Evolution of the Electroluminescence Spectra and the Acoustic Emission of the Epitaxial Structures of GaAsP

The dependence of the spectral position of the electroluminescence bands of epitaxial light-emitting diode n ⁺–n–p structures (GaAs_0.15P_0.85) on the density of a direct heterojunction current at different successive instants of time — before an acoustic emission and after it — has been revealed. The shifts of the electroluminescence bands accompanied by acoustic emission can be divided into three types according to the density of the current: (1) short-term shifts due to relaxation of the defect structure of a sample — at relatively low currents, (2) the magnitude of the reverse shift being determined by the current density — at large currents, and (3) formation of an IR band (1.5–1.1 eV) with irreversible degradation changing in the red (1.75 eV) and green (2.19 eV) bands of the electroluminescence spectrum — at ultrahigh currents (100–200 A/cm²).     

Study on the impact of polar stratospheric clouds on high resolution mid-IR limb emission spectra

Satellite observations of polar stratospheric clouds (PSCs) in the mid-infrared by high resolution limb emission spectrometers like the Michelson Interferometer for Passive Atmospheric Sounding have been simulated. For particles with radius the scattered tropospheric radiance accounts for a significant part of the continuum signal and leads to absorption line features overlaid over the stratospheric emission spectrum. The scattered radiance shows a strong dependence on particle size up to about radius with a maximum around 3-4. The contribution of scattered radiation depends heavily on tropospheric cloud coverage and earth surface temperature. Distinction of PSCs of different composition is possible for small particles due to differences in the imaginary part of the refractive index. For particles with radii between 1 and the simulated spectra for various PSC compositions differ due to different real parts of the refractive index. For larger particles no distinction is possible any more. Solar radiance scattered by PSCs is important for wavenumbers larger than about . For a forward scattering geometry with 30° between the position of the sun and the limb viewing direction solar contribution exceeds the terrestrial scattered radiation by about a factor of 10.     

Luminescence in GaN co-doped with carbon and silicon

GaN samples, containing various concentrations of carbon and doped intentionally with silicon, have been grown heteroepitaxially on sapphire using metal-organic-chemical-vapor deposition. Previous electrical and optical data, together with Density Functional calculations, have suggested that carbon is incorporated at acceptor and donor substitutional sites in this material; the relative importance of each is determined by the Fermi level position and the growth conditions. Here the luminescence behavior of these materials is examined in more detail, including spectral, temperature, and time dependences under ultraviolet light and electron beam excitation conditions. Particular attention is given to the commonly observed “yellow band” at , a blue luminescence at seen only in samples where carbon is the majority dopant, and ultraviolet bands near . Our data suggest that the latter two bands are both donor-acceptor related with the final state being the negatively charged state of a carbon atom substituting for nitrogen. In samples where carbon is the majority dopant, extended luminescence excitation at low temperatures results in large changes in the brightness of the yellow and blue luminescence bands. These effects are similar to other recent observations of luminescence metastability in high resistivity GaN, and we suggest that carbon plays a crucial role in this phenomenon.     

Analysis of the hot bands in the 2ν9 band region of propyne-d3

The rovibrational spectrum of 2ν₉ band of CD₃CCH is overlapped by two prominent hot bands identified as (2ν₉⁰+ν₁₀^±1)(E)←ν₁₀^±1(E) and 3ν₉^±1(E)←ν₉^±1(E), where ν₁₀ and ν₉ are the degenerate CCC and CCH bending fundamental vibrations, respectively. Assignment of lines to the transitions of these hot bands were carried out with the help of the high-resolution spectra recorded at ∼195 K and at room temperature. Molecular parameters for these hot bands have been obtained from the rotational analysis of the partially resolved K-structure lines. Only Q-head of the third hot band , originating from the lower 2ν₁₀ state could be identified.     

Fast helium production in interactions of 3.7 A GeV <Superscript>24</Superscript>Mg with emulsion nuclei

We have studied the properties of the relativistic helium fragments emitted from the projectile in the interactions of ²⁴Mg ions accelerated at an energy of 3.7 A GeV with emulsion nuclei. The total, partial nuclear cross-sections and production rates of helium fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass and energy of the incident projectile nucleus are investigated. The yields of multiple helium projectile fragments disrupted from the interactions of ²⁴Mg projectile nuclei with hydrogen H, light CNO and heavy AgBr groups of target emulsion nuclei are discussed and they indicate that the breakup mechanism of the projectile seems to be independent of the target mass. Limiting fragmentation behavior of fast-moving helium fragments is observed in both the projectile and target nuclei. The multiplicity distributions of helium projectile fragments emitted in the interactions of ²⁴Mg projectile nuclei with the different target nuclei of the emulsion are well described by the KNO scaling presentation. The mean multiplicities of the different charged secondary particles, normally defined shower, grey and black ( n_s, n_g and n_b) emitted in the interactions of 3.7 A GeV ²⁴Mg with the different groups of emulsion nuclei at different ranges of projectile fragments are decreasing when the number of He fragments stripped from projectile increases. These values of n_i ( i = s, g, b and h particles) in the events where the emission of fast helium fragments were accompanied by heavy fragments having Z 3 seem to be constant as the He multiplicity increases, and exhibit a behavior independent of the He multiplicity.     

Exact eigenstates for a class of models describing multiphoton processes in the presence of seven bosonic modes

With recent advances in Bose-Einstein condensation (BEC)[1—3], there has beenmuch interest in nonlinear processes in the various disciplines of physics, such asnonlinear multi-wave mixing processes[4]. Now, great efforts are devoted to constructingthe nonlinear quantized models to numerate the energy spectra and eigenstates of thesenonlinear processes[5—8]. But there still remain some problems with regard to interactionsamong several bosonic modes, for example, how to explicitly obtain the…     

High Refractive-Index Microspheres as Optical Cavity Structure

Microspheres of refractive index of n_D > 2.0 have been investigated. The organic-inorganic hybrid microspheres of n_D = 1.72 were prepared by the vibrating orifice technique using titanium-tetra-n-butoxide (TTBu) and diphenyldimethoxysilane (DPhDMS). For lasing demonstration, Eu³⁺-doped microspheres were prepared using europium (III) thenoyltrifluoroacetonate [Eu(TTFA)₃] as the dopant. The particles have good spherical shape, smooth surface and high optical transparency. The diameters of the particles could be controlled to within 0.1 m. Subsequent heating of the microspheres at 550°C under oxygen atmosphere resulted in an increase in the refractive index up to n_D = 2.6 with retention of the spherical shape. Resonant emission was confirmed from Eu^{3 +}-doped microspheres after heating at 400–550°C, by pumping with the 514.5 nm line of a CW- Ar⁺laser.     

IR spectra,conformational lability,and intermolecular interactions in long-chain aliphatic compounds

Investigations of the conformational lability and intermolecular interactions in long-chain aliphatic compounds (LACs), namely, in carboxylic acid derivatives (alkyl- and alkoxybenzoic acids; alkylcyclohexanecarboxylic acids and their completely or partially fluoroalkyl-substituted derivatives), 4-cyano-4-p-alkoxybiphenyls, 4-cyano-4-p-alkylbiphenyls, and cholesterol p-n-butyloxybenzoate are reviewed. Major attention is paid to experimental and theoretical IR spectroscopy data. Differential thermal analysis, polarization microscopy, and X-ray diffraction data are also taken into account. A more detailed treatment is presented on IR spectrum simulation based on data about the conformational lability of molecules and their specific (H-bonding) intermolecular interactions. The first mechanism is responsible for the conformational type of polymorphism in LACs and for the structure of the latter in solid crystal (SC) and liquid crystal (LC) states and in isotropic liquids (ILs). The second mechanism complements the structure-forming aspect of polymorphism in carboxylates, which is due to a rearrangement of hydrogen bond systems in H-complexes during polymorphic transitions to the LC and IL states. Both mechanisms are reflected in IR absorption spectra. A more adequate interpretation is possible in order to explain the many spectral features associated with the structure of LAC polymorphs and their H-complexes if these mechanisms are taken into account.Original Russian Text Copyright © 2004 by L.M. BabkovTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 389–397, May–June, 2004.     

Surface diffusion of dysprosium on the W(1 1 1) facet

Diffusion of dysprosium on the (1 1 1) facet of a tungsten micromonocrystal was investigated by means of spectral analysis of field emission current fluctuations. The experimental spectral density functions of the current fluctuations were analysed by using Gesley and Swanson’s theoretical spectral density function, which enables to determine the surface diffusion coefficient D for dysprosium. Derived from the temperature dependence of D, the diffusion activation energy E is presented for some Dy coverages θ_(1 1 1). In the temperature range 400–600 K, the E first drops from 1.25 eV per atom at θ₍₁₁₁₎≈0.25 ML to 0.48 eV per atom at θ₍₁₁₁₎≈1 ML (corresponding to the minimum of the work function of the system), then increases to 1.03 eV per atom at θ₍₁₁₁₎≈1.3 ML. The results are discussed from the aspects of the substrate structure and interaction in the adsorbed layer.