Investigation of a Contamination Film Formed by the Electron Beam Irradiation

Technical Physics - In the study of materials on electron probe devices in the field of action of the electron beam, a contaminating hydrocarbon film is formed, which affects the experimental...     

Application of transition radiation in a small dihedral angle to detection of relativistic particles

The features of transition radiation excited by a relativistic particle in a dihedral angle with an opening comparable to the angular divergence of transition radiation are considered. It is shown that the radiation distribution in the dihedral angle is more sensitive to the direction of emitting particle motion and to the position of the surface intersection by the particle, than the radiation excited when a plane surface is intersected. It is indicated that the spectral radiation density in the small dihedral angle is higher than the density of radiation excited when a plane surface is intersected. These features offer additional opportunities to use transition radiation in systems for measuring particle parameters.     

Effect of vibronically induced spin-orbit coupling of electronic ππ* states on nonradiative intersystem crossing: Naphthalene

The effect of (I) S ₁(¹ B _2u ) ? T ₁(³ B _1u ) and (II) S ₁ ? T ₂ (³ B _3g ) ? T ₁ transitions in naphthalene on the rate constant K _ST ^s of the S ₁ ? T ₁ nonradiative transitions to all triplet sublevels s = z, y, x of the T ₁ state has been investigated in the approximation of vibronically induced spin-orbit couplings, taking into account all out-of-plane vibrational modes. The shapes of the vibrational modes that are most active in these transitions are determined. The calculated values K _ST = (0.33–0.75) × 10⁷ s^?1, obtained with allowance for the I and I + II transitions, are consistent with the experimental values (K _ST)_exp found by different researchers. It is established in all calculation versions that K _ST > K _ST ^z > k _ST ^x . This relation is in qualitative agreement with the known magnetooptical data.     

Backscattering of Relativistic Electrons Incident on a Planar Foil at a Small Angle to Its Surface

Photographs of cross sections of an electron beam backscattered from a thin tungsten target have been obtained on a dosimetric film. The procession of images makes it possible to obtain the spatial distribution of backscattered particles. The angles of back reflection θ_br of electron beams from foils have been measured. A 7.4-MeV microtron has been used as a source of electrons. The experiments have been performed with a tungsten foil 386 mg/cm² (200 μm) thick and a tantalum foil 1328 mg/cm² (800 μm) thick. Particles have been injected at an angle of α = 10° to the foil surface. The Monte Carlo simulation of the scattering of relativistic electrons incident on a planar target at small angles to its surface has been performed. The spatial and energy distributions of backscattered particle fluxes both transmitted through the target and reflected from it have been calculated. The dependences of fluxes on the direction of injection of particles and on the material and thickness of the target have been considered.     

Optical Spectra of GaSe and GaS Crystals of Different Thicknesses

Physics of the Solid State - The transmission spectra of GaSe and GaS crystals of different thicknesses prepared by mechanical stratification of bulk crystals have been investigated. The...     

Optical investigation of the vertical diffusion of manganese in planar structures based on CdTe and Cd1 − x Mg x Te with ultrathin MnTe layers

The emission spectra of planar structures based on CdTe and Cd_{1 ? x} Mg _x Te containing periodically built-in MnTe layers with a nominal thickness of one monolayer have been investigated. The luminescence spectra and luminescence excitation spectra of manganese ions and excitons, as well as the dependences of the spectra on the temperature and magnetic field strength, are used to determine the actual distribution of manganese ions. The full width at half-maximum of the profile describing the change in the concentration of manganese in the growth direction of the structures is estimated to be 7–8 monolayers.     

Non-self-sustained discharge in nitrogen with a condensed dispersed phase

A non-self-sustained discharge in nitrogen with a condensed dispersed phase is studied experimentally for the first time under atmospheric pressure at room temperature. It is shown that macroparticles strongly affect the current-voltage characteristics as well as the stability of the discharge process. A numerical simulation of dust particle charging in nitrogen is carried out at room temperature and cryogenic temperatures under continuous medium conditions. It is shown that a considerable charge is accumulated at macroparticles in the nitrogen beam plasma. As the gas temperature decreases, the charge of macroparticles in nitrogen increases, while in argon their charge decreases. For this reason, the Coulomb interaction parameter for dust particles in nitrogen increases strongly upon a transition from room to cryogenic temperature, while in argon this parameter decreases. It is also shown that the characteristic time of dust particle charging is shorter than 1 μs for a beam current density of 90 μA/cm², while the neutralization of the charge takes milliseconds. Possible mechanisms of the influence of the dust component on the characteristics of non-self-sustained discharge are considered.     

Relaxation dynamics of Mn2+ intraion excitation in Cd0.5Mn0.5Te: Dependence on the optical pumping level

A study is reported of the Mn²⁺ intracenter 3d luminescence in a dilute Cd_0.5Mn_0.5Te magnetic semiconductor at pulsed excitations of up to 3.5 MW/cm². At high excitation levels and at a temperature of 77 K, the kinetics varies strongly over the emission band profile. The luminescence decay curve can be resolved into a fast and a delayed component, which correspond to the excitation of extended and localized states in the manganese ion system. The fast relaxation of the extended states is largely determined by the up-conversion. As the temperature is lowered, the contribution of the fast component at the center of the emission band and in its low-energy wing decreases because of the weakening role of the extended states lying above the mobility edge.     

Optical properties of a polymer host matrix containing mercuric iodide microcrystals

Microcrystals of mercuric iodide have been grown in a polymer matrix with pores 200 nm in diameter. The absorption and luminescence spectra indicate the formation of microcrystals of two (red and orange) modifications in the host matrix. The temperature dependence of the emission spectra and the evolution of absorption and emission spectra in the course of sample ageing have been studied. The evolution of the spectra is governed by the transition from the orange to red modification and the increase in size of microcrystals.     

Rapid luminescence saturation of the Mn2+ 3d shell in the Cd1−x MnxTe dilute magnetic semiconductor with a high manganese concentration

The dependence of manganese-ion intracenter-luminescence intensity on optical excitation level has been studied in the Cd_1−x Mn_xTe dilute magnetic semiconductor with 0.4<x<0.7. It is shown that the intracenter luminescence saturates due to effective nonlinear quenching already at low excitation levels. Mechanisms are proposed which can provide nonlinear quenching and offer a qualitative explanation for the temperature dependence of the luminescence saturation in samples with different manganese concentrations. Fiz. Tverd. Tela (St. Petersburg) 41, 49–53 (January 1999)