共查询到20条相似文献,搜索用时 15 毫秒
1.
A. A. Kuzubov N. S. Eliseeva Z. I. Popov A. S. Fedorov M. V. Serzhantova V. M. Denisov F. N. Tomilin 《JETP Letters》2013,97(11):634-638
The energy of the sorption and diffusion of lithium atoms on the reconstructed (4 × 2) (100) silicon surface in the process of their transport into near-surface layers, as well as inside crystalline silicon, at various lithium concentrations have been investigated within the density functional theory. It has been shown that single lithium atoms easily migrate on the (100) surface and gradually fill the surface states (T3 and L) located in channels between silicon dimers. The diffusion of lithium into near-surface silicon layers is hampered because of high potential barriers of the transition (1.22 eV). The dependences of the binding energy, potential barriers, and diffusion coefficient inside silicon on distances to the nearest lithium atoms have also been examined. It has been shown that an increase in the concentration of lithium to the Li0.5Si composition significantly reduces the transition energy (from 0.90 to 0.36 eV) and strongly increases (by one to three orders of magnitude) the lithium diffusion rate. 相似文献
2.
R. A. Zhachuk S. A. Teys B. Z. Olshanetsky 《Journal of Experimental and Theoretical Physics》2011,113(6):972-982
The diffusion of strontium atoms on the Si(111) surface at room temperature has been investigated using scanning tunnel microscopy
and simulation carried out in terms of the density functional theory and the Monte Carlo method. It has been found that the
reconstruction of a clean silicon surface with a 7 × 7 structure has a profound effect on the diffusion process. The average
velocity of motion of a strontium atom in a unit cell of the 7 × 7 structure has been calculated. The main diffusion paths
of a strontium atom and the corresponding activation energies have been determined. It has been demonstrated that the formation
of scanning tunnel microscope images of the Si(111)-7 × 7 surface with adsorbed strontium atoms is significantly affected
by the shift of the electron density from the strontium atom to the nearest neighbor silicon adatoms in the 7 × 7 structure. 相似文献
3.
P. K. Hung P. H. Kien 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):119-125
The tracer-diffusion and structure of polymorphic states of amorphous solid
is studied by mean of the statistic relaxation technique and simplex
analysis. Several different metastable states of amorphous iron have been
constructed based on the model containing 2 × 105 atoms. All models have
almost the same pair radial distribution functions, but they differ in the
potential energy per atom and the density. We found a large number of
vacancy-simplexes which varies according to the relaxation and serves as a
diffusion vehicle. New diffusion mechanism for tracer-diffusion is found of
which the elementary diffusion process likes a collapse of “microscopic
bubble” in amorphous matrix. This includes a jump of diffusing atom and the
collective movement of a large number of neighboring atoms. The diffusion
constant D determined in accordance with considered diffusion mechanism is in
reasonable agreement with experimental data. The decrease in diffusion
constant D upon thermal annealing is explained by the reducing
vacancy-simplex concentration which is caused by both the local atomic
rearrangement and the elimination of excess free volume. 相似文献
4.
The heights of barriers for the injection of electrons and holes from silicon in SiOx have been calculated in the tight binding approximation without any fitting parameters. The dependence of the electronic structure of silicon-enriched amorphous silicon oxide SiOx on the degree of enrichment has been found. The calculations have been performed with the parameterization of the matrix elements of the tight binding Hamiltonian proposed in our previous work. This parameter involves a change in the localization region of valence electrons of an insulated atom at its introduction into a solid. It has been shown that the inclusion of this change makes it possible to calculate the electronic structure without fitting parameters using the parameters of individual atoms as initial data. This circumstance allows the calculation in the absolute energy scale with zero corresponding to the energy of the electron in vacuum. 相似文献
5.
The electronic structure of amorphous silicon nitride SiN x enriched with silicon as a function of its chemical composition has been calculated in the tight-binding approximation without fitting parameters. A new method of parametrization of the matrix elements of the tight-binding Hamiltonian has been proposed with allowance for the variation of the localization region of the valence electrons of the isolated atom in the process of its incorporation into a solid. It has been shown that allowance for these variations makes it possible to calculate the electronic structure using the parameters of the isolated atoms as the initial data. The latter circumstance allows the calculation on the absolute energy scale with zero corresponding to the energy of the electron in vacuum. 相似文献
6.
We have invoked a simple pattern recognition scheme in kinetic Monte Carlo simulations of post-deposition evolution of two dimensional islands on fcc(1 1 1) surfaces. On application of the technique to the diffusion of small Cu clusters (8-100 atoms) on Cu(1 1 1) we find that, at room temperature, clusters with certain magic numbers show stick-slip type of motion with striking patterns rather than the random paths followed by the others. At higher temperatures all clusters display random motion. The calculated diffusion coefficients show dependence on size and temperature with an effective barrier ranging between 0.62 eV and 0.84 eV. Small asymmetries in diffusion barriers lead to a large difference in the frequencies of adatom diffusion along the two types of micro-facetted steps on Cu(1 1 1) leading to consequences in their shape evolution. The pattern recognition scheme revealed 49 basic periphery single atom diffusion processes whose activation energy barriers were calculated using the nudged elastic band technique and interatomic potentials from the embedded atom method. 相似文献
7.
K. N. Tu 《Applied Physics A: Materials Science & Processing》1991,53(1):32-34
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 相似文献
8.
The phenomenon of dynamic collective displacements of atoms in face-centered cubic crystals has been revealed using molecular dynamics method. This phenomenon plays an important role in the vacancy mechanism of diffusion. The vacancy mechanism is provided by the collision of two regions of collective atomic displacements that move a migrating atom and a vacancy toward each other. The collective thermal atomic displacements from crystal lattice sites occur as a result of the nonuniform momentum distribution of atoms according to the Maxwellian distribution. Owing to their statistical nature, the degree of correlation of the atomic displacements depends neither on the temperature nor on the interatomic interaction potential. 相似文献
9.
The segregation of a vacancy and phosphorus on inclined grain boundaries in crystalline silicon has been calculated. It has been found that the distribution of defects at boundaries under study depends both on the nature of a defect and on the local structure of the boundary. The parameters characterizing the local deformation of the tetrahedral environment of an atom at the boundary have been proposed. A linear correlation has been found between the energy of the distribution and proposed parameters. 相似文献
10.
The structure and dynamics of amorphous surfaces are poorly understood. The present work develops methods employing classical molecular dynamics (MD) simulations to elucidate these phenomena on amorphous silicon. Careful relaxation of the initial ensemble and taking account of exchange with the bulk yield surface diffusion coefficients in good agreement with experiment. Randomly oriented dimer pairs dominate the surface structure. Diffusion proceeds by several pathways, which all differ in basic character from those typically observed on crystalline silicon. The primary pathways involve single atoms and dimer pairs, which typically move only one or two atomic diameters before reincorporating into the surface. Frequent vertical migration takes place between the first two atomic layers. 相似文献
11.
Abstract X-ray diffraction has been measured for crystalline silicon, crystalline germanium, amorphous silicon and amorphous germanium at temperatures down to 100 K and pressures up to 20 GPa using a diamond anvil cell and synchrotron radiation. The structural phase transitions, including amorphization, take place in the pressure-temperature range. It has been found that the structures after the phase transitions strongly depend on the path in the pressure-temperature diagram through which the system undergoes the phase transitions. For any of the aforementioned four materials, the high-pressure phase with the p-Sn structure is quenched during a release of pressure at 100 K, and transforms into an amorphous state when heated up to around 2 GPa. The path dependence of the states is discussed in relation to the pressure dependence of the heights of the energy barriers which have to be overcome when phase transitions occur. The effect of a structural disorder on the phase transition is also discussed by comparing the experimental results for the crystalline and amorphous materials. 相似文献
12.
W. Felsch 《Zeitschrift für Physik A Hadrons and Nuclei》1969,219(3):280-299
In a previous paper a method has been described to produce thin films of amorphous iron by simultaneous condensation of iron and small additions of oxygen, silicon, or germanium onto a substrate at 20 °K. During annealing the amorphous films crystallize within a narrow range of temperature. In this paper the magnetic properties of these films are investigated. By a new lowtemperature ?gnetometer the magnetization curves can be registered for the different states of annealing. It results that even in the amorphous state iron is ferromagnetic. Below a critical concentration of the oxygen, silicon, or germanium admixtures the magnetic moment of the iron atoms is smaller and the coercive force is greater in the amorphous than in the crystalline structure. Above that concentration the magnetic moments in the two structures are equal, whereas the coercive force of the amorphous films is smaller than that of the crystalline ones. The results are explained by a concentration depending short range order in the amorphous films. 相似文献
13.
Structural and dynamical properties of hydrogen in crystalline and amorphous silicon are analyzed by ab initio molecular dynamics simulations. In the crystalline case we focus mainly on the diffusion process of an isolated positively charged hydrogen impurity at high temperature, finding important dynamical effects. In the amorphous case we analyze the local order and the dynamical properties corresponding to an atomic hydrogen concentration of
11%, typical of a device quality material. We find that hydrogen atoms form monohydride complexes and show interesting clustering effects. In both crystalline and amorphous cases, our results are in good agreement with available experimental data and give unique insight into the microscopic details of hydrogen incorporation in silicon. 相似文献
14.
锑烯(antimonene)是继石墨烯和磷烯之后出现的新型二维材料,在锂离子电池等领域受到关注.本文基于第一性原理的密度泛函理论,计算研究了锑烯对Li原子的吸附特性,包括Li原子的最稳定吸附构型、吸附密度以及吸附Li原子的扩散路径.结果表明:Li原子最稳定的吸附位置位于谷位,即底层Sb原子之上、顶层三个Sb原子中心位置,吸附能为1.69 eV,吸附距离为2.81?;能带计算发现,锑烯为带隙宽度1.08 eV的间接带隙半导体,吸附Li原子后费米能级上升进入导带,呈现出金属性;原子分波态密度分析发现, Sb原子的p电子态和Li原子的p和s电子态形成明显的共振交叠,表现出杂化成键的特征;随着吸附Li原子数量增加,锑烯晶格结构和电子结构发生较大变化.通过微动弹性带方法计算发现, Li原子在锑烯表面的扩散势垒为0.07 eV,较小的势垒高度有利于快速充放电过程. 相似文献
15.
应用分子动力学模拟方法研究了氧化硅团簇在不同的切削 深度下切削单晶硅粗糙峰的过程, 考察了切削过程中粗糙峰和氧化硅团簇形态变化、团簇的受力状况、粗糙峰原子配位数和温度分布等. 模拟结果表明: 切削深度小于0.5 nm时, 被去除的材料以原子或者原子簇形式存在, 并黏附在颗粒表面被带走; 当切削深度增大至1 nm时, 材料的去除率增大, 并形成大的切屑. 在切削过程中, 由于压力和温度的升高, 粗糙峰切削区域的单晶硅转变为类似Si-Ⅱ相和Bct5-Si相的过渡结构, 在切削过程后的卸载阶段, 过渡结构由于压力和温度的下降转变为非晶态结构. 相似文献
16.
在密度泛函理论计算的基础上,利用微动弹性带(nudged elastic band)方法研究了氧原子在Zr(0001)表面附近的扩散.首先计算了氧原子从稳定的表面面心立方(SFCC)位置向表面六角密排位置的扩散激活能(0.77 eV);然后计算了氧原子从稳定的SFCC位置扩散到表面下第1层与第2层之间的八面体间隙位置,再继续向表面下第2层与第3层之间的八面体间隙位置扩散的激活能,在此过程中氧原子需克服两个能垒,其激活能分别为2.14和2.57 eV.结果表明,氧原子在Zr(0001)表面上方的扩散比较容易,而氧原子向Zr(0001)表面下的扩散相对较难.
关键词:
Zr(0001)表面
微动弹性带
氧的扩散 相似文献
17.
《Journal of Electron Spectroscopy and Related Phenomena》2002,125(2):89-98
We have measured and analyzed Co K-edge X-ray absorption near edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) near edge spectra in crystalline and amorphous GdCo2 alloys. We have used a semi-relativistic full multiple scattering approach to the analyses of the XMCD spectra. A general formula is obtained which is applicable to randomly oriented systems in space. Useful information is obtained on both the electronic and geometric structure around a Co atom. The difference in XANES and XMCD spectra between crystalline and amorphous GdCo2 is well explained by models referring to the anomalous X-ray scattering result, where three Gd atoms in the second shell are removed away. The calculated XANES are not so sensitive to the electronic structure, whereas the calculated XMCD spectra are rather sensitive to the spin polarization on Co atoms. The result shows that the spin polarization on Co atoms in GdCo2 alloys is smaller than that in Co metals. 相似文献
18.
The structure of nickel (Ni), iron (Fe), and magnesium (Mg) adatoms on the aluminum (Al) truncated octahedron is studied using molecular dynamics and the analytic embedded atom method. First, the energy barriers of several typical diffusion processes of Ni, Fe, and Mg adatoms on the Al truncated octahedral cluster were calculated using the nudged elastic band method. The calculated energy barriers were found to be related to the surface energy and atomic radius of the adatom and substrate atom. The result shows that the incorporation of Ni and Fe atoms into Al core easily occurs, and the Mg atom should segregate at the surface of the Al cluster. Thus, the growth of Ni, Fe and Mg on the Al truncated octahedron with 1289 atoms was simulated at several temperatures. In the Ni–Al and Fe–Al cases, the core-shell structure was not obtained. For the Mg–Al system, a good Mg shell on the Al core was found at lower temperatures, and an almost perfect truncated octahedron with more Al shells emerged with an increase in temperature. 相似文献
19.
Dynamic quadrupole polarizability of lithium atom has been calculated in its ground state using linked cluster many-body perturbation theory. Van der Waals constants have been calculated for dipole-quadrupole and quadrupole-quadrupole interactions of lithium atoms with helium and other lithium atoms. The results compare well with other available values. 相似文献
20.
Nuclear magnetic resonance has been successfully applied to the study of the microstructure of hydrogenated amorphous silicon and related materials. It has been used to determine the local bonding and structural environment of the host atoms, the hydrogen, and the dopants. First, we review some of these NMR experimental results on the hydrogen microstructure in hydrogentaed amorphous semiconductors and compare the results on plasma deposited hydrogenated amorphous silicon (a-Si:H), remote hydrogen plasma deposited a-Si:H, thermally annealed a-Si:H, doped a-Si:H, microcrystalline Si and amorphous (Si, Ge):H alloys. A common feature is that these materials exhibit a heterogeneous distribution of hydrogen bonded to the semiconductor lattice in dilute and clustered phases. In addition, the lattice contains voids of varying number and size that contain non-bonded molecular hydrogen whose quantity is altered by deposition conditions and thermal treatment. Second, we review some aspects of the local bonding structure of dopants in a-Si:H. A significant fraction of the dopants are found to be in dopant-hydrogen clusters similar to those proposed to explain hydrogen passivation in crystalline silicon. Implications of the determined local structure on the doping efficiency are discussed. 相似文献