Author: Sweta GoelPublisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 3
Book Description
Molecular Dynamics Simulation of Surface Diffusion of Silicon and Hydrogen on Single Crystal Silicon Surfaces
Author: Sweta GoelPublisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 3
Book Description
Characterization of Surface Diffusion and Adatom Hopping of Single Crystal Silicon Surfaces Using "density-functional" Inspired Molecular Dynamics Simulation
Author: Sweta GoelPublisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 2
Book Description
CVD XV
Author: Mark Donald AllendorfPublisher: The Electrochemical Society
ISBN: 9781566772785
Category : Technology & Engineering
Languages : en
Pages : 826
Book Description
Molecular Dynamics Simulations of Si Binding and Diffusion on the Native and Thermal Silicon Oxide Surfaces
Author: Saketh BharadwajaPublisher:
ISBN:
Category : Amorphous substances
Languages : en
Pages : 103
Book Description
Amorphous silicon (a-Si) thin-film solar cells grown via plasma-enhanced chemical vapor deposition (PECVD) are of significant technological interest. As a result, there is significant interest in understanding the physical processes which control the a-Si thin-film structure and morphology. In particular, since the early stages of a-Si growth on the silicon oxide substrate play a key role in determining the subsequent evolution, it is important to obtain a better understanding of this stage of a-Si growth. The key objectives of the work presented in this thesis are to obtain a better understanding of the structure and morphology of the silicon-oxide substrate used in a-Si growth via PECVD as well as of the key processes of Si diffusion on the substrate which control the nucleation of a-Si islands. In particular, motivated by experimental and simulation results, we have carried out molecular dynamics simulations of the formation of a thermal silicon oxide substrate (corresponding to oxide formation at high-temperature) as well as of the room-temperature oxidation of "native" silicon oxide thin-films. In addition, for the case of a native silicon oxide surface, we have studied the binding energies, binding sites, and diffusion barriers for Si diffusion in order to gain insight into the critical length-scales for a-Si island formation. In the case of thermal silicon oxide formed at high temperature, our molecular dynamics simulations were carried out using an effective Munetoh potential which takes into account the "average" charge transfer as well as bond angles and energies. In this case, due to the relatively high temperature the surface was found to be extremely rough and highly disordered, while the thin-film structure was found to be amorphous. In contrast, in our simulations of the formation of native silicon oxide thin-films at room temperature, a more sophisticated ReaxFF potential was used which properly takes into account the effects of O2 molecular dissociation and rebinding at the surface, as well as the long-range Coulomb interaction and local charge-transfer. We have also studied the binding and diffusion of Si atoms for this case in order to try to explain recent experiments and simulations in which it was shown that 3D a-Si islands with a typical island diameter of approximately 30 A are formed in the early stages of growth. For the case of native silicon-oxide our results for the oxygen penetration profile and surface roughness were found to be in good qualitative agreement with experiments. Our results also indicate that while the typical binding energies for Si adatoms on the SiO2 surface are significantly lower than for Si/Si(100), due to the disordered structure of the surface the barriers for diffusion are typically significantly higher. As a result, at the deposition temperature of 200oC used in low-temperature PECVD, these sites may act like "trapping sites" for deposited Si atoms. We note that these results are consistent with recent experiments on the relaxation of SiO2 microstructures at high temperatures. However, they also imply that the characteristic length-scale for 3D islands in the early stages of a-Si growth via PECVD cannot be explained by a combination of homogenous diffusion and a critical island-size, as is typically found in epitaxial growth.
High Temperature Structure Formation and Surface Diffusion of Silver on Silicon Surfaces
Author: Dirk WallPublisher: Cuvillier Verlag
ISBN: 3736942710
Category : Science
Languages : en
Pages : 240
Book Description
Kurzbeschreibung Die vorliegende Arbeit beschäftigt sich mit Oberflächendiffusion und Strukturbildung an Oberflächen, speziell im Fall Silber auf Silizium. Unterschiedliche Methoden werden kombiniert um Si(001) und Si(111) Oberflächen als auch dazwischen liegende Orientierungen zu untersuchen. niedrigenergetische Elektronenmikroskopie (LEEM) und photoemissions Elektronenmikroskopie (PEEM) wurden verwendet um die Wachstumsdynamik und den Einfluss von Oberflächendiffusion auf die Strukturbildung an Oberflächen unter Ultrahochvakuum (UHV) Bedingungen zu untersuchen. Es wurden ein- und multi-kristalline Ag Inseln und selbstorganisierte Ag Drähte auf unterschiedlichen Si Oberflächen untersucht. Hierfür wurde Ag bei hohen Temperaturen auf Oberflächen aufgebracht, wobei die meisten Untersuchungen in-situ erfolgten. Die Struktur der Ag Inseln und Drähte und deren Orientierung zum Substrat wurde hauptsächlich mit niederenergetischer Elektronenbeugung an kleinen Bereichen (µ-LEED), hochauflösender niederenergetischer Elektronenbeugung (SPA-LEED) und Rasterelektronenmikroskopie (SEM) untersucht. Für die SEM Untersuchungen wurden die präparierten Proben aus dem UHV entnommen um sie in ein SEM zu transferieren und eine statistisch bessere Aussagekraft zu erreichen. Ag(001) und Ag(111) Inseln wurden bei Temperaturen von bis zu 700°C gewachsen. Mit steigender Wachstumstemperatur verändert sich die überwiegende Form der Inseln von hexagonal zu dreieckig. Die relative Drehung zum Substrat wurde Untersucht und mit einem modifizierten gitter-koinzidenz Modell (CSL) verglichen. Der Vergleich zeigt eine ausgesprochen gute Übereinstimmung der experimentellen Daten mit der Theorie, bei der praktisch alle Drehwinkel erklärt werden. Oberflächendiffusionsfelder wurden beim thermischen Zerfall und während der Desorption von Silberinseln untersucht. Um die Inseln bilden sich ein oder mehrere konzentrische rekonstruktionsbedingte Zonen. Ein einfaches kontinuum Diffusionsmodell zur Erklärung des Zerfallsmechanismus wird vorgestellt. Das Modell beinhaltet ein bereits zuvor präsentiertes Modell als einen Spezialfall und wurde in Zusammenarbeit mit J. Krug und I. Lohmar an der Universität zu Köln entwickelt. Unterschiedlichste Diffusionsparameter können mit diesem Modell bestimmt werden und stimmen sehr gut mit Literaturvergleichswerten überein. Der Zerfall der Inseln auf vizinalen Oberflächen kann nicht mehr mit diesem Modell erklärt werden, da eine Anisotropie auftritt, die die Rotationssymmetrie aufhebt. SPA-LEED Resultate zur Multistufenbildung und Facettierung sowie numerische Simulationen werden hinzugezogen und können mit Hilfe eines in der Literatur bekannten Modells praktisch alle experimentellen Daten erklären und so ein fast all-umfassendes Verständnis der Ursachen der Anisotropie erzeugen. Die Ergebnisse werden auch auf Ergebnisse zu Indium auf vizinalem Silizium angewendet und können auch hier die Überraschende Isotropie erklären. Außer den Inseln bilden sich auf Si(001) auch noch Drähte. Das Wachstum dieser Drähte wurde untersucht um eine Diskussion in der Literatur über die Ursache der Drahtbildung aufzuklären. Einkristalline Drähte wurden auf sehr genau orientiertem Si(001) und auf vizinalen Flächen präpariert. Alle Drähte orientieren sich entlang einer der beiden Hauptsymmetrierichtungen der Oberfläche. Ihr Wachstum ist thermisch aktiviert und erstaunlicherweise unabhängig von der Fehlneigung. Dennoch richten sich die Drähte mit zunehmender Fehlneigung und damit Stufendichte parallel zu den Stufenkanten aus. Die Resultate können jedoch die Diskussion ob Diffusionsanisotropie oder Verspannung die Ursache für das Drahtwachstum sind nicht aufklären, da diese zu stark ineinander überkoppeln. Dennoch kommen wir zu dem Entschluss, dass die Drahtausrichtung durch die zunehmende Diffusionsanisotropie verursacht wird. Description The present work deals with surface diffusion and structure formation, mainly for the case of Silver on Silicon surfaces. Various techniques are combined to investigate flat and vicinal surfaces oriented in the Si(001) and Si(111) directions as well as intermediate orientations. Low energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) were used to study the growth dynamics and diffusion involved in structure formation in ultrahigh vacuum (UHV) conditions. The investigated structure formation deals with single- and multi-crystalline Ag islands and self-organized Ag wires on various Si surfaces. Ag was deposited at elevated temperatures, while the investigations were mainly carried out in-situ. The structure of the grown Ag islands and wires was investigated with either small area low energy electron diffraction (µ-LEED), spot profile analyzing-low energy electron diffraction (SPA-LEED), or scanning electron microscopy (SEM). The SEM investigations were the only investigations, where the sample was extracted from the UHV and were carried out to improve the statistical significance of the data. Ag(001) and Ag(111) islands were grown at elevated temperatures of up to 700°C. With increasing growth temperature, the shape of the islands transformed from hexagonally shaped to triangular. The relative rotation to the substrate was investigated and compared to a modified coincidence site lattice approach (CSL) which agreed very well with the experimental results. Practically all of the significant rotation angles could be explained by the CSL model. Surface diffusion fields were investigated during the decay of islands in the process of desorption. These islands are surrounded by one or several concentric adsorbate induced reconstruction zones. A simple continuum diffusion model is presented, explaining the decay mechanism. The model contains a previously presented model as a special case and was developed in collaboration with J. Krug and I. Lohmar at the University of Cologne. Several diffusion parameters are extracted from the model and are in excellent agreement with values in literature. The decay of Ag islands on vicinal Si substrates no longer yields concentric circular zones, but the zones become anisotropic, and the model can no longer be applied due to the no lack of rotational symmetry. A model from the literature is used to explain the data in combination with SPA-LEED results on multi-step formation and faceting and numerical simulations. Only a combination of all these techniques is capable of a thorough and all-embracing explanation of surface diffusion. The results are compared to the system of Indium on vicinal Si(001) surfaces. Here, in contrast to Ag on vicinal Si(001), no anisotropy is found and the drawn picture can also explain the surprising diffusion isotropy. Among the islands that were used for the diffusion investigations, on Si(001), wires form. The growth of these single crystalline wires was investigated and an attempt has been taken to clear an ongoing discussion about the cause of the wire formation. The single crystalline wires were grown on flat and vicinal Si(001) surfaces. All wires align to one of the two principal directions of the substrate. Their growth is thermally activated and surprisingly independent of the substrate vicinality. The wires align with the step edges as the sample vicinality and with it the step density is increased. The results cannot lead to a clear decision on which of the discussed phenomena diffusion anisotropy or strain are the cause for self-organized wire formation on vicinal Si(001) surfaces. We can, however, come to the conclusion, that the wire alignment is much more closely linked to the diffusion anisotropy than the formation itself. We therefore state, that the diffusion anisotropy is a possible cause for the wire alignment, restricting the wire growth to one of the possible two directions with increasing diffusion anisotropy.
Elementary Surface Reactions of Hydrogen and Oxygen on Silicon
Author: Markus B. RaschkePublisher: Herbert Utz Verlag
ISBN: 9783896755643
Category :
Languages : en
Pages : 206
Book Description
A Study of the Adsorption and Diffusion Behavior of a Single Polydimethylsiloxane Chain on a Silicon Surface by Molecular Dynamics Simulation
Author: Dan MuEnergy Research Abstracts
Author: Scientific and Technical Aerospace Reports
Author: Diffusivity in Silicon 1953 to 2009
Author: David J. FisherPublisher: Trans Tech Publications Ltd
ISBN: 3038133817
Category : Technology & Engineering
Languages : en
Pages : 230
Book Description
This work is essentially an update of previous compilations of information on the diffusivity of elements in semiconductor-grade silicon. It subsumes the data contained in B.L.Sharmas monograph on Diffusion in Semiconductors (Trans Tech Publications, 1970), plus the data contained in Diffusion and Defect Data (Diffusion in Silicon) Volume 45 (1986), Defect and Diffusion Forum (Diffusion in Silicon - 10 years of Research) Volumes 153-155 (1998), Defect and Diffusion Forum (Diffusion in Silicon - a Seven-Year Retrospective) Volume 241 (2005) and the latest data from recent Semiconductor Retrospectives: Defect and Diffusion Forum, Volumes 245-246, Volumes 261-262, Volume 272 and Volume 282. In addition, the resultant 400 items of data were analysed in the hope of finding some unifying correlation. It was indeed found that all of the points (each the average of many independent measurements) seemed to fall on a number of distinct straight lines passing through the origin of a plot of activation energy versus atomic radius. However, it remained unclear how these correlations could be explained.