New method of determining the young’s Modulus of (Ga,Mn)As nanowhiskers with a scanning electron microscope

Arrays of (Ga,Mn)As nanowhiskers have been grown by molecular-beam epitaxy. The scanning electron microscopy study of the surface morphology of the samples has revealed the appearance of mechanical vibrations of individual nanowhiskers. To describe the vibrations, a model has been developed for the determination of the Young’s modulus of (Ga,Mn)As nanowhiskers.     

Computer simulation of the structure and raman spectra of GaAs polytypes

The structure, energy of formation, and Raman spectra of several polytypes (3C, 2H, 4H, and 8H) of gallium arsenide GaAs have been investigated using quantum mechanical calculations based on the local density functional theory. It has been found that the energy of the formation of hexagonal polytypes increases with an increase in the length of the periodicity and approaches the value corresponding to the ground state, i.e., to the structure of the 3C polytype. It has been shown that the calculated frequencies of normal vibrations of different polytypes are consistent, with good accuracy (±6 cm^?1), with the scheme of folding of the phonon branches. In the calculated Raman spectra of the polytypes, there are new lines (forbidden in the spectrum of the 3C polytype) which can serve as characteristic lines of other polytypes. Similar lines can be found in the Raman spectra of GaAs nanowhiskers. This result has opened up new prospects for the application of Raman spectroscopy to the characterization of the structure of these nano-objects.     

Self-organization of lamellae and permeability of microporous oriented polypropylene films

The effect of the annealing temperature T _ann of extruded polypropylene films on the structure of membranes prepared by the uniaxial extension of annealed films with the subsequent thermal fixation has been investigated using small-angle X-ray scattering and scanning electron microscopy. It has been shown that an increase in the permeability of membranes with increasing temperature T _ann is due to the self-organization of elements of the lamellar structure of the polymer as a result of the ordering and aggregation of particles.     

Transverse field effect in graphene ribbons

It is shown that a graphene ribbon, a ballistic strip of carbon monolayer, may serve as a quantum wire whose electronic properties can be continuously and reversibly controlled by an externally applied transverse voltage. The electron bands of armchair-edge ribbons undergo dramatic transformations: The Fermi surface fractures, Fermi velocity and effective mass change sign, and excitation gaps are reduced by the transverse field. These effects are manifest in the conductance plateaus, van Hove singularities, thermopower, and activated transport. The control over one-dimensional bands may help enhance effects of electron correlations, and be utilized in device applications.     

Metastable modifications in mercury diiodide nanocrystals

The formation of the HgI₂ crystalline phase in pores of various porous matrices and on their surfaces was studied. Based on the analysis of the evolution of the HgI₂ optical spectra and electron and atomicforce microscopy data, it was shown that the formation of microcrystals of the stable red α modification is preceded by the formation and growth of particles of metastable yellow (β′) and orange modifications. The absorption edge of the β′ phase at T = 77 K is formed by excitonic transitions with an energy of ～2.7 eV. The Raman spectra of the β′ phase were compared to the spectra of known metastable yellow modifications.     

Design of the New Control System for Linac-200

Physics of Particles and Nuclei Letters - The construction of an experimental facility with test electron beams is under way at the Dzhelepov Laboratory of Nuclear Problems at the Joint Institute...     

TOF-SIMS 5 instrument sensitivity to matrix elements in GeSi Layers: Analysis based on recording of complex secondary ions

Ge _x Si_{1 − x} layers are investigated by means of secondary ion mass spectrometry (SIMS). Experimental results obtained with the use of a TOF-SIMS 5 instrument are presented. To surmount the so-called matrix effect, SIMS analysis is performed by using complex secondary ions: Ge₂⁻, CsGe⁺, and Cs₂Ge⁺.     

Properties of Silver Nanoparticles in the Presence of Dysprosium

Technical Physics - Various methods of binding rare-earth metal ions with nanoparticles make it possible to obtain materials with new properties. The “green” synthesis method has been...     

Asymptotics of the necessary sample size under small error probabilities

The asymptotics of the necessary sample size is considered in testing close hypotheses when the error probabilities vanish. Proceedings of the XVII Seminar on Stability Problems for Stochastic Models, Kazan, Russia, 1995, Part III.     

Components of the low-temperature heat capacity of rare-earth hexaborides

The temperature dependence of heat capacity C _p(T) was studied for nine rare-earth hexaborides MB₆(M=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) at temperatures of 5–300 K. Using the correspondence principle for lattice heat capacities of isostructural compounds, the lattice contribution C ₁(T) and the excess contribution ΔC(T) to the heat capacity of the hexaborides were determined. The lattice heat capacity C ₁(T) is represented as the sum of the Debye contributions of the metal and boron sublattices: C ₁(T)=C _M (T)+6C _B(T). The Debye temperatures π_M and π_B of the metal and boron sublattices were determined. The anomalies in the excess heat capacity ΔC(T)=C _p (T)?C ₁(T) are related to the magnetic ordering effects, the Schottky contribution, and the Jahn-Teller effect.