Optical Properties of Pure and Eu Doped ZnSe Films Deposited by CSVS Technique

Pure (ZnSe) and europium doped (ZnSe:Eu) zinc selenide films were evaporated onto glass substrates using the close-spaced vacuum sublimation (CSVS) technique at different deposition conditions (substrate temperature). The fundamental optical parameters such as optical density, extinction coefficient, refraction index, real and imaginary parts of optical dielectric constant, band gap were evaluated in transparent region of transmittance and absorbance spectrum. Optical spectroscopy analysis shown that in both cases deposited films had a high level of transmittance values (55-65 % for ZnSe films and 80-90 % for ZnSe:Eu films). Moreover, evaluated values of the films optical band gap were in the range of Eg = (2.63-2.69) eV for ZnSe films and Eg = (2.77-2.81) eV for ZnSe:Eu for films with increasing of the films substrate temperature. Fourier-transformed infra-red (FTIR) analysis of deposited ZnSe and ZnSe:Eu films shown that all investigated samples are well-crystalline and identified vibrations are typical for II-VI semiconductors

Correlated Interball/ground-based observations of isolated substorm: The pseudobreakup phase

International audienceWe study the isolated substorm that occurred after a long quiet period, which showed all of the substorm signatures except for the first half hour of the expansion phase, which could be characterized as a pseudobreakup sequence, rather than a full-scale substorm onset. During the considered event, the substorm's instability leads to a current disruption, which starts at the near-Earth plasma sheet and then propagates tailward. Based on auroral observations, the analysis of geosynchronous plasma injections, and the plasma sheet observations at ~15 RE at the meridian of auroral substorm development we show that (1) before and probably during "pseudobreakup phase", the plasma sheet stayed cold and dense, (2) during the pseudobreakup phase, particle injections at 6.6 RE were only seen in unusually low energy components, and (3) the electron precipitation into the ionosphere was very soft. We conclude that the basic difference between pseudobreakups and "real" substorm activations was found in the low energy of all manifestations. We suggest that high density and low electron temperature in the plasma sheet are the reasons for low energization in the magnetic reconnection operated on closed field lines in the plasma sheet, as well as the weak field-aligned acceleration, as predicted by the Knight's relationship. The low Hall conductivity could then be the reason for the weak ground magnetic effects observed. This explanation suggests that the role of the ionospheric conductivity is "passive" as the plasma sheet, rather than the ionosphere, controls the development of the magnetospheric instability