In situ transmission electron microscopy study of the nucleation and grain growth of Ge2Sb2Te5 thin films

The nucleation and grain growth of the Ge₂Sb₂Te₅ (GST) thin films were studied using high voltage electron microscope operated at 1250 kV. As a result, we have found that 2 nm-sized nucleus forms as a cluster which atoms are arranged regularly at the stage of nucleation prior to the formation of grains having crystal structure. The high-resolution transmission electron microscopy study and fast-Fourier transformations revealed that coexistence of face-centered-cubic (FCC) and hexagonal structure occurs, and formation of twin defect is found in the hexagonal structure during the grain growth as the annealing temperature is increased. GST grain having the hexagonal structure grow from the surface, and the growth proceeded perpendicular to the [0 0 0 1], namely the path parallel to the (0 0 0 1) plane. Consequently, grain growth to a large-scale result in a lengthened shape.     

Retrieval of the vertical distribution of chemical components in the mesosphere from simultaneous measurements of ozone and hydroxyl distributions

We propose a method for retrieval of directly unmeasurable concentrations of minor gas constituents of the mesosphere from available experimental data using simplified models of atmospheric photochemical systems. The method is used for processing of the results of simultaneous measurements of ozone and hydroxyl concentrations within the framework of the CRISTA-MAHRSI satellite experiments. As a result, vertical distributions of concentrations of three more key chemical components of the mesosphere, namely, atomic oxygen, atomic hydrogen, and hydroperoxide, were retrieved. It is shown that a limiting altitude-dependent ratio between OH and O₃ concentrations is valid in the mesosphere and lower thermosphere. It is found that CRISTA-MAHRSI data satisfy this ratio up to an altitude of 87 km, but a strong discrepancy between theory and experiment arises in the upper region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 9, pp. 760–769, September 2006.     

On the effect of longitude-dependent fields on convection in stellar atmospheres

In rotating stellar convective zones, heat transfer is shown to be associated with unbalanced azimuth forces arising in the radially ascending (heated) or descending (cold) matter. The presence of a longitude-dependent magnetic field generates additional azimuth forces, hence, new ways of compensating for the unbalanced forces. Generally speaking, this magnetic field is variable but may be nearly static in layers where convective equilibrium is replaced by radiative equilibrium. The condition for the coexistence of the static and usual fields is derived. To this end, an axisymmetric azimuth magnetic field of energy comparable to the energy of rotation should be introduced into models under consideration. In such configurations, conditions for magnetic field generation, as in the Sun, may appear.     

Effects of pH and citric acid contents on characteristics of ester-derived BaFe12O19 powder

The single domain size of BaFe₁₂O₁₉ powder with crystallite sizes less than 200 nm was produced using a citric acid precursor method. Fe³⁺ and Ba²⁺, in a molar ratio of 12, were chelated by COOH⁻ in an aqueous solution. After ethylene glycol additions, esterification, dehydration, and calcination led to the formation of ester-derived BaFe₁₂O₁₉ powder. High pH and/or high citric acid contents in the starting solution are required to complete chelate metallic ions in the solution and to form pure barium ferrite powder at 1073 K. Pure single magnetic domain BaFe₁₂O₁₉ particles of M(30 kOe)≈54 emu/g, M_r≈28 emu/g, and H_c≈3.7 kOe were produced using [citric acid]/[metallic ions]=1.5 and pH7.     

Effect of a magnetic field on the starting stress and mobility of individual dislocations in silicon

The strong effect of a magnetic field on the starting stress and mobility of individual dislocations is discovered in silicon grown by the Czochralski method with a high concentration of dissolved oxygen. It is shown that exposure of dislocations preliminarily introduced into the sample to a magnetic field considerably reduces the starting stresses for the motion of these dislocations. The effect is not observed in samples with a low oxygen concentration. It is assumed that the magnetic field induces singlet-triplet transitions in thermally excited states of silicon-oxygen complexes in the dislocation core, thus stimulating a change in the state (atomic configuration) of oxygen already located at dislocations. As a result, the mean binding energy of oxygen with a dislocation decreases.     

Study of the viscoelastoplastic deformation of an element of a body with a three-branch loading path

Institute of Mechanics, Academy of Sciences of the Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 27, No. 12, pp. 26–33, December, 1991.     

Completeness and unbiased estimation of mean vector in the multivariate group sequential case

We consider estimation after a group sequential test about a multivariate normal mean, such as a χ² test or a sequential version of the Bonferroni procedure. We derive the density function of the sufficient statistics and show that the sample mean remains to be the maximum likelihood estimator but is no longer unbiased. We propose an alternative Rao-Blackwell type unbiased estimator. We show that the family of distributions of the sufficient statistic is not complete, and there exist infinitely many unbiased estimators of the mean vector and none has uniformly minimum variance. However, when restricted to truncation-adaptable statistics, completeness holds and the Rao-Blackwell estimator has uniformly minimum variance.     

On the possibility of applying kinoform elements in mirror projectors for EUV lithography

The potential of the technology of reflective diffraction (holographic) optical elements intended for the EUV range is considered, and their application in projection lithography is discussed.     

Study of HfSiO film prepared by electron beam evaporation for high-k gate dielectric applications

The purpose of this paper is to report some experimental results with HfSiO films formed on silicon substrates by electron beam evaporation (EB-PVD) and annealed at different temperatures. The images of atomic force microscope (AFM) indicated that HfSiO film annealed at 900 °C was still amorphous, with a surface roughness of 0.173 nm. X-ray photoelectron spectroscopy (XPS) analysis revealed that the chemical composition of the film was (HfO₂)₃(SiO₂) and Hf-Si-O bonds existed in the annealed film. Electrical measurements showed that the equivalent oxide thickness (EOT) was 4 nm, the dielectric constant was around 6, the breakdown voltage was 10 MV/cm, the fixed charge density was −1.2 × 10¹² cm⁻², and the leakage current was 0.4 μA/cm² at the gate bias of 2 V for 6 nm HfSiO film. The annealing after deposition effectively reduced trapping density and the leakage current, and eliminated hysteresis in the C-V curves. Annealing also induced SiO₂ growth at the interface.