Molecular dynamics simulation of Co thin films growth on Cu(001)

Results of MD simulations of the structure of ultrathin films of Co on Cu(001) are presented. Growth conditions corresponding to vacuum evaporation as well as laser ablation are considered. The dynamics of the growth process and the structure of the as-deposited films are investigated as a function of the kinetic energy of adatoms. The effect of fast interdiffusion due to a high impact energy is observed. Tight-binding potentials in the second-moment approximation are used. Co–Cu interaction parameters are determined from ab-initio electronic structure calculations.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Sobolev embedding theorems for a class of anisotropic irregular domains

Sufficient conditions for the embedding of a Sobolev space in Lebesgue spaces on a domain depend on the integrability and smoothness parameters of the spaces and on the geometric features of the domain. In the present paper, Sobolev embedding theorems are obtained for a class of domains with irregular boundary; this class includes the well-known classes of σ-John domains, domains with the flexible cone condition, and their anisotropic analogs.     

Sub-10-fs supercontinuum radiation generated by filamentation of few-cycle 800 nm pulses in argon

Focusing 12 fs pulses of 800 nm with moderate energy (0.35 mJ) into atmospheric-pressure argon (Ar) gives rise to filamentation (self-focusing) and a supercontinuum with a very broad pedestal, extending to 250 nm. According to the present understanding, the short wavelengths are produced by self-phase modulation in the self-steepened trailing edge of the pulse. Pulses in this spectral range might thus be intrinsically short. Indeed we demonstrate this by extracting the light near the end of the filament, terminating self-focusing by a pressure gradient at a pinhole, beyond which the Ar is pumped away. We obtain pulses of 9.7 fs in the region of 290 nm without the necessity of compression.     

Theoretical analysis of impurity precipitation in nanopores in crystals. II: Kinetics of impurity cluster growth in pores

The kinetics of the formation of impurity clusters in subsurface nanopores in crystals is studied theoretically. A physical model of precipitation of the impurity phase in nanopores in a sample with sinks of various types is developed. This model forms the basis for the calculation of the annealing kinetics of copper containing subsurface pores and cobalt impurity atoms. The optimal annealing conditions are determined in which cobalt atoms diffuse predominantly into pores and form impurity clusters in them.     

The crossover from collective motion to periphery diffusion for two-dimensional adatom-islands on Cu(111)

The diffusion of two-dimensional adatom-islands (up to 100 atoms) on Cu(111) has been studied, using the self-learning kinetic Monte Carlo method (Trushin et?al 2005 Phys. Rev. B 72 115401). A variety of multiple-?and single-atom processes are revealed in the simulations, and the size dependences of the diffusion coefficients and effective diffusion barriers are calculated for each. From the tabulated frequencies of events found in the simulation, we show a crossover from diffusion due to the collective motion of the island to a regime in which the island diffuses through periphery-dominated mass transport. This crossover occurs for island sizes between 13 and 19 atoms. For islands containing 19-100 atoms the scaling exponent is 1.5, which is in good agreement with previous work. The diffusion of islands containing 2-13 atoms can be explained primarily on the basis of a linear increase of the barrier for the collective motion with the size of the island.     

多光子过程中相位退相干时两原子布局数反转

利用全量子理论的方法,研究了存在相位退相干时多光子T-C模型中两个二能级原子与二项式光场相互作用系统中两原子的布居数反转。讨论了相位退相干系数、二项式光场系数、最大光子数、跃迁光子数对原子布居数反转的影响。结果表明：相位退相干减少了原子布居数反转的振幅、破坏了原子的量子特性。改变跃迁光子数,可以改变原子间布居数反转演化周期及演化强度。当二项式光场的最大光子数增大时,原子布居差的崩塌-回复现象就会逐渐消失。相位退相干因子不变时, 二项式光场从相干态过渡到数态过程中,原子布居的振荡频率由大变小,周期性的崩塌与回复现象逐渐消失。     

The First Principles Investigations of the Thermoelectric Properties of GaN with p- and n-Type Doping

We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type.