Room Temperature Incorporation of Arsenic Atoms into the Germanium (001) Surface**

Germanium has emerged as an exceptionally promising material for spintronics and quantum information applications, with significant fundamental advantages over silicon. However, efforts to create atomic-scale devices using donor atoms as qubits have largely focused on phosphorus in silicon. Positioning phosphorus in silicon with atomic-scale precision requires a thermal incorporation anneal, but the low success rate for this step has been shown to be a fundamental limitation prohibiting the scale-up to large-scale devices. Here, we present a comprehensive study of arsine (AsH₃) on the germanium (001) surface. We show that, unlike any previously studied dopant precursor on silicon or germanium, arsenic atoms fully incorporate into substitutional surface lattice sites at room temperature. Our results pave the way for the next generation of atomic-scale donor devices combining the superior electronic properties of germanium with the enhanced properties of arsine/germanium chemistry that promises scale-up to large numbers of deterministically placed qubits.     

Ab initio analysis of some fluoride and oxide structures doped with Pr and Yb

Doping effects are analyzed by means of the ab initio perturbed ion (aiPI) method via substitution of the fluorides and oxides of zirconium, hafnium, and thorium. Lattice relaxation is simulated through the calculation of vibrational breathing modes and substitutional effects on the compound are thereby analyzed. In addition, the band gaps (in the pure species) and impurity levels (where substitutional ions Pr⁺⁴ and Yb⁺³ are considered in the doped species) of the fluorides are estimated via the transition energy calculated at the aiPI‐optimized geometry of the pure and doped crystal clusters by means of the configuration interaction with single excitations (CIS) method that accounts for electronic correlation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

多次透射反射红外光谱法灵敏和准确地测量单晶硅中间隙氧和代位碳的含量

建立了室温下使用多次透射反射红外光谱法(MTR-IR)测量单晶硅中间隙氧和代位碳含量的新红外光谱吸收方法,在理论和实验上证明了MTR-IR优于常规使用的单次垂直透射红外(IR)吸收测量方法。与IR法相比较,MTR-IR法的优点为:(1)间隙氧在1107 cm^-1处和代位碳在605 cm^-1处的吸收峰与MTR-IR法中红外光透过硅片的的次数N(6~12)成线性增加的正比例关系,因此单晶硅中间隙氧和代位碳含量的检测限至少比IR法低一个数量级;(2)MTR-IR法测量薄硅片如0.2 mm的厚度时产生的干涉条纹强度是单次垂直透射红外吸收法(IR)的1/23、是单次Brewster角透射红外吸收法的1/11;(3)单次垂直透射红外吸收法(IR)1次只测量样品上的1个点,MTR-IR法则在更长的样品上1次测量多个样品点,每次测量更具有代表性。理论计算和实验结果都证实了MTR-IR吸收法测量晶体硅中间隙氧和代位碳杂质含量的高灵敏度、可靠性和重复性。     

多次透射反射红外光谱法灵敏和准确地测量单晶硅中间隙氧和代位碳的含量

建立了室温下使用多次透射反射红外光谱法(MTR-IR)测量单晶硅中间隙氧和代位碳含量的新红外光谱吸收方法,在理论和实验上证明了MTR-IR优于常规使用的单次垂直透射红外(IR)吸收测量方法。与IR法相比较,MTR-IR法的优点为:(1)间隙氧在1 107 cm^-1处和代位碳在605 cm^-1处的吸收峰与MTR-IR法中红外光透过硅片的的次数N(6~12)成线性增加的正比例关系,因此单晶硅中间隙氧和代位碳含量的检测限至少比IR法低一个数量级;(2)MTR-IR法测量薄硅片如0.2 mm的厚度时产生的干涉条纹强度是单次垂直透射红外吸收法(IR)的1/23、是单次Brewster角透射红外吸收法的1/11;(3)单次垂直透射红外吸收法(IR)1次只测量样品上的1个点,MTR-IR法则在更长的样品上1次测量多个样品点,每次测量更具有代表性。理论计算和实验结果都证实了MTR-IR吸收法测量晶体硅中间隙氧和代位碳杂质含量的高灵敏度、可靠性和重复性。     

Structural and electronic properties of fluorinated boron nitride nanotubes

The effects of F doping on the structural and electronic properties of the (5, 5) single-walled boron nitride nanotube (BNNT) are investigated by using the density functional theory method. The chemiadsorption of F maintains the hexagonal BN network, increases the lattice constant, and introduces acceptor impurity states. On the other hand, substitutional doping of F destroys the hexagonal BN network, decreases the lattice constant, but does not alter the insulating feature of the BNNT. The observed insulator-to-semiconducting transition, a lattice contraction, and a highly disordered atom arrangement in the sidewall of BNNTs upon F doping appear to be most reasonably attributed to a codoping of dominating substitutional F over chemiabsorbed F, which can induce deep donor impurity states, a lattice contraction, and a destruction of the hexagonal BN network simultaneously.     

Density functional embedding approach to the Mn impurities in NaBr crystals

We have performed density functional calculations for three 19‐atom clusters, two 25‐atom clusters, and one 18‐atom cluster, each embedded in a Madelung potential that takes into account the long‐range electrostatic interactions of the ion lattice of a NaBr crystal. One of the three 19‐atom and one of the two 25‐atom clusters model bulk crystalline NaBr; the others model a Mn²⁺ impurity trapped in a cubically symmetric crystalline electric field (CEF) site of the NaBr host. One of the latter has the NaBr bulk interatomic distance, while in the others relaxation of the Br atoms around the metallic impurity has been considered. The 18‐atom cluster models a relaxed Mn impurity Na vacancy system. All of our calculated clusters have a Na site at the center, and they all include at least first and second nearest‐neighbor host atoms. In the center of the doped clusters the Mn impurity replaces the missing Na ion. The electronic structure of the embedded impurity ion in its local environment was computed self‐consistently by means of all‐electron density functional theory (DFT) techniques. We have examined the lattice relaxation around the impurity and calculated the hyperfine coupling constants (HFCC). The results for the Mn electronic structure and for the HFCC are in agreement with experimental results using electron paramagnetic resonance measurements. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 34–46, 2000     

Reactivity of <Emphasis Type="Italic">N</Emphasis>-(chlorodimethylgermyl)methyl and <Emphasis Type="Italic">N</Emphasis>-(chlorodimethylsilyl)methyl derivatives of lactams and amides toward Grignard reagents

N-[(Chlorodimethylgermyl)methyl]lactams and -amides containing a five-coordinate germanium atom react with Grignard reagents chemoselectively by the Ge-Cl bond to form four-coordinate germanium compounds. The method of competitive reactions was used to establish that respective five-coordinate germanium and silicon compounds are almost equally reactive toward Grignard reagents but much more reactive than model four-coordinate germanium and silicon compounds.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1462–1465.Original Russian Text Copyright © 2004 by Bylikin, Shipov, Kramarova, Artamkina, Negrebetskii, Baukov.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis,psychotropic and anticancer activity of 2,2‐dimethyl‐5‐[5′‐trialkylgermyl(silyl)‐2′‐hetarylidene]‐1,3‐dioxane‐4,6‐diones and their analogues

A series of 2,2‐dimethyl‐5‐(5′‐R‐hetarylidene)‐1,3‐dioxane‐4,6‐diones has been synthesized for examing a structure–activity relationship. Furyl and thienyl derivatives of Meldrum's acid possess neurotropic activity comprising both depriming and activating components. Comparison of acute toxicity of carbon, silicon and germanium analogues in the furan series of the compounds has demonstrated that the germanium derivative is 11.5 times less toxic than the carbon analogue and four times less toxic than the silicon derivative. 2,2‐Dimethyl‐5‐(5′‐triethylsilyl‐2′‐thenylidene)‐1,3‐dioxane‐4,6‐dione has moderate toxicity with the highest neurotropic and cytotoxic activity Copyright © 2003 John Wiley & Sons, Ltd.     

C和As共掺杂的γ-Si3N4电子性质的密度泛函理论研究

采用密度泛函理论研究了C和As共掺杂的γ-Si3N4的电子性质. 当晶体中少量的四配位硅原子被碳原子所取代, 同时用少量的砷原子取代氮原子, 晶体结构的带隙可以被调整; 当n(C)/n(Si)≈0.063, n(As)/n(N)≈0.047时, 材料会发生绝缘体到金属的转变. 从态密度图中可以观察到价带顶端的能量明显上升. 讨论了关于这种共掺杂所引起的带隙较大减小的可能原因和潜在的应用.     

Effect of dimensionality of a crystal lattice on the properties of a localized impurity

The changes of electron density due to the presence of a localized impurity in a crystal lattice are examined in dependence on the lattice dimensionality. The Koster–Slater impurity model developed for the case of a three‐dimensional simple cubic lattice has been taken as the basis of examinations. Ordinary bound states, virtual bound states, and delocalized electron states are considered in each lattice case. For the delocalized states extended in a one‐dimensional lattice the amplitude of the oscillatory changes of the electron density due to the impurity perturbation does not decrease with the distance from the impurity position, whereas for a two‐dimensional lattice this amplitude decreases roughly proportionally to the reciprocal value of the square root of the distance from the impurity. Let us note that a well‐known amplitude characterizing the decrease of the oscillatory change of the electron density in a three‐dimensional system is proportional to the reciprocal value of the third power of the distance from the impurity position. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 61–78, 2000     

Structural disturbance and lattice relaxation in molecular crystal packing calculations

Lattice calculations on impurity-containing crystals are reported, made with the help of standard intermolecular potentials. A lattice containing a substitutional impurity, or a vacancy, relaxes in its vicinity, the equilibrium structure being little changed in either orientation or translation. The small changes do however enable the strain energy to be greatly reduced. The energies are sensitive to the assumed intermolecular potentials but the optimised structures are rather insensitive. An impurity larger than the host (tetracene in anthracene) adopts closely the host orientation. This applies also to a smaller impurity (e.g. napthalene in anthracene) but in this case the impurity may move away from the lattice site to one of two inversion related displaced positions. The cage surrounding a vacant site relaxes little, leaving the “hole” more or less intact. Lattice relaxations found in this way seem too small to accommodate guest—host photochemical reactions in those lattices which, in the pure crystal, are photochemically stable.     

The valence band relaxation energies of silicon and germanium during photoelectron emission

The valence band relaxation energies of the intrinsic semiconductors silicon and germanium are estimated using a classical and a quantum-mechanical method and are found to be similar in magnitude to values reported for conductors and insulators. It is shown that the XPS electronic valence band structures of Si and Ge reflect the cohesive energies when the binding energies are corrected for relaxation effects.     

Simulation of the geometric and electronic structures and properties of extrinsic defects involving germanium in lead telluride

Cluster simulation of the bulk and surface of crystalline lead telluride has been performed in the framework of the hybrid density functional theory B3LYP method with the use of the LANL2 pseudopotential with the corresponding double-zeta basis set. Different variants of doping germanium atoms in a PbTe single crystal and at its surface have been examined. Clusters of different sizes have been considered. For the optimal cluster, containing 112 atoms, the state where a germanium atom occupies a cationic position is the most stable. Impurity atoms, as well as impurity atoms and vacancies, show a weak tendency for association. Formation of a singular surface is accompanied by differential relaxation. The charge state of germanium atoms in the bulk and at the surface is virtually the same and somewhat decreases upon association with vacancies.     

Structural and electronic properties of La‐doped CaTiO3 crystal

There is experimental and computational evidence that some important properties such as electrical conductivity and ferroelectricity in the CaTiO₃ crystal change according to the dopant states. Using an INDO quantum‐chemical computational method modified for crystal calculations we explore the stability of the La‐doped CaTiO₃ crystal in both phases, cubic and orthorhombic. The calculations are carried out by means of the supercell model based on the LUC (large unit cell) approach as it is implemented into the CLUSTERD computer code. The equilibrium geometry for impurity is found together with the crystalline lattice distortions. Atomic displacements and relaxation energies are analyzed in a comparative manner for the two crystallographic phases. A new effect of electron transfer from the local one‐electron energy level within the band‐gap to the conduction band is observed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Origin of improved visible photocatalytic activity of nitrogen/hydrogen codoped cubic In2O3: first-principles calculations

We have employed DFT calculations to carry out an accurate analysis of the effect of N- and NH-doping on the visible photocatalytic activity in the cubic In(2)O(3). In the substitutional N-doped In(2)O(3), the 2p impurity states of N induce a red shift in the optical absorption, while in the interstitial N-doping the red shift is dominantly caused by the localized π antibonding states of NO. When a H atom is accompanied by a N impurity in the lattice, the H atom acts as a charge donor and compensates the hole state created by N-doping, thus the energy level of the impurity states is reduced. As a result, the mixing of impurity states and the valence band is enhanced. At the same nitrogen dopant concentration, NH-codoping yields a larger band gap narrowing, especially for the interstitial NH-codoping. The theoretical calculations presented in this work explain well the previous experimental results of the enhanced visible photocatalytic activity in NH-codoped cubic In(2)O(3).     

Single crystal EPR study of VO(II)-doped cadmium potassium phosphate hexahydrate: A substitutional incorporation

Single crystal EPR studies of VO(II)-doped cadmium potassium phosphate hexahydrate (CPPH) have been carried out at room temperature. The angular variation spectra in the three orthogonal planes indicate that the paramagnetic impurity has entered the lattice only substitutionally in place of Cd(II). Spin Hamiltonian parameters have been obtained from single crystal data. Powder spectra show a set of eight parallel and perpendicular features indicating the presence of only one site. The admixture coefficients have been calculated from the data, which agree well with the literature values.     

Effect of substitutionally boron‐doped single‐walled semiconducting zigzag carbon nanotubes on ammonia adsorption

We investigate the binding of ammonia on intrinsic and substitutionally doped semiconducting single‐walled carbon nanotubes (SWCNTs) on the side walls using density functional calculations. Ammonia is found to be weakly physisorbed on intrinsic semiconducting nanotubes while on substitutional doping with boron its affinity is enhanced considerably reflected with increase in binding energies and charge transfer. This is attributed to the strong chemical interaction between electron rich nitrogen of ammonia and electron deficient boron of the doped SWCNT. On doping, the density of states are changed compared to the intrinsic case and additional levels are formed near the Fermi level leading to overlap of levels with that of ammonia indicating charge transfer. The doped SWCNTs thus are expected to be a potential candidate for detecting ammonia. © 2014 Wiley Periodicals, Inc.     

Swelling of a polymer brush by a poor solvent

The addition of a small amount of a poor solvent impurity (methanol) to a theta solvent (cyclohexane) is found to cause appreciable swelling (≈30% increase of the average brush height) in a model end‐grafted polystyrene (PS) brush layer. This unusual type of swelling is not observed if octadecyltrichlorosilane (OTS) is first grafted to the portion of the silicon substrate uncovered by the grafting end‐groups of the PS chains. Brush swelling in the absence of OTS surface protection is interpreted as arising from a segregation of methanol to the solid substrate and the resulting modification of the polymer–surface interaction. We also observe that the addition of a small amount of methanol to an adsorbed PS layer exposed to cyclohexane causes rapid film delamination from the silicon substrate. Together these observations imply a strong influence of surface active impurities on the structure and adhesive stability of polymer layers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4126–4131, 2004     

Rhodium‐Catalyzed Asymmetric Synthesis of Silicon‐Stereogenic Dibenzosiloles by Enantioselective [2+2+2] Cycloaddition

A rhodium‐catalyzed asymmetric synthesis of silicon‐stereogenic dibenzosiloles has been developed through a [2+2+2] cycloaddition of silicon‐containing prochiral triynes with internal alkynes. High yields and enantioselectivities have been achieved by employing an axially chiral monophosphine ligand, and the present catalysis is also applicable to the asymmetric synthesis of a germanium‐stereogenic dibenzogermole. Preliminary studies on the optical properties of these compounds are also described.     

A comparative first-principles study of orbital hybridization in two-dimensional C, Si, and Ge

Information on orbital hybridization is very important to understand the structural, physical, and chemical properties of a material. Results of a comparative first-principles study on the behaviours of orbital hybridization in the two-dimensional single-element phases by carbon, silicon, and germanium are presented. From the well-known three-dimensional hexagonal lonsdaleite structure, in which the atoms are in ideal sp(3)-bonding, the layer spacing along c-axis is gradually stretched to simulate the evolutions of structural and electronic properties from three-dimensional to two-dimensional lattice configurations in the three materials. A turning point of the total system energy due to the sp(3) to sp(2) transition is observed during this process in carbon. In contrast, no such phenomenon is found in silicon and germanium. The differences in electronic structure and bonding behaviour are further examined through comparative investigation of atomic angular-momentum projected density of states and electronic energy band spectrums of these materials. We demonstrate that the valence electronic orbital in the two-dimensional hexagonal crystals of Si and Ge shows sp(3)-like behaviour for the partial hybridization of s and p(z), which leads to their different lattice configurations to graphene. The role of π-bonds in stabilizing the flat configuration of graphene is also discussed.