Effect of isotropic stress on dislocation bias factor in bcc iron: an atomistic study

The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a₀/2〈1 1 1〉{1 1 0} screw, a₀/2〈1 1 1〉{1 1 0} edge and a₀〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom.     

Study of gold nanocluster sputtering under 38-keV Au ion bombardment by a classical molecular dynamics method

The computer simulation of the interaction of 38-keV Au₁ ions with isolated spherical Au _N nanoclusters of diameters 2.6 and 18 nm is performed in the framework of the classical molecular dynamics (MD) method. The distribution of the absorbed energy ε per one atom of the irradiated cluster and the sputtering yields are analyzed for different ratios of the nanocluster diameter D to the average projective range R _p of the bombarding ion. It is established that the small values of the absorbed energy (ε ? ε_max = E/N) are most probable for D < R _p, and either small (ε ? ε_max) or the maximum possible (ε ～ ε_max) values are mainly realized for D ≤ R _p. It is shown that the total sputtering yield depends weakly on the impact parameter. It is demonstrated for the first time that the irradiated cluster, as a whole, can be ejected by direct impact with a probability of approximately 6–13%. Such events are realized in the cases where the bombarding ion causes secondary cluster-atom emission in the dominant direction to a substrate, with the result that an unsputtered cluster fraction acquires momentum in the opposite direction. This recoil effect can be one of the mechanisms for desorption of nanoclusters deposited on the surface under ion (or cluster) bombardment.     

Measurement of spin-rotation parameters in elastic π + p scattering at a momentum of 1.62 GeV/c and calibration of a carbon polarimeter

Experimental data on the spin-rotation parameters A and R in elasticπ ⁺ p interaction were obtained for the first time at a momentum of p _π = 1.62 GeV/c. These data are necessary for unambiguously reconstructing the amplitude of pion-nucleon scattering and, hence, for deducing a correct spectrum of nonstrange baryon resonances. In order to obtain results for the polarization parameters A and R with the minimum possible systematic error, the carbon polarimeter used was preliminarily calibrated in a dedicated experiment; that is, the analyzing power was measured in proton-carbon scattering for incidentproton energies in the range T _p =0.7–1.3 GeV. The experimental data reported in the present article were obtained by a collaboration of researchers from the Petersburg Nuclear Physics Institute and Institute of Theoretical and Experimental Physics (ITEP, Moscow) at the ITEP synchrotron.     

Spectral dependent kinetics of the EHD luminescence in As-doped Ge

Following pulsed laser excitation of As-doped Ge with impurity concentrations between 10¹⁵-10¹⁷cm^-3, we observe the electron-hole drop (EHD) and excitonic luminescence decay. The spectrum resolved no-phonon (NP) EHD luminescence kinetics are found to depend on its spectral position. “Plateaus” on the kinetic curves for the high energy side of NP-spectrum are observed at high excitation. The data suggest this luminescence is due to the states which are in dynamical equilibrium during some time after excitation pulse.     

Microwave heating and evaporating of a large electron-hole drop in pure Ge

At the large microwave power level, we have observed a sharp increase of the m.w. absorption in magnetic field and an appearance of steps in the m.w. absorption kinetics. These steps are connected with the intense evaporation of drops caused by the m.w. field, which provides the existence of the dense cloud of free carriers surrounding the drop. The density of the cloud has been found to depend strongly on magnetic field.     

EHD size distribution in pure Ge at pulse optical excitation

The cyclotron resonance (CR) kinetics of free carriers surrounding electron-hole drops (EHD) was investigated in pure Ge (N_D = N_A = 10¹¹cm^?3). We observed the fast decay of the CR amplitude at the long delay time after the excitation pulse [1], that may be connected with intense evaporation of the drops, when the EHD radius has achieved the critical value. The method for investigation of EHD size distribution was proposed for case of pulse excitation. The Gaussian EHD size distribution has been found.     

Pincer ligands based on α-amino acids: V. New generation chiral receptors for the recognition of amino acid enantiomers in aqueous environment

Selective recognition of enantiomers of amino acids valine, methionine, phenylalanine, serine, and tyrosine by a binuclear copper complex with an azomethine obtained from 2,6-diformyl-4-methylphenol and L-valine was studied by means of spectrophotometry. The binding constants of individual enentiomers were estimated for valine, phenylalanine, methionine, serine, and tyrosine, and the enantioselectivity factors were evaluated. The isomers of serine and tyrosine (with respect to the first stage) were recognized with a considerable enantioselectivity (1.34 and 5.46 respectively), whereas the binding constants of valine and phenylalanine enantiomers are virtually indistinguishable.     

Positron annihilation in vacancies at grain boundaries in metals

The behavior of vacancies in selected coherent grain boundaries (GBs) in Fe and Ni is studied by means of molecular dynamics simulations. Corresponding positron lifetimes are calculated using the atomic superposition method. There is a difference between the vacancy behavior in Fe and Ni in dependence on temperature. In Ni, vacancies at GBs appear to diminish substantially their free volume (and lifetime) with the increasing temperature, which can be attributed to ‘vacancy delocalization’. Contrary, GB vacancies remain stable up to apparently higher temperatures in Fe.     

Thermodynamical calculation of multiexciton complexes system in lightly doped Si: A contribution of excited states of the multiexciton complexes

We propose the ideal equilibrium approximation for the study of multiexciton complexes system. The composition of the system is calculated using the shell model. The resulting temperature dependences of the complexes concentrations in Si : P agree with the known experimental data. We also stress the role of the contribution of excited states of the complexes.     

Sandwich Double‐Decker Lanthanide(III) “Intracavity” Complexes Based on Clamshell‐Type Phthalocyanine Ligands: Synthesis,Spectral, Electrochemical,and Spectroelectrochemical Investigations

Phthalocyanine compounds of novel type based on a bridged bis‐ligand, denoted “intracavity” complexes, have been prepared. Complexation of clamshell ligand 1,1′‐[benzene‐1,2‐diylbis(methanediyloxy)]bis[9(10),16(17),23(24)‐tri‐tert‐butylphthalocyanine] (^clam,tBuPc₂H₄, 1 ) with lanthanide(III) salts [Ln(acac)₃] ? n H₂O (Ln=Eu, Dy, Lu; acetylacetonate) led to formation of double‐deckers ^clam,tBuPc₂Ln ( 2 a – c ). Formation of high molecular weight oligophthalocyanine complexes was demonstrated as well. The presence of an intramolecular covalent bridge affecting the relative arrangement of macrocycles was shown to result in specific physicochemical properties. A combination of UV/Vis/NIR and NMR spectroscopy, MALDI‐TOF mass‐spectrometry, cyclic voltammetry, and spectroelectrochemistry provided unambiguous characterization of the freshly prepared bis‐phthalocyanines, and also revealed intrinsic peculiarities in the structure–property relationship, which were supported by theoretical calculations. Unexpected NMR activity of the paramagnetic dysprosium complex 2 b in the neutral π‐radical form was observed and examined as well.