@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 (𝐿𝑖𝑁𝑏π‘₯π‘‡π‘Ž1-π‘₯𝑂3, 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} } @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{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} }