@phdthesis{Melnik2018, author = {Melnik, Nauka}, title = {Untersuchung des Strahlungsdrucks auf d{\"u}nne Folien unter Weltraumbedingungen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-45847}, school = {BTU Cottbus - Senftenberg}, year = {2018}, abstract = {Trifft elektromagnetische Strahlung auf einen K{\"o}rper, geben die Photonen ihren Impuls ab, bei einer idealen Reflexion sogar den doppelten Impuls. Auf die Oberfl{\"a}che des bestrahlten K{\"o}rpers wird somit eine Kraft ausge{\"u}bt. Dieser Strahlungsdruck ist extrem gering, jedoch ergeben sich unter speziellen Bedingungen, wie bei einer Anwendung im luftleeren Raum des Weltalls, konkrete effektive Einsatzbereiche. Die Anwendung des Strahlungsdrucks als Antriebsmittel im Bereich der Raumfahrt ist der Ausgangspunkt folgender Dissertation. Großfl{\"a}chige reflektierende Folien k{\"o}nnen den Strahlungsdruck der Sonne als spezielles Antriebsmittel f{\"u}r Raumfahrzeuge, sogenannte Sonnensegler, nutzen. Ziel dieser Arbeit ist die Entwicklung einer Messeinrichtung zur Analyse der Kraftwirkung durch sonnen{\"a}hnliche Strahlung auf d{\"u}nne, reflektierende Folien. Des Weiteren wird die Messeinrichtung durch verschiedene Messreihen verifiziert, auftretende Effekte werden charakterisiert. Die Messeinrichtung ist in einer Hochvakuumkammer installiert. Der Strahlungsdruck wird durch eine 1600W Xenon Lampe mit sonnen{\"a}hnlichem Spektrum auf eine 7,5 µm dicke, mit Aluminium beschichtete Kaptonfolie ausge{\"u}bt. Die resultierende Krafteinwirkung auf die Folienoberfl{\"a}che wird mittels einer Pr{\"a}zisionswaage gemessen. In mehreren Testreihen werden Folienproben unterschiedlichen Bestrahlungsst{\"a}rken ausgesetzt. Die experimentell ermittelten Messdaten best{\"a}tigen die theoretisch berechneten Werte des Strahlungsdrucks. Dar{\"u}ber hinaus zeigt sich im Verlauf der Experimente ein bisher unbeachteter Effekt. An der Folienoberfl{\"a}che haften unter Atmosph{\"a}re Wassermolek{\"u}lschichten, welche im Vakuum zun{\"a}chst an der Folie haften bleiben. Diese Molek{\"u}le werden erst bei Bestrahlung von der Oberfl{\"a}che desorbiert. Der Impuls durch die entweichenden Molek{\"u}le ist um ein Vielfaches gr{\"o}ßer als der Impuls der Photonen. Dieser Effekt beeintr{\"a}chtigt die Strahlungsdruckmessung. Um die st{\"o}renden Einfl{\"u}sse zu eliminieren, sind in einer Testprozedur Randbedingungen definiert worden.}, subject = {Strahlungsdruck; Sonnensegel; Pr{\"a}zisionswaage; Desorption; Radiation pressure; Solar sailing; High precision balance; Desorption; Strahlungsdruck; Sonnensegel ; Extraterrestrische Physik}, language = {de} } @phdthesis{Varlamova2013, author = {Varlamova, Olga}, title = {Self-organized surface patterns originating from femtosecond laser-induced instability}, isbn = {978-3-95404-604-1}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-29530}, school = {BTU Cottbus - Senftenberg}, year = {2013}, abstract = {The phenomenon of laser-induced periodic surface structures (LIPSS), or ripples, generated by near-infrared radiation with the central wavelength around 800 nanometer (λlaser ≈ 800 nm) and pulse duration about of 100 femtosecond (τpulse ≈ 100 fs) on solid targets is considered in this dissertation. The main aim of the work is a better understanding of the fundamental processes of laser-matter interaction resulting in pattern formation by femtosecond (fs) laser ablation. The problem is of great interest both in fundamental and applied science. The knowledge of the underlying physical mechanisms will provide the opportunity to control surface nanostructuring, which has a big application potential in many modern technologies. Femtosecond LIPSS observed at the bottom of ablation crater reveal a large variety of features including nanostructures with periods below 100 nm. Moreover, the ripple size depends mainly on the irradiation dose/absorbed laser energy and is rather insensitive to the variation of laser wavelength or incidence angle. The orientation of the structures is dictated by laser polarization. All these experimental observations and an astounding similarity of the structures to other patterns originating from instabilities led to the idea to attribute the femtosecond laser nanostructuring to a self-organized pattern formation from laser-induced surface instability. In this dissertation, surface pattern formation upon femtosecond laser ablation is considered in the framework of an adopted surface erosion model, based on the description of spontaneous pattern formation on surfaces bombarded with high-energy ions. We exploit the similarity to ion-beam sputtering and extend a corresponding model for laser ablation by including laser polarization. It has been found that an asymmetry in the deposition and dissipation of the incident laser energy, related to the laser polarization, results in a corresponding dependence of coefficients in a nonlinear equation of the Kuramoto-Sivashinsky type. The surface morphologies calculated in the framework of this model for different configurations of the incident laser electric field show an excellent qualitative agreement with structures observed in ultra-short pulse ablation experiments. In this work, properties of the periodic surface structures induced upon femtosecond laser ablation are studied in detail, focusing on a systematic investigation of the main control parameters regulating the pattern formation process. The results support the non-linear self-organization mechanism of pattern formation from laser-induced surface instability.}, subject = {Oberfl{\"a}chenstruktur; Mikromechanik; Laserablation; Ultrakurzzeitlaser; Femtosekundenlaserablation; Laser-induzierte Oberfl{\"a}chenstrukturierung; Ripples; Selbstorganisierte Strukturbildung; Femtosecond laser ablation; Laser-induced surface patterning; Ripples; Selforganized pattern formation}, language = {en} } @phdthesis{Mankovics2015, author = {Mankovics, Daniel}, title = {Luminescence investigation of bulk solar silicon and silicon thin films on glass substrate}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-35196}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {The aim of this work is to study the optical properties of crystal defects in multicrystalline solar silicon and poly-/microcrystalline silicon thin films on glass substrate. First a setup for photoluminescence imaging on multicrystalline silicon solar wafers was developed. This system is suitable for detecting band-to-band luminescence as well as defect-related luminescence at room temperature on large-scale wafers at different stages of their processing. Spectroscopic photoluminescence investigations of multicrystalline silicon solar wafers indicated a new intense luminescence line at ≈ 0.91 eV at room temperature. The origin of this line is probably found in a specific grain boundary. Furthermore, luminescence in the region of 0.8 eV was investigated in detail, and it was found that probably oxygen is responsible for a peak at 0.77 eV at 80 K. Electroluminescence investigations at room temperature at both materials exhibit extended defect structures such as grain boundaries. Furthermore, it can be concluded that electroluminescence imaging in reverse bias mode indicate on serious breakdown points in solar cells, which can lead to destruction of solar cells and modules. By comparing defect-related and reverse bias electroluminescence images, a difference in the spatial distribution of defects emitting D1 radiation and defects emitting light under reverse bias beyond -12 V is detectable. In addition, there seems to be a correlation in the distribution of non-doping impurities and photoluminescence. Concerning this, vertical slabs of two silicon blocks were examined by means of Fourier-transform infrared spectroscopy and photoluminescence. A correlation of the distributions of interstitial oxygen and the band-to-band luminescence profiles could be found. Additionally, a correlation between D3/D4 luminescence profile and nitrogen distribution in the blocks was observed. Finally, the growth process, particularly the transition from amorphous to microcrystalline silicon by PECVD, was studied by combined photoluminescence and Raman investigations. Formation of silicon nano-grains was detected by means of photoluminescence and Raman spectroscopy.}, subject = {Silicon; Defects; Photoluminescence; Luminescence imaging; Silicon thin films; Silizium; Defekte; Photolumineszenz; Lumineszenz-Imaging; Silizium-D{\"u}nnfilme; Silicium; D{\"u}nnschichttechnik; Solarzelle; Fehleranalyse}, language = {en} } @phdthesis{Costache2006, author = {Costache, Florenta}, title = {Dynamics of ultra-short laser pulse interaction with solids at the origin of nanoscale surface modification}, isbn = {978-3-8322-6465-9}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus-3674}, school = {BTU Cottbus - Senftenberg}, year = {2006}, abstract = {This thesis addresses fundamental physical processes which take place at the surface region of a target during and after the interaction with ultra-short laser pulses. The general goal is to bring together different phenomena and discuss the non-equilibrium nature of the interaction of femtosecond laser pulses (tp < 100 fs) with various materials, in particular dielectrics and semiconductors. Different experiments, using various techniques, are designed to explore the basic mechanisms of laser ionization, defect creation, electron-lattice energetic transfer, charged particles desorption, optical breakdown, phase transformations and surface morphological changes. Such processes are shown to depend strongly on the laser intensity. Thus, they are analyzed for intensities over four orders of magnitude (10^11-10^14 W/cm2), around the surface optical breakdown (damage) threshold intensity. First, experimental studies using time-of-flight mass spectrometry indicate that non-resonant intense ultra-short laser pulses can efficiently ionize a dielectric (semiconducting) material leading to emission of electrons as well as charged particles, i.e. atomic ions and large clusters, and neutral particles. Under these irradiation conditions, the ionization processes can be at best described by multiphoton ionization and ionization at defects sites. The structural defects provide the means for an increased positive ion desorption rate. A multiple pulse incubation effect in the ion yield can be well related with the reduction of the multi-pulse damage threshold with increasing intensity. Following the initial electron excitation and emission, positive ions are released from the surface in a substantial amount with high ion velocities indicative of a localized microscopic electrostatic expulsion. With increasing intensity, the amount of ions gets larger and larger and their velocity distribution exhibits a bimodal structure. Also, in these conditions, negative ions are detected. The ion desorption can arise from a combination of a localized electrostatic repulsion (macroscopic Coulomb explosion) and a thermal 'explosive' mechanism. The later becomes more important with increasing intensity. The very fast energy input and particle emission result in a transient perturbation and deformation of the target lattice. Using pump-probe experiments the temporal evolution of lattice dynamics can be analyzed upon single-pulse excitation for many different target materials. This deformation is indicated to be a material characteristic. It is associated with the generation of transient defects in dielectrics or fast phase transitions in semiconductors and metals. Therefore, it could well give estimates of lifetime of transient defect states or electron-phonon relaxation times.At last the surface morphology after ablation is analyzed, with emphasis on the laser-induced surface periodic patterns (ripples). The patterns observed appear to be very different from the 'classical' ripples formed after long pulse ablation. They can have periods much smaller than the incident wavelength and are rather insensitive to the variation of the laser wavelength and angle of incidence. We show that control factors are laser beam polarization and the irradiation dose. Additionally, the patterns exhibit features pointing toward a chaotic origin. Their possible formation mechanism is likely linked with the non-equilibrium nature of the interaction.}, subject = {Ultrakurzer Lichtimpuls; Nanostruktur; Oberfl{\"a}chenstruktur; Ultra-kurze Laser Pulse; Flugzeit-Massenspektrometrie; Teilchen-Emission; Ultraschnelle Gitterdynamik; Ripples; Femtosecond laser pulses; Time-of-Flight mass spectrometry; Particle emission kinetics; Ultrafast lattice dynamics; Ripples}, language = {en} } @phdthesis{Zwierz2014, author = {Zwierz, Radoslaw}, title = {Plasma enhanced growth of GaN single crystalline layers from vapour phase}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-30710}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Gallium nitride (GaN) is a III-V semiconductor, characterized by direct, wide band gap of 3.4 eV at RT. As a material of particular interest for opto- and power electronics applications, it has been thoroughly studied in recent years. Utilization of GaN homoepitaxy in manufacturing of laser diodes (LDs), light-emitting diodes (LEDs), power devices, etc. would be beneficial in terms of reducing defect density, thus improving their lifetime and performance. Yet cost-effective process for providing native GaN substrates has not been established so far. The focus of this work is put on development of a new method to grow single crystalline GaN layers from Ga vapour. Our approach exploits microwave (MW) plasma as a source of excited nitrogen species, in contrast to classical physical vapour transport (PVT)-based technique, in which ammonia (NH3) serves as a source of reactive nitrogen. Novelty of MW plasma enhanced growth of GaN from vapour lies in MW nitrogen plasma formation in the vicinity of the seed, at moderate pressure (200 - 800 mbar range), and concurrent physical vapour transport of Ga to the growth zone. Simulations of the growth setup (HEpiGaN software) and of the MW plasma source (CST Microwave software) have followed the extensive investigations of material properties. The growth setup and the MW plasma source, with the resonance cavity being its crucial part, have been constructed and implemented into the existing growth reactor. The stability of MW plasma in function of temperature and pressure has been studied along with its influence on the seed temperature, and thus on the growth conditions. Furthermore, optical emission spectroscopy (OES) has been utilized for in-situ characterization of the growth atmosphere. Studies on the interaction of Ga vapour with the nitrogen discharge were interpreted on the basis of the level structure of lower excited states of Ga. Deposition experiments have been conducted, using sapphire seeds, GaN, AlN and AlGaN templates, while GaN single crystalline layers have been grown on sapphire and GaN templates. Characterization of GaN layers have been done by various methods, i.e. structure of layers by scanning electron microscopy (SEM), their composition by energy dispersive X-ray spectroscopy (EDX) and secondary ion mass spectrometry (SIMS), and crystal quality by high resolution X-ray diffraction (HRXRD). Results of the characterization together with outcome of OES measurements revealed importance of carbon for the sub-atmospheric MW plasma enhanced growth of GaN from vapour. In addition, this fact was confirmed by experiments in the setup with reduced carbon content. Possible routes for GaN synthesis have been discussed, with the most probable being CN-assisted GaN formation. While CN was detected in the plasma spectra, there was no evidence for the existence of GaN molecules in vapour phase.}, subject = {GaN; Vapour growth; Microwave plasma; Z{\"u}chtung aus der Gasphase; Plasma; Galliumnitrid; Gasphase; Plasma}, language = {en} } @article{HanReiterSchlipfetal.2023, author = {Han, Weijia and Reiter, Sebastian and Schlipf, Jon and Mai, Christian and Spirito, Davide and Jose, Josmy and Wenger, Christian and Fischer, Inga A.}, title = {Strongly enhanced sensitivities of CMOS compatible plasmonic titanium nitride nanohole arrays for refractive index sensing under oblique incidence}, series = {Optics Express}, volume = {31}, journal = {Optics Express}, number = {11}, publisher = {Optica Publishing Group}, address = {Washington, DC}, issn = {1094-4087}, doi = {10.1364/OE.481993}, pages = {17389 -- 17407}, year = {2023}, abstract = {Titanium nitride (TiN) is a complementary metal-oxide-semiconductor (CMOS) compatible material with large potential for the fabrication of plasmonic structures suited for device integration. However, the comparatively large optical losses can be detrimental for application. This work reports a CMOS compatible TiN nanohole array (NHA) on top of a multilayer stack for potential use in integrated refractive index sensing with high sensitivities at wavelengths between 800 and 1500 nm. The stack, consisting of the TiN NHA on a silicon dioxide (SiO2) layer with Si as substrate (TiN NHA/SiO2/Si), is prepared using an industrial CMOS compatible process. The TiN NHA/SiO2/Si shows Fano resonances in reflectance spectra under oblique excitation, which are well reproduced by simulation using both finite difference time domain (FDTD) and rigorous coupled-wave analysis (RCWA) methods. The sensitivities derived from spectroscopic characterizations increase with the increasing incident angle and match well with the simulated sensitivities. Our systematic simulation-based investigation of the sensitivity of the TiN NHA/SiO2/Si stack under varied conditions reveals that very large sensitivities up to 2305 nm per refractive index unit (nm RIU-1) are predicted when the refractive index of superstrate is similar to that of the SiO2 layer. We analyze in detail how the interplay between plasmonic and photonic resonances such as surface plasmon polaritons (SPPs), localized surface plasmon resonances (LSPRs), Rayleigh Anomalies (RAs), and photonic microcavity modes (Fabry-P{\´e}rot resonances) contributes to this result. This work not only reveals the tunability of TiN nanostructures for plasmonic applications but also paves the way to explore efficient devices for sensing in broad conditions.}, subject = {TiN; Plasmonics; Plasmonik; Plasmonik; Photonik; Titannitrid; Plasmonics; Photonics}, language = {en} } @article{OleynikRyzhakSchlipfetal.2025, author = {Oleynik, Paul and Ryzhak, Diana and Schlipf, Jon and Alvarado Chavarin, Carlos and Yamamoto, Yuji and Berkmann, Fritz and Ratzke, Markus and Fischer, Inga Anita}, title = {Influence of illumination conditions on photoluminescence enhancement in an Al/Si/Ge metasurface}, series = {Optics Express}, volume = {34}, journal = {Optics Express}, number = {1}, publisher = {Optica Publishing Group}, address = {Washington D.C.}, issn = {1094-4087}, doi = {10.1364/OE.577751}, pages = {78 -- 86}, year = {2025}, abstract = {Strong field enhancement supported by metasurfaces at resonance can be used to control and enhance the spontaneous emission rate of emitters. This is particularly relevant for emitters with comparatively low quantum yield such as germanium. Here, we investigate the µ-photoluminescence response obtained from a hybrid metasurface comprising a square lattice of Al/Si/Ge pillars. We explore how variations in excitation energy, excitation intensity and number of excited meta-atoms affect the spectral dependence of the photoluminescence signal and, in particular, the contribution of the metasurface to it. Our metasurface exhibits a magnetic dipole collective lattice resonance, whose contribution to the photoluminescence signal increases with increasing number of excited meta-atoms. Measuring only one metasurface under different illumination conditions can potentially be an alternative approach to probe the transition between finite-size effects and collective effects.}, subject = {Field enhancement; Germanium; Light emitting diodes; Photonic crystals; Quantum light sources; Scanning electron microscop}, language = {en} } @article{SenguelReiterLotfietal.2025, author = {Seng{\"u}l, Akant and Reiter, Sebastian and Lotfi, Zahra and Efremenko, Julia and Laroussi, Arwa and Corley-Wiciak, Agnieszka Anna and Ratzke, Markus and Mirsky, Vladimir M. and Wenger, Christian and Fischer, Inga Anita}, title = {Titanium nitride plasmonic nanohole arrays with polymer coating : optical properties and their humidity-induced modifications}, series = {Optical Materials Express}, volume = {16}, journal = {Optical Materials Express}, number = {2}, publisher = {Optica Publishing Group}, address = {Washington D.C.}, issn = {2159-3930}, doi = {10.1364/OME.578871}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-72739}, pages = {184 -- 196}, year = {2025}, abstract = {The use of titanium nitride (TiN) for the fabrication of plasmonic structures such as nanohole arrays (NHAs) can enable their integration into optoelectronic devices on the silicon (Si) platform, for example, for the realization of on-chip chemical sensors and biosensors based on refractometric transduction. With a corresponding functionalization of the TiN nanohole arrays, these ultra-compact devices can be utilized in the development of various affinity sensors and sensor systems, such as cost-effective electronic noses for the early detection of gases in the food industry or agriculture. In this work, we focus on two types of coating for functionalization of TiN nanohole arrays: electrochemically synthesized poly-N-methylaniline and layer-by-layer deposited polyacrylic-acid/poly-allylamine (PAA/PAH). Our investigation comprises the experimental characterization of the optical properties of TiN nanhole arrays coated with polymer layers of different thicknesses as well as a comparison with simulation results. We demonstrate the potential of our setup sensing applications by measuring changes in optical properties of TiN nanohole arrays coated with PAA/PAH upon exposure to air of different humidity.}, subject = {Chemical sensors; Extraordinary optical transmission; Localized surface plasmon resonance; Optical coatings; Optical properties; Refractive index}, language = {en} }