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1.
Binding energies of a hydrogenic donor in a spherical GaAs quantum dot surrounded by Ga1-xA4xAs matrix are calculated. The results are presented for realistie barrier heights corresponding to different values of x (x 〈 0.4). The calculations are performed under two different conditions: (i) a spherical dot with square well confinement and (ii) a dot with parabolic potential well confinement. The results show that (i) the donor ionization energies are always higher under parabolic confinement as compared to a dot of the same radius under square well confinement and (ii) the oscillator strengths coupling ground state with excited states are two orders larger under parabolic confinement. Our results are in agreement with the results of other researchers. 相似文献
2.
Effects of Radius and Orientation of Single-Walled Carbon Nanotubes on Their Nonlinear Tensile Deformation Behaviour 下载免费PDF全文
By capturing the atomic information and reflecting the behaviour governed by a nonlinear potential function, an analytical molecular mechanics approach is applied to establish the constitutive relation for single-walled carbon nanotubes (SWCNTs). The nonlinear tensile deformation curves of zigzag and armchair nanotubes with different radii are predicted, and the elastic properties of these SWCNTs are obtained. A conclusion is made that the nanotube radius has little effect on the mechanical behaviour of SWCNTs subject to simple tension, while the nanotube orientation has larger influence. 相似文献
3.
Electronic and structural properties of N-vacancy in AlN nanowires: A first-principles study 下载免费PDF全文
The stability and electronic structures of AlN nanowires with and without N-vacancy are investigated using firstprinciples calculations.We find that there is an inverse correlation between formation energy and diameter in ideal AlN nanowires.After calculating the formation energies of N-vacancy at different sites in AlN nanowires with different diameters,we find that the N-vacancy prefers to stay at the surface of the nanowires and it is easier to fabricate them under Al-rich conditions.Through studying the electronic properties of AlN nanowires with N-vacancies,we further find that there are two isolated bands in the deep part of the band gap,one of them is fully occupied and the other is half occupied.The charge density indicates that the half-fully occupied band arises from the Al at the surface,and this atom becomes an active centre. 相似文献
4.
Based on the general theory of dislocation and kink, we have constructed the three kink models corresponding to the 1/2 (111){011} and 1/2 (111){112} edge dislocations (EDs) in bcc Fe using the molecular dynamics method. We found that the geometric structure of a kink depends on the type of ED and the structural energies of the atom sites in the dislocation core region, as well as the geometric symmetry of the dislocation core and the characteristic of the stacking sequence of atomic plane along the dislocation line. The formation energies and widths of the kinks on the 1/2 (111){011} and 1/2 (111){112} EDs are calculated, the formation energies are 0.05eV and 0.04eV, and widths are 6.02b and 6.51b, respectively (b is the magnitude of the Burgers vector). The small formation energies indicate that the formation of kink in the edge dislocation is very easy in bcc Fe. 相似文献
5.
An ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximations has been utilized to investigate the electronic structure, atomic geometry, formation energy to provide a better understanding of properties of Ni disilicide. The vacancy and interstitial formation energies largely depend on the atomic chemical potentials. The formation energies of vacancies Vsi and VNi are in the range of 0.04-0.56 eV and 1.25-2.3eV, respectively and the formation energies of Si and Ni interstitials are 3.89-4.42eV and 0.67-1.71 eV,respectively. The smaller Ni interstitial formation energy is in agreement with the experimental result that Ni interstitial atom is dominant diffusion species in NiSi2. 相似文献
6.
Structural, curvature and electronic properties of Rh adsorption on armchair single-walled carbon nanotube 下载免费PDF全文
This paper systematically studies the rolling effects of the (n, n) single-wall carbon nanotubes (SWCNT) with different curvatures on Rh adsorption behaviours by using density functional theory. The outside charge densities of SWCNTs are found to be higher than those inside, and the differences decrease with the increase of the tube radius. This electronic property led to the discovery that the outside adsorption energies are higher than the inside ones, and that the differences are reduced with the increase of the tube radius. Partial density of states and charge density difference indicate that these strong interactions induce electron transfer between Rh atoms and SWCNTs. 相似文献
7.
The geometric, energetic, electronic structures and optical
properties of ZnO nanowires (NWs) with hexagonal cross sections are
investigated by using the first-principles calculation of plane wave
ultra-soft pseudo-potential technology based on the density
functional theory (DFT). The calculated results reveal that the
initial Zn-O double layers merge into single layers after structural
relaxations, the band gap and binding energies decrease with the
increase of the ZnO nanowire size. Those properties show great
dimension and size dependence. It is also found that the dielectric
functions of ZnO NWs have different peaks with respect to light
polarization, and the peaks of ZnO NWs exhibit a significant
blueshift in comparison with those of bulk ZnO. Our results gives
some reference to the thorough understanding of optical properties
of ZnO, and also enables more precise monitoring and controlling
during the growth of ZnO materials to be possible. 相似文献
8.
YAN Hai-Qing TANG Chen LIU Ming ZHANG Hao 《理论物理通讯》2005,44(4):727-730
We present a global optimization method, called the real-code genetic algorithm (RGA), to the ground state energies. The proposed method does not require partial derivatives with respect to each variational parameter or solving an eigenequation, so the present method overcomes the major difficulties of the variational method. RGAs also do not require coding and encoding procedures, so the computation time and complexity are reduced. The ground state energies of hydrogenic donors in GaAs-(Ga,Al)As quantum dots have been calculated for a range of the radius of the quantum dot radii of practical interest. They are compared with those obtained by the variational method. The results obtained demonstrate the proposed method is simple, accurate, and easy implement. 相似文献
9.
Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field 下载免费PDF全文
The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field. 相似文献
10.
Synthesis and Photoluminescence Properties of GaAs Nanowires Grown on Fused Quartz Substrates 下载免费PDF全文
GaAs nanowires are synthesized on fused quartz substrates by using molecular beam epitaxy via a vapor-liquidsolid mechanism with gold as the catalyst. High resolution-transmission electron microscopy is used to probe crystal quality and growth direction. Miero-photolumineseenee measurements are carried out to examine the optical properties of GaAs NWs. The low-temperature photoluminescenee (PL) emission of nanowires (NWs) has a peak at 1.513eV, 2meV lower than the zinc blende GaAs free exciton energy. The temperature-dependent band gap of NWs is seen to be somewhat different from that observed in bulk OaAs, and the PL rapidly quenches above 150K, with an activation energy of 6.3meV reflecting the presence of the longitudinal twins' structure. 相似文献