmission electron microscope. For each ion, the focused ion beam implantation created an array of amorphous regions in the crystalline membrane. Annealing causes solid phase epitaxial regrowth to take place, but we show that the resulting microstructure depends on the ion species. For Ga(+) and Au(+), precipitates remain after recrystallization, while for Si(++), dislocation loops form around the periphery of each implanted spot. We attribute these loops to defects formed during solid phase epitaxial regrowth, with controlled placement of the loops possible.}, language = {en} } @unpublished{SchwarzPastoetterTranetal., author = {Schwarz, Tobias and Past{\"o}tter, Angelina and Tran, Trung and Schlosser, Marc and Kaulen, Corinna and Lechner, Alfred and Kammler, Martin and Slabon, Adam}, title = {Effect of Temperature on the Growth of Cu(I)O Nanocubes: The Impact of the Copper Precursor Species}, series = {SSRN}, journal = {SSRN}, publisher = {Elsevier}, doi = {10.2139/ssrn.4909639}, abstract = {Cuprous oxide (Cu2O) nanoparticles 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 nanoparticles were analyzed by SEM, PXRD, and ATR-IR. We discovered that the chemical composition of the Cu2O nanoparticles remained unaffected by the synthesis temperature. However, morphology and size of the nanoparticles showed a strong temperature dependency. This could be attributed to the temperature induced formation of cupric oxide (CuO) species from the copper hydroxide (Cu(OH)2 ) precursor which also functions as copper precursor for the Cu2O nanoparticle 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 nanoparticles nanocubes with smaller edge lengths as well as octahedrons were obtained.}, language = {en} } @article{SokolowskiTintenBlomeBlumsetal., author = {Sokolowski-Tinten, Klaus and Blome, Christian and Blums, Juris and Dietrich, Clemens and Tarsevitch, Alexander and Horn-von Hoegen, Michael and von der Linde, Dietrich and Cavalleri, Andrea and Kammler, Martin and Uschmann, Ingo and Foerster, Eckhart}, title = {Femtosecond X-ray Diffraction Study of Large Amplitude Coherent Optical Phonons in Laser-Excited Bismuth}, series = {Conference on Lasers and Electro-Optics, 1-6 June 2003, Baltimore, Maryland}, journal = {Conference on Lasers and Electro-Optics, 1-6 June 2003, Baltimore, Maryland}, publisher = {Optical Society of America}, abstract = {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.}, language = {en} }