Clusters Of Ge Research Articles

Epidemiological investigation, determination of related factors, and spatial-temporal cluster analysis of wild type pseudorabies virus seroprevalence in China during 2022.

Pseudorabies virus (PRV) is a linear DNA virus with a double-stranded structure, capable of infecting a diverse array of animal species, including humans. This study sought to ascertain the seroprevalence of Pseudorabies Virus (PRV) in China by conducting a comprehensive collection of blood samples from 16 provinces over the course of 2022. The presence of PRV gE antibodies was detected through the utilization of an enzyme-linked immunosorbent assay (ELISA) technique. Logistic regression analysis was conducted to identify potential related factors associated with the serologic status of PRV gE at the animal level. Additionally, the SaTScan 10.1 software was used to analyze the spatial and temporal clusters of PRV gE seroprevalence. A comprehensive collection of 161,880 samples was conducted, encompassing 556 swine farms throughout the country. The analysis revealed that the seroprevalence of PRV gE antibodies was 12.36% (95% confidence interval [CI], 12.20% to 12.52%) at the individual animal level. However, at the swine farm level, the seroprevalence was considerably higher, reaching 46.22% (95% CI, 42.08% to 50.37%). Related factors for PRV infection at the farm level included the geographic distribution of farms and seasonal variables. Moreover, five distinct high seroprevalence clusters of PRV gE were identified across China, with the peak prevalence observed during the months of April through June 2022. Our findings serve as a valuable addition to existing research on the seroprevalence, related factors, and temporal clustering of PRV gE in China. Furthermore, our study provides a reference point for the development of effective strategies for the prevention and control of pseudorabies and wild virus outbreaks.

Evidence for Kinetic Limitations as a Controlling Factor of Ge Pyramid Formation: a Study of Structural Features of Ge/Si(001) Wetting Layer Formed by Ge Deposition at Room Temperature Followed by Annealing at 600 °C.

The article presents an experimental study of an issue of whether the formation of arrays of Ge quantum dots on the Si(001) surface is an equilibrium process or it is kinetically controlled. We deposited Ge on Si(001) at the room temperature and explored crystallization of the disordered Ge film as a result of annealing at 600 °C. The experiment has demonstrated that the Ge/Si(001) film formed in the conditions of an isolated system consists of the standard patched wetting layer and large droplike clusters of Ge rather than of huts or domes which appear when a film is grown in a flux of Ge atoms arriving on its surface. We conclude that the growth of the pyramids appearing at temperatures greater than 600 °C is controlled by kinetics rather than thermodynamic equilibrium whereas the wetting layer is an equilibrium structure.PACS: Primary 68.37.Ef; 68.55.Ac; 68.65.Hb; 81.07.Ta; 81.16.Dn

Adsorption of CO on pure and mixed clusters of tin and germanium up to five atoms: A theoretical study

The adsorptions of the CO molecule on the neutral mixed clusters of Sn and Ge up to five atoms are investigated theoretically. Electronic structures of the cluster-CO complexes are obtained by global optimization of the energy surface using Monte Carlo simulation coupled with simulated annealing followed by pseudopotential plane wave density functional theory calculations. An aug-cc-pVTZ basis set for C and O and aug-cc-pVTZ-pp for Sn and Ge atoms are employed. The CO adsorption energies and Gibbs free energy are calculated to establish the kinetic and thermodynamic stability of the cluster-CO complexes. The variations of adsorption energy, HOMO–LUMO gap, and NBO charge on CO fragment with the size of the clusters are reported. The CO adsorptions on Sn–Ge mixed clusters are confirmed by studying correlations among different parameters such as the increase in C–O bond length, the red shift in C–O stretching frequency, CO binding energy, changes in Gibbs free energy, and NBO charge on CO.

Recent theoretical progress on electronic and structural properties of clusters: Permanent electric dipoles, magnetism, novel caged structures, and their assemblies

We present a brief account of the recent progress in the theoretical understanding of the electronic and structural properties of clusters of metals and semiconductors from ab initio calculations. The origin of the recently observed permanent electric dipoles in Nb clusters, the occurrence of magnetism in clusters of non-magnetic elements such as Pd, Rh, and Ru, as well as the findings of the metal encapsulated clusters of Si, Ge, Sn, and Pb are discussed. Empty caged clusters of Si, Ge, and Sn have also been shown to be stable with H capping. These can be functionalized by exohedral doping for different applications while endohedral doping of the cages can be used to tailor highest occupied-lowest unoccupied molecular orbital gaps as well as the magnetic properties. Assemblies of such clusters could lead to novel nanostructures and new phases of these materials.

Smallest Magic Caged Clusters of Si, Ge, Sn, and Pb by Encapsulation of Transition Metal Atom

Ten atom clusters of X = Si, Ge, Sn, and Pb are known to be magic, suggesting that addition of an atom to such clusters is generally unfavorable. However, here we report using an ab initio ultrasoft pseudopotential method that these clusters can be further stabilized by doping of a Ni or Pt atom, leading to some of the smallest metal encapsulated clusters of these elements. For Si and Ge, doping of Ni is optimal while for Sn and Pb, Pt is the best. Our results agree with the recent observations of strong abundances and magic nature of X10Co- clusters of these elements. These findings could lead to the development of novel cluster-based nanomaterials for optoelectronic and other nanoscale applications.

Metal-doped magic clusters of Si, Ge, and Sn: The finding of a magnetic superatom

Studies on divalent-metal (M)-atom-doped XNM (X=Si, Ge, and Sn, N=8–12 and 14) clusters, using ab initio pseudopotential plane wave method, show that the well known nine- and ten-atom capped prism units as well as 12- and 14-atom clusters of these elements can transform to magic clusters with higher symmetries and larger highest occupied–lowest unoccupied molecular orbital gaps. Most strikingly doping of X12 with Mn leads to an icosahedral superatom, Mn@X12, X=Ge and Sn with a high magnetic moment of 5 μB, enriching the family of M-doped clusters of semiconductors for possible nanodevice applications.

Novel caged clusters of silicon: Fullerenes, Frank-Kasper polyhedron and cubic

We review recent findings of metal (M) encapsulated caged clusters of Si and Ge obtained from computer experiments based on an ab initio pseudopotential method. It is shown that one M atom changes drastically the properties of Si and Ge clusters and that depending upon the size of the M atom, cages of 14, 15, and 16 Si as well as Ge atoms are formed. In particular M@Si16 silicon fullerene has been obtained for M= Zr and Hf, while a Frank-Kasper polyhedron has been obtained for M@X16, X = Si and Ge. These clusters show high stability and large highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) gaps which are likely to make these species strongly abundant. A regular icosahedral M@X12 cluster has also been obtained for X = Ge and Sn by doping a divalent M atom. Interactions between clusters are rather weak. This is attractive for developing self-assembled cluster materials.

Metal-encapsulated caged clusters of germanium with large gaps and different growth behavior than silicon.

Metal ( M)-encapsulated caged clusters of Ge are studied using the ab initio pseudopotential plane-wave method and the generalized gradient approximation for the exchange-correlation energy. Depending upon the size of the M atom, we find Frank-Kasper polyhedral M@Ge(16) for M= Ti, Zr, Hf, and capped decahedral or cubic M@Ge(14) and M@Ge(15) clusters for several M atoms. The growth behavior differs from the one found in M@Si(n) clusters. The highest-occupied-lowest-unoccupied molecular orbital gaps are, however, similarly large or even higher in some cases. Cr@Ge(16) and Fe@Ge(15) are magnetic. The weak interaction between the clusters makes such species attractive for cluster assembled materials.

Metal-encapsulated icosahedral superatoms of germanium and tin with large gaps: Zn@Ge12 and Cd@Sn12

Metal (M)-encapsulated clusters of Ge and Sn, Zn@Ge12 and Cd@Sn12, are obtained from total energy calculations using ab initio pseudopotential plane wave method and generalized gradient approximation for the exchange-correlation energy. These have perfect icosahedral symmetry and large highest occupied–lowest unoccupied molecular orbital gap of about 2 eV. It lies in the optical region and makes these species attractive for cluster assembled optoelectronic materials. Calculations on silicon clusters doped with Be show a different behavior.

ChemInform Abstract: Discrete and Linked Homoatomic Clusters of the Elements Ge, Sn, and Pb

ChemInform Abstract: Discrete and Linked Homoatomic Clusters of the Elements Ge, Sn, and Pb

Properties of pure and compound clusters of Si, Ge, and Pb.

The properties of monoelemental Si, Ge, and Pb clusters and those of compound Si-Pb and Ge-Pb clusters have been studied by using semiempirical methods of the modified neglect of differential overlap type. The cluster size is 10\ensuremath{\leqslant}N\ensuremath{\leqslant}90 and in compound clusters a fraction \ensuremath{\leqslant}0.5 of Si and Ge atoms is replaced by Pb. The calculations support and extend the results of recent first-principles calculations of silicon clusters. They indicate, in fact, that for Si, Ge, and Pb elongated and spherical structures are both possible, the first lying lower in binding energy at large N. Noticeable relaxation is observed in compound clusters whose binding energies, bond lengths, and angles are substantially altered, with respect to the monoelemental ones, by the inclusion of the metallic element. \textcopyright{} 1996 The American Physical Society.

Growth mode of Ge on GaAs(100)

The surface morphology of single- and multilayer Ge films on GaAs(100) has been studied using low-energy electron diffraction and scanning tunneling microscopy (STM). After deposition of 0.5 monolayer, the Ge atoms form dimers with Ga atoms after annealing to 875 K, resulting in a (1×2) ordered surface layer. A Ge multilayer deposited at 700 K shows a mixture of (1×2) and (2×1) phases. When annealed at higher temperatures, the (2×1) structure begins to disappear, and, eventually, only the (1×2) phase remains after annealing at 875 K. STM images of the surface reveal faceted clusters of Ge that are surrounded by relatively smooth areas of (1×2) order. Based on these observations, we suggest that the Ge film grows on GaAs(100) by the Stranski–Krastanov mechanism at high temperatures. Because the lattice strain is negligible, the driving force for this growth mode is a reduction in the total surface energy by minimizing substrate-induced electronic effects. Comparison of Ge growth on GaAs(100), GaAs(110), and Si(100) substrates shows the important role of surface and bulk electronic structure in determining the growth mode. The observed antiphase-domain-free GaAs growth on Ge/GaAs(100) is explained based on our results.

ChemInform Abstract: Structure and Properties of Ionized and Neutral Condensed Clusters of Si, Ge, Sn, and Pb

AbstractReview: (analysis of recent experimental data and theoretical models including general trends in ionization potentials and electron affinities; 34 refs.

Structure and properties of ionized and neutral condensed clusters of Si, Ge, Sn, and Pb

The relative abundances of medium-size clusters X(+,−,0)n of X=Si, Ge, Sn, or Pb, with 7≤n≤30, as prepared in various ways after vapor-phase condensation, are determined by enthalpic, entropic, and dynamic factors. Valence electronic structure determines chemical trends in (magic number) peaks in these relative abundances. Theoretical models of the valence structure explain these trends in detail. New cylindrical structures are identified at n=15, 18, and 21 for X(−)n with X=Si and Ge. General trends in ionization potentials and electron affinities are discussed.

ChemInform Abstract: Semiconductor Cluster Beams: One and Two Color Ionization Studies of Six and Gex.

AbstractAstudy of small Clusters of Si and Ge in a supersonic beam is carried out to investigate the differences between Clusters of semiconducting elements and those of metals.

Semiconductor cluster beams: One and two color ionization studies of Six and Gex

Supersonic beams of clusters of Si and Ge atoms have been produced by laser vaporization followed by supersonic expansion in a helium carrier. The cluster beams were characterized by F2(7.9 eV) and ArF(6.4 eV) excimer laser ionization accompanied by time-of-flight mass analysis. In addition, the feasibility of a resonant two-photon ionization (R2PI) spectroscopic study was explored by two-color experiments involving initial excitation with the second (2.36 eV) and third (3.54 eV) harmonics of the Nd:YAG followed by excimer laser ionization. All two-photon ionization processes were found to produce extensive fragmentation of the larger clusters. The observed fragmentation pattern for the silicon and germanium clusters were remarkably similar to each other, but drastically different from that seen for metal clusters in the same apparatus. Unlike metal clusters, which tend to lose one atom at a time, these semiconductor clusters appear to fragment by a fission process, the daughter ions falling almost exclusively in the size range from 6 to 11 atoms. Time delay studies in the two-color experiments established that clusters of both Si and Ge have excited electronic states with lifetimes of approximately 100 ns. This again is dramatically different from the behavior found with metal clusters, and indicates the feasibility of R2PI spectroscopy on these cold semiconductor particles. The existence of such long-lived excited states indicates that there is probably an energy gap between the band of electronic states being excited and the ground electronic state.

Cluster model approach for electronic structure of Si and Ge(111) and GaAs(110) surfaces

For the purpose of exploring how realistic a cluster model can be for semiconductor surfaces, extended Huckel theory calculations are performed on clusters modeling Si and Ge(111) and GaAs(110) surfaces as prototypes. Boundary conditions of the clusters are devised to be reduced. The ideal, relaxed, and reconstructed Si and Ge(111) surfaces are dealt with. Hydrogen chemisorbed (111) clusters of Si and Ge are also investigated as prototypes of chemisorption systems. Some comparison of the results with finite slab calculations and experiments is presented. The cluster-size dependence of the calculated energy levels, local densities of states, and charge distributions is examined for Si and Ge(111) clusters. It is found that a 45-atom cluster which has seven layers along the [111] direction is large enough to identify basic surface states and study the hydrogen chemisorption on Si and Ge(111) surfaces. Also, it is presented that surface states on the clean Si and Ge(111) clusters exist independent of relaxation. Further, the calculation for the relaxed GaAs(110) cluster gives the empty and filled dangling-orbital surface states comparable to experimental data and results of finite slab calculations. The cluster approach is concluded to be a highly useful and economical one for semiconductor surface problems.