Search query: THERMODYNAMICS AND KINETICS OF NANOCLUSTER FORMATION ON SEMICONDUCTOR SURFACES: THE EXAMPLE OF SI GROWTH ON SIC(0001)

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abstract: The molecular beam epitaxial growth of Si on SiC is investigated as a prototypical system for the formation of nanoclusters on semiconductor surfaces without interface intermixing effects. The investigation clearly indicates the presence of both equilibrium and non equilibrium effects with regard to the island formation. The existence of an equilibrium wetting layer thickness dequ independent from deposition rate R and temperature T is shown from the wetting behaviour of Si on SiC(0001) associated with a change in the surface reconstruction. After 3D island formation dequ is still present between the 3D islands, what clearly confirms that the growth mode of Si is Stranski Krastanov. The equilibrium wetting layer thickness is well described by equilibrium theory of heteroepitaxial growth considering strain as well as interface effects. At d dequ and conditions that are close to the equilibrium surplus Si atoms always aggregate instantly into 3D islands. Under dynamical conditions of growth far from equilibrium, the range of 2D layer by layer growth can be extended to an excess wetting layer thickness (dcrit dequ) Investigation of (dcrit dequ) as function of R and T indicated a transition from thermodynamically to kinetically controlled regimes of 2D 3D transition by a change in deposition condition. Furthermore, the 2D 3D transition initially starts with the formation a larger 2D islands and the simultaneous formation of smaller 3D islands, which likely acts as precursors for the formation and growth of larger 3D islands. For the growth of islands during further deposition surface mass transport of adatoms is rate controlling. Post deposition annealing of the highly stressed excess wetting layer (d dequ) gives rise to 3D island nucleation after deposition was stopped, what could be a long lasting process because adatoms stem mainly from the wetting layer decomposition.
author_names: Andreas Fissel
title: THERMODYNAMICS AND KINETICS OF NANOCLUSTER FORMATION ON SEMICONDUCTOR SURFACES: THE EXAMPLE OF SI GROWTH ON SIC(0001)
year: 2019

abstract: Colloid and surface chemistry scope and variables sedimentation and diffusion and their equilibrium solution thermodynamics osmotic and Donnan equilibria the rheology of dispersions static and dynamic light scattering and other radiation scattering surface tension and contact angle application to pure substances adsorption from solution and monolayer formation colloidal structures in surfactant solutions association colloids adsorption at gas solid interfaces van der Waals forces the electrical double layer and double layer interactions electrophoresis and other electrokinetic phenomena electrostatic and polymer induced colloid stability appendix A examples of expansions encountered in this book appendix B units CGS SI interconversions appendix C statistics of discrete and continuous distributions of data appendix D list of worked out examples.
author_names: Paul C Hiemenz

Raj Rajagopalan
title: Principles of colloid and surface chemistry
year: 1977

abstract: Part 1 Equilibria: fundamentals of pure component adsorption equilibria practical approaches of pure component adsorption equilibria pure component adsorption in microporous solids multicomponent adsorption equilibria heterogeneous adsorption equilibria. Part 2 Kinetics: fundamentals of diffusion and adsorption in porous media diffusion and adsorption in porous media Maxwell Stefan approach analysis of adsorption kinetics in a single homogeneous particle analysis of adsorption kinetics in a zeolite particle analysis of adsorption kinetics in a heterogeneous particle. Part 3 Measurement techniques: time lag analysis in diffusion and adsorption in porous media analysis of steady state and transient diffusion cells adsorption and diffusion measurement by a chromatography method kinetics of a batch adsorber.
author_names: Duong D Do
title: Adsorption analysis equilibria and kinetics
year: 1998

abstract: Recently, small particles have been shown to exhibit a melting temperature which depends on the particle size. The various possible experimental methods have been compared and measurements of the melting points of small gold particles have been made using a scanning electron diffraction technique. This method was applied to particles having diameters down to 20 \AA{ Consideration of the size distribution over an entire sample makes it necessary to carry out a careful analysis of the experimental results in order to deduce the melting temperature of particles having a well defined diameter. The experimental results are quantitatively in good agreement with two phenomenological models. The first model describes the equilibrium condition for a system formed by a solid particle, a liquid particle having the same mass, and their saturating vapor phase. The second model assumes the preexistence of a liquid layer surrounding the solid particle and describes the equilibrium of such a system in the presence of the vapor phase. In order to permit a better comparison between both models, a new expression for the thermodynamic equilibrium condition has been derived in the present work. In the case of the first model, the agreement was obtained using only the physical constants of massive gold. In applying the second model, however, one is compelled to assume the existence of a liquid layer having a thickness of about 6 \AA{
author_names: Philippe A Buffat

J P Borel
title: Size effect on the melting temperature of gold particles
year: 1976

abstract: We present two new hybrid meta exchange correlation functionals, called M06 and M06 2X. The M06 functional is parametrized including both transition metals and nonmetals, whereas the M06 2X functional is a high nonlocality functional with double the amount of nonlocal exchange (2X) and it is parametrized only for nonmetals.The functionals, along with the previously published M06 L local functional and the M06 HF full Hartree Fock functionals, constitute the M06 suite of complementary functionals. We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree Fock theory for 403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero point energies. We recommend the M06 2X functional for applications involving main group thermochemistry, kinetics, noncovalent interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application in organometallic and inorganometallic chemistry and for noncovalent interactions.
author_names: Yan Zhao

Donald G Truhlar
title: The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06 class functionals and 12 other functionals
year: 2008

abstract: Abstract Graphene, a single atomic layer of graphite, has been the focus of recent intensive studies due to its novel electronic and structural properties. Metals grown on graphene also have been of interest because of their potential use as metal contacts in graphene devices, for spintronics applications, and for catalysis. All of these applications require good understanding and control of the metal growth morphology, which in part reflects the strength of the metal graphene bond. Also of importance is whether the interaction between graphene and metal is sufficiently strong to modify the electronic structure of graphene. In this review, we will discuss recent experimental and computational studies related to deposition of metals on graphene supported on various substrates (SiC, SiO 2 and hexagonal close packed metal surfaces) Of specific interest are the metal graphene interactions (adsorption energies and diffusion barriers of metal adatoms) and the crystal structures and thermal stability of the metal nanoclusters.
author_names: Xiaojie Liu

Yong Han

James W Evans

Albert K Engstfeld

Rolf Jurgen Behm

Michael C Tringides

Myron Hupalo

Haiqing Lin

Li Hua Huang

Kai-Ming Ho

David Victor Appy

Patricia A Thiel

Cai-Zhuang Wang
title: Growth morphology and properties of metals on graphene
year: 2015

abstract: Semiconductor nanowires refer to crystal structures with diameters as small as a few nanometers and lengths up to tens of micrometers or even millimeters. Nanowires can be produced either through conventional subtractive nanofabrication processes, via lithography and etching, or through additive nanomaterial growth methods. The quality of "top down" fabricated nanowires are in principle determined by the starting material, although the size reduction techniques used to fabricate these structures inevitably introduce damage (e.g. roughness) that can degrade overall quality. The top down approach, which relies heavily on the precision of the lithography and etching tools, also becomes less cost effective when scaling to ca. 10 nm size regimes. In this chapter we focus on nanowires produced through "bottom up" growth methods, in which the critical dimension (e.g. the nanowire diameter) is limited not by lithography precision but controlled during chemical synthesis with atomic resolution. In particular, the catalyst mediated vapor liquid solid (VLS) process is discussed in detail since this approach enables the growth of a broad range of nanowire materials with controlled structure, morphology, composition, and doping.
author_names: Lin Chen

Wei Lu

Charles M Lieber
title: Chapter 1:Semiconductor Nanowire Growth and Integration
year: 2014

abstract: By exploiting the extremely large effective cross sections {10}\ensuremath{ }17} {10}\ensuremath{ }16}\mathrm{cm}{2}\mathrm{molecule} available from surface enhanced Raman scattering (SERS) we achieved the first observation of single molecule Raman scattering. Measured spectra of a single crystal violet molecule in aqueous colloidal silver solution using one second collection time and about $2\ifmmode\times\else\texttimes\fi{{10}{5}\mathrm{W}\mathrm{cm}{2} nonresonant near infrared excitation show a clear `fingerprint' of its Raman features between 700 and $1700{\mathrm{cm}\ensuremath{ }1} Spectra observed in a time sequence for an average of 0.6 dye molecule in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1, 2, or 3 molecules.
author_names: Katrin Kneipp

Harald Kneipp

Lev T Perelman

Irving Itzkan

Ramachandra R Dasari

M S Feld
title: Single Molecule Detection Using Surface Enhanced Raman Scattering (SERS)
year: 1997

abstract: Nanostructured surfaces can be broadly defined as substrates in which the typical features have dimensions in the range 1?100?nm (although the upper limit of 100?nm may be relaxed to greater sizes in some cases, depending on the material and the specific property being investigated) The recent surge of interest in these systems stems from the remarkable effects that may arise from the critical size reduction. Interesting novel properties (catalytic, magnetic, ferroelectric, mechanical, optical and electronic) occur as we reduce the dimensions from a practically infinite (and periodic) solid crystal to a system composed of a relatively small number of atoms. So far, nanostructured materials or nanomaterials are perhaps the only sub field of nanoscience that has made the transition from fundamental science to real world applications, thus becoming a technology (a good example of this are nanostructured surface coatings) This paper describes some selected examples of recent progress in the study of nanostructured surfaces. Surface reconstructions, which occur either naturally or as a consequence of the interaction with adsorbates, are discussed because of their importance in model chemical reactions and for their potential use as templates for the ordered growth of nanostructures. Supramolecular assemblies and molecular nanostructures, resulting from the balance between molecule?molecule and molecule?surface interactions, are described because of their fundamental interest and their potential use in nanoelectronic devices. Recent progress in the growth of semiconductor nanostructures, in particular Ge?Si and InAs?GaAs, is briefly reviewed. A few selected examples of nanostructured functional materials, such as ferroelectric and magnetic nanostructures, are discussed in view of their potential for applications in future data storage devices. Nanostructured materials used in catalysis and gas sensor applications are briefly described. Finally, perspectives and future challenges in this emerging field of research are also discussed.
author_names: Federico Rosei
title: Nanostructured surfaces: challenges and frontiers in nanotechnology
year: 2004

abstract: Throughout this thesis, we have studied ZnO and its properties in a bottom up manner through a dimensionality range starting from 0D nanoparticles to 3D bulk phases. For the 0D clusters and the 2D nanofilms studied we also considered the effect of a support in models designed to study ZnO thin film growth on the Ag(111) surface. In chapter 3, we have studied ZnO nanoclusters on a Ag support and compared their properties with free space ZnO nanoclusters. In this chapter we highlighted the importance of the presence of the support during the global optimization of the clusters (i.e. as opposed to global optimization of the clusters in free space and then introducing a support) Our results show that the presence of the support strongly affects the energetic stability ranking of the nanocluster isomers. More drastically, after a certain cluster size, the support also stabilizes selectively 2D type structures, which are not stable in free space, with respect to the 3D clusters. The extra stabilization of supported 2D clusters is attributed mainly to the contact area, which is evidently greater for 2D clusters where all the atoms can interact with the surface. The importance of the contact are is also observed for 3D clusters, as ellipsoid bubbles or inflated double layer clusters being of lower energy than more spherical clusters on the support whereas the latter, more symmetric 3D clusters are more stable in free space. Matching of the cluster structure with the surface morphology was found to be another factor determining cluster stability. The Zn3O3 sixmembered ring, which is one of the main motifs for both 3D and 2D clusters, matches best with the Ag(111) surface because it follows the same six fold (C6) symmetry (or its trigonal C3 subgroup with a three fold axis, taking into account the distinction between Zn and O atoms) However because of the lattice size differences, such matching dies away for larger ZnO clusters. The preferential stabilities of the 2D structures of ZnO clusters can be seen as the initial stages of thin film growth and is found to be in line with the experimentally observed layered ZnO sheets on the Ag(111) surface. In Chapter 4, we have considered a full 2D ZnO sheet on Ag(111) surface and also investigated also how H atoms interact with it. Following our results for ZnO nanoclusters on the Ag surface, we highlighted the importance of the degree of 2D ZnO:Ag(111) unit cell commensurability for calculating accurate sheeton substrate binding energies. We have found a 8:9 commensurate monolayer to be more favored with interatomic potentials and a 7:8 commensurate monolayer with DFT calculations, where the latter is found in experiment. Our calculations showed no evidence of charge transfer or covalent bonding between the Ag(111) surface and the 2D ZnO sheet, but did show that the ZnO sheet and the Ag(111) surface exhibit small structural distortions in order to maximize their mutual interaction. Calculations of the unsupported 2D ZnO sheet interacting with hydrogen provided strong evidence for H forming a low energy Zn 4s H 1s multi center bonding state when passing through a Zn3O3ring of the 2D ZnO sheet, thus allowing for relatively facile H transport through the sheet. In chapter 5, we have extended our study of supported 2D ZnO nanofilms with higher coverage models, including triangular islands on top of two full monolayers, prepared to model the experimental system. Our results showed that the triangular adlayer islands induce a transition to the WZ structure in the island core and in local region in the two layers immediately below the island core. The islands are also found to have BCT structured reconstructions on their edges and T1 structured reconstructions on their corners. These models are found to better match the experimental structural data for the experimental 2.7 ML Ag supported ZnO film with respect to models assuming a purely layered or a purely WZ structure. In chapter 6, we focused on 4ML nanofilms and compared bulk and the 4 ML nanofilm poymorphism of ZnO. Our results revealed that the stability range of nanofilms and their energetic ordering are radically different than that of bulk polymorphs. We have developed a method to generate a wide range of new low energy nanofilm and bulk polymorphs using nets as a basis, and showed that there exist at least three nanofilm structures with trigonal basal plane symmetry compatible epitaxial growth on fcc metal (111) surfaces that are more stable than layered ZnO. While confirming the previous theoretical studies predicting the BCT ZnO phase as being the lowest energy free standing nanofim for small thicknesses, we obtained a range of structurally related and near energetically degenerate phases, indicating there exists BCT polytypism. With increasing thickness we found that atomically reconstructed wz ZnO becomes more stable than BCT ZnO for ~14 MLs, and is always more stable than non reconstructed wz ZnO. We have also stressed the influence of strain on polymorphism by showing that BCT ZnO and layered ZnO nanofilms are unstable to novel polymorphs under in plane strain. Together with the T1 structures and BCT structures which were also predicted as reconstructions on island corners in the previous chapter, our results strongly suggest that many new nanofilm polymorphs should be experimentally accessible, and in some cases, may have even already been observed. In chapter 7, we focused on bulk polymorphism and, specifically, investigated the effect of nanoporosity. Our results showed that both energetic instability and band gap increase with nanoporosity and we predicted that nanoporosity could induce band gap increases of up to ~1.5 eV relative to wurtzite ZnO. We showed that the band gap increase is related with bandwidth changes in the conduction band and the valance band. We suggested that the underlying physical mechanism for this effect is that introducing nanoporosity, and thus periodic internal void space, restricts extended orbital overlaps and thus decreases bandwidths. Due to the generality of this argument, we expect that nanoporosity could similarly affect bandgap values in a wide range of materials and could be employed as a band gap engineering method.
author_names: Ilker Demiroglu
title: Effect of Dimensionality and Polymorphism on the properties of ZnO
year: 2014