The scattering of H2 from Si(100) has been studied using pulsed molecular beam techniques and quantum state-specific detection methods. These studies can be used to test theoretical calculations and give insight into new theories of molecule-surface interactions, a fundamental study in a diverse field of science and technology. In this work, time-of-flight (TOF) spectra of the elastic scattering of H2(v=1. J=1) and H2(v=0, J=1) from clean Si were recorded over a wide range of surface temperatures. Two data processing strategies were developed to extract rich kinematic information from the scattering experiments, e.g., mean translational energy exchange, absolutely survival probability, and angular and speed distribution of the scattered molecules. No such set of quantitative results has been reported before for this system. Compared with close packed metal surfaces, these scattering experiments from a covalently bonded semiconductor surface showed a completely distinct dynamics, e.g. the finding of energy gain instead of loss from the substrate, much broader angular distribution and some counterintuitive surface temperature effects. From the studies of molecules/surface scattering experiments, the thermal excitation on Si(100) surface which depends on surface temperature can substantially alter the adsorption barrier and its distribution, and therefore changes the kinematics of scattered molecules. As a result, even the most basic understanding of the dynamics has to include phonon excitation and deexcitation of the silicon substrate. / text

No description available.

ABSTRACT PREPARATION OF PLZT THIN FILMS BY CHEMICAL SOLUTION DEPOSITION AND THEIR CHARACTERIZATION Kaplan, Burkan M.S., Department of Metallurgical and Materials Engineering Supervisor: Prof. Dr. Macit &Ouml / zenbaS November 2005, 125 pages In this study, La3+ was substituted into lead zirconate titanate (PZT) system by Pb1-xLax(ZryTi1-y)1-x/4O3 nominal stochiometry and it was processed via chemical solution deposition on (111)-Pt/Ti/SiO2/Si-(100) substrate.PLZT solutions were prepared by mixing two solutions, one of which was obtained by dissolving lead acetate and lanthanum acetate hydrate in 2 methoxyethanol at high temperature. This solution was then mixed with the second solution containing zirconium propoxide and titanium isopropoxide. 40ml/0.4M solution was prepared and spin coated on Pt/Ti/SiO2/Si substrates at 3000 rpm for 30 seconds. After 4 coating cycles, film thickness was reached to 600 nm. A systematic study was carried out in different regions of PLZT phase diagram tetragonal, rhombohedral and on the morphotropic phase boundry (MPB) to obtain optimized results of ferroelectric, dielectric and optical properties of the material. During the period of the work, effect of parameters on these properties such as heat treatment conditions, chemical composition of the film, microstructure and thickness of the film was investigated. The films were characterized structurally and electrically. For structural properties, X-ray diffraction technique (XRD), energy dispersive spectrometry (EDS) and Scanning Electron Microscope (SEM) were used to observe phases and surface characterization. For electrical measurements, ferroelectric tester was used to obtain dielectric constant, loss tangent and hysteresis curves. Optical transmittance of the films was also investigated by UV-VIS Spectrophotometer and optical film constants were calculated by modified envelope method. It was observed that the optimum heat treatment conditions were achieved at 7500C for 3 hours. The highest ferroelectric and dielectric properties such as remanent polarization and dielectric constant were obtained using that temperature. The dielectric constant of the films was measured in the frequency range of 1kHz-1MHz and remained almost constant in this region. The change of dielectric constant and ferroelectric hysteresis loops were obtained as a function of Zr/Ti ratio and La content. The grain size as a function of sintering temperature and La content was investigated. It was seen that as the sintering temperature was increased, the grain size of the films increased. The same tendency was also observed when the La content was increased. Fatigue behavior of PLZT thin films was also investigated by Radiant Ferroelectric Tester at 50 kHz and &plusmn / 15V. Change of remanent polarization (Pr) as a function of cumulative switching cycles (N) was drawn with the log scale of x-axis. Furthermore, leakage current characteristics of the films were also obtained by the ferroelectric tester at &amp / #61617 / 15V. It has been observed that as the La content of the film was increased, leakage current of the PLZT films decreased. Keywords: PLZT, (111)-Pt/Ti/SiO2/Si-(100) substrate, Chemical Solution Deposition.

Nesta tese, utilizamos técnicas de química quântica para o estudo de sistemas contendo átomos de silício e nitrogênio. Nesse contexto, o trabalho aqui apresentado procurou concentrar-se em três tópicos principais: aglomerados de silício e nitrogênio, a superfície Si(100) e a interação de um átomo de nitrogênio com essa superfície. Estudamos inicialmente os aglomerados de fórmula SiNN e Si3N2, onde procuramos caracterizar de forma rigorosa a estabilidade e a natureza das ligações químicas das várias espécies. Com relação ao sistema SiNN, os resultados utilizando cálculos de alto nível mostraram a necessidade de novos dados experimentais para a caracterização inequívoca dessa espécie. Além disso, obtivemos os primeiros resultados para as propriedades de quatro novas estruturas. Estudamos a estrutura de várias espécies com fórmula Si3N2, e obtivemos como mínimo global uma estrutura planar contendo apenas ligações Si-N. Para a simulação da superfície Si(100) utilizamos os aglomerados de fórmula Si9H12 e Si15H16. Apenas a metodologia do Funcional da Densidade indicou a existência de uma estrutura distorcida para o Si9H12. Os cálculos CASSCF mostraram a necessidade do uso de funções multideterminantais. Com relação ao aglomerado Si15H16, obteve-se uma estrutura distorcida com os dímeros alternados como a forma mais estável. Entretanto, o uso do CASSCF mostrou ser a forma simétrica a mais estável. Com base no estudo dos aglomerados Si9H12 e Si15H16, partimos para a investigação dos mecanismos envolvidos no processo de interação e incorporação de átomos de nitrogênio na superfície de silício. Estruturas com simetria de spin quarteto e dupleto foram estudadas, sendo os mecanismos bastante semelhantes, com o nitrogênio interagindo inicialmente com um dos silícios dímeros para em seguida poder formar duas outras estruturas, uma com o nitrogênio ligado aos dois silícios dímeros e outra com o nitrogênio inserido no interior do aglomerado. Esta última estrutura corresponde à forma mais estável. Os resultados mostram claramente que a reação é bastante favorável do ponto de vista energético. Questionamos também o uso de vínculos durante a otimização das estruturas por impedir um devido relaxamento apropriado dos átomos de silício da primeira e segunda camadas. / In this thesis, quantum chemical techniques were used to study molecular systems containing silicon and nitrogen atoms. ln this context, the work was concentrated on three main topics: silicon-nitrogen clusters, the Si(100) surface, and the interaction of a nitrogen atom with that surface. We studied initially the clusters SiNN and Si3N2, where we tried to characterize with rigour the stability and the nature of the chemical bonds of the various species. Concerning the system SiNN, using high level calculation, the results showed the necessity of new experimental data for the unequivocal characterization of this species. Moreover, the properties of four new structures were described for the first time in this study. The structures of various species with formula Si3N2 were studied, and the global minimum corresponds to a planar structure containing only Si-N bonds. For the simulation of Si(100) surface, the clusters Si9H12 and Si15H16 were used. Density Functional Theory predicted the existence of an asymmetric geometry for the Si9H12 cluster. The CASSCF calculations showed the necessity of using multideterminantal wave functions. Concerning the Si15H16 cluster, the most stable structure corresponds to a distorted one with alternated dimers. However, the CASSCF methodology showed that the symmetric structure is the most stable. Based on the results for the Si9H12 and Si15H16 clusters, we started to investigate the mechanism involved in the interaction and incorporation of a nitrogen atom into the silicon surface. Structures with quartet and doublet spin symmetry were studied, being their mechanisms very similar, with the nitrogen atom interacting initially with one silicon dimer; after that two other structures can be formed, one with the nitrogen bonded to two silicon dimers, and the other with the nitrogen bonded to one silicon dimer and two internal silicons. This last structure corresponds to the most stable species. The results show clearly that the reaction is very favorable energetically. The use of geometrical constraints during the optimization was questioned since it prevents the proper relaxation of the silicon atoms in the first and second layers.

Nesta tese, utilizamos técnicas de química quântica para o estudo de sistemas contendo átomos de silício e nitrogênio. Nesse contexto, o trabalho aqui apresentado procurou concentrar-se em três tópicos principais: aglomerados de silício e nitrogênio, a superfície Si(100) e a interação de um átomo de nitrogênio com essa superfície. Estudamos inicialmente os aglomerados de fórmula SiNN e Si3N2, onde procuramos caracterizar de forma rigorosa a estabilidade e a natureza das ligações químicas das várias espécies. Com relação ao sistema SiNN, os resultados utilizando cálculos de alto nível mostraram a necessidade de novos dados experimentais para a caracterização inequívoca dessa espécie. Além disso, obtivemos os primeiros resultados para as propriedades de quatro novas estruturas. Estudamos a estrutura de várias espécies com fórmula Si3N2, e obtivemos como mínimo global uma estrutura planar contendo apenas ligações Si-N. Para a simulação da superfície Si(100) utilizamos os aglomerados de fórmula Si9H12 e Si15H16. Apenas a metodologia do Funcional da Densidade indicou a existência de uma estrutura distorcida para o Si9H12. Os cálculos CASSCF mostraram a necessidade do uso de funções multideterminantais. Com relação ao aglomerado Si15H16, obteve-se uma estrutura distorcida com os dímeros alternados como a forma mais estável. Entretanto, o uso do CASSCF mostrou ser a forma simétrica a mais estável. Com base no estudo dos aglomerados Si9H12 e Si15H16, partimos para a investigação dos mecanismos envolvidos no processo de interação e incorporação de átomos de nitrogênio na superfície de silício. Estruturas com simetria de spin quarteto e dupleto foram estudadas, sendo os mecanismos bastante semelhantes, com o nitrogênio interagindo inicialmente com um dos silícios dímeros para em seguida poder formar duas outras estruturas, uma com o nitrogênio ligado aos dois silícios dímeros e outra com o nitrogênio inserido no interior do aglomerado. Esta última estrutura corresponde à forma mais estável. Os resultados mostram claramente que a reação é bastante favorável do ponto de vista energético. Questionamos também o uso de vínculos durante a otimização das estruturas por impedir um devido relaxamento apropriado dos átomos de silício da primeira e segunda camadas. / In this thesis, quantum chemical techniques were used to study molecular systems containing silicon and nitrogen atoms. ln this context, the work was concentrated on three main topics: silicon-nitrogen clusters, the Si(100) surface, and the interaction of a nitrogen atom with that surface. We studied initially the clusters SiNN and Si3N2, where we tried to characterize with rigour the stability and the nature of the chemical bonds of the various species. Concerning the system SiNN, using high level calculation, the results showed the necessity of new experimental data for the unequivocal characterization of this species. Moreover, the properties of four new structures were described for the first time in this study. The structures of various species with formula Si3N2 were studied, and the global minimum corresponds to a planar structure containing only Si-N bonds. For the simulation of Si(100) surface, the clusters Si9H12 and Si15H16 were used. Density Functional Theory predicted the existence of an asymmetric geometry for the Si9H12 cluster. The CASSCF calculations showed the necessity of using multideterminantal wave functions. Concerning the Si15H16 cluster, the most stable structure corresponds to a distorted one with alternated dimers. However, the CASSCF methodology showed that the symmetric structure is the most stable. Based on the results for the Si9H12 and Si15H16 clusters, we started to investigate the mechanism involved in the interaction and incorporation of a nitrogen atom into the silicon surface. Structures with quartet and doublet spin symmetry were studied, being their mechanisms very similar, with the nitrogen atom interacting initially with one silicon dimer; after that two other structures can be formed, one with the nitrogen bonded to two silicon dimers, and the other with the nitrogen bonded to one silicon dimer and two internal silicons. This last structure corresponds to the most stable species. The results show clearly that the reaction is very favorable energetically. The use of geometrical constraints during the optimization was questioned since it prevents the proper relaxation of the silicon atoms in the first and second layers.

In dieser Arbeit wurde die atomare Struktur von Si(100)- und Ge(100)-Oberflächen untersucht, die mit metallorganischer chemischer Gasphasenabscheidung (MOCVD) für anschließende Heteroepitaxie von III-V-Halbleitern präpariert wurden. An der III-V/IV Grenzfläche werden atomare Doppelstufen auf der Substratoberfläche benötigt, um Antiphasenunordnung in den III-V-Schichten zu vermeiden. Die MOCVD-Prozessgasumgebung beeinflusst die Domänen- und Stufenbildung der Si- und Ge(100)-Oberfläche sehr stark. Deswegen wurden in situ Reflexions-Anisotropie-Spektroskopie (RAS) und Ultrahochvakuum-(UHV)-basierte oberflächensensitive Messmethoden verwendet, um die verschiedenen Oberflächen zu charakterisieren. In situ RAS ermöglicht die Identifizierung der Oberflächenstruktur und somit Kontrolle über die Oberflächenpräparation, insbesondere der Domänenbildung auf Si- und Ge(100). Beide Oberflächen wechselwirken stark mit dem H2-Prozessgas, was zu Monohydrid-Bedeckung während der Präparation führt und sogar zu Si-Abtrag während Präparation unter hohem H2-Druck. Die Erzeugung von Leerstellen auf den Terrassen bewirkt eine kinetisch bedingte Oberflächenstruktur, basierend auf Diffusion von Leerstellen und Atomen. Dadurch kommt es zu ungewöhnlichen DA-Doppelstufen auf verkippten Si(100)-Substraten während auf exakten Substraten ein schichtweiser Abtrag stattfindet. Unter niedrigem H2-Druck bildet sich eine energetisch bedingte Domänen- und Stufenstruktur. Während das H2-Prozessgas keinen direkten Einfluss auf die Stufen- und Domänenbildung von verkippten Ge(100)-Oberflächen zeigt, ist der Einfluss von Gruppe-V-Elemente entscheidend. Die As-terminierten Ge(100)-Oberflächen bilden eindomänige Oberflächen unterschiedlicher Dimerorientierung und Stufenstruktur abhängig von Temperatur und As-Quelle. Angebot von P an Ge(100)-Oberflächen durch Heizen in Tertiärbutylphosphin führt zu einer ungeordneten, P-terminierten Ge(100)-Oberfläche, die instabiler als die Ge(100):As-Oberfläche ist. / In this work, the atomic surface structure of Si(100) and Ge(100) surfaces prepared in metalorganic chemical vapor phase deposition (MOCVD) ambient was studied with regard to subsequent heteroepitaxy of III-V semiconductors. At the III-V/IV interface, double-layer steps on the substrate surface are required to avoid anti-phase disorder in the epitaxial film. The MOCVD process gas ambient strongly influences the domain and step formation of Si and Ge(100) surfaces. Therefore, in situ reflection anisotropy spectroscopy (RAS) and ultra-high vacuum-based (UHV) surface sensitive methods were applied to investigate the different surfaces. In situ RAS enabled identification of the surface structure and the crucial process steps, leading to complete control of Si and Ge(100) surface preparation. Both surfaces strongly interact with H2 process gas which leads to monohydride termination of the surfaces during preparation and Si removal during processing in high H2 pressure ambient. The generation of vacancies on the terraces induces a kinetically driven surface structure based on diffusion of vacancies and Si atoms leading to an energetically unexpected step structure on vicinal Si(100) substrates with DA-type double-layer steps, whereas Si layer-by-layer removal occurs on substrates with large terraces. Processing in low H2 pressure ambient leads to an energetically driven step and domain structure. In contrast, H2-annealed vicinal Ge(100) surfaces show no direct influence of the H2 ambient on the step structure. At the Ge(100) surface, group-V elements strongly influence step and domain formation. Ge(100):As surfaces form single domain surfaces with different majority domain and significantly different step structures depending on temperature and As source, respectively. In contrast, exposure to P by annealing in tertiarybutylphosphine leads to a very disordered P-terminated vicinal Ge(100) surface which is less stable compared to the Ge(100):As surfaces.

Im Rahmen dieser Arbeit werden zwei Perylen-Derivate als Zwischenschichten in Ag/organischen Schichten/GaAs(100)-Heterostrukturen eingesetzt, um den Einfluss von unterschiedlichen chemischen Endgruppen auf die chemischen und strukturellen Eigenschaften beider Grenzflächen, sowie auf die Morphologie, Struktur und Kristallinität von organischen Schichten zu charakterisieren. Die molekularen Schichten von 3,4,9,10-Perylentetracarbonsäure Dianhydrid (PTCDA) und Dimethyl-3,4,9,10-Perylentetracarbonsäure Diimid (DiMe-PTCDI) werden durch organische Molekularstrahldeposition (OMBD) im Ultrahochvakuum auf S-passivierten GaAs(100):2x1-Substraten hergestellt. Weiterhin wird der Einfluss des Substrats untersucht, indem PTCDA-Wachstum auf H-passiviertem Si(100):1x1 durchgeführt wird. Als Hauptcharakterisierungsmethode wird die Ramanspektroskopie eingesetzt. Diese ist eine nicht-destruktive Methode, die auch in situ Untersuchungen des Wachstumsprozesses ermöglicht. Die komplementäre Infrarotspektroskopie sowie die Rasterkraftmikroskopie, Rasterelektronenmikroskopie und Röntgenbeugung (XRD) werden zur Ergänzung des Verständnisses der Heterostruktureigenschaften verwendet. Die Empfindlichkeit von Raman- und Infrarot-Spektroskopien auf die chemisch unterschiedlichen Endgruppen wird durch experimentelle Untersuchungen an PTCDA- und DiMe-PTCDI-Kristallen, beziehungsweise dicken Schichten und mit Hilfe theoretischer Berechnungen nachgewiesen. So wird zum ersten Mal eine vollständige Zuordnung der Schwingunsfrequenzen zu den internen Schwingungsmoden von DiMe-PTCDI vorgeschlagen. Im niedrigen Frequenzbereich der Ramanspektren werden die externen molekularen Schwingungsmoden, oder molekularen „Phononen“, die eine Signatur der Kristallinität darstellen, beobachtet. Die Phononen von DiMe-PTCDI werden in dieser Arbeit zum ersten Mal in einem Ramanexperiment beobachtet. Mittels resonanter Ramanspektroskopie wird die Detektion von C-H-Deformationsmoden und C-C-Streckmoden sogar im Sub-Monolagenbereich molekularer Bedeckung auf Halbleiteroberflächen möglich. Anhand dieser Ramanspektren konnte die Art der Wechselwirkung zwischen Molekülen und passivierten Oberflächen näher charakterisiert werden. Zusätzliche Information bringen die GaAs LO- und Plasmon-gekoppelten LO- Phononen, deren Intensitätsverhältnis im Ramanspektrum die Bandverbiegung im GaAs-Substrat widerspiegelt. Die Kristallinität der hergestellten organischen Schichten mit Dicken größer als 2 nm wird durch Beobachtung der molekularen „Phononen“ nachgewiesen. Als allgemeine Tendenz konnte bewiesen werden, dass mit steigender Substrattemperatur während des Wachstums größere Kristalldomänen entstehen. Weiterhin wird eine Methode vorgeschlagen, um den Anteil von zwei PTCDA- Kristallphasen mit ähnlichen Gitterparametern anhand der Raman- beziehungsweise XRD-Spektren zu bestimmen. Durch ihre sehr gute Ordnung können die DiMe-PTCDI- Schichten als Modellsystem dienen, um eine Methode zu entwickeln, die die Molekülorientierung im Bezug zum Substrat aus polarisationsabhängigen Raman- und Infrarotmessungen bestimmt. Bei der Metall-Bedampfung wird die Empfindlichkeit der Ramanstreuung an internen molekularen Schwingungsmoden von PTCDA und DiMe-PTCDI-Schichten durch oberflächenverstärkte Ramanstreuung (SERS) erhöht. Anhand der unterschiedlichen Signalverstärkungsmechanismen werden Informationen über die Ag/Molekül- Wechselwirkung und die Morphologie der Ag-Schichten abgeleitet.

abstract: This dissertation presents research findings regarding the exploitation of localized surface plasmon (LSP) of epitaxial Ag islands as a means to enhance the photoluminescence (PL) of Germanium (Ge) quantum dots (QDs). The first step of this project was to investigate the growth of Ag islands on Si(100). Two distinct families of Ag islands have been observed. “Big islands” are clearly faceted and have basal dimensions in the few hundred nm to μm range with a variety of basal shapes. “Small islands” are not clearly faceted and have basal diameters in the 10s of nm range. Big islands form via a nucleation and growth mechanism, and small islands form via precipitation of Ag contained in a planar layer between the big islands that is thicker than the Stranski-Krastanov layer existing at room-temperature. The pseudodielectric functions of epitaxial Ag islands on Si(100) substrates were investigated with spectroscopic ellipsometry. Comparing the experimental pseudodielectric functions obtained for Si with and without Ag islands clearly identifies a plasmon mode with its dipole moment perpendicular to the surface. This observation is confirmed using a simulation based on the thin island film (TIF) theory. Another mode parallel to the surface may be identified by comparing the experimental pseudodielectric functions with the simulated ones from TIF theory. Additional results suggest that the LSP energy of Ag islands can be tuned from the ultra-violet to the infrared range by an amorphous Si (α-Si) cap layer. Heterostructures were grown that incorporated Ge QDs, an epitaxial Si cap layer and Ag islands grown atop the Si cap layer. Optimum growth conditions for distinct Ge dot ensembles and Si cap layers were obtained. The density of Ag islands grown on the Si cap layer depends on its thickness. Factors contributing to this effect may include the average strain and Ge concentration on the surface of the Si cap layer. The effects of the Ag LSP on the PL of Ge coherent domes were investigated for both α-Si capped and bare Ag islands. For samples with low-doped substrates, the LSPs reduce the Ge dot-related PL when the Si cap layer is below some critical thickness and have no effect on the PL when the Si cap layer is above the critical thickness. For samples grown on highly-doped wafers, the LSP of bare Ag islands enhanced the PL of Ge QDs by ~ 40%. / Dissertation/Thesis / Doctoral Dissertation Physics 2015

The Si(100) surface and Ga surface phases up to 1 ML on their oxidation have been studied by XPS and LEED. The selective growth of Ga on the SiO2/Si structures fabricated by EBL has been analyzed using SEM and AFM methods. It was proved that Ga clusters grow in structures beside the oxide. The structure of alumina on Ni3Al(111) and NiAl(110) substrates was fully determined by combining the results of STM measurements and DFT simulations. It was determined the alumina/NiAl(110) does not form a suitable template for ordered Fe and Co clusters growth. However, the next research confirmed the alumina/Ni3Al(111) forms template appropriate to clusters growth purpose.

Room-temperature chemisorption of hexacyclic aromatic hydrocarbons on the 2x1, sputtered, oxidized and H-terminated Si(100) surfaces, as well as those upon post treatments of hydrogenation, oxidization and electron irradiation have been investigated by using thermal desorption spectrometry (TDS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). This work focuses on the effects of the functional groups (phenyl, methyl, vinyl, heteroatom, and H atom) in the chemisorbed aromatic hydrocarbons (benzene, toluene, xylene isomers, styrene and pyridine) on organic functionalization of the Si(100) surface, particularly on such surface processes as cycloaddition, dative adsorption, hydrogen abstraction, desorption, dissociation, diffusion, and condensation polymerization. Unlike the earlier notion that hydrogen evolution in the hydrocarbon/Si(100) systems is the result of hydrocarbon dissociation (into smaller hydrocarbon fragments and H atoms) on the surface, condensation polymerization of the adsorbed aromatic hydrocarbons is proposed in the present work, in order to explain the higher-temperature hydrogen evolution feature in the toluene/Si(100) system. This hypothesis is supported by our TDS results for other hydrocarbon adsorbates, especially in the pyridine/Si(100) system where electron-induced condensation polymerization has been observed at room temperature. The improved techniques in the TDS experiments developed in the present work have enabled us to observe condensation polymerization and the effect of H on the surface processes (via surface reconstruction) on Si(100) for the first time. New analysis methods have also been developed to determine the adsorption coverage from the AES data, and this work has not only improved the accuracy of the elemental-coverage evaluation, but also provided a means to estimate the rate and the order of chemisorption. By using the density functional theory with the Gaussian 98 program, the adsorption geometries and the corresponding adsorption energies of various adsorption phases have been calculated. These computational results have provided useful insights into the chemisorption structures on the Si(100) surface. The present work also presents the development of three kinetics models for hydrogen evolution in the aforementioned aromatic-hydrocarbon systems on Si(100). Based on a modified collision theory with consideration of diffusion, these theoretical models have proven to be quite successful in simulating the observed TDS profiles and in estimating the kinetic parameters for the analysis of condensation polymerization in 2-dimensional diffusion systems. The present work illustrates that TDS experiments can be used effectively with quantum computation and theoretical kinetics modelling to elucidate the intricate nature of organosilicon surface chemistry.