Characterization of silicon sites in monoclinic zeolite ZSM-5 using 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) and molecular modelling

An attempt has been made to correlate the experimentally observed 29Si MAS NMR chemical shifts of monoclinic phase of highly siliceous ZSM-5 with their electronic properties. In order to incorporate the influence of next neighbor atoms on the 29Si chemical shielding of central SiO4, a pentameric cluster model (H12Si5O16) has been chosen. Each of the 24 crystallographically distinct Si sites, of ZSM-5 framework has been modelled by such cluster models. Based on semi-empirical quantum chemical calculations, a multiple linear regression analysis of the various electronic properties with the 29Si chemical shifts has been attempted. The relative difference in 29Si chemical shifts for the Si sites in ZSM-5 is reasonably accounted, although quantitative prediction may require non-empirical quantum chemical calculations.     

Epitaxial growth of a low-density framework form of crystalline silicon: a molecular-dynamics study

Crystal growth processes of low-density framework forms of crystalline silicon, named Si clathrates ( Si34 and Si46), during solid phase epitaxy (SPE) have been successfully observed in molecular-dynamics simulations using the Tersoff potential. The activation energy of SPE for Si34 has been found to correspond with the experimental value ( approximately 2.7 eV) for the cubic diamond phase, while the SPE rates of Si46 are much lower than that of Si34. The structural transition from Si46 to Si34 can be also observed during the Si46-[001] SPE. The present results suggest that new wide-gap Si semiconductors with clathrate structures can be prepared using epitaxial growth techniques.     

The adsorption of Cs on the Si(100)2 × 1 surface

LEED observations have shown that the existing model for Cs adsorption on Si(100) is incomplete. It has been found that adsorption occurs only onto the raised surface sites and is progressive through 1Cs : 3Si, 2Cs : 3Si and finally 1Cs : 1Si structures. The transition from 2Cs : 3Si to 1Cs : 1Si involves a change in the Cs bonding which has been shown to be responsible for the detailed caesiation behaviour.     

Study on optical and electrical properties of gold-doped silicon fabricated by femtosecond laser

Microstructured silicon (Si) materials have been fabricated by femtosecond (fs) laser ablation and have been hyperdoped with gold (Au) impurities. The ablated Si materials showed large and thermostable infrared absorption at 1.1–2.5 μm wavelengths, which was contributed by sub-band absorption and laser-induced defects absorption. The Au–Si alloy was formed after laser irradiation onto the Au-coated Si surface, which was determined by XRD characterization. Using N-type Si substrate, the fabricated Au-doped Si performed lower sheet carrier density due to the self-compensation effect between deep donor and acceptor energy lever of Au in bulk Si material. From Hall measurement, both the p- and n- types of Au-doped Si samples can be obtained by controlling the type of Si substrate.     

Si_3分子基态(X~1A_1)的结构与分析势能函数

应用群论及原子分子反应静力学方法推导Si分子的电子态及其离解极限,在B3P86/CC-PVTZ水平上,对Si3分子基态进行优化计算,得出Si3基态的单重态能量最低,其稳定构性为的C2V构型,平衡核间距Re=0.2176nm、∠213=79.7°,能量为-869.2057a.u..同时计算出基态的简正振动频率:对称伸缩振动频率ν(B2)=547.6446cm-1,弯曲振动频率ν(A1)=185.6100cm-1和反对称伸缩振动频率ν(A1)=559.6090cm-1.在此基础上,使用多体项展式理论方法,导出了基态Si3分子的全空间解析势能函数,该势能函数准确再现了Si3(C2V)平衡结构.     

Measurement of the interfacial energy between amorphous Si and crystalline Si

The experimental data of crystallization of amorphous Si thin films on single crystal Si substrates and on inert substrates have been analysed by a kinetic model of phase transformation. On the basis of the analysis, the interfacial energy between amorphous Si and crystalline Si has been calculated to be about 0.30 eV/atom and the number of Si atoms in the critical nucleus to be about 110.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Structural investigations of the Yb  Si(111) - 2x1, 5x1 and 3x1 overlayers

The YbSi interface has been investigated in the sub-monolayer regime employing Ion Scattering Spectroscopy (ISS), Auger Electron Spectroscopy (AES) and Low Energy Electron Diffraction (LEED). Three different structures, YbSi(111) 2x1, YbSi(111) 5x1, and YbSi(111) 3x1, have been established by heat treatments of the interfaces. The structures consist of a stable overlayer of Yb atoms on the Si(111) surfaces. The distance of the Yb atoms to the uppermost layer of Si atoms has been estimated by comparing the YbSi ISS intensity ratio with the predictions of a model based on classical scattering theory and a Thomas-Fermi-Moliére potential. The height of the Yb atoms relative to the substrate toplayer was found to be 1.9 ± 0.3→.     

稳定In/Si表面的LEED研究

利用LEED图形拟合的方法对大量不同取向In/Si表面的稳定性和小面化进行了研究，新发现了In覆盖度在1/2单层原子以下的三个稳定表面：Si(214)-In，Si(317)-In和Si(436)-In，以及In覆盖度在1单层原子左右的两个稳定表面Si(101)-In和Si(313)-In.此外还确定了In覆盖度在1单层原子左右的6个稳定In/Si表面的家族领地以及In覆盖度在1/2单层原子以下的4个稳定In/Si表面的家族领地.特别值得注意的是 Si(103)-In的家族领地相当大，甚至比最稳定的Si(1 关键词： 硅表面 铟 稳定表面 家族领地     

Si quantum dot structures and their applications

This paper presents briefly the history of emission study in Si quantum dots (QDs) in the last two decades. Stable light emission of Si QDs and NCs was observed in the spectral ranges: blue, green, orange, red and infrared. These PL bands were attributed to the exciton recombination in Si QDs, to the carrier recombination through defects inside of Si NCs or via oxide related defects at the Si/SiOx interface. The analysis of recombination transitions and the different ways of the emission stimulation in Si QD structures, related to the element variation for the passivation of surface dangling bonds, as well as the plasmon induced emission and rare earth impurity activation, have been presented.The different applications of Si QD structures in quantum electronics, such as: Si QD light emitting diodes, Si QD single union and tandem solar cells, Si QD memory structures, Si QD based one electron devices and double QD structures for spintronics, have been discussed as well. Note the significant worldwide interest directed toward the silicon-based light emission for integrated optoelectronics is related to the complementary metal-oxide semiconductor compatibility and the possibility to be monolithically integrated with very large scale integrated (VLSI) circuits. The different features of poly-, micro- and nanocrystalline silicon for solar cells, that is a mixture of both amorphous and crystalline phases, such as the silicon NCs or QDs embedded in a α-Si:H matrix, as well as the thin film 2-cell or 3-cell tandem solar cells based on Si QD structures have been discussed as well. Silicon NC based structures for non-volatile memory purposes, the recent studies of Si QD base single electron devices and the single electron occupation of QDs as an important component to the measurement and manipulation of spins in quantum information processing have been analyzed as well.     

Oxidation behaviour of nickel silicides investigated by AES and XPS

The oxygen interaction with Ni silicide surfaces in a wide range of composition, from NiSi₂ to Ni₃Si, has been investigated at room temperature by AES and XPS techniques. It has been found that the Si oxidation is enhanced over that of pure Si in all the Ni-Si compounds, and that the strongest oxidation occurs in Ni richer silicides. In general, oxygen bonds with Si leaving the metal unoxidized, but in Ni₃Si evidence for the occurrence of Ni oxidation has been found at high exposures.     

Si–Si bond as a deep trap for electrons and holes in silicon nitride

A two-stage model of the capture of electrons and holes in traps in amorphous silicon nitride Si₃N₄ has been proposed. The electronic structure of a “Si–Si bond” intrinsic defect in Si₃N₄ has been calculated in the tight-binding approximation without fitting parameters. The properties of the Si–Si bond such as a giant cross section for capture of electrons and holes and a giant lifetime of trapped carriers have been explained. It has been shown that the Si–Si bond in the neutral state gives shallow levels near the bottom of the conduction band and the top of the valence band, which have a large cross section for capture. The capture of an electron or a hole on this bond is accompanied by the shift of shallow levels by 1.4–1.5 eV to the band gap owing to the polaron effect and a change in the localization region of valence electrons of atoms of the Si–Si bond. The calculations have been proposed with a new method for parameterizing the matrix elements of the tightbinding Hamiltonian taking into account a change in the localization region of valence electrons of an isolated atom incorporated into a solid.     

Ordered Si/Si–O nanowire array and its optical properties

Glancing angle deposition (GLAD) has been employed to fabricate the Si/Si–O nanowires (NWs). The perpendicular NW on silicon substrate shows the amorphous nature. The visible light emission from the NWs was observed from the Si/Si–O nanoparticles. High light absorption inside the Si/Si–O NW structure was recorded.     

Distribution of <Superscript>28</Superscript>Si, <Superscript>29</Superscript>Si,and <Superscript>30</Superscript>Si isotopes under plastic deformation in subsurface layers of Si: B crystals

The redistribution of ²⁸Si, ²⁹Si, and ³⁰Si isotopes in subsurface layers of Si: B single crystals after their plastic deformation has been revealed. It has been found that the distribution profile of ²⁸Si and ²⁹Si isotopes becomes smoother after deformation, whereas the ³⁰Si isotope distribution remains unchanged. A change in the subsurface profile of the ²⁹SiO oxide is observed, which indicates the migration of the ²⁹Si isotope in the composition of oxygen complexes during plastic deformation.     

Features of atomic processes at the formation of a wetting layer and nucleation of three-dimensional Ge islands on Si(111) and Si(100) surfaces

The intermediate stages of the formation of a Ge wetting layer on Si(111) and Si(100) surfaces under quasiequilibrium grow conditions have been studied by means of scanning tunneling microscopy. The redistribution of Ge atoms and relaxation of mismatch stresses through the formation of surface structures of decreased density and faces different from the substrate orientation have been revealed. The sites of the nucleation of new three-dimensional Ge islands after the formation of the wetting layer have been analyzed. Both fundamental differences and common tendencies of atomic processes at the formation of wetting layers on Si(111) and Si(100) surfaces have been demonstrated. The density of three-dimensional nuclei on the Si(111) surface is determined by changed conditions for the surface diffusion of Ge adatoms after change in the surface structure. Transition to three-dimensional growth on the Si(100) surface is determined by the nucleation of single {105} faces on the rough Ge(100) surface.     

GS-MBE生长的GaP/Si的XPS研究

利用X射线光电子能谱(XPS)深度剖析方法对气体源分子束外延(GS-MBE)生长的GaP/Si异质结构进行了详细的分析.其结果表明:(1)外延层内Ga、P光电子峰与GaP相相符,且组份分布均匀,为正化学比GaP.(2)在不同富PH₃流量条件下生长的样品,其表面富P量稍有不同,而GaP外延层内的测试结果相同.界面也未见有P的富集.(3)XPS剖析至GaP/Si界面附近,随外延层界面向衬底过渡,Si2p光电子峰向高结合能方向移动,且其结合能高于原衬底p型Si,接近于n型Si.但Ga、P光电子峰未发现有明显能移.(4)在XPS检测限内,外延层内和界面都未见有C、O等沾污.这一研究表明:无污染的本底超高真空、相对过剩的富₃生长环境、成功的Si衬底清洗方法等措施保证了GS-MBE生长出正化学比GaP/Si外延异质结构.     

透射式GaAs光电阴极抗光反射膜的研究

本文计算了在透射式GaAs光电阴极的窗玻璃和GaAlAs缓冲层之间引入Si₃N₄或SiO₂膜使光电阴极的入射光反射率所产生的变化,并测量了Si₃N₄膜、SiO₂膜和SiO₂/Si₃N₄复合膜对阴极反射率的影响。理论计算和测量表明,Si₃N₄膜和SiO₂/Si₃N₄复合膜可有效地降低光电阴极对入射光的反射率。当Si₃N₄膜的厚度约为100nm时,可使光电阴极的反射率降低近60%。本文结果为科学地选择透射式GaAs光电阴极所需的的抗光反射膜提供了依据。     

Solid phase epitaxial growth of Si on Si---Sb surface phases for the formation of δ-doped layers and δiδi-superlattices

The SPE growth of Si on Si---Sb surface phases has been studied by LEED and AES techniques. The surface phases studied were the disordered Si(100)---Sb and the ordered one. Both surface phases have an Sb coverage of about one monolayer. Structures with single δ-doped layers and a δiδi-superlattice have been grown. The structural perfection of the grown Si films has been characterized on the basis of LEED data. The peculiarities of the annealing behaviour of Si films thinner than 10 nm have been detected.     

Band engineering of silicon for light emission: First-principles approach to the effect of co-doping with nitrogen and fluorine

A Si-based light emitter has long been the final key component for electronic and photonic integrated circuits on Si, because Si has an indirect band gap. Atomistic and electronic structures and energy gains of formation of possible nitrogen (N) and fluorine (F) complexes in Si have been researched from first-principles, in order to engineer the band structure of Si for light emission. The calculated results show that the substitutional nitrogen N_S and bond center fluorine F_BC pair complex has large stabilization energy, and that the pair-complex-doped Si has direct band gap, which is reduced with respect to that of Si. These results lead to the possibilities of doping-based engineering of Si optical properties with introduction of deep-level impurity and charge compensation.     

Surface plasmon polaritons assisted diffraction in metal films with subwavelength hole array

Metal films grown on Si wafer have been perforated with a periodic hole array and anomalous enhanced transmission in the subwavelength regime has been observed. High-order transmission peaks up to Si(2,2) are clearly revealed due to the large dielectric constant of Si against that of the air. Si(1,1) peak splits into two branches at oblique incidence both in TE and in TM polarization, which confirms that anomalous enhanced transmission is a surface plasmon polaritons (SPPs) assisted diffraction phenomenon.     

Characterization of ion beam sputter deposited W and Si films and W/Si interfaces by grazing incidence X-ray reflectivity, atomic force microscopy and spectroscopic ellipsometry

An ion beam sputtering system, which uses a commercial ECR microwave based plasma ion source, has been designed and fabricated in-house for deposition of soft X-ray multilayer mirrors. To begin with, in the ion beam sputtering system W, Si thin films, W/Si bi-layer and W/Si/W tri-layer samples have been deposited on c-Si substrates as precursors to W/Si multilayer stack. The samples have been characterized by grazing incidence X-ray reflectivity (GIXR), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE) techniques. By analyzing the results, density, thickness, surface roughness of the single layer samples and interface width of the bi-layer and tri-layer samples have been estimated.