Formation of Ge nanoripples on vicinal Si (1110): from Stranski-Krastanow seeds to a perfectly faceted wetting layer

Ge growth on high-indexed Si (1110) is shown to result in the spontaneous formation of a perfectly {105} faceted one-dimensional nanoripple structure. This evolution differs from the usual Stranski-Krastanow growth mode because from initial ripple seeds a faceted Ge layer is formed that extends down to the heterointerface. Ab?initio calculations reveal that ripple formation is mainly driven by lowering of surface energy rather than by elastic strain relief and the onset is governed by the edge energy of the ripple facets. Wavelike ripple replication is identified as an effective kinetic pathway for the transformation process.     

Doping induced disorder in trans-polyacetylene: A spectroscopic and dynamical study

The results of lattice dynamical calculations on pristine and doped trans- polyacetylene are summarized and a reinterpretation of the vibrational spectrum is suggested. The possibility of the existence in the doped system of a centrosymmetrical molecular defect, consistent with the infrared spectrum, alternative to the soliton defect is discussed.     

A numerical study of Langevin QCD with dynamical quarks

QCD with four flavours of dynamical staggered quarks of mass ma=0.1 is simulated on a 4⁴ lattice, using two versions of the second order Langevin algorithm with bilinear noise: the naive version and one which compensates for the non-integrable term which appears to first order in the discrete Langevin time step size. Comparison with the results of an exact numerical computation of the fermion determinant reveals that these algorithms yield accurate results only at rather small values of the step size. The correction due to the non-integrable term is quantitatively unimportant for such step sizes.     

A numerical study of lattice QED with dynamical fermions

Using the pseudo-fermion method U(1) lattice gauge theory with dynamical staggered fermions is studied. The plaqette energy, the chiral order parameter and the Polyakov line have been measured. With fermions of mass 0.20 and 0.25 a phase transition is observed, separating the strong coupling regime from a phase where chiral symmetry is restored.     

Ferromagnetism and disorder: a dynamical mean-field study

We investigate ferromagnetism in the periodic Anderson model with diagonal disorder. Using dynamical mean-field theory in combination with the modified perturbation theory, the disorder can be included in the calculation consistently, which turns out to be equivalent to the coherent potential approximation method. Disorder generally reduces the Curie temperature and can for certain configurations completely suppress ferromagnetic order. This can be ascribed to the enhanced quasiparticle damping and the special structure of the density of states.     

Magnetism in PrIr2Si2: A single crystal study

We present the results of magnetization, susceptibility and specific-heat measurements of the high-temperature (HT) and low-temperature (LT) phases of PrIr₂Si₂ performed on single-crystalline samples. The HT and LT phases adopt the tetragonal CaBe₂Ge₂-type and ThCr₂Si₂-type structure, respectively. We have found no magnetic phase transition for the HT phase at temperatures down to 2 K. On the other hand, the LT phase apparently orders antiferromagnetically (AF) at 45.5 K and undergoes a transition to another AF phase at T_t=23.7 K. Complexity of the magnetic phase diagram is amplified by two metamagnetic transitions induced by magnetic field applied along the c-axis at temperatures below T_t. The results will be discussed with respect to other polymorphic compounds PrNi₂As₂ and UCo₂Ge₂.     

Lattice dynamical study of platinum

Acta physica Academiae Scientiarum Hungaricae - A modified angular force model which takes into account the effect of electron-ion interaction on the basis ofSharma andJoshi model along with the...     

First-principles molecular-dynamics study of native oxide growth on Si(001)

Through first-principles molecular dynamics we study the low-temperature oxidation of the Si(001) surface from the initial adsorption of an O2 molecule to the formation of a native oxide layer. Peculiar features of the oxidation process are the early, spontaneous formation of Si4+ species, and the enhanced reactivity of the surface while the reactions proceed, until saturation is reached at a coverage of 1.5 ML. The channels for barrierless oxidation are found to be widened in the presence of both boron and phosphorous impurities.     

A channeled ion energy loss study of the surfactant-mediated growth of Ge on Si(100)

Scattered ion energy distribution for the system Sb/Ge/Si(100) are studied using transmission ion channeling. One monolayer (ML) of Sb was deposited on the clean Si(100) surface prior to deposition of one ML of Ge at 350°C. Experimental energy distributions for the <100>, {110}, and “random” directions are compared with simulated energy distributions obtained by overlapping trial absorbate positions (relative to bulk positions) with ion positions in the channel at the beam-exit surface. Ion positions and energies are calculated via a Monte Carlo simulation of channeling that incorporates a model for channeled ion energy loss. We find that the energy distributions clearly show that the surfactant, Sb, moves to the surface upon Ge deposition at 350°C. Further, our results are consistent with the sites recently reported by Grant et al. [Surf. Sci. 316 (1994) L1088], for Sb deposited on Ge/Si(100), namely, tilted Sb dimers on Ge asymmetrically displaced from bulk sites.     

Optical modification of semiconductor surfaces through the nanoripples formation using ultrashort laser pulses: Experimental aspects

We review the studies of nanoripples formation on various semiconductor species using ultrashort pulses and different experimental conditions. We present recent studies in this field and discuss the fabrication of 2D periodic nanostructures formed on the surface of semiconductor crystals applying a method of two-beam interference of femtosecond laser. Further, we discuss the short-period ripples formation and present the studies of the semiconductors with different bandgaps potentially suitable for generation of sub wavelength nanoripples. We also show the method of formation of the nanoholes and nanodots on the surface of different semiconductors. Ripples formation using different laser parameters and ambient media is analyzed with the objective of identifying conditions of forming short-period nanoripples. Finally, we discuss the formation of extended homogeneous laser-induced periodic surface structures using few-cycle laser pulses.     

Calculation of lattice dynamical properties from electronic energies: Application to C,Si and Ge

It is shown that lattice dynamical properties of insulators can be calculated directly from the electronic band structure using the “special points” method. The shear modulii and zone boundary transverse acoustic phonon frequencies of C, Si and Ge are calculated with no adjustable parameters, with results in reasonable agreement with experiment.     

CeO2的电子结构，光学和晶格动力学性质：第一性原理研究

基于考虑了Ce-4f电子间的库仑作用U和交换作用J的LDA+U方案,应用第一性原理计算系统研究了CeO₂的电子结构,光学和晶格动力学性质.电荷密度和电子局域函数的分布特征表明,CeO₂是属于共价键的绝缘体.介电常数、玻恩有效电荷张量和声子色散曲线的计算值和相应的实验结果符合得比较好. 关键词： 电子结构 光学性质 晶格动力学 第一性原理计算     

STM study of SiC crystallite growth on vicinal Si(111) surfaces

The initial stage of epitaxial growth of cubic β-SiC on vicinal Si(111) misoriented towards the [112&#x0304;] direction is studied by scanning tunneling microscopy in ultra-high vacuum. The clean Si(111) surface contains terraces separated by groups of atomic steps. The separation between the atomic steps within a group is observed to be approximately equal to the length of the long axis of the Si(111)7 × 7 unit cell. We postulate that the SiC forms three-sided pyramids with surfaces of (110) orientation. The pyramids are located mostly at the step edges and are sharper than the end of the tip. This results in a series of identically shaped tip images located at the step edges, which display the structure of the tip.     

Electronic coherence in delta-Pu: a dynamical mean-field theory study

A combination of density functional theory and the dynamical mean-field theory (DMFT) is used to calculate the magnetic susceptibility, heat capacity, and the temperature dependence of the valence band photoemission spectra for delta-Pu. We predict that delta-Pu has a Pauli-like magnetic susceptibility near ambient temperature, as in experiment, indicating that electronic coherence causes the absence of local moments. Additionally, we show that volume expansion causes a crossover from incoherent to coherent electronic behavior at increasingly lower temperatures.