Electron flow enhancement with a diamond membrane

Secondary electron emission from 2.5-to 5.0-μm thick diamond films (membranes) is considered. The process is studied in the reflection regime, where secondary electrons leave the front surface of the membrane exposed to primary electrons, and in the transmission regime, where primary electrons cause secondary emission from the opposite surface. The secondary emission coefficient is determined based on the behavior of 0.1-to 30-keV electrons in the solid. In the reflection regime, the secondary emission coefficient may be higher than 100 for electron energies of about 3 keV; in the transmission regime, it is no more than 5 even for 30-keV electrons. The emissivity of the membranes in the transmission regime can be improved, specifically, by using porous membranes, which allow one to obtain characteristics similar to those in the reflection regime. Experimental data obtained agree with calculations. The production of diamond films, including porous membranes, is described.     

Flow of rarefied gases in a capillary screen at different temperatures

An experimental study was made of the flow of the gases He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CO₂, and CH₄ in the range of Knudsen numbers of 10⁴–10^?1 at room temperature in a capillary screen. A study was also made of the flow of a number of inert and diatomic gases at temperatures of 77.2 and 194.7 °K in an orifice and in a capillary screen. The relative flow rates were determined in the free-molecular mode of flow. The coefficients of accomodation of tangential momentum are calculated for the gases studied at different temperatures.     

Structural, electronic and magnetic properties of η carbides (Fe3W3C, Fe6W6C, Co3W3C and Co6W6C) from first principles calculations

First-principles FLAPW-GGA calculations have been performed with the purpose to determine the peculiarities of the structural, electronic, magnetic properties and stability for a family of related η carbides M₃W₃C and M₆W₆C (where M=Fe and Co). The geometries of all phases were optimized and their structural parameters, theoretical density, cohesive and formation energies, total and partial densities of states, atomic magnetic moments have been obtained and analyzed in comparison with available theoretical and experimental data.     

Electronic Structure,Mechanical and Dynamical Stability of Hexagonal Subcarbides M<Subscript>2</Subscript>C (M = Tc,Ru, Rh,Pd, Re,Os, Ir,and Pt): Ab Initio Calculations

Ab initio calculations were used to study the properties of a series of hexagonal (Fe₂N-like) subcarbides M₂C, where M = Tc, Ru, Rh, Pd, Re, Os, Ir, and Pt, and to calculate their equilibrium structural parameters, electronic properties, phase stability, elastic constants, compression modulus, shear modulus, Young’s modulus, compressibility, Pugh’s indicator, Poisson ratio, elastic anisotropy indices, and also hardness, Debye temperature, sound velocity, and low-temperature heat capacity. It is found based on these results that all the subcarbides are mechanically stable; however, their formation energies E_form are positive with respect to a mixture of d-metal and graphite. In addition, the calculation of the phonon spectra of these subcarbides shows the existence of negative modes, which indicates their dynamical instability. Thus, a successful synthesis of these subcarbides at normal conditions is highly improbable.     

The paramagnetic state (μ+e−) in silicon and tellurium at high temperature

The paramagnetic state (⁺e^–) in Si and Te was observed in a longitudinal magnetic field. The mean lifetimes of these states were obtained: _Si = 1.45(3) s, _Te = 12.5(8) s at 290 K, _Te = 12(2) s at 250 K.