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Oxide materials display a wide range of physical properties. Recently, doped complex oxides have drawn considerable attention for various applications including thermoelectrics. Doped complex oxide materials have high Seebeck coefficients (S) and electrical conductivities (o) comparable to other doped semiconductors but low thermoelectric figure of merit ZT values due to their poor thermal conductivities. For example, niobium doped strontium titanate (SrNbxTi_1-xO₃ or simply Nb:STO) has a power factor comparable to that of bismuth telluride. Semiconductor nanostructures have demonstrated a decrease in thermal conductivity (κ) resulting in an increase in the thermoelectric figure of merit (ZT). Nanostructures of doped oxides like niobium doped strontium titanate, may also lead to decreased κ and a corresponding increase in ZT. The major impediment to nanostructured oxide thermoelectric materials is the lack of suitable fabrication techniques for testing and eventual use. Electron Beam Lithography (EBL) was used to pattern poly-methyl-methacrylate (PMMA) resists on undoped single crystalline SrTiO₃ (STO) substrates which were then filled with Nb:STO using Pulsed Laser Deposition (PLD) at room temperature. This technique produced nanowires and nanodots with critical dimensions below 100 nm, and a yield of approximately 95%. In addition to scanning electron microscopy and atomic force microscopy morphological studies of the patterned oxide, thin film analogues were used to study composition, crystallinity and electrical conductivity of the material in response to a post deposition heat treatment. Since the thin films were grown under similar experimental parameters as the oxide nanostructres, the patterned oxides are believed to be stoichiometric and highly crystalline. The study found that using a combination of EBL and PLD, it is possible to produce highly crystalline, doped complex oxide nanostructures with excellent control over morphology. Furthermore, the technique is applicable to nearly all materials and provides the capability of patterning doped oxide materials without the requirement of etching or multiple lithography steps makes this approach especially interesting for future fundamental materials research and novel device fabrication. / Master of Science

Layered transition metal dichalcogenides (TMDs) are potentially ideal semiconducting materials due to their in-plane carrier transport and tunable bandgaps, which are favorable properties for electrical and optoelectronic applications. However, the ability to make p-n junctions is the foundation of semiconductor devices, and therefore the ability to achieve reproducible p- and n-type doping in TMD semiconducting materials is critical. In this work, p-type substitutional doping of pulsed laser deposited WS2 films with niobium is reported. The synthesis technique of the PLD target with dopant incorporation which also ensures host material stoichiometry is presented. Hall electrical measurements confirmed stable p-type conductivity of the grown films. Structural characterization revealed that there was no segregation phase of niobium in the fabricated films and x-ray phtoelectron spectroscopy (xps) characterization suggest that the p-type doping is due to Nb4+ which results in p-type behavior. Stable hole concentrations as high as 10E21(cm-3) were achieved. The target fabrication and thin film deposition technique reported here can be used for substitutional doping of other 2D materials to obtain stable doping for device applications.

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: In this investigation the formation of thin film manganites and their electrical characteristics is studied. In order to see the effect of oxidation states on magneto-resistivity, 80% of Mn is replaced by Fe. Pulsed laser deposition (3 J/cm2), carried out in oxygen partial pressures ranging from 0.01 mbar to 1.00 mbar was used to fabricate the thin films from two target compositions, namely La2CaMn2.94Feo.0609 and La2CaMno.6Fe2.409. Films were deposited on Si< 100 >, MgO< 100 >, SrTi03< 100 > and LaAl03< 100 > single crystal substrates. Samples were characterized by RBS, AFM, SEM, and XRD. Electrical measurements were also carried out. One of the main characterization techniques in this investigation is Rutherford Backscattering Spectrometry (RBS). It has been shown that RBS is a very powerful characterization technique when used in conjunction with the RUMP simulation program. The effect of various parameters can be determined beforehand by RUMP simulation of the thin film structures to be investigated. Simulation shows that RBS is an excellent characterization tool for determining film thickness and stoichiometry. The role of oxygen uptake in La2CaMn3_xFexOg was investigated as the oxidation states of elements in manganite materials have a large effect on their magnetoresistive properties. The height of the La signal can be used as a measure of the oxygen content. RBS spectra of films deposited on single crystal silicon substrates at different ambient pressures show that the fit between simulated and measured RBS spectra improves with higher oxygen pressures, thereby indicating better quality manganite material. The RBS spectra also show that the films have good stoichiometry. Atomic force microscopy was used to determine the roughness of the thin films. The annealed film (average roughness 4.5 nm) shows a surface smoother than the non-annealed film (average roughness 5.3 nm). SEM measurements show that in the case of samples having a high Fe content, the crystallite size varies between about 0.04 11m and 0.10 11m, while for samples with high manganese content, the crystallinity varies between 0.03 jJ,m and 0.06jLm. Manganites were analyzed using Bragg-Brentano (28) X-ray diffraction. Measurements show that manganite films cannot be grown epitaxially on Si< 100 > and MgO< 100 > single crystals due to a large lattice mismatch. In the case of SrTi03 and LaAl03 several reflections and sharp peaks from the film can be seen, indicating reasonable epitaxial growth. SEM measurements of the samples however show polycrystallinity. Complete epitaxy has thus not occurred, but many grains have an epitaxial orientation. Resistance versus temperature (the room temperature to about 100 K) in zero magnetic field was measured for a La2CaMno.06Fe2.409 thin film and maximum resistance corresponding to about 108 K was found. At higher temperatures the resistance decreases as temperature increases. The manganite thin film therefore shows semiconductor behaviour. Resistance measurements carried out at different magnetic fields (0 - 1 T) show a small positive magnetoresistance of 0.83 %. Usually the magnetoresistance phenomenon is measured at higher magnetic fields and this could be the reason for our low value as well as the fact that the iron content could be too high. / AFRIKAANSE OPSOMMING: In hierdie ondersoek is die formasie en karakterisering van dunlagie manganiete ondersoek. Om die effek van oksidasie-toestand op magnetoresistiwiteit te bepaal, is 80% van die Mn verplaas deur Fe. Pulseerde laser deposissie(3 J/cm2), is uitgevoer by 'n parsiële suurstof druk tussen 0.10 en 1.00 mbar deur gebruik te maak van La2Ca Mn2.94Feo.o609 en La2CaMno.6Fe2.409 teiken skywe. Dunlagies was gedeponeer op Si<IOO>, MgO<IOO>, SrTi03<100> en LaAl03<100> enkelkristal substrate. Die dunlagies is daarna ge-karakteriseer met behulp van Rutherford terugverstrooing (RBS), atoom krag mikroskopie(AFM), skandeer elektronmikroskopie (SEM) en xstraal diffraksie(XRD). Elektriese metings is ook uitgevoer. Een van die hoof tegnieke wat gebruik is in hierdie ondersoek is Rutherford terugverstrooing (RBS) van 2 Mev alfa-deeltjies. In hierdie navorsing is aangetoon dat RBS saam met spektra simulasie(RUMP), 'n besondere kragtige metode is om die stoichiometrie en dikte van manganiet lagies te bepaal. Die rol van die opname van suurstof in die dunlagies was ondersoek, aangesien die oksidasie toestand van manganiet lagies 'n groot effek het op hulle magnetoresistiwiteit. Die hoogte van die La sein is gebruik as 'n maatstaf van suurstof inhoud. RBS spektra van dunlagies gevorm op enkelkristal silikon substrate by verskillende parsiële suurstof drukke wys dat die passing tussen gemete en gesimuleerde spektra verbeter by hoër suurstof drukke, wat beter kwaliteit manganiet materiaal aandui. Die RBS spektra het ook aangetoon dat die stoichiometrie van die lagies uitstekend is. Atoom krag mikroskopie(AFM) is gebruik om die grofheid van die oppervlaktes van die dunlagies te bepaal. Lagies wat by 750 grade celsius uitgegloei is ( gemiddelde gladheid van 4.5 nm) was gladder as films wat nie na ablasie uitgegloei is nie (gemiddelde gladheid van 5.3 nm). SEM metings toon ook dat dunlagies met 'n hoë Fe inhoud 'n kristalliet deursnit het van 0.04 tot 0.10 mikrometer en die met 'n hoë mangaan inhoud 'n poli-kristalliniteit het van tussen 0.03 en 0.06 mikrometer het. Bragg-Brentano(twee-theta) X-straal diffraksie meting wys dat manganiet films nie epitaksieël op Si<IOO> en MgO<IOO> enkelkristal substrate gevorm kan word nie, weens 'n groot verskil in die kristal-rooster parameters. SEM metings van die monsters wys polikristalliniteit. Algehele epitaksie het dus nie plaasgevind nie, maar verskeie kristalliete het 'n epitaksiële orientasie. Weerstand metings is gemaak by temperature so laag as 100 Kelvin vir La2CaMno.o6Fe2.409dunlagies en 'n maksimum weerstand is by 108 Kelvin gevind. By hoër temperature het die weerstand afgeneem soos die temperatuur toeneem, wat halfgeleier gedrag aandui. Weerstand metings by verskillende magneetvelde (0 tot I Tesla) wys 'n klein magnetoresistiwiteits effek van 0.83%. Gewoonlik word magnetoresistiwiteit gemeet by hoë magneet velde (ongeveer 6 Tesla). Dit, sowel as die hoë Fe samestelling van die monsters kan die rede wees vir die lae magnetoresistiwiteit wat waargeneem word.

Thesis (PhD (Physics))--University of Stellenbosch, 2002. / Includes bibliography. / ENGLISH ABSTRACT: High temperature superconductivity is an important topic in contemporary solid state physics, and an area of very active research. Due to it’s potential for application in low temperature electronic devices, the material has attracted the attention of researchers in the electronic engineering and material science fields alike. Moreover, from a fundamental point of view, several questions remain unanswered, related to the origin of superconductivity of this class of materials and the nature of quantised magnetic flux present in magnetised samples. In this work, flux creep phenomena in a thin superconducting YBa₂Cu₃O₇ film deposited by pulsed laser deposition, is investigated near the critical temperature 0 ≤ Tc – T ≤ 10 K. Creep activation energy U0 and critical current density jc were determined as a function of temperature close to Tc, providing important data to a problem of high-Tc superconductivity which is still a matter of debate. In particular it is still an open question whether restoring the temperature in a creep freezing experiment in fact restores the film to it's original state before the freezing. The most important novel results concern the regime of critical fluctuations in the vicinity Tc - T < 1 K. We studied the isothermal relaxation of trapped magnetic flux, and determined that the long time decay follows a power law, where the exponent is inversely proportional to the creep activation energy. The temperature dependence of the critical current density jc(T) of the YBa₂Cu₃O₇ film close to Tc was obtained during warming runs. It was determined that jc(T) follows a square root dependence on T to high accuracy in the range 0.2 ≤ Tc – T ≤ 1.5 K. During flux creep experiments an interesting phenomenon called creep freezing related to the strong temperature dependence of the relaxation rate was observed. A pronounced slowing of relaxation with only a small drop in temperature from a starting temperature close to Tc was detected. Experiments were conducted by initiating an isothermal flux decay run. At a certain point the temperature was slightly lowered, and the flux decay stopped within experimental accuracy. When the temperature was restored to the initial value, the flux decay resumed at the previous rate before cooling. An argument based on vortex drift velocity was employed to explain the phenomenon qualitatively. During the course of this investigation, a pulsed laser deposition (PLD) system was designed and built from scratch. PLD involves the interaction of a focussed laser pulse with a multielemental solid target material. Material ablated from the target forms a fast moving plume consisting of atomic and molecular particles, directed away from the target, and towards a usually heated substrate on which the particles condense layer by layer to form a thin film. The substrate temperature and background gas are carefully controlled to be conductive to the growth of a desired phase of the multi-elemental compound. The PLD system proved to be quite versatile in the range of materials that could be deposited. It was used to deposit thin films of different materials, most notable were good quality superconducting YBa₂Cu₃O₇, thermochromic VO2, and magnetoresistive LaxCa1-xMnO3. Metallic Au and Ag layers were also successfully deposited on YBa2Cu3O7 thin films, to serve as protective coatings. The critical temperatures of the best superconducting films were 90 K as determined by resistivity measurement. The optimal deposition conditions to deposit high quality superconducting YBa₂Cu₃O₇ thin films was found to be: deposition temperature 780°C, laser energy density 2-3 J/cm2, oxygen partial pressure 0.2 mbar, and target-substrate distance 35 mm. This yields film with Tc ~ 90 K. It was found that deposition temperature plays the predominant role in determining the quality of YBa₂Cu₃O₇ thin films deposited by PLD. / AFRIKAANSE OPSOMMING: Hoë temperatuur supergeleiding is tans ’n aktuele onderwerp van vastetoestandfisika en dit is ’n gebied van baie aktiewe navorsing. Weens die potensiaal vir toepassings van hoë temperatuur supergeleiers in elektronika, het dié klas materiale die aandag van fisici and elektronici getrek. Verskeie fundamentele vraagstukke bly steeds onbeantwoord, veral met betrekking tot die oorsprong van supergeleiding in hierdie materiale en die gedrag van gekwantiseerde magnetiese vloed (“vortekse”) in gemagnetiseerde monsters. In hierdie werk word diffusie van vortekse in dun supergeleidende YBa₂Cu₃O₇ films ondersoek naby die kritieke temperatuur (0 ≤ Tc - T ≤ 10 K). Die temperatuur afhanklikheid van die diffusie aktiveringsenergie U0 en die kritieke stroomdigtheid jc word bepaal naby Tc. Dit verskaf belangrike inligting tot probleme in hoë temperatuur supergeleiding wat tans nog onbeantwoord bly. In die besonder is dit steeds ’n ope vraag of die herstel van die aanvanklike temperatuur in ’n vloedstollings eksperiment waarlik die film tot die oorspronklike toestand herstel. Die belangrikste nuwe resultate hou verband met die gebied van kritieke fluktuasies van die orde parameter in die omgewing 0 < Tc - T < 1 K. Ons het die isotermiese ontspanning van vortekse verstrik in die kristalstruktuur bestudeer, en bepaal dat die lang tydsverval ’n magsverwantskap handhaaf, waar die eksponent omgekeerd eweredig is aan U0. Die temperatuur afhanklikheid van die kritieke stroomdigtheid jc(T) van die YBa₂Cu₃O₇ film naby Tc is bepaal tydens verhittingslopies. Daar is bevind dat naby Tc, jc ’n vierkantswortel verband met T volg, tot hoë noukeurigheid in die gebied 0.2 ≤ Tc – T ≤ 1.5 K. Gedurende vorteksdiffusie eksperimente is ’n interessante verskynsel naamlik vloedstolling (“flux freezing”) waargeneem. Dit hou verband met die sterk temperatuur afhanklikheid van die vervaltempo van die magnetiese moment van ’n gemagnetiseerde film. ’n Skerp daling van die vervaltempo, weens slegs ’n klein temperatuurdaling vanaf die begin temperatuur naby Tc, is waargeneem. Gedurende eksperimente is daar aanvanklik ’n isotermiese vloedontspanning teweeg gebring. Op ’n sekere tydstip is die temperatuur effens verlaag, waarby die vloedontspanning tot stilstand gekom het binne grense van waarneming. Wanneer die temperatuur weer herstel is na die oorspronklike, het die vloedontspanning voortgegaan teen die tempo voor die temperatuurverlaging. ’n Verklaring wat gebaseer is op vorteks dryfsnelheid was aan die hand gedoen om hierdie gedrag te verklaar. ’n Groot komponent van die projek was om die dun YBa₂Cu₃O₇ films self te vervaardig. Tydens hierdie ondersoek, is ’n gepulseerde laser deposisie (“PLD”) sisteem eiehandig ontwerp en gebou. PLD behels die interaksie van ’n gefokuseerde laser puls met ’n teiken bestaande uit ’n multi-element vastestofverbinding. Materiaal wat verdamp (“ablate”) word, vorm ’n snelbewegende pluim bestaande uit atomiese en molekulêre deeltjies. Dit beweeg vanaf die teiken na ’n verhitte substraat, waarop die deeltjies kondenseer om laag vir laag ’n dun film te vorm. Die substraat temperatuur en agtergrond gas word sorgvuldig beheer om die groei van die verlangde fase van die multi-element verbinding teweeg te bring. Die PLD sisteem is baie veeldoelig ten opsigte van die verskeidenheid materiale wat suksesvol neergeslaan kan word. Dit was aangewend om verskillende materiale neer te slaan, onder andere supergeleidende YBa₂Cu₃O₇, termochromiese VO2, en magnetoresistiewe LaxCa1-xMnO3. Geleidende Au en Ag lagies is ook suksesvol neergeslaan op YBa₂Cu₃O₇ dun films, om te dien as beskermingslagies. Die kritieke temperatuur van die beste supergeleidende films was 90 K soos bepaal deur weerstandsmetings. Die optimale neerslaan toestand vir hoë kwaliteit YBa₂Cu₃O₇ dun films was: substraat temperatuur 780°C, laser energiedigtheid 2 - 3 J/cm2, suurstofdruk 0.2 mbar, en teiken-substraat afstand 35 mm. Daar is bevind dat die substraat temperatuur die deurslaggewende rol speel tydens die neerslaan proses om die kwaliteit van die supergeleidende films te bepaal.

Thesis (MEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. / The Josephson effect of high-temperature superconducting nanobridge structures is studied worldwide. Until now, nanobridges are generally fabricated with focused ion beam milling on planar thin films. These nanobridges are employed as weak links in superconducting quantum interference devices (SQUIDs) and used in superconducting flux flow transistors and devices. This project had two main objectives: to improve the sidewall angle of photoresist lines, with the aid of atomic force microscopy (AFM) nanolithography; and to fabricate hightemperature Josephson junctions by constricting superconductive YBCO lines on MgO substrates with AFM nanolithography. The entire fabrication process is explained including photolithography, deposition of the YBCO thin films with pulsed laser deposition (PLD), nanolithography and wet etching. Although the testing of the junctions did not show any Josephson behaviour, it could be demonstrated that nanobridge structures can successfully be created by AFM nanolithography. The entire fabrication process has been demonstrated in detail for the benefit of future research.

My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO2 films were deposited on Al2O3 substrates by pulsed-laser deposition. Xray- diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5 K. The Fe-doped SnO2 samples exhibit ferromagnetic behaviour at 300 and 5 K. Zero-field-cooled and field-cooled curves indicate super paramagnetic behavior above the blocking temperature of 100 K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. It was found that a Sn0.98Cr0.02O2 film became ferromagnetic at room temperature after annealing in H2. We have calculated the activation energy and found it decreasing with the annealing, which is explained by the increased oxygen vacancies/defects due to the H2 treatment of the films. The ferromagnetism may be associated with the presence of oxygen vacancies although AMR was not observed in the samples. Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates by pulsed laser deposition. XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD patterns except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with post deposition annealing of the HfO2 films.

Hydrogen exposure of insulating d0-titanates, such as SrTiO3 (STO), has displayed the formation of intriguing conducting states. These conducting states form through the use of forming gas (N2/H2) annealing or hydrogen plasma exposure, where hydrogen gas is exposed to high energy microwaves. The exposure of STO to hydrogen causes metallic conductivity due to the introduction of hydrogen cations on some of the oxygen sites. However, the optical properties of this hydrogen-exposed STO have not been well-studied. Further, Ba0.5Sr0.5TiO3 (BST), an insulating dielectric, also shows changes in its conductivity upon hydrogen exposure. Unlike STO where the conductivity of the hydrogen-exposed material has been characterized, the optical, electronic, and transport properties of hydrogen exposed BST have not been studied. Thus, by studying hydrogen-exposed BST and STO, our understanding of the effects of hydrogen on insulators can be enhanced. In the first study, the effects of the exposure of insulating dielectric BST thin films to a hydrogen plasma is presented. These BST thin films are deposited on GdScO3 (GSO) substrates via Pulsed Laser Deposition (PLD). After deposition, the thin films are exposed to a hydrogen plasma. Just five minutes of hydrogen plasma exposure is enough to induce conductivity in the BST thin film. This conducting state is dominated by the interplay of disorder and strong electron correlations introduced during hydrogen exposure. Further, the optical properties indicate the formation of a transparent conductor, as the introduction of disorder and strong correlations has not changed the optical properties of the BST thin film in the visible spectrum. BST demonstrates an example of a new type of transparent conductor that utilizes large effective mass carriers to generate conductivity. In the second study, the effects of hydrogen doping on the surface of STO is explored. The conducting heterointerface that forms between PLD-deposited thin films of LaAlO3 (LAO) on STO is used as the standard to explore this hydrogen surface doping. The optical, electronic, and transport properties of water-leached and buffered hydrofluoric acid (BHF) etched heterointerfaces are characterized and compared. The recently developed water-leaching method is compared with the well-known BHF etching method, which has been shown to unintentionally dope the STO surface with fluorine and hydrogen. Both methods generate single-terminated atomically flat STO substrate surfaces that are ideal for heterointerface formation. After deposition, the optical, electronic, and transport properties of both the water-leached and BHF-etched heterointerfaces show no meaningful difference, demonstrating that water-leaching may also unintentionally dope the STO substrate surface with hydrogen. However, these results confirm that water-leaching generates a high-quality conducting heterointerface without the safety concerns of BHF.

Transition metal oxides have attracted widespread attention due to their broad range of fascinating exotic phenomena such as multiferroicity, superconductivity, colossal magnetoresistance and metal-to-insulator transition. Due to the interplay between spin, charge, lattice and orbital degrees of freedom of strongly correlated d electrons, these physical properties are extremely sensitive to the external perturbations such as magnetic field, charge carrier doping and pressure, which provide a unique chance in search for novel exotic quantum states. Ruthenate systems are a typical strongly correlated system, with rich ordered states and their properties are extremely sensitive to external stimuli. Recently, the experimental observation of spin-orbit coupling induced Mott insulator in Sr2IrO4 as well as the theoretical prediction of topological insulating state in other iridates, have attracted tremendous interest in the physics of strong correlation and spin-orbit coupling in 4d/5d compounds. We observe an itinerant ferromagnetic ground state of Ca2RuO4 film in stark contrast to the Mott-insulating state in bulk Ca2RuO4. We have also established the epitaxial strain effect on the transport and magnetic properties for the (Ca,Sr)2RuO4 thin films. For Sr2IrO4 thin films, we will show that the Jeff = 1/2 moment orientation can be modulated by epitaxial strain. In addition, we discovered novel Ba7Ir3O13+x thin films which exhibit colossal permittivity. / acase@tulane.edu

Perovskite oxides are a very versatile material class with a large variety of outstanding physical properties. A subgroup of these compounds particularly tempting to investigate are oxides involving high-\(Z\) elements, where spin-orbit coupling is expected to give rise to new intriguing phases and potential application-relevant functionalities. This thesis deals with the preparation and characterization of two representatives of high-\(Z\) oxide sample systems based on KTaO\(_3\) and BaBiO\(_3\). KTaO\(_3\) is a band insulator with an electronic valence configuration of Ta 5\(d\)\(^0\) . It is shown that by pulsed laser deposition of a disordered LaAlO\(_3\) film on the KTaO\(_3\)(001) surface, through the creation of oxygen vacancies, a Ta 5\(d\)\(^{0+\(\delta\)}\) state is obtained in the upmost crystal layers of the substrate. In consequence a quasi two dimensional electron system (q2DES) with large spin-orbit coupling emerges at the heterointerface. Measurements of the Hall effect establish sheet carrier densities in the range of 0.1-1.2 10\(^{14}\) cm\(^2\), which can be controlled by the applied oxygen background pressure during deposition and the LaAlO\(_3\) film thickness. When compared to the prototypical oxide q2DESs based on SrTiO\(_3\) crystals, the investigated system exhibits exceptionally large carrier mobilities of up to 30 cm\(^2\)/Vs (7000 cm\(^2\)/Vs) at room temperature (below 10 K). Through a depth profiling by photoemission spectra of the Ta 4\(f\) core level it is shown that the majority of the Ta 5\(d\)\(^0\) charge carriers, consisting of mobile and localized electrons, is situated within 4 nm from the interface at low temperatures. Furthermore, the momentum-resolved electronic structure of the q2DES \(buried\) underneath the LaAlO\(_3\) film is probed by means of hard X-ray angle-resolved photoelectron spectroscopy. It is inferred that, due to a strong confinement potential of the electrons, the band structure of the system is altered compared to \(n\)-doped bulk KTO. Despite the constraint of the electron movement along one direction, the Fermi surface exhibits a clear three dimensional momentum dependence, which is related to a depth extension of the conduction channels of at least 1 nm. The second material, BaBiO\(_3\), is a charge-ordered insulator, which has recently been predicted to emerge as a large-gap topological insulator upon \(n\)-doping. This study reports on the thin film growth of pristine BaBiO\(_3\) on Nb:SrTiO\(_3\)(001) substrates by means of pulsed laser deposition. The mechanism is identified that facilitates the development of epitaxial order in the heterostructure despite the presence of an extraordinary large lattice mismatch of 12 %. At the heterointerface, a structurally modified layer of about 1.7 nm thickness is formed that gradually relieves the in-plane strain and serves as the foundation of a relaxed BBO film. The thereupon formed lattice orders laterally in registry with the substrate with the orientation BaBiO\(_3\)(001)||SrTiO\(_3\)(001) by so-called domain matching, where 8 to 9 BaBiO\(_3\) unit cells align with 9 to 10 unit cells of the substrate. Through the optimization of the deposition conditions in regard to the cation stoichiometry and the structural lattice quality, BaBiO\(_3\) thin films with bulk-like electronic properties are obtained, as is inferred from a comparison of valence band spectra with density functional theory calculations. Finally, a spectroscopic survey of BaBiO\(_3\) samples of various thicknesses resolves that a recently discovered film thickness-controlled phase transition in BaBiO\(_3\) thin films can be traced back to the structural and concurrent stoichiometric modifications occuring in the initially formed lattice on top of the SrTiO\(_3\) substrate rather than being purely driven by the smaller spatial extent of the BBO lattice. / Komplexe Metalloxide mit Perowskitstruktur sind bekannt für ihre große Vielfalt einzigartiger physikalischer Eigenschaften. Eine interessante Untergruppe dieser Materialien sind Verbindungen von Elementen mit hoher Ordnungszahl \(Z\), in denen neue, durch Spin-Bahn Kopplung getriebene Phasen und anwendungsrelevante Funktionalitäten erwartet werden. Diese Arbeit handelt von der Präparation und Charakterisierung zweier Probensysteme, die auf eben solchen Materialien mit hoher \(Z\) basieren. KTaO\(_3\) ist ein Bandisolator, der im Grundzustand eine Ta 5\(d\)\(^0\) Valenz besitzt. Durch gepulste Laserdeposition von ungeordnetem LaAlO\(_3\) auf der KTaO\(_3\)(001) Oberfläche, werden die obersten Schichten des Substratkristalls durch die Erzeugung von Sauerstofffehlstellen dotiert. Es bildet sich ein quasi zweidimensionales metallisches Elektronensystem (q2DES) an der Grenzfläche der Heterostruktur aus. Messungen des Hall-Effekts ergeben Schichtladungsträgerdichten im Bereich von 0.1-1.2 10\(^{14}\) cm\(^2\), welche durch Anpassung des Sauerstoffhintergrunddrucks während der Deposition bzw. durch die Dicke der abgeschiedenen LaAlO\(_3\) Schicht beeinflusst werden können. Mit Werten von 30 cm\(^2\)/Vs (7000 cm\(^2\)/Vs) bei Raumtemperatur (unter 10 K), besitzt das q2DES in LaAlO\(_3\)/KTaO\(_3\) im Vergleich zu ähnlichen Elektronensystemen in SrTiO\(_3\) bemerkenswert große Ladungsträgerbeweglichkeiten. Aus dem Tiefenprofil des Photoemissionspektrums des Ta 4\(f\) Rumpfniveaus ergibt sich, dass sich der Großteil der Ta 5\(d\) Ladungsträger, bestehend aus mobilen und lokalisierten Elektronen, innerhalb einer Schicht von 4 nm Dicke befindet. Die Vermessung der elektronischen Bandstruktur des vergrabenen q2DES mit Hilfe winkelaufgelöster Photoelektronenspektroskopie mit harter Röntgenstrahlung zeigt, dass das Elektronensystem, vermutlich wegen des starken Potentialgradients an der Grenzfläche, eine modifizierte elektronische Struktur gegenüber n-dotiertem Bulk-KTaO\(_3\) aufweist. Trotz der Einschränkung der Bewegung der Elektronen entlang einer Richtung, besitzt die Fermifläche des Systems eine dreidimensionale Struktur, woarus auf eine Tiefenausdehnung der metallischen Zustände von mindestens 1 nm geschlossen werden kann. Undotiertes BaBiO\(_3\) ist durch die Ausbildung einer Ladungsordnung isolierend. Unter Elektronendotierung gilt das Material als Kandidat für einen oxidischen topologischen Isolator. In dieser Studie wird die Deposition von BaBiO\(_3\) auf Nb:SrTiO\(_3\)(001) Substraten untersucht. Dabei wird der Mechanismus identifiziert, der epitaktisches Wachstum von BaBiO\(_3\), trotz einer Gitterfehlanpassung von 12 %, ermöglicht: Eine 1.7 nm dicke Lage mit abweichender Kristallstruktur an der Grenzfläche entkoppelt das Filmgitter vom Substrat, sodass darüber vollständig relaxiertes BaBiO\(_3\) aufwachsen kann. Dieses weist eine epitaktische Orientierung von BaBiO\(_3\)(001)||SrTiO\(_3\)(001) auf, die durch die Ausbildung von lateralen Gitterdomänen, bei denen 8 bzw. 9 BaBiO\(_3\) auf 9 bzw. 10 SrTiO\(_3\) Einheitszellen ausgerichtet sind, gewährleistet wird. Die Stoichiometrie und die strukturelle Qualität der BaBiO\(_3\) Filme werden durch eine systematische Anpassung der Depositionsbedingungen optimiert. Die Valenzbandstruktur der Proben stimmt gut mit Rechnungen der Dichtefunktionaltheorie überein, was darauf hindeutet, dass die Filme hinsichtlich der elektronischen Eigenschaften mit BaBiO\(_3\) Einkristallen vergleichbar sind. Eine abschließende Untersuchung eines schichtdickenabhängigen Phasenübergangs in BaBiO\(_3\) Dünnfilmen, von dem kürzlich in der Literatur berichtet wurde, belegt, dass dieser nicht allein auf die Ausdehnung des Kristallgitters, sondern auch auf strukturelle und stoichiometrische Modifikationen der untersten Filmlagen zurückzuführen ist.