@article{KotGawlińskaNęcekPożarowskaetal.2025, author = {Kot, Małgorzata and Gawlińska-Nęcek, Katarzyna and Pożarowska, Emilia and Henkel, Karsten and Schmeißer, Dieter}, title = {Photosensitivity and carrier densities of perovskite solar absorbers}, series = {Advanced Science}, volume = {12}, journal = {Advanced Science}, number = {16}, publisher = {Wiley}, address = {Weinheim}, issn = {2198-3844}, doi = {10.1002/advs.202412711}, year = {2025}, abstract = {Dark and light current-voltage characteristics of perovskite solar absorbers are analyzed in terms of their carrier densities. The analysis reveals p-type large polarons as a dominant carrier type in the investigated perovskite solar cells. The mechanism causing photosensitivity is attributed to the dissociation (and pairing) of bipolarons to large polarons (and vice versa) that are controlled by the internal potential Γ. As an example, the polaron concept is tested for a formamidinium lead triiodide perovskite solar cell. The individual steps of the data analysis are demonstrated and determine the ionicity factor of this perovskite film, quantify the density of the large polarons, and predict the gain and loss of photo-induced carriers. It is deduced that a reversible light-on/off operation can only occur when the bias voltage never exceeds a critical value of the internal potential. The results gained in this study suggest that the novel analysis can be successively applied on different hybrid perovskite materials, too.}, subject = {Bipolarons; Ionicity factor; Large polarons; Perovskite solar cells}, language = {en} } @article{MoralesGertigKotetal.2025, author = {Morales, Carlos and Gertig, Max and Kot, Małgorzata and Alvarado, Carlos and Schubert, Markus Andreas and Zoellner, Marvin Hartwig and Wenger, Christian and Henkel, Karsten and Flege, Jan Ingo}, title = {In situ X-ray photoelectron spectroscopy study of atomic layer deposited ceria on SiO₂ : substrate influence on the reaction mechanism during the early stages of growth}, series = {Advanced Materials Interfaces}, volume = {12}, journal = {Advanced Materials Interfaces}, number = {5}, publisher = {Wiley}, address = {Weinheim}, issn = {2196-7350}, doi = {10.1002/admi.202400537}, year = {2025}, abstract = {Thermal atomic layer deposition (ALD) of cerium oxide using commercial Ce(thd)4 precursor and O₃ on SiO₂ substrates is studied employing in-situ X-ray photoelectron spectroscopy (XPS). The system presents a complex growth behavior determined by the change in the reaction mechanism when the precursor interacts with the substrate or the cerium oxide surface. During the first growth stage, non-ALD side reactions promoted by the substrate affect the growth per cycle, the amount of carbon residue on the surface, and the oxidation degree of cerium oxide. On the contrary, the second growth stage is characterized by a constant growth per cycle in good agreement with the literature, low carbon residues, and almost fully oxidized cerium oxide films. This distinction between two growth regimes is not unique to the CeOx/SiO₂ system but can be generalized to other metal oxide substrates. Furthermore, the film growth deviates from the ideal layer-by-layer mode, forming micrometric inhomogeneous and defective flakes that eventually coalesce for deposit thicknesses above 10 nm. The ALD-cerium oxide films present less order and a higher density of defects than films grown by physical vapor deposition techniques, likely affecting their reactivity in oxidizing and reducing conditions.}, subject = {ALD; Cerium oxide; Growth model; In-situ; XPS}, language = {en} } @phdthesis{Ganie2025, author = {Ganie, Umar Bashir}, title = {Thermal analysis of lithium niobate tantalate bulk mixed crystals}, doi = {10.26127/BTUOpen-6981}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-69813}, school = {BTU Cottbus - Senftenberg}, year = {2025}, abstract = {This study comprehensively investigated the thermal properties and phase behavior of lithium niobate-tantalate (𝐿𝑖𝑁𝑏𝑥𝑇𝑎1-𝑥𝑂3, LNT) solid solutions. The research used experimental techniques to explore the variation of the ferroelectric Curie temperature (Tc) as a function of composition. LNT single crystals were grown using the Czochralski method. The elemental composition of niobium (Nb) and tantalum (Ta) in these crystals was determined using X-ray fluorescence (XRF) analysis. Small, compositionally homogeneous samples were then selected for differential scanning calorimetry (DSC) measurements to determine specific heat capacities (Cp). The DSC measurements revealed a linear decrease in Tc with increasing Ta concentration in the LNT solid solution crystals. Additionally, the ferroelectric transition width was observed to be narrower in mixed crystals compared to pure LT. Differential Thermal Analysis (DTA) and crystal growth experiments were performed further to understand the phase behavior of LNT solid solutions. The heats of fusion for the end members, LN and LT, were measured using DTA, yielding values of 103 kJ/mol at 1531 K for LN and 289 kJ/mol at 1913 K for LT. These values were used as input parameters in a thermodynamic solution model implemented in the Factsage software. The solution model enabled the calculation of a phase diagram for LNT solid solutions, which was further optimized in the Calphad Factsage. Thermodynamic parameters for the Gibbs free energy of mixing of the solid solution were also generated. The resulting phase diagram showed good agreement with the experimental data. Additionally, the temperature-dependent thermal conductivity of pure LN, LT, and LNT solid solutions and selected doped LN and LT crystals (Mg, Zn) was investigated. Measurements were conducted across a temperature range from 300 K to 1300 K. The findings indicated that thermal conductivity increases with temperature, especially above 800 K, with a more pronounced effect in tantalum-rich solutions. The interplay of the Nb/Ta ratio and doping effects was particularly significant at high temperatures. These insights into the thermal conductivity of LNT and doped LN and LT crystals are crucial for optimizing growth conditions. Understanding thermal conductivity helps ensure homogeneous crystallization during the growth process, which remains a challenge in the production of LNT single crystals.}, subject = {Thermal conductivity; Lithium niobate tantalate; Mixed crystals; Crystal growth; Thermal analysis; Phase diagram; Mischkristalle; Kristallz{\"u}chtung; Thermische Analyse; Phasendiagramm; W{\"a}rmeleitf{\"a}higkeit; Tantalate; Lithium; Niob; Mischkristall; Phasendiagramm; Temperaturabh{\"a}ngigkeit; Phasengleichgewicht}, language = {en} } @article{ZschechLechowskiKuturkovaetal.2024, author = {Zschech, Ehrenfried and Lechowski, Bartlomiej and Kuturkova, Kristina and Panchenko, Luliana and Kr{\"u}ger, Peter and Clausner, Andr{\´e}}, title = {Laboratory X-ray microscopy of 3D nanostructures in the hard X-ray regime enabled by a combination of multilayer X-ray optics}, series = {Nanomaterials}, volume = {14}, journal = {Nanomaterials}, number = {2}, publisher = {MDPI}, address = {Basel}, issn = {2079-4991}, doi = {10.3390/nano14020233}, year = {2024}, abstract = {High-resolution imaging of buried metal interconnect structures in advanced microelectronic products with full-field X-ray microscopy is demonstrated in the hard X-ray regime, i.e., at photon energies > 10 keV. The combination of two multilayer optics—a side-by-side Montel (or nested Kirkpatrick-Baez) condenser optic and a high aspect-ratio multilayer Laue lens—results in an asymmetric optical path in the transmission X-ray microscope. This optics arrangement allows the imaging of 3D nanostructures in opaque objects at a photon energy of 24.2 keV (In-Kα X-ray line). Using a Siemens star test pattern with a minimal feature size of 150 nm, it was proven that features < 150 nm can be resolved. In-Kα radiation is generated from a Ga-In alloy target using a laboratory X-ray source that employs the liquid-metal-jet technology. Since the penetration depth of X-rays into the samples is significantly larger compared to 8 keV photons used in state-of-the-art laboratory X-ray microscopes (Cu-Kα radiation), 3D-nanopattered materials and structures can be imaged nondestructively in mm to cm thick samples. This means that destructive de-processing, thinning or cross-sectioning of the samples are not needed for the visualization of interconnect structures in microelectronic products manufactured using advanced packaging technologies. The application of laboratory transmission X-ray microscopy in the hard X-ray regime is demonstrated for Cu/Cu6Sn5/Cu microbump interconnects fabricated using solid-liquid interdiffusion (SLID) bonding.}, subject = {X-ray microscopy; High-resolution radiography; Nanostructure; Advanced packaging; R{\"o}ntgenmikroskopie; Hochaufl{\"o}sende Radiographie; Nanostruktur; Erweiterte Verpackung; Nanostruktur; R{\"o}ntgenmikroskopie; Radiographie}, language = {en} } @article{RichterRachowIsraeletal.2023, author = {Richter, Jana and Rachow, Fabian and Israel, Johannes and Roth, Norbert and Charlafti, Evgenia and G{\"u}nther, Vivien and Flege, Jan Ingo and Mauss, Fabian}, title = {Reaction mechanism development for methane steam reforming on a Ni/Al2O3 catalyst}, doi = {10.3390/catal13050884}, year = {2023}, abstract = {In this work, a reliable kinetic reaction mechanism was revised to accurately reproduce the detailed reaction paths of steam reforming of methane over a Ni/Al2O3 catalyst. A steadystate fixed-bed reactor experiment and a 1D reactor catalyst model were utilized for this task. The distinctive feature of this experiment is the possibility to measure the axially resolved temperature profile of the catalyst bed, which makes the reaction kinetics inside the reactor visible. This allows for understanding the actual influence of the reaction kinetics on the system; while pure gas concentration measurements at the catalytic reactor outlet show near-equilibrium conditions, the inhere presented temperature profile shows that it is insufficient to base a reaction mechanism development on close equilibrium data. The new experimental data allow for achieving much higher quality in the modeling efforts. Additionally, by carefully controlling the available active surface via dilution in the experiment, it was possible to slow down the catalyst conversion rate, which helped during the adjustment of the reaction kinetics. To assess the accuracy of the revised mechanism, a monolith experiment from the literature was simulated. The results show that the fitted reaction mechanism was able to accurately predict the experimental outcomes for various inlet mass flows, temperatures, and steam-to-carbon ratios.}, subject = {1D modeling; Reaction rates; Methane steam reforming; Fixed-bed reactor experiments; Nickel catalyst; 1D-Modellierung; Reaktionsgeschwindigkeiten; Methan-Dampfreformierung; Festbettreaktor-Experimente; Nickel-Katalysator; Katalysator; Reaktionsmechanismus; Festbettreaktor; Steamreforming; Reaktionsgeschwindigkeit}, language = {en} } @phdthesis{Kutukova2023, author = {Kutukova, Kristina}, title = {In-situ study of crack propagation in patterned structures of microchips using X-ray microscopy}, doi = {10.26127/BTUOpen-6256}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-62567}, school = {BTU Cottbus - Senftenberg}, year = {2023}, abstract = {The motivation of this thesis was to control crack steering into regions of engineered 3D-nanopatterned structures with high fracture toughness and to determine the local critical energy release rate for crack propagation in 3D-nanopatterned systems. On-chip copper interconnect structures of advanced microchips, insulated by organosilicate glasses, were chosen as an example system to study fracture on small scale, since this is a well-defined 3D- nanopatterned system and since a high mechanical robustness is requested for microchips. An experiment for in-situ high-resolution 3D imaging of the fracture behavior of 3D-nanopatterned structures and of the kinetics of microcrack propagation in solids was designed and applied, combining a miniaturized micromechanical test and high-resolution X-ray imaging. Particularly, a miniaturized piezo-driven double cantilever beam test set-up (micro- DCB) was integrated in a laboratory X-ray microscope, and nano X-ray computed tomography was applied for high-resolution 3D imaging of the microcrack evolution in the on-chip interconnect stack of microchips manufactured in the 14 nm technology node. The measured geometry of the microcrack at several loading steps during the micro-DCB test and the subsequent data analysis based on linear elastic fracture mechanics and the Euler-Bernoulli beam model were the basis for the development and application of a new methodology to determine the critical energy release rate for crack propagation in sub- 100 nm regions of a processed wafer quantitatively. It was experimentally proven that specially designed metallic guard ring structures at the rim of the microchips dissipate energy in such a way that the microcrack propagation is efficiently slowed down and eventually stopped, i.e. they are effective to prevent mechanical damage of microchips. It was demonstrated that it is possible to steer the microcrack in a controlled way by tuning the fracture mode mixity locally at the crack tip. The established concept for a controlled crack propagation provides the basis for further fundamental studies of the fracture behavior of nanoscale materials and structures. The results have significant effects for the understanding of fracture mechanics at small scales, e.g. in microchips, but also in other nanopatterned materials, e.g. in bio-inspired, hierarchically structured engineered materials. The experimental results gathered at realistic microelectronic products provide valuable information to control the crack path in on-chip interconnect stacks for design-for-reliability in semiconductor industry and to manufacture mechanically robust microchips in leading-edge technology nodes. The experimental study of controlled microcrack steering into regions with high fracture toughness provides knowledge for the design of guard ring structures in microchips to stop the propagation of microcracks, e.g. generated during the wafer dicing process.}, subject = {R{\"o}ntgenmikroskopie; In-situ-Rissausbreitung; On-Chip-Interconnect-Stacks; Bruchmechanik; Schutzringstrukturen; X-ray microscopy; In-situ crack propagation; On-chip interconnect stacks; Fracture mechanics; Guard ring structures; Rissausbreitung; Mikroriss; Bruchverhalten; Bruchmechanik; Nanostrukturiertes Material; Chip; R{\"o}ntgenmikroskopie}, language = {en} } @phdthesis{Mahmoodinezhad2022, author = {Mahmoodinezhad, Ali}, title = {Atomic layer deposition and characterization of metal oxide thin films}, doi = {10.26127/BTUOpen-6134}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-61343}, school = {BTU Cottbus - Senftenberg}, year = {2022}, abstract = {This thesis describes low temperature growth of wide band gap metal oxide thin films deposited by thermal (T-) and plasma-enhanced (PE-) atomic layer deposition (ALD) techniques in which high quality materials are grown with atomic level precision. Metal oxides are extensively investigated due to their exceptional physical and chemical properties, including relatively wide band gap, high dielectric constant and high thermal stability. This variety of properties results in a wide range of different applications. Thin films of indium oxide (InOx), gallium oxide (GaOx), zinc oxide (ZnOx), and quaternary InOx/GaOx/ZnOx (IGZO), in addition to the well-known aluminum oxide (AlOx), and the catalyst cerium oxide (CeOx), have proven to be superior candidates for many applications; from microelectronics and optoelectronics to gas sensor devices. The demanding requirements of low-temperature deposition processes for thermal sensitive substrates, which include high layer homogeneity and conformality over large areas, makes ALD a pioneer deposition technique. Although many oxides have been grown by TALD and PEALD, the deposition of wide band gap oxides at low temperatures are rarely reported and/or being investigated. In this work, the deposition method of the individual binary oxide films and combining the respective binary processes into the developed super-cycle growth of quaternary compound have been investigated at relatively low-temperatures by TALD and PEALD. Besides, the growth characteristics and chemical properties of the deposited films were evaluated by in-situ and ex-situ characterization techniques such as spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS), where the influence of ALD process parameters on the growth mechanism and films composition are discussed in detail for any potential applications.}, subject = {Thermal atomic layer deposition; Plasma-enhanced atomic layer deposition; Indium gallium zinc oxide; Aluminum oxide; Cerium oxide; Thermische Atomlagenabscheidung; Plasmaunterst{\"u}tzte Atomlagenabscheidung; IGZO; AlOx; CeOx; Tieftemperatur; Atomlagenabscheidung; Beschichtung; Metallschicht; D{\"u}nne Schicht; Aluminiumoxide; Ceroxide; Indiumoxide}, language = {en} } @phdthesis{Akhtar2022, author = {Akhtar, Fatima}, title = {Graphene synthesis under Si-CMOS compatible conditions}, doi = {10.26127/BTUOpen-5927}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-59270}, school = {BTU Cottbus - Senftenberg}, year = {2022}, abstract = {Due to the unique electronic band structure, graphene has opened the great potential to extend the functionality of a large variety of graphene-based devices in health and environment, energy storage, or various microelectronic applications, to mention a few. At this point, the implementation of graphene into Silicon (Si) semiconductor technology is strongly dependent on several key challenges. Among them, high-quality and wafer-scale graphene synthesis on CMOS compatible substrates is of the highest importance. Though large-area graphene can be achieved on substrates like copper, platinum, silicon carbide, or single-crystal Ni, however, high growth temperatures, unavailability of large scale, or contamination issues are the main drawbacks of their usage. In this PhD work, 8-inch scale graphene synthesis is attempted on alternative substrates such as epitaxial Germanium on Si and polycrystalline Nickel on Si. To achieve the growth of the highest quality of graphene, this work focuses on the investigations of various nucleation and growth mechanisms, substrate-graphene interfaces, effects of different substrate orientations, and detailed microscopic and macroscopic characterization of the grown films. Finally, it should also be stressed that the experiments in this work were carried out in a standard BiCMOS pilot-line, making this study unique, as its results might directly pave the way to further graphene integration and graphene-based device prototyping in mainstream Si technologies.}, subject = {Graphene; Chemical vapor deposition; Growth; Oxidation; Germanium; Nickel; Graphen; CVD; Wachstum; Oxidation; Graphen; Keimbildung; Wachstum; CVD-Verfahren; Nickel; Germanium}, language = {en} } @phdthesis{Hartmann2018, author = {Hartmann, Claudia}, title = {Surface and interface characterization of CH₃NH₃PbI₍₃₋ₓ₎Clₓ and CsSnBr₃ perovskite based thin-film solar cell structures}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-46358}, school = {BTU Cottbus - Senftenberg}, year = {2018}, abstract = {The chemical and electronic structure of hybrid organometallic (CH₃NH₃PbI₍₃₋ₓ₎Clₓ) and inorganic (CsSnBr₃) perovskite materials on compact TiO₂ (c-TiO₂) is studied using x-ray and electron based spectroscopic techniques. The morphology and local elemental composition of CH₃NH₃PbI₍₃₋ₓ₎Clₓ, used as absorbers in PV devices, defining the film quality and influencing the performance of respective solar cells is studied in detail by using photoemission electron microscopy (PEEM). An incomplete coverage, with holes reaching down to the c-TiO₂ was revealed; three different topological regions with different degrees of coverage and chemical composition were identified. Depending on the degree of coverage a variation in I oxidation and the formation of Pb⁰ in the vicinity of the c-TiO₂ is found. The valence band maxima (VBM) derived from experimental data for the perovskite and c-TiO₂, combined with information from literature on spiro-MeOTAD suggests an energy level alignment resulting in an excellent charge selectivity at the absorber/spiro-MeOTAD and absorber/c-TiO₂ interfaces respectively. Further, the derived energy level alignment indicates a large recombination barrier (~2 eV), preventing shunts due to direct contact between c-TiO₂ and spiro-MeOTAD in the pin-holes. In-situ ambient pressure hard x-ray photoelectron spectroscopy (AP-HAXPES) studies of 60 and 300 nm CH₃NH₃PbI₍₃₋ₓ₎Clₓ have been performed under varies conditions (i.e. vacuum/water and dark/UV light) to gain insight into the degradation mechanism responsible for the short lifetime of the absorber. The 60 nm perovskite forms Pb⁰ in water vapor (non-defined illumination) in presence of x-rays. The 300 nm perovskite sample shows a complex behavior under illumination/dark. In water vapor/dark the perovskite dissolves into its organic (MAI) and inorganic (PbI₂) components. Under illumination PbI₂ further decomposes to Pb⁰ induced by UV light and x-rays. For alternative inorganic CsSnBr₃ perovskites, the impact of SnF₂ on the chemical and electronic structure is studied to identify its role for the improved performance of the solar cell. HAXPES and lab-XPS measurements performed on CsSnBr₃ with and without SnF₂ indicate two Sn, Cs, and Br species in all samples, where the second Sn species is attributed to oxidized Sn (Sn⁴⁺). When adding SnF₂ to the precursor solution, the coverage is improved and less Sn⁴⁺ and Cs and Br secondary species can be observed, revealing an oxidation inhibiting effect of SnF₂. Additionally, SnF₂ impacts the electronic structure, enhancing the density of states close to the VBM.}, subject = {Perovskite; Photoelectron spectroscopy; Thin-film solar cell; Solid-state physics; Photovoltaics; Photovoltaik; Festk{\"o}rperphysik; D{\"u}nnschichtsolarzelle; Photoelektronenspektroskopie; Perowskite; Fotovoltaik; Halbleiter; D{\"u}nnschichtsolarzelle; Perowskit; Photoelektronenspektroskopie}, language = {en} } @phdthesis{Rouissi2017, author = {Rouissi, Zied}, title = {Role of substrates morphology and chemistry in ALD HfO₂ on Si(111)-H terminated surfaces as model}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-42418}, school = {BTU Cottbus - Senftenberg}, year = {2017}, abstract = {This work presents an approach to investigate fundamental aspects concerning the early stage of the atomic layer deposition (ALD) growth process on stepped surfaces. The first interaction between precursors and surface is strongly important for the ALD growth that it is still far away from the status to be completely understood. For this purpose, a few ALD-cycles withtetrakis(dimethylamido)hafnium (TDMAH) and trimethylaluminum (TMA) as metallic precursors and water (H₂O) as oxidant has been performed in order to study the initial metal oxide film growth on stepped surfaces such as silicon Si(111)-H terminated, highly oriented pyrolytic graphite (HOPG) and silver deposited HOPG (Ag-HOPG). These investigations have been carried out at various substrate temperatures, where scanning tunneling microscopy (STM) has been used systematically to probe the ALD features. This technique is delivering unique knowledge about the locality and the density of nucleation's sites on the different substrates. The data collected are then subjected to a mathematical model to understand the growth and to determine the effect of the surface morphology and chemistry on the behavior of the nucleation. The in-situ cycle-by-cycle STM investigation of 4 initial ALD cycles of TDMAH and H₂O on Si(111)-H terminated at room temperature (RT) and at 280°C displays two regimes of growth: In Regime I (1st - 2nd cycle) an increase in roughness in the first cycle to 0.2nm and 0.34nm respectively for RT and 280°C with a partial surface coverage of 71\% and 54\% is observed. In the 2nd cycle, the coverage increased to ~98\% and 94\% maintaining the same film height of the 1st cycle. A complete layer is formed in this regime. The results are discussed in reference to the Puurunen model. Following this model, the determination of the reaction mechanism in relation to the number of Hf atoms/nm² attached to the surface reveals that two ligands exchanges occur at RT and one ligand exchange at 280°C in the first regime. In addition, the origin of the reaction saturation was determined to be caused by the steric hindrance effect. In this first regime, the growth model is governed by random deposition followed by Mullins diffusion as determined from the universal values found for the roughness dynamic exponents (α, β, 1/z) of the film.}, subject = {ALD; Stepped surface; Morphology; Growth statistics; STM; Gestufte Oberfl{\"a}che; Wachstumsstatistik; Morphologie; Rastertunnelmikroskopie (RTM); Halbleiteroberfl{\"a}che; Schichtwachstum; Atomlagenabscheidung; Rastertunnelmikroskopie}, language = {en} }