Nucleation and growth of Ge nanoclusters on the Si(111)‐(7 × 7) surface studied by scanning tunneling microscopy

Nucleation and growth of two‐dimensional Ge nanoclusters on the Si(111)‐(7 × 7) surface at elevated substrate temperatures have been studied using scanning tunneling microscopy. The uniformity of the Ge nanoclusters is improved with the increase of substrate temperature, and ordered Ge nanoclusters are formed on the faulted and unfaulted halves of (7 × 7) unit cell at substrate temperature of 200 °C. It is proposed that the Ge nanoclusters consist of six Ge atoms with three on top of the center adatoms and others on the rest atoms within one half of a unit cell. Copyright © 2014 John Wiley & Sons, Ltd.     

Germacyclobutenes: Generation by 1,1‐Carbalumination or 1,1‐Carbagallation and Their Photophysical Properties

Aluminium‐ and gallium‐functionalised alkenylalkynylgermanes, R¹₂Ge(C?C?R²)[C{E(CMe₃)₂}?C(H)?R²] (E=Al, Ga), exhibit a close contact between the coordinatively unsaturated Al or Ga atoms and the α‐C atoms of the intact ethynyl groups. These interactions activate the Ge?C(alkynyl) bonds and favour the thermally induced insertion of these C atoms into the E?C(vinyl) bonds by means of 1,1‐carbalumination or 1,1‐carbagallation reactions. For the first time the latter method was shown to be a powerful alternative to known metallation processes. Germacyclobutenes with an unsaturated GeC₃ heterocycle and endo‐ and exocyclic C?C bonds resulted from concomitant Ge?C bond formation to the β‐C atoms of the alkynyl groups. These heterocyclic compounds show an interesting photoluminescence behaviour with Stokes shifts of >110 nm. The fascinating properties are based on extended π‐delocalisation including σ*‐orbitals localised at Ge and Al. High‐level quantum chemical DFT and TD‐DFT calculations for an Al compound were applied to elucidate their absorption and emission properties. They revealed a biradical excited state with the transfer of a π‐electron into the empty p‐orbital at Al and a pyramidalisation of the metal atom.     

Dicalcium heptagermanate Ca2Ge7O16 revised

The structure of dicalcium heptagermanate, previously described with an orthorhombic space group, has been redetermined in the tetragonal space group . It contains three Ge positions (site symmetry 1, ..2 and 2.22, respectively), one Ca position (..2) and four O atoms, all on general 8i positions (site symmetry 1). A sheet of four‐membered rings of Ge tetrahedra (with Ge on the 8i position) and isolated Ge tetrahedra (Ge on the 4g position) alternate with a sheet of Ge octahedra (Ge on the 2d position) and eightfold‐coordinated Ca sites along the c direction in an ABABA… sequence. The three‐dimensional framework of Ge sites displays a channel‐like structure, evident in a projection on to the ab plane.     

Formation of short-range order in Al–Ge–Fe melts: influence of composition

ABSTRACT

The short-range order in Al–Ge–Fe melts has been studied by X-ray diffraction and reverse Monte Carlo simulations in wide concentration range. Influence of the replacement of one component by another while the content of third component is constant on the formation of a local structure of ternary melts has been discussed. It has been shown that at Ge content less than 30 аt. % Ge atoms are uniformly distributed in the volume of the Al–Ge–Fe melts and atomic clusters with structure similar to the liquid germanium are formed at content more than 30 аt. % Ge. The addition of the third component (Ge or Al) to the binary Al–Fe or Fe–Ge melts, correspondingly, results in competition between Al and Ge atoms in formation of the local structure around Fe atoms. The obtained concentration dependences of the nearest neighbour distances point out that the ternary interactions take place in the Al–Fe–Ge melts.     

Ge(I) BROMIDE: A NEW SOURCE FOR GERMANIUM CLUSTER COMPOUNDS

Ge(I)Br represents a good starting material for the synthesis of Ge cluster compounds which feature in addition to ligand bound Ge atoms also naked Ge atoms. The synthetic concept, the structures, and bond properties of a Ge₈ and a Ge₉ cluster compound are reported.     

Synthese und Strukturen von Bis(amino)germa- und -stanna-Chalkogeniden

Synthesis and Structures of Bis(amino)germa and -stanna Chalcogenides The cyclic bis(amino)germylene 1 and the -stannylene 2 react with elemental S, Se and Te to yield oxydation products of the general formula Me₂Si(NtBu)₂MEl₂M(NtBu)₂SiMe₂ (M = Ge, El = S ( 4 ), El = Se ( 5 ), El = Te ( 6 ); M = Sn, El = Se ( 9 ), El = Te ( 10 )). As may be deduced from X-ray structures ( 4, 5, 6, 9, 10 ) all compounds show similar central skeletons: the three spirocyclicly connected four-membered rings SiN₂M (2x) and MEl₂M are oriented in an orthogonal way to oneanother. The germanium and the tin atoms thus are in a distorted tetrahedral coordination while the chalcogen atoms only have two neighbours in acute angles. If 1 is allowed to react with trimethylamine-N-oxide, the oxygen is transferred to germanium and [Me₂Si(NtBu)₂GeO]₃ ( 3 ) is formed. Contrarily to the other compounds 3 can be described as a trimer. There is a central almost planar Ge₃O₃ six-membered ring, the germanium atoms serving as spiro-cyclic centres to three GeN₂Si four-membered rings (X-ray structure of 3 ). In the central four-membered rings of 4, 5, 6, 9 and 10 no transanular bonding between the chalcogen atoms have to be considered although these atoms have small distances to oneanother. The mean M-El distances have been found to be: Ge? O 1.762(5), Ge? S 2.226(3), Ge? Se 2.363(3), Ge? Te 2.592(5), Sn? Se 2.536(3), Sn? Te 2.741(3) Å.     

DFT characterization of nanostructured germanium surfaces induced by cobalt atoms

By deposition in ultra‐high vacuum of cobalt on a Ge(111)–c(2 × 8) surface, Mocking et al. obtained a surface reconstruction. In the present paper, we analyse the related atomic structure, proposed by these authors, by means of density functional theory calculations. The surface presents ordered clusters that consist of six Ge atoms arranged in a triangle, lying above three Co atoms. The latter are located at substitutional positions within the top plane of the Ge(111) first bilayer. These clusters are similar to what is obtained on part of the Co‐induced Si(111) surface. For this surface, the clusters are terminated either by six Si atoms or by one, two or three adatoms above the six Si atoms. As the Co–Ge clusters systematically display six protrusions in the scanning tunnelling microscopy measurements by Mocking et al., we investigated why Ge adatoms are not present. Comparison of the Gibbs energy, interatomic distances, as well as charge density indicates that Ge adatoms on top of Co‐Ge clusters are less stable than Si adatoms in the Co‐Si system. Copyright © 2013 John Wiley & Sons, Ltd.     

Multicolor Photoluminescence in ITQ-16 Zeolite Film

Exploring the native defects of zeolites is highly important for understanding the properties of zeolites, such as catalysis and optics. Here, ITQ-16 films were prepared via the secondary growth method in the presence of Ge atoms. Various intrinsic defects of ITQ-16 films were fully studied through photoluminescence and FTIR characterizations. It was found that both the as-synthesized and calcined ITQ-16 films displayed multicolor photoluminescence including ultraviolet, blue, green and red emissions by exciting upon appropriate wavelengths. The results indicate that Si-OH and non-bridging oxygen hole centers(NBOHCs) are responsible for the origin of green and red emissions at 540-800 nm, while according to a variety of emission bands of calcined ITQ-16 film, blue emission bands at around 446 and 462 nm are attributed to peroxy free radicals(≡SiO₂·), ultraviolet emissions ranging from 250 nm to 450 nm are suggested originating from a singlet-to-triplet transition of two-fold-coordinated Si and Ge, respectively.     

2-D analysis of Ge implanted SiO2 surfaces by laser-induced breakdown spectroscopy

2-D elemental distribution of Ge in silicon oxide substrates with differing implantation doses of between 3 × 10¹⁶ cm^− 2 and 1.5 × 10¹⁷ cm^− 2 has been investigated by Laser-Induced Breakdown Spectroscopy (LIBS). Spectral emission intensity has been optimized with respect to time, crater size, ablation depth and laser energy. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) coupled with Energy-Dispersive X-Ray Spectroscopy (EDX) have been utilized to obtain crater depth, morphology and elemental composition of the sample material, respectively. LIBS spectral data revealed the possibility of performing 2-D distribution analysis of Ge atoms in silicon oxide substrate. EDX analysis results confirmed that LIBS is capable to detect Ge atoms at concentrations lower than 0.2% (atomic). LIBS as a fast semi-quantitative analysis method with 50 µm lateral and 800 nm depth resolution has been evaluated. Results illustrate the potential use of LIBS for rapid, on-line assessment of the quality of advanced technology materials during the manufacturing process.     

平面五配位硅、 锗XBe5H6(X=Si,Ge)团簇

采用密度泛函理论PBE0方法, 在aug-cc-pVTZ水平上理论预测了含平面五配位硅和锗原子的XBe₅H₆ (X=Si, Ge)团簇. 势能面系统搜索及高精度量化计算表明, 它们均为全局极小结构. XBe₅H₆(X=Si, Ge)团簇整体呈完美的扇形结构: Si/Ge原子被5个金属Be原子配位; 4个H原子以桥基方式与Be原子相键连, 剩余的2个 H原子以端基方式与两端的Be原子成键. 化学键分析表明, XBe₅H₆(X=Si, Ge) 团簇中XBe₅单元具有完全离域的1个π及3个σ键, 外围铍氢间形成4个Be—H—Be 三中心二电子(3c-2e)键及2个定域的Be—H键. XBe₅单元上离域的2π及6σ电子赋予体系π和σ双重芳香性, 并使Si/Ge原子满足八隅律（或八电子规则）. 能量分解-化学价自然轨道分析揭示, Si/Ge和Be₅H₆之间主要为电子共享键.     

REMGa3Ge and RE3Ni3Ga8Ge3 (M = Ni, Co; RE = rare-earth element): new intermetallics synthesized in liquid gallium. X-ray, electron, and neutron structure determination and magnetism

New quaternary intermetallic phases REMGa(3)Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE(3)Ni(3)Ga(8)Ge(3) (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa(3)Ge, a = 4.1748(10) A, c = 23.710(8) A, V = 413.24(2) A(3), I4/mmm, Z = 4; Gd(3)Ni(3)Ga(8)Ge(3), a = 4.1809(18) A, c = 17.035(11) A, V = 297.8(3) A(3), P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa(3)Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa(4)Ge(2)] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE(3+) free ions.     

Cooperative GeN Bond Activation in Aluminium‐Functionalised Aminogermanes and Spontaneous Imine Elimination via an Intermediate Germyl Cation

Hydrometallation of iPr₂N?Ge(CMe₃)(C?C?CMe₃)₂ with H?M(CMe₃)₂ (M=Al, Ga) affords alkenyl–alkynylgermanes in which the Lewis‐acidic metal atoms are not coordinated by the amino N atoms but by the α‐C atoms of the ethynyl groups. These interactions result in a lengthening of the Ge?C bonds by approximately 10 pm and a comparably strong deviation of the Ge?C?C angle from linearity (154.3(1)°). This unusual behaviour may be caused by steric shielding of the N atoms. Coordination of the metal atoms by the amino groups is observed upon hydrometallation of Et₂N?Ge(C₆H₅)(C?C?CMe₃)₂, bearing a smaller NR₂ group. Strong M?N interactions lead to a lengthening of the Ge?N bonds by 10 to 15 pm and a strong deviation of the M atoms from the MC₃ plane by 52 and 47 pm, for Al and Ga, respectively. Dual hydrometallation is achieved only with HAl(CMe₃)₂. In the product, there is a strong Al?N bond with converging Al?N and Ge?N distances (208 vs. 200 pm) and an interaction of the second Al atom to the phenyl group. Addition of chloride anions terminates the latter interaction while the activated Ge?N bond undergoes an unprecedented elimination of EtN?C(H)Me at room temperature, leading to a germane with a Ge?H bond. State‐of‐the‐art DFT calculations reveal that the unique mechanism comprises the transfer of the amino group from Ge to Al to yield an intermediate germyl cation as a strong Lewis acid, which induces β‐hydride elimination, with chloride binding being crucial for providing the thermodynamic driving force.     

Synthesis, X-ray diffraction studies, and DFT calculations on hexacoordinated germanium derivatives: the case of germaspirobis(ocanes)

Synthesis of the title compounds, viz. [RN(CH2CHR'O)2]2Ge (1, R = Me, R' = H; 2, R = Me, R' = Ph; 3, R = Ph, R' = H), by the reaction of 2 equiv of corresponding dialkanolamines RN(CH2CHR'OH)2 (4, R = Me, R' = H; 5, R = Me, R' = Ph; 6, R = Ph, R' = H) with (AlkO)4Ge is reported. Composition and structures of all novel compounds were established by 1H and 13C NMR spectroscopy and mass spectrometry as well as elemental analysis data. The single-crystal X-ray diffraction of 2 has clearly indicated the presence of two transannular interactions Ge<--N in the compound. N atoms are cis-orientated. The compound 3 possesses long Ge...N distances. The structural data obtained from geometry optimizations by DFT calculations on 1-3 reproduces experimental results. Both cis- and trans-isomers were studied, and cis-configuration was found to be more thermodynamically stable for all three compounds. The transition states for possible cis <--> trans rearrangement processes in 1-3 were calculated. The properties of the Ge-O and Ge<--N bonds in 1-3 were analyzed by the AIM approach. The interactions between the Ge atom and N atoms as well as O atoms possess predominantly ionic character.     

(EnH2)2Ge2S6的合成与结构表征

用溶剂热方法制备了(EnH2)2Ge2S6单晶.单晶X射线衍射分析结果表明,(EnH2)2Ge2S6属单斜晶系,P2(1)/n空间群,晶胞参数a=0.67125(5)nm,b=1.12290(4)nm,c=1.07518(4)nm,β=92.288(2)°,Z=2.利用DSC及TG分析研究了其热稳定性,结果表明,该化合物在200℃以下能够稳定存在.     

Nature of the coordination bond in the GeCl4-trimethylamine complex

Quantum-chemical computations were performed for the GeCl₄ ← N(CH₃)₃ system using the MP2/6-31G(d) method with total optimization of its geometry and at different fixed Ge…N distances (from 2.0 to 4.5 Å). The coordination bond in the complex results from the involvement of different AOs of Ge and N atoms (along with other atoms in the molecule) in the formation of a number of MOs. The number of these MOs increases with decreasing Ge…N distance, thus reducing the total energy of a molecule and stabilizing it. The coordination bond and the covalent bond are of the same nature. When the distance between the components of the system is reduced, the partial negative charges of N, C, and all Cl atoms increase; the partial positive charges of Ge and H increase as well.     

Some observations on the chemiluminescence of atoms in acetylene flames supported by air and argon-oxygen mixtures

A study has been made of the chemiluminescent emission of As, Bi, Cd, Ge, Hg, I, Mo, Pb, Sb, Se, Sn, Te, V and Zn in the primary combustion zones of air-acetylene and argon-oxygen-acetylene flames, supported at an open burner port during the aspiration of aqueous solutions of their salts. In general, elements having excitation, potentials greater than 4 eV show considerably greater atomic chemiluminescence in the primary zone than “thermal” atomic emission in the interconal region. Various mechanisms are suggested for the energy-transfer reactions between metal atoms and excited flame species, particularly carbon monoxide.     

"Nanoscale zippers" in Gd5(SixGe(1-x))4: symmetry and chemical influences on the nanoscale zipping action

One critical parameter influencing the structural nature of the phase transitions in magnetocaloric materials Gd5(SixGe(1-x))4 is the Si/Ge ratio (x/1-x), because transition temperatures and structures depend crucially on this value. In this study, single-crystal X-ray diffraction indicates that Si and Ge atoms are neither completely ordered nor randomly mixed among the three crystallographic sites for these elements in these structures. Ge atoms enrich the T sites linking the characteristic slabs in these structures, while Si atoms enrich the T sites within them. Decomposition of the total energy into site and bond energy terms provides a rationale for the observed distribution, which can be explained by symmetry and electronegativity arguments. For any composition in Gd5(SixGe(1-x))4, a structure map is presented that will allow for a rapid assessment of the specific structure type.     

Reactions of organochlorosilanes with chloro-and organogermanes in the presence of aluminum chloride

The effect of substituents at the silicon and germanium atoms in reactions of organochlorosilanes with chloro-and organogermanes in the presence of aluminum chloride was studied. The only occurring process is the exchange of the chlorine atoms at Ge for the phenyl groups from Si; an increase in the number of methyl groups or chlorine atoms at Si promotes formation of phenyltrichlorogermane, and an increase in the number of phenyl groups or replacement of the chlorine atom at the Si atom by hydrogen leads to the formation of di-and triphenylchlorogermanes. Neither phenyl nor other radicals are transferred back from Ge to Si in the course of reactions of phenylgermanes with methylchlorosilanes in the presence of aluminum chloride; the only occurring processes are the exchange of the phenyl or methyl radicals bonded to Ge for the Cl atom bonded to Al and the disproportionation of phenylchlorogermanes.     

具有方石英拓扑结构的微孔硫代锗锌酸盐的溶剂热合成与表征

微孔化合物是一类重要的材料,广泛地应用于催化、吸附及分离等领域。目前已知的微孔材料绝大多数为无机氧化物或氟氧化物,20世纪80年代末,Bedard等首先报道了微孔硫属化物的合成．这类化合物除具有微孔材料的性质外,还具有半导体性质,在电催化、光催化、太阳能电池及新型光电子材料如量子点(dots)及反量子点(antidots)材料方面有着广泛的应用前景,     

Ab initio calculations of complexes of group IVA element tetrachlorides: II. Dynamics of complex formation of GeCl4 with pyridine

RHF/6-31G(d) calculations of the trans-octahedral complex of GeCl₄ with pyridine were performed with full geometry optimization and at varied coordinate of the complexation reaction. The results obtained do not confirm the hypothesis that the complex is formed owing to interaction of the N atom with unoccupied d orbitals of the Ge atom. The complex formation is initiated by the interaction of the coordination centers (Ge and N), resulting in mutual approach of the system components, their polarization, and, when the distance between the components becomes sufficiently short, transfer of the electron density from the H and C atoms of the electron donor to the Cl atoms of the acceptor. In the process, a multicentered bond involving all the atoms of the Ge coordination polyhedron is formed.