Thermally activated de-excitation of the EL2 metastable state in GaAs

Measurements of absorption in the near infrared have been performed on n-type and undoped semi-insulating GaAs containing EL2 the main native defect in GaAs. The whole band of absorption related to EL2 disappeared after 1 μm light illumination when the crystal was cooled to helium temperatures. Measurements of the thermally activated recovery of EL2 absorption have been made. The rate of the de-excitation is well described by the formula: r = 1.7 · 10¹² · exp (−0.36 eV/kT) + 1.6 · 10⁻⁹ · n · exp (−0.085 eV/kT) s⁻¹ where n [cm⁻³] is the concentration of free electrons.     

Thermally activated delayed fluorescence host materials based on triphenylphosphine oxide derivatives

Abstract

Novel thermally activated delayed fluorescence (TADF) host molecules for blue electrophosphorescence were developed by combining the electron donor acridine derivatives with the electron acceptor triphenylphosphine oxide unit in a single molecule based on density functional theory. We obtained the energies of the first excited singlet (S₁) and triplet (T₁) states of the TADF materials by performing procedures in accordance with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to the ground state using dependence on the charge transfer amounts for the optimal Hartree-Fock percentage in the exchange-correlation of TD-DFT. Using DFT and TD-DFT calculations, the significant separation between the HOMO and LUMO caused a small difference in energy (ΔE_ST) between the S₁ and T₁ states. The host molecules retained high triplet energy and showed great potential for use in blue phosphorescent organic light-emitting diodes. The results also showed that these molecules are promising TADF host materials because they demonstrate a low barrier to hole and electron injection, balanced charge transport for both holes and electrons, and small ΔE_ST.     

Thermally activated stress relief in garnet layers grown by liquid phase epitaxy

The lattice misfit of (Lu, Tb)₃Fe₅O₁₂ epitaxial layers grown in compression on Gd₃Ga₅O₁₂ substrates has been found to decrease as a result of annealing at temperatures between 1000 and 1300°C. The deformation rate is thermally activated and depends on the degree of compressive misfit stress at the annealing temperature, the layer thickness and the reducing nature of the anneal atmosphere. Layers which were in tension at the annealing temperature (obtained by using Y₃Fe₅O₁₂ as the substrate material) did not exhibit stress relief. The process has been found to occur nonhomogeneously by the formation of regions of almost total relief which grow and multiply with continued annealing. The shape symmetry of these regions is consistent with dislocation climb in {112} planes. The results are interpreted in terms of a mechanism involving dislocation climb loops (∽1μm diameter) which develop as a result of the formation of oxygen vacancies.     

Defect Structure of Zirconium Carbide

Crystallography Reports - In the equilibrium state, carbon vacancies in the zirconium carbide lattice are ordered (spaced by maximum distances from each other) to minimize the lattice energy, which...     

Thermally Stimulated Luminescence of Montmorillonite Clay

X-ray excited luminescence (XL) spectra of montmorillonite clay at RT showed a broad emission band around 380 nm with two shoulders at 340, 450 nm eitherside two sharp peaks and two shoulders are seen at 465, 487, and 548, 576 nm, respectively. The 548 and 576 nm peaks enhanced their intensity at LNT. Whereas thermally stimulated luminescence (TSL) revealed an intense glow peak at 355 K and a weak shoulder around 400 K. Room temperature annealing studies indicated that the 355 K glow peak is not as stable as 400 K shoulder which turns out to be a peak on RT annealing. The X-ray excited luminescence has been attributed to radiative recombination of electrons with holes which are associated with SiO^3-₄, AlO^4-₄ radicals and divalent impurities available in the naturally available clay. TSL is also understood on similar lines. Glow peak reactions are proposed tentatively and their trap parameters have been calculated.     

Microstructures on Zirconium Trisulphide Single Crystals

Physical vapour transport grown single crystals of zirconium trisulphide have been examined by optical microscope, and the study of growth patterns on their finished surfaces reveal the screw dislocation mechanism by which the crystals have grown.     

Photoluminescence from Thermally Treated CaO Single Crystals

Photoluminescence emission and excitation spectra of CaO single crystals change strongly by annealing in air while rapid quenching does not produce new bands. The increase of an excitation band at 340 nm and the shift of the emission peaks are the main annealing effects observed. These changes, which are reduced by increasing the crystal thickness, have been found to be localized in the surface.     

Thermally stimulated depolarisation current in sodium-potassium borosilicate glass

The thermally stimulated depolarisation current (TSDC) has been measured in sodium-potassium borosilicate glass of composition 15% Na₂O, 13.64% K₂O, 19.47%B₂O₃ 51.89% SiO₂. Gold and aluminium electrodes were used for these measurements and TSDC curves of NaK borosilicate glass were obtained by varying the polarising temperature T_p and polarising voltage V_p in a systematic manner. The observed peaks were remarkably reproducible. Partial heating experiments were performed to investigate the activation energy of the thermally released carriers. By an analysis of the current peaks, the relaxation time τ(T) and hence the activation energy of relaxation of the carriers were determined. Results of dc measurements on the same samples are presented for comparison.     

Thermally Stimulated Depolarisation Currents in Urea and Thiourea

Thermally stimulated depolarisation currents (TSDC) are observed in Urea and Thiourea. Urea gives a single TSDC peak at 278° K, while for Thiourea there is a prominent peak at 290°K and the spectrum below 290°K is little complicated. The prominent peaks are interpreted in terms of molecular relaxations. For Urea, space charge polarisation peak above RT was also observed.     

Thermally Stimulated Discharge Current Studies in Thin Films of Polyacrylamide

TSDC of pure polyacrylamide films of thickness 22 μ grown by isothermal solution growth technique has been studied as a function of polarizing field and polarizing temperature at a constant heating rate of 0.09 K s¹ In these studies only one TSDC peak was observed and the temperature corresponding to this peak was found to be independent of polarizing field strength but dependent on polarizing temperature. The activation energies, relaxation parameters and charge associated with the peak were evaluated. The origin of TSDC is discussed.     

Infrared Optical Characterization of Thermally Oxidized CuInSe2 Single Crystals

Infrared reflectivity spectra of thermally oxidized CuInSe₂ single crystals are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. A Kramers-Kronig analysis of the spectra reveals seven vibrational modes with frequencies which agree with mode frequencies in In₂O₃. No vibrational modes due to Cu–O and Se–O bonds could be observed. The results obtained are compared with previous studies of oxidized CuInSe₂ crystals.     

Thermally oxidized zirconium nanostructured films grown on Si substrates

Zirconium thin films grown on Si substrates by a planar magnetron sputtering system were thermally oxidized at oxygen ambient within 523‐823 K resulting in zirconium oxide films with various stoichiometries. XRD analysis of the ex situ oxidized films revealed the phases at different oxidation temperatures. To achieve a reasonable fit between the experimental and SIMNRA simulated RBS spectra of the prepared samples; it was required to introduce a SiO₂buffer layer in the simulated target between Si substrate and ZrO₂ film. The presence of this intermediate SiO₂ layer was confirmed by observation of SiO₂ phase in the XRD patterns of all the thermally oxidized samples. Using RBS analysis data, the effect of oxidation temperature on the stoichiometry of zirconium oxide films and thickness of ZrO_xand SiO₂ films were investigated. XRD patterns of thermally oxidized Zr films also revealed that crystallization of zirconium oxide films was initiated at about 673 K and was almost completed at 823 K. Diffusion of oxygen atoms through surface layer was investigated and the effective activation energy for oxygen mass transport was estimated to be 1.75 eV using RBS data and Arrhenius relation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermally stimulated currents in disordered solids at fractional heating

Thermally stimulated currents (TSCs) in disordered solids, registered at fractional sample heating, are investigated theoretically. The Gobrecht–Hofmann method of determining trap distribution in energy gap is extended to the case of significant carrier retrapping. Two specific cases, when the TSCs are limited either by carrier recombination or by carrier neutralization on collecting electrode, are considered. The accuracy of proposed method is estimated from the analysis of TSC curves, calculated numerically for exponential and Gaussian trap distributions.     

非水解溶胶-凝胶法制备硅酸锆晶须初探

以无水四氯化锆为锆源,正硅酸乙酯(TEOS)为硅源,氟化锂为矿化剂,乙醇为溶剂,炭黑为还原剂,采用非水解溶胶-凝胶法制备硅酸锆晶须,研究了炭黑种类与坩埚密封程度对硅酸锆晶须生长的影响.结果表明:相对于比表面积过小的炭黑8001或比表面积过大的超级活性炭,竹炭更利于硅酸锆晶须的生长;采用敞开坩埚方式热处理时能获得直径为30 ～ 90 nm,长径比为6～15,沿[001]方向择优生长的硅酸锆晶须,半敞开或密封的反应体系均不能形成硅酸锆晶须.     

Morphology and Structure of Thermally Induced Microdefects in High-Temperature Treated Czochralski-Silicon

The morphology and structure of amorphous precipitates grown by thermal annealing in the temperature range from 1100 °C to 1200 °C are investigated by means of highvoltage electron microscopy. It is shown that there exist some characteristic morphological types which are equivalent to the equilibrium forms of the cubic diamond structure itself or which can be derived from these. For the growth process an oxygen diffusion-controlled mechanism is deduced. Structural aspects are discussed on the basis of this mechanism.     

非晶前驱体碳热还原法制备超细硼化锆粉体

利用ZrO2-B2O3-C反应体系碳热还原的基本原理,分别选用八水合氧氯化锆(ZrOCl2·8H2O)、硼酸(H3BO3)和蔗糖(C11H22OH)作为ZrO2、B2O3和C的来源,柠檬酸(C6H8O7)为络合剂,采用溶胶-凝胶法制得硼化锆的非晶前驱体,经过碳热还原反应热解制备出超细硼化锆粉体.分别研究了硼酸、蔗糖用量和热解温度对产物的物相组成的影响.采用红外光谱仪、热重-差热分析仪、X射线衍射仪、比表面积分析仪和扫描电镜对硼化锆前驱体及热解产物进行表征和分析.结果表明:初始原料中八水合氧氯化锆:硼酸:裂解碳(物质的量比)=1:4:10时,可在相对较低温度下(1300℃)热解得到硼化锆粉体,且随着热解温度的升高硼化锆粉体的纯度也越高.当热解温度为1600℃、热解时间为2h时碳热还原反应完成,产物中只有硼化锆;硼化锆颗粒呈球形或类球形,粒径分布在0.2～0.6 μm之间、比表面积为74 m2/g.     

The Influence of the Specimen Surface on Thermally Induced Structural Changes

Transmission electron microscopy has been particularly fruitful for studying phase transformations and other thermally induced structural changes. Investigations of such reactions can be carried out either by in-situ hot stage electron microscopy using thin foils or by monitoring the structure after various times of annealing of bulk specimens outside the microscope. Observations after annealing clearly provide no information about the temporal relationship between changes which have occurred. Dynamic studies in the microscope are capable of providing this information, however, the proximity of the foil surface is a complicating factor.