Structural changes of NaCl and Si single crystal surfaces under ion bombardment

The surface structural changes under ion bombardment of NaCl and Si monocrystalline specimens are followed using electron microscopic technique. Formations and regions with circular symmetry are registered on the surface of NaCl and Si single crystals. Qualitative interpretation of the generation mechanism of the circular formations is made. The ion bombardment is used for the visualization of the surface structure of the specimens by the method of crystal selfdecoration.     

High quality nanocrystalline silicon thin film fabricated by inductively coupled plasma chemical vapor deposition at 350 °C

High quality nanocrystalline silicon (nc-Si) film was deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) without substrate RF bias at 350 °C. The nc-Si with a dense crystalline structure of the columnar type grew from the bottom to the top of the nc-Si film. A troublesome incubation layer did not exist at the bottom of the fabricated nc-Si film. A grain size of 40 nm was measured by using a SEM image. When a RF bias of 100 and 200 W was applied to the substrate to induce ion bombardment on the substrate, the crystalline structure and grains were not observed and a-Si deposition became dominant. The transition from nc-Si deposition into a-Si deposition can be attributed to ion bombardment which prevents nucleation and crystal growth at the surface of deposition. This shows that the reduction of ion bombardment can be a key factor to fabricate high quality nc-Si film. By using ICP-CVD with no substrate RF bias, ion bombardment can be reduced, while the density of plasma is kept high, so that high quality nc-Si can be fabricated due to the enhancement of crystalline growth on the surface.     

Infrared and Raman spectroscopy of particle-beam induced damage of silicon carbide

The damaging of 6H-SiC by ion implantation (Ar⁺, 320 keV) leads to the formation of a light-absorbing surface layer with a thickness of about 0.4 μm and a dielectric function which indicates a disordering of the crystal structure. Raman spectra show the existence of amorphous carbon, silicon and silicon carbide. Ion bombardment with 1.4 MeV He⁺ ions generates a 3 μm thick surface layer with small lattice distortions and light-absorbing centers and a 0.4 μm thick interface layer with a larger refractive index.     

离子轰击增强金刚石膜与Si衬底结合力的进一步研究

由于金刚石与Si有较大的表面能差,利用化学气相沉积(CVD)制备金刚石膜时,金刚石在镜面光滑的Si表面上成核困难,而负衬底偏压能够增强金刚石在镜面光滑Si表面上的成核,表明金刚石核与Si表面的结合力也得到增强.本文分析衬底负偏压引起的离子轰击对Si表面产生的影响之后,基于离子轰击使得Si衬底表面产生了微缺陷(凹坑)增大了金刚石膜与Si衬底结合的面积,理论研究了离子轰击对金刚石膜与Si衬底结合力的影响.     

Oriented action of some solid substrates to liquid crystal layer

The orienting action of three types of layers on liquid crystal is investigated. Homogeneous orientation of the liquid crystal layer is obtained under the action of a transparent conductive SnO₂ film and carbon film. Such an orientation is achieved with gelatin films as well. Homeotropic orientation of the liquid crystal can be also obtained by exposing the latter to ion bombardment with Ar ions.     

X-ray photoelectron spectroscopy of bulk glassy Se under Ar ion bombardment

It has been found that Ar ion bombardment produces reversible changes in the XPS structure of the valence band of glassy Se. The result of ion bombardment is that the 4 p bonding and non-bonding peaks merge to give a single broad peak at a binding energy similar to that of the non-bonding peak. This merger of the bonding and non-bonding peaks occurs in density of state calculations when the dihedral angle between adjacent bonds is allowe to take any angle. It is concluded, therefore, that ion bombardment introduces a random dihedral angle into the glassy structure, which subsequently relaxes to give the fixed dihedral angle, but with a random direction which density of states calculations and diffraction work indicate as the structure of the glass.     

New aspect of diffraction of a highly divergent characteristic X-ray beam

A new way of implementing the diffraction of a highly divergent characteristic X-ray beam has been developed. This method is based on the formation of a diffraction image by the X rays exiting particular (active) points on the crystal surface which lie on hyperbolas. There is a correspondence between the points on the crystal surface and the points in the diffraction image. Local distortions of the crystal structure lead to local deviations of the diffraction lines from proper hyperbolas. This method makes it possible to reveal the block structure of crystals, separate blocks, and estimate the degree of misorientation.     

不同表面活性剂对纳米ZnO/ZrO2的制备和脱硫性能的影响

研究不同表面活性剂对采用共沉淀-真空冷冻干燥法制备的ZnO/ZrO2纳米催化剂的结构和物相变化的影响,并在模拟烟气中利用气相色谱仪进行脱除SO2性能的测定.结果表明,表面活性剂的引入可以降低纳米ZrO2的平均晶粒度.与吐温80、PEG-400和PVA相比,柠檬酸铵和DBS抑制晶核生长的能力更大,从而纳米ZrO2的平均晶粒尺寸更小,脱硫率更高;由于PEG-400具有络合正离子的能力,可防止纳米活性组分的团聚和长大,其催化吸收SO2的性能最好.     

溅射环境下基片表面所受到的轰击能量研究

溅射环境下基于薄膜的沉积速率和Langmuir探针测出的基片位置处离子流通量量化了单位时间内基片表面微区所接受的溅射中性原子的轰击能量Ec1和各种轰击离子传递给基片的轰击能量Ec2;Ec1和Ec2的数量级近似相同,Ec1和Ec2同时作用于基片表面微区加速了薄膜沉积过程中最表层原子的表面扩散进程,Ec1和Ec2持续作用所引起的能量积淀和温升效应可促进薄膜表层下方原子的体扩散进程。     

在钛酸钠纤维表面吸附生长SnO_2量子点

本文研究了水热条件下SnO_2纳米晶体在钛酸钠纤维表面的吸附生长特性.采用水热法,以钛酸钠晶体纤维和适量的SnCl_4· 5H_2O为前驱物,水热反应条件为pH值11,填充度68;,反应温度120 ℃、150 ℃,反应时间24 h,在钛酸钠纤维表面生长了金红石相SnO_2纳米晶体,晶体尺度约为5 nm.实验结果显示钛酸钠晶体表面具有很强的表面活化能.     

Investigations on the defect depth of electroerosive-cut Te single crystals by reflection electron diffraction (RHEED)

Results of the experimentally determined defect depth due to electroerosive working of Te single crystals as a function of crystal orientation and electric cutting energy by RHEED are given. The abrasion of the disturbed surface layer was made by chemical etch polishing as well as by bombardment with Ar⁺ ions. The defect depths determined from the RHEED patterns depend on the crystal orientation and the applied cutting energy. In case of the lowest cutting energy, it has a value of about 3 μm for the (0001)-orientation and 6 μm for the (101 0)-orientation, the corresponding values for the highest cutting energy are about 8 μm and 20 μm, respectively. It is discussed in how far defect depths determined from the interpretation of RHEED patterns correspond to the “real defect depths” which can be determined by other measuring techniques.     

Structural and electrical properties of epitaxial metal films grown on argon ion bombarded and annealed (001)InP

A study has been made of intimate metal-InP contacts prepared by metal beam epitaxy in ultra-high vacuum Oxygen and carbon contamination was removed from the (001)InP surface by bombardment with 500 eV Ar⁺ ions. On annealing to 250°C, In islands appeared on the surface and c(2×8) reconstruction was observed. Gold and silver films were found to grow epitaxially on the InP at ?40°C but the electrical properties indicate greatly reduced Schottky barrier heights and non-ideal current-voltage characteristics which may be attributed to non-stoichiometry and damage at the semiconductor surface resulting from the ion bombardment.     

Thermodynamic analysis of GaAs growth by molecular beam epitaxy at the surface structure transition from 3 × 1 to 4 × 2

The molecular beam epitaxy (MBE) growth of GaAs layers on a single crystal is studied in relation with the stability domain of the GaAs compound in the Ga-As binary system. The growth parameters, i.e. The Ga and As impinging atomic flows, are compared to the necessary flows as calculated by thermodynamics. In order to take into account in the real growth situation, which is not strictly at equilibrium, the flow balance at the surface of the crystal between the impinging flows and the growth and evaporated flows is written for quasi-equilibrium growth conditions, including condensation and evaporation coefficients that split the “so-called” sticking coefficient in parts related to the condensation or the evaporation phenomenon for each gaseous species. A comparison between the quasi-equilibrium simulation of the growth and the experiment is made with the assumption that the surface structure transition from gallium-stabilized to arsenic-stabilized surface corresponds to the growth of a GaAs crystal at its solidus boundary rich in gallium. The surface structure transitions are observed by reflection high energy electron diffraction (RHEED) and the impinging atomic flows are carefully calibrated and also controlled by RHEED oscillations as observed after gallium or arsenic excess as deposited on the surface. The results show that the growth is effectively performed close to equilibrium conditions as evidenced by the values of the condensations and evaporation coefficients. The evaporation coefficient of gallium is 0.4, showing that this component is the supersaturated one at the surface, and this value agrees with theoretical predictions for an evaporation process (during growth) controlled by the surface diffusion process of monoatomic species between steps.     

LGAS晶体的微结构及声表面波特性研究

本文采用第一性原理计算了La3Ga5-xSiAlxO14 (LGAS)压电晶体几何结构、能带和态密度.并研究了其在X、Y和Z切型的声表面波速度、机电耦合系数及能流角.当x=0.5时,构建了La3Ga4.5SiAl0.5O14晶体的1×1×2超晶胞结构,发现A1原子替代2d四面体位置的Ga原子时体系总能量最低,体积最小,因此是最稳定的状态.与石英相比,LGAS具有声表面波速度较低、机电耦合系数较大且存在能流角为零的切型等优点.掺Al元素降低了成本但对结构和声表面波特性影响不大.Y切0是较好的切型,可用于制备声表面波器件.     

Penetration depth of tin in float glass

Experimental results on float glass by recent analytical techniques — ESCA, photon emission induced by ion bombardment and ellipsometry — support the conclusion that tin from a metal bath penetrates with relatively high concentration only in the first few nanometers from the surface.     

Structure investigations of the Ge-GeO2 system by high-resolution electron microscopy

The crystal structure of thermally oxidized Ge was investigated by high-resolution electron microscopy (HREM), mainly the interface Ge/oxide. Under special conditions the reaction Ge + O₂ → GeO₂ which takes place at (111) surface planes leads to suitable thin crystal regions. The GeO₂ occurs normally as amorphous films on the crystal surface. Furthermore, hexagonal GeO₂ can grow at the interface Ge/oxide by a topotaxial reaction; the orientation relation between these two lattices was ascertained. Intensive electron irradiation was used to initiate and to observe structure changes in boundary regions.     

Remote plasma deposition of microcrystalline silicon thin-films: Film structure and the role of atomic hydrogen

Microcrystalline silicon films grown in an expanding thermal plasma, i.e. in the absence of ion bombardment, are found to be porous and rich in nano-sized voids. By carrying out an extensive investigation on the material quality of films deposited in the amorphous-to-microcrystalline transition regime, on the microcrystalline silicon growth development, and on the influence of the substrate temperature, it is concluded that the inferior material quality is related to the lack of a sufficient amount of amorphous silicon tissue. As possible cause for the insufficient amount of amorphous silicon tissue, the interaction of atomic hydrogen with amorphous silicon films has been studied in order to highlight a possible competition between film growth and H-induced etching of amorphous silicon, and between film growth and H-induced surface/film modification. The etch rates obtained are too low to compete with film growth. Furthermore, atomic H cannot be considered responsible for the poor quality of amorphous tissue present in the microcrystalline silicon films, as the H up-take mainly takes place in divacancies. These results suggest that ion bombardment may be a necessary condition to provide good quality microcrystalline silicon films.     

Theory of X-ray diffraction from a nonideal crystal with a trapezoidal cross section

The theory of X-ray diffraction from a nonideal lateral crystal with a trapezoidal cross section in the Born (kinematical) approximation has been developed. Distortions of the crystal structure are caused by continuous (nonrandom) lattice strains and randomly distributed defects. Continuous lattice strain is a combination of elastic bending of atomic planes and a linear variation in the interplanar spacing with increasing distance from the crystal surface. Within the method of triple-crystal X-ray diffraction, numerical simulation of the angular intensity distribution of coherent and diffuse scattering has been performed for different continuous and random lattice strains in the lateral and vertical directions.     

1,3,5-三(羧基甲氧基)苯镍配位聚合物的合成、晶体结构及性质研究

采用溶剂热法,1,3,5-三(羧基甲氧基)苯为定向配体和乙酸镍反应构筑了一个新型的金属配位聚合物[Ni(TB)2(H2O)2]n·2H2O,其中H3TB=1,3,5-三(羧基甲氧基)苯,通过元素分析、IR及X射线单晶衍射对配合物结构进行表征,并研究其荧光性质、热稳定性及Hirshfeld表面作用力.单晶结构分析表明,该...     

Sublattices in crystals

A method of representation of a crystal structure as a set of its constituent Bravais sublattices is developed. The conditions for compatibility of sublattices related to the same or different systems are formulated and the connection matrices for primitive parallel-translation vectors of the crystal lattice and the sublattices are determined. A method of alignment of the first Brillouin zones of the sublattices with the first Brillouin zone of the crystal is described. It is shown that alignment may lead to quasi-degeneration of the energy levels in the case of weak hybridization of the sublattice states. A relationship between the sublattice method and the method of an extended unit cell is established.