L’objectif globale de cette thèse est l’étude de la croissance de plots de siliciure de cobalt (CoSi2) individuels combinés à une surface semi-isolante de silicium hydrogénée (Si(100):H) afin de créer un environnement propice à l’interconnexion de molécules fonctionnalisées, prémisse des circuits moléculaires. Cette étude, liée au contexte de l’électronique moléculaire ascendante, est réalisée à l’aide d’un microscope à effet tunnel (STM) à basse température (9 K) sous ultra-vide. Ce travail de thèse débute par l’étude de l’adsorption d’atomes de Co, à basse température (12 K) sur la surface de Si(100)-2x1. Nos investigations nous ont permis d’observer, pour la première fois, des sites d’adsorption à la surface et des sites interstitiels métastables en surface et subsurface. Grâce aux excitations électroniques induites par les électrons tunnels, certains sites d’adsorption ont pu être manipulés sur la surface de Si(100). Cette étude préliminaire est suivie par la croissance de plots de siliciure de cobalt individuels sur le Si(100) dont les propriétés électroniques ont été étudiées à basse température (9 K). Ceci nous a permis d’identifier deux géométries de plot de CoSi2 de tailles nanométriques dont le caractère métallique est démontré et ayant de faibles barrières de Schottky à l’interface métal/semi-conducteur. Dans un second temps, nous avons examiné les propriétés de molécules de Co-TPP individuelles et de leurs interactions avec les surfaces de Si(100) et de Si(100) hydrogénées. Les topographies STM révèlent différentes conformations d’adsorption ayant des propriétés physico-chimiques particulières telles qu’une fonction bistable intramoléculaire, ainsi que des propriétés électroniques surprenantes permettant de sonder la physisorption totale ou partielle de l’adsorbat. Un troisième volet de cette thèse adresse la possibilité d’exploiter les propriétés intrinsèques de la surface de Si(100):H afin de créer des ponts moléculaires grâce au couplage successif de liaisons pendantes créées sur la surface du Si(100):H. Les mesures de spectroscopie tunnel effectuées sur ces structures exhibent des états inoccupés caractéristiques du couplage orbitalaire entre les liaisons pendantes dont l’énergie est fonction de l’orientation de la ligne déshydrogénée sur la surface. Finalement, après avoir vérifié que le processus d’hydrogénation ne perturbe pas le caractère métallique des plots de CoSi2, nous avons pu exploiter nos connaissances acquises lors des chapitres précédents. Ceci nous a permis d’étudier, pour la première fois, le contact entre molécules de Co-TPP et plots métalliques. Grâce aux techniques de manipulation latérale, les molécules de Co-TPP ont pu être déplacées et contactées aux plots métalliques. La spectroscopie tunnel effectuée sur différentes molécules montre, d’une part, qu’en fonction de leur orientation par rapport à l’îlot de CoSi2, la structure électronique de chaque molécule est modifiée de manière spécifique. D’autre part, nous avons observé que la position de la mesure des spectres tunnels influe sur le gap de la molécule associé, révélant probablement une signature du transport électronique entre la molécule et le plot métallique. L’ensemble de ces résultats ouvre de nouvelles perspectives extrêmement riches et prometteuses pour la réalisation de circuits moléculaires planaires comme prototype d’études fondamentales. / For the fabrication of molecular circuitsThe overall objective of this thesis is to study the growth of individual cobalt silicide (CoSi2) dots combined with a semi-insulating hydrogenated silicon surface (Si(100):H) to create a controlled and suitable environment for the interconnection of functionalized molecules, the premises to molecular circuits. This study, related to the context of the bottom-up molecular electronics, is performed using a scanning tunneling microscope (STM) at low temperature (9 K) under ultrahigh vacuum. This thesis begins with the study of the adsorption of Co atoms on the surface of Si (100)-2x1 kept at low temperature (12 K). Our investigations have led us to observe, for the first time, adsorption sites that are either stable or metastable interstitial sites on the surface and/or subsurface. With electronically induced excitations, some of the Co adsorption sites have been modified or manipulated on the Si(100) surface. This preliminary study is followed by the growth of individual cobalt silicide dots on the Si(100) while their properties are investigated at low temperature (9 K). This allowed us to identify two different types of silicide dots of nanometric sizes whose metallic character is demonstrated while low Schottky barriers at the metal/semiconductor interface are identified. In a second step, we examined the properties of individual Co-TPP molecules and their interactions with the Si(100) and hydrogenated Si(100) surfaces. The STM topographies reveal various conformations with specific properties such as an intra-molecular bistable function, as well as surprising electronic properties that allow probing the physisorbed parts of the adsorbate. A third part of this thesis addresses the possibility of exploiting the intrinsic properties of the Si(100):H surface to create molecular bridges through successive coupling of dangling bonds created at the surface of Si(100):H. Tunnel spectroscopy measurements carried out on these structures exhibit unoccupied states orbitals, signature of the coupling between dangling bonds, whose energy depends on the orientation of the dangling bond lines across the hydrogenated surface. Finally, after checking that the hydrogenation process of the Si(100) surface does not disturb the metallic character of the CoSi2 dots, we used our knowledge gained in previous chapters. This allowed us to study, for the first time, the contact between molecules of Co-TPP and metal dots. With lateral manipulation techniques, the Co-TPP molecules have been displaced and contacted to metallic pads. The tunneling spectroscopy performed on different molecules shows, firstly, that depending on their orientation relative to the CoSi2 dot, the electronic structure of each molecule is modified in a specific manner. On the other hand, we observed that the conductance spectrum influences the gap of the associated molecule, indicating a signature of electron transport between the molecule and the metal pad. Taken together, these results open new extremely rich and promising perspectives for the realization of planar molecular circuit as a prototype for fundamental studies.

SiGe is a significant enabling technology for therealization of integrated circuits used in high performanceoptical networks and radio frequency applications. In order tocontinue to fulfill the demands for these applications, newmaterials and device structures are needed. This thesis focuseson new materials and their integration into heterojunctionbipolar transistor (HBT) structures as well as using devicesimulations to optimize and better understand the deviceoperation. Specifically, a SiGeC HBT platform was designed,fabricated, and electrically characterized. The platformfeatures a non-selectively grown epitaxial SiGeC base,in situdoped polysilicon emitter, nickel silicide,LOCOS isolation, and a minimum emitter width of 0.4 μm.Alternately, a selective epitaxy growth in an oxide window wasused to form the collector and isolation regions. Thetransistors exhibited cutoff frequency (fT) and maximum frequency of oscillation (fMAX) of 40-80 GHz and 15-45 GHz, respectively.Lateral design rules allowed the investigation of behavior suchas transient enhanced diffusion, leakage current, and theinfluence of parasitics such as base resistance and CBC. The formation of nickel silicide on polysiliconSiGe and SiGeC films was also investigated. The formation ofthe low resistivity monosilicide phase was shown to occur athigher temperatures on SiGeC than on SiGe. The stability of themonosilicide was also shown to improve for SiGeC. Nickelsilicide was then integrated into a SiGeC HBT featuring aselectively grown collector. A novel, fully silicided extrinsicbase contact was demonstrated along with the simultaneousformation of NiSi on thein situdoped polysilicon emitter. High-resolution x-ray diffraction (HRXRD) was used toinvestigate the growth and stability of SiGeC base layers forHBT integration. HRXRD proved to be an effective, fast,non-destructive tool for monitoring carbon out-diffusion due tothe dopant activation anneal for different temperatures as wellas for inline process monitoring of epitaxial growth of SiGeClayers. The stability of the SiGe layer with 0.2-0.4 at% carbonwhen subjected to dopant activation anneals ranging from1020-1100&#176C was analyzed by reciprocal lattice mapping.It was found that as the substitutional carbon increases theformation of boron clusters due to diffusion is suppressed, buta higher density of carbon clusters is formed. Device simulations were performed to optimize the DC and HFperformance of an advanced SiGeC HBT structure with low baseresistance and small dimension emitter widths. The selectivelyimplanted collector (SIC) was studied using a design ofexperiments (DOE) method. For small dimensions the lateralimplantation straggle has a significant influence on the SICprofile (width). A significant influence of the SIC width onthe DC gain was observed. The optimized structure showedbalanced fT/fMAXvalues of 200+ GHz. Finally, SOI BJT transistorswith deep trench isolation were fabricated in a 0.25μmBiCMOS process and self-heating effects were characterized andcompared to transistors on bulk silicon featuring deep trenchand shallow trench isolation. Device simulations based on SEMcross-sections and SIMS data were performed and the resultscompared to the fabricated transistors. Key words:Silicon-Germanium(SiGe), SiGeC,heterojunction bipolar transistor(HBT), nickel silicide,selectively implanted collector(SIC), device simulation, SiGeClayer stability, high resolution x-ray diffraction(HRXRD),silicon-on-insulator(SOI), self-heating.

In dieser Dissertation wird die Darstellung tetrelreicher Seltenerdmetall–Verbindungen in den Systemen SE:Tt (SE = La, Nd, Sm, Gd, Tb, Ho, Lu; Tt = Si, Ge) und die Charakterisierung ihrer Eigenschaften beschrieben. Diese Verbindungen, welche mittels der Hochdruck–Hochtemperatur–Methode dargestellt wurden, zeigen neuartige Verknüpfungsmuster in der Tetrel–Partialstruktur. Neben der Charakterisierung der Verbindungen hinsichtlich der thermischen Stabilität und der physikalischen Eigenschaften bei Normaldruck wurde bei den Germanium–reichen Seltenerdmetall–Verbindungen eine Untersuchung der Veränderungen der Kristallstruktur bei Variation des Drucks oder der Temperatur vorgenommen. Die dargestellten Seltenerdmetall–Trisilicide SESi3 (SE = Gd, Ho, Lu) kristallisieren tetragonal isotyp zu YbSi3. LuSi3 zeigt Supraleitung mit Tc = 7.0 K. In den Systemen Gd–Si und SE–Ge (SE = La, Nd, Sm, Gd, Tb) wurden die Verbindungen GdSi5 und SEGe5 (SE = La, Nd, Sm, Gd, Tb) synthetisiert. Sie kristallisieren orthorhombisch isotyp zu LaGe5. Durch in–situ Röntgenbeugungsexperimente bei erhöhten Temperaturen kann die Existenz metastabiler Germanium–ärmerer Verbindungen SE2Ge9 (SE = Nd, Sm) nachgewiesen werden. Es handelt sich um Defektvarianten der Verbindungen SEGe5 (SE = Nd, Sm). Die strukturelle Verwandtschaft zum Aristotyp SEGe5 wird anhand einer Gruppe–Untergruppe–Beziehung aufgezeigt. Eine alternative Synthesemethode zur Darstellung tetrelreicher Verbindungen mit Gerüststrukturen bei extremen Reaktionsbedingungen stellt das Spark–Plasma–Sinterverfahren (SPS) dar. Die Darstellung der Clathratphase Ba8Ga16±xGe30∓x (x = 0, 1) erfolgte mittels SPS aus den Precursoren BaGa2±x (x = 0, 0.125) und Germanium. Die Untersuchungen der thermoelektrischen Eigenschaften zeigen, dass durch Variation der nominellen Zusammensetzung sowohl n–leitende als auch p–leitende Eigenschaften erhalten werden können. / In this thesis the synthesis of tetrel–rich rare–earth metal compounds in the systems RE:Tt (RE = La, Nd, Sm, Gd, Tb, Ho, Lu; Tt = Si, Ge) and the characterization of their properties is described. These compounds, synthesized by means of high–pressure high–temperature method, show new structural motifs in the tetrel partial structure. The compounds were characterized with respect to their thermal stability and their physical properties at ambient pressure. In addition, the changes in the crystal structure of the germanium-rich rare–earth metal compounds by variation of pressure or temperature were investigated. The synthesized rare–earth trisilicides SESi3 (SE = Gd, Ho, Lu) crystallize tetragonal, isotypic to YbSi3. LuSi3 is a superconductor with Tc = 7.0 K. In the systems Gd–Si and SE–Ge (SE = La, Nd, Sm, Gd, Tb) the compounds GdSi5 and SEGe5 (SE = La, Nd, Sm, Gd, Tb) were synthesized. They crystallize orthorhombic isotypic to LaGe5. Using in-situ high–temperature X-ray experiments the metastable germanium-poorer compounds SE2Ge9 (SE = Nd, Sm) could be observed. These compounds are defect variants of the pentagermanides SEGe5 (SE = Nd, Sm). The structural relationship to the aristotype SEGe5 is given via a group-subgroup relation. An alternative synthesis route for the preparation of tetrel–rich compounds with framework structures at extreme reaction conditions is the spark plasma sintering method (SPS). The clathrate phase Ba8Ga16±xGe30∓x (x = 0, 1) was synthesized from the precursors BaGa2±x (x = 0, 0.125) and germanium by means of SPS. The investigation of the thermoelectric properties shows, that through variation of the nominal composition both n-type and p-type conduction properties can be obtained.

The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

<p>SiGe is a significant enabling technology for therealization of integrated circuits used in high performanceoptical networks and radio frequency applications. In order tocontinue to fulfill the demands for these applications, newmaterials and device structures are needed. This thesis focuseson new materials and their integration into heterojunctionbipolar transistor (HBT) structures as well as using devicesimulations to optimize and better understand the deviceoperation. Specifically, a SiGeC HBT platform was designed,fabricated, and electrically characterized. The platformfeatures a non-selectively grown epitaxial SiGeC base,<i>in situ</i>doped polysilicon emitter, nickel silicide,LOCOS isolation, and a minimum emitter width of 0.4 μm.Alternately, a selective epitaxy growth in an oxide window wasused to form the collector and isolation regions. Thetransistors exhibited cutoff frequency (f_T) and maximum frequency of oscillation (f_MAX) of 40-80 GHz and 15-45 GHz, respectively.Lateral design rules allowed the investigation of behavior suchas transient enhanced diffusion, leakage current, and theinfluence of parasitics such as base resistance and C_BC. The formation of nickel silicide on polysiliconSiGe and SiGeC films was also investigated. The formation ofthe low resistivity monosilicide phase was shown to occur athigher temperatures on SiGeC than on SiGe. The stability of themonosilicide was also shown to improve for SiGeC. Nickelsilicide was then integrated into a SiGeC HBT featuring aselectively grown collector. A novel, fully silicided extrinsicbase contact was demonstrated along with the simultaneousformation of NiSi on the<i>in situ</i>doped polysilicon emitter.</p><p>High-resolution x-ray diffraction (HRXRD) was used toinvestigate the growth and stability of SiGeC base layers forHBT integration. HRXRD proved to be an effective, fast,non-destructive tool for monitoring carbon out-diffusion due tothe dopant activation anneal for different temperatures as wellas for inline process monitoring of epitaxial growth of SiGeClayers. The stability of the SiGe layer with 0.2-0.4 at% carbonwhen subjected to dopant activation anneals ranging from1020-1100&#176C was analyzed by reciprocal lattice mapping.It was found that as the substitutional carbon increases theformation of boron clusters due to diffusion is suppressed, buta higher density of carbon clusters is formed.</p><p>Device simulations were performed to optimize the DC and HFperformance of an advanced SiGeC HBT structure with low baseresistance and small dimension emitter widths. The selectivelyimplanted collector (SIC) was studied using a design ofexperiments (DOE) method. For small dimensions the lateralimplantation straggle has a significant influence on the SICprofile (width). A significant influence of the SIC width onthe DC gain was observed. The optimized structure showedbalanced f_T/f_MAXvalues of 200+ GHz. Finally, SOI BJT transistorswith deep trench isolation were fabricated in a 0.25μmBiCMOS process and self-heating effects were characterized andcompared to transistors on bulk silicon featuring deep trenchand shallow trench isolation. Device simulations based on SEMcross-sections and SIMS data were performed and the resultscompared to the fabricated transistors.</p><p><b>Key words:</b>Silicon-Germanium(SiGe), SiGeC,heterojunction bipolar transistor(HBT), nickel silicide,selectively implanted collector(SIC), device simulation, SiGeClayer stability, high resolution x-ray diffraction(HRXRD),silicon-on-insulator(SOI), self-heating.</p>

4H-SiC-based bipolar junction transistors (BJTs) are attractive devices for high-voltage and high-temperature operations due to their high current capability, low specific on-resistance, and process simplicity. To extend the potential of SiC BJTs to power electronic industrial applications, it is essential to realize high-efficient devices with high-current and low-loss by a reliable and wafer-scale fabrication process. In this thesis, we focus on the improvement of the 4H-SiC BJT performance, including the device optimization and process development. To optimize the 4H-SiC BJT design, a comprehensive study in terms of cell geometries, device scaling, and device layout is performed. The hexagon-cell geometry shows 42% higher current density and 21% lower specific on-resistance at a given maximum current gain compared to the interdigitated finger design. Also, a layout design, called intertwined, is used for 100% usage of the conducting area. A higher current is achieved by saving the inactive portion of the conducting area. Different multi-step etched edge termination techniques with an efficiency of &gt;92% are realized. Regarding the process development, an improved surface passivation is used to reduce the surface recombination and improve the maximum current gain of 4H-SiC BJTs. Moreover, wafer-scale lift-off-free processes for the n- and p-Ohmic contact technologies to 4H-SiC are successfully developed. Both Ohmic metal technologies are based on a self-aligned Ni-silicide (Ni-SALICIDE) process. Regarding the device characterization, a maximum current gain of 40, a specific on-resistance of 20 mΩ·cm2, and a maximum breakdown voltage of 5.85 kV for the 4H-SiC BJTs are measured. By employing the enhanced surface passivation, a maximum current gain of 139 and a specific on-resistance of 579 mΩ·cm2 at the current density of 89 A/cm2 for the 15-kV class BJTs are obtained. Moreover, low-voltage 4H-SiC lateral BJTs and Darlington pair with output current of 1−15 A for high-temperature operations up to 500 °C were fabricated. This thesis focuses on the improvement of the 4H-SiC BJT performance in terms of the device optimization and process development for high-voltage and high-temperature applications. The epilayer design and the device structure and topology are optimized to realize high-efficient BJTs. Also, wafer-scale fabrication process steps are developed to enable realization of high-current devices for the real applications. / <p>QC 20170810</p>

In dieser Dissertation wird die Darstellung tetrelreicher Seltenerdmetall–Verbindungen in den Systemen SE:Tt (SE = La, Nd, Sm, Gd, Tb, Ho, Lu; Tt = Si, Ge) und die Charakterisierung ihrer Eigenschaften beschrieben. Diese Verbindungen, welche mittels der Hochdruck–Hochtemperatur–Methode dargestellt wurden, zeigen neuartige Verknüpfungsmuster in der Tetrel–Partialstruktur. Neben der Charakterisierung der Verbindungen hinsichtlich der thermischen Stabilität und der physikalischen Eigenschaften bei Normaldruck wurde bei den Germanium–reichen Seltenerdmetall–Verbindungen eine Untersuchung der Veränderungen der Kristallstruktur bei Variation des Drucks oder der Temperatur vorgenommen. Die dargestellten Seltenerdmetall–Trisilicide SESi3 (SE = Gd, Ho, Lu) kristallisieren tetragonal isotyp zu YbSi3. LuSi3 zeigt Supraleitung mit Tc = 7.0 K. In den Systemen Gd–Si und SE–Ge (SE = La, Nd, Sm, Gd, Tb) wurden die Verbindungen GdSi5 und SEGe5 (SE = La, Nd, Sm, Gd, Tb) synthetisiert. Sie kristallisieren orthorhombisch isotyp zu LaGe5. Durch in–situ Röntgenbeugungsexperimente bei erhöhten Temperaturen kann die Existenz metastabiler Germanium–ärmerer Verbindungen SE2Ge9 (SE = Nd, Sm) nachgewiesen werden. Es handelt sich um Defektvarianten der Verbindungen SEGe5 (SE = Nd, Sm). Die strukturelle Verwandtschaft zum Aristotyp SEGe5 wird anhand einer Gruppe–Untergruppe–Beziehung aufgezeigt. Eine alternative Synthesemethode zur Darstellung tetrelreicher Verbindungen mit Gerüststrukturen bei extremen Reaktionsbedingungen stellt das Spark–Plasma–Sinterverfahren (SPS) dar. Die Darstellung der Clathratphase Ba8Ga16±xGe30∓x (x = 0, 1) erfolgte mittels SPS aus den Precursoren BaGa2±x (x = 0, 0.125) und Germanium. Die Untersuchungen der thermoelektrischen Eigenschaften zeigen, dass durch Variation der nominellen Zusammensetzung sowohl n–leitende als auch p–leitende Eigenschaften erhalten werden können. / In this thesis the synthesis of tetrel–rich rare–earth metal compounds in the systems RE:Tt (RE = La, Nd, Sm, Gd, Tb, Ho, Lu; Tt = Si, Ge) and the characterization of their properties is described. These compounds, synthesized by means of high–pressure high–temperature method, show new structural motifs in the tetrel partial structure. The compounds were characterized with respect to their thermal stability and their physical properties at ambient pressure. In addition, the changes in the crystal structure of the germanium-rich rare–earth metal compounds by variation of pressure or temperature were investigated. The synthesized rare–earth trisilicides SESi3 (SE = Gd, Ho, Lu) crystallize tetragonal, isotypic to YbSi3. LuSi3 is a superconductor with Tc = 7.0 K. In the systems Gd–Si and SE–Ge (SE = La, Nd, Sm, Gd, Tb) the compounds GdSi5 and SEGe5 (SE = La, Nd, Sm, Gd, Tb) were synthesized. They crystallize orthorhombic isotypic to LaGe5. Using in-situ high–temperature X-ray experiments the metastable germanium-poorer compounds SE2Ge9 (SE = Nd, Sm) could be observed. These compounds are defect variants of the pentagermanides SEGe5 (SE = Nd, Sm). The structural relationship to the aristotype SEGe5 is given via a group-subgroup relation. An alternative synthesis route for the preparation of tetrel–rich compounds with framework structures at extreme reaction conditions is the spark plasma sintering method (SPS). The clathrate phase Ba8Ga16±xGe30∓x (x = 0, 1) was synthesized from the precursors BaGa2±x (x = 0, 0.125) and germanium by means of SPS. The investigation of the thermoelectric properties shows, that through variation of the nominal composition both n-type and p-type conduction properties can be obtained.

The presented thesis deals with the utilization of TOF-LEIS analytical method in the area of nanostructure analysis. A new procedure for depth profiling of the elemental composition of the sample, based on the alternate measurement with the DSIMS method, was established. The TOF-LEIS method is able to detect the interface between the layers before its mixing by the ion beam of the DSIMS method. Furthermore, a procedure of TOF-LEIS spektra modification was established to obtain the actual concentration of elements in the sample by reduction of a multiple collision contribution. By comparison of TOF-LEIS spectra with the results received by the DSIMS method the ratio of molybdenum and silicon ion yields was obtained. In the next section advantages of the TOF-LEIS method in combination with XPS during analysis of thermal stability of gold nanoparticles are presented. The mutual complementarity of both methods is shown and final conclusions are supported by electron microscopy images. The final section deals with a newly assembled apparatus for the TOF-SARS analytical method and shows its possibilities regarding the detection of hydrogen on the graphene.

Die Arbeit befaßt sich mit der Messung und Analyse der spezifischen Wärme verschiedener stark korrelierter Elektronensysteme bei tiefen Temperaturen und hohen Magnetfeldern. Zunächst wird der im Rahmen dieser Arbeit verwendete, auf der Meßmethode der thermischen Relaxation beruhende Aufbau des Kalorimeters (Einsatzbereich 0.05K&amp;lt;T&amp;lt;4K und 0&amp;lt;B&amp;lt;12T) ausführlich erläutert. Danach werden die Ergebnisse von Messungen an den drei Schwere-Fermionen-Verbindungen CeCu2Si2, CeNi2Ge2 und YbRh2Si2 dargelegt. Wenngleich alle drei Systeme bei tiefen Temperaturen durch den für Schwere-Fermionen-Systeme charakteristischen, stark erhöhten elektronischen Beitrag zur spezifischen Wärme gekennzeichnet sind zeigen sich deutliche Unterschiede im beobachteten Grundzustandsverhalten. An CeCu2Si2 wird die für T&amp;lt;1K auftretende Konkurrenz zwischen einem supraleitenden und einem magnetischen Grundzustand ausführlich studiert. In YbRh2Si2 zeigt sich bei einer für 4f-Systeme bemerkenswert tiefen Temperatur von ca. 70mK ein Übergang in eine magnetische Phase, während der Grundzustand von CeNi2Ge2 wegen stark ausgeprägter Probenabhängigkeiten immer noch kontrovers diskutiert wird. Des weiteren zeigen alle drei Verbindungen deutliche Abweichungen vom Verhalten einer Fermi-Flüssigkeit. Die Theorie der Fermi-Flüssigkeit hat sich für metallische Verbindungen als sehr erfolgreich auch bei der Beschreibung des Verhaltens eines Systems aus stark wechselwirkenden Ladungsträgern erwiesen. Warum diese Theorie auf die untersuchten Verbindungen nicht anwendbar zu sein scheint, wird im Rahmen moderner Modellvorstellungen wie z. B. der Nähe zu einem quantenkritischen Punkt diskutiert. Die an Sr2RuO4, dem ersten Kupfer-freien Perowskit Supraleiter, durchgeführten Messungen der spezifischen Wärme dokumentieren das Auftreten von zwei Zusatzbeiträgen für T&amp;lt;Tc, die eine Interpretation der spezifischen Wärme des supraleitenden Zustands von Sr2RuO4 im Hinblick auf die Topologie des Ordnungsparameters deutlich erschweren.