衬底对宽带隙CGS薄膜的影响

分别在Al∶ ZnO(ZAO)薄膜和Mo薄膜两种不同衬底材料上,采用“三步法”共蒸发工艺沉积了约0.8 μm厚的CuGaSe2(CGS)薄膜,用X射线衍射仪测量薄膜的织构,研究不同衬底材料对CGS薄膜的影响.在ZAO薄膜底电极上沉积的CGS薄膜的(112)衍射峰强度较Mo薄膜底电极上减弱,(220/204)衍射峰反而增强.     

Singlet Excitation Energy Migration in the Glassy and Single Crystalline States of 1,3-Diphenyl-5-(p-chlorophenyl)-2-pyrazoline

The crystal and molecular structure of the title compound were determined: a = 14.375(3), b = 11.534(3), c = 7.972(2) Å, α = 71.694(5), β = 79.125(5), γ - 74.861(5)°; space group PI. Refinement including all of the observed reflections (3145) leads to R = 0.086 (R_w= 0.074).

The molecular form in the crystalline state is fully extended in agreement with the suggestion by Birner et al. (Mol. Cryst. Liq. Cryst., 80, 11 (1982)), based on a NDDO-semiempirical calculation.

Whereas for the molecular form in the nematic liquid crystalline state a slightly parallel arrangement (～ 60°) of the dipole moment components perpendicular to the long axis is proposed, in the crystalline state these components are at an angle ～ 120° to each other, and somewhat antiparallel.

Preceding the melting point by approximately 10 degrees, DSC and thermal microscopy signals were observed; these depend eventually on solid-state polymorphism.     

Migration and Annihilation of Triplet Excitation Energy in the Charge-Transfer Anthracene-Tetrachlorophtalic Anhydride Crystal

Abstract

The emission spectra of the charge-transfer crystal of anthracene-tetrachlorophtalic anhydride were studied in the 1.7-300 K temperature range. Delayed fluorescence was observed over the whole temperature range. At temperatures below ～40 K it results from heterogenous (mobile exciton-trapped exciton) triplet-triplet annihilation. At higher temperatures it is due to homogenous triplet-triaplet annihilation. The existence of mobile excitons is also proved by the character of the ESR lines which are very narrow Lorentzians. The phosphorescence, observed only in the range 1.7–40 K, originates from at least two different kinds of traps with energies ～6 cm^?1 and ～140 cm^?1, respectively. The vibrational structure of the phosphorescence is identical to that of anthracene, with 0—0 band blue-shifted by ～400cm^?1. A kinetic model of trapping and detrapping of triplet excitons as well as the nature of the traps are discussed.     

Effect of an External Electric Field on Electronic Excitation Energy Transfer in Molecular Crystals

While several mechanisms can be imagined by which an external electric field can affect electronic excitation energy transfer in crystals, the simplest possibility involves changing the energy level spacings of neighboring molecules. Energy transfer from one molecule to another is affected by an energy mismatch or loss of resonance. In a band model, presumably valid at low temperatures, this loss of resonance decreases the exciton bandwidth and reduces the exciton group velocity. When the bandwidth is comparable to the inhomogeneous broadening, an abrupt decrease in the rate of energy transfer can be expected, reflecting the phenomenon of Anderson localization. At higher temperatures, the energy mismatch can be accommodated by phonon emission and absorption processes. The dependence of the energy transfer rate constant on electric field and temperature for the case of coherent energy transfer and for the limit of incoherent energy transfer is predicted for a simple model system.     

Dependence of Energy Band Gap and Lattice Constant of III-V Semiconductors on Electronegativity Difference of the Constituent Elements

The dependence of the energy bandgap and lattice constant of III-V semiconductors on the electronegativity difference of the constituent elements were investigated. Some empirical expressions for estimating the energy bandgap and lattice constant with respect to solid compositions for mixed crystals were obtained. The results for some material systems predicted by electronegativity difference approach (ENDA) are compared with those obtained experimentally and those calculated by classical interpolation techniques (IT). The agreement between them is quite good, and it is demonstrated that ENDA is a simple and useful method for designing III-V mixed crystals.     

Excitation pattern of the blue emission in Ge-doped silica

The luminescence of Ge-doped glassy SiO₂ has been investigated at room temperature using a deuterium lamp as the excitation source in the ultraviolet and vacuum ultraviolet energy range. Two emission bands are observed around 3 and 4 eV as the excitation increases from 4.5 to 8 eV. The peak shift and bandwidth broadening of the emission around 3 eV indicate the overlapping of several bands. We carried out a Gaussian best-fit approach of the detected spectra and extracted the excitation spectra of three distinct emission: a 2.9 eV band with two excitation channels at 4.7 and 5.3 eV and no contribution above 6 eV and the well-known composite β-band (3.1 eV). The latter is resolved into two Gaussian components whose excitation spectra present three main excitations around 5.1, 6.5 and 7.3 eV.     

Proton Spin Relaxation in the Rod Micelles of Type I CM Mesophases

The dynamics of the hydrocarbon chains in lyotropic nematic type I cylindrical micellar liquid crystals prepared with D₂O has been selectively studied by Zeeman and rotating frame nuclear spin-lattice relaxation. The measurements of the proton spin-lattice relaxation time T ₁ as a function of frequency and temperature demonstrate that relatively fast local fluctuations of individual amphiphilic chains relax the proton spins at high magnetic fields. This process is facilitated also by the rapid diffusive motion of the chains within the micellar units. The rotating frame Zeeman relaxation time T _1x, is associated at room temperature with a long correlation time of ~11 μs. Slow micellar orientational fluctuations have been assigned to this characteristic time.     

Proton Spin-Lattice Relaxation Dispersion Study of the Ferroelectric Smectic Phases in Dobambc

The frequency dispersion of the proton spin-lattice relaxation rates T^?1 ₁ in the ferroelectric smectic phases of DOBAMBC has been determined in the MHz region and analyzed in terms of the order fluctuations, self-diffusion, and rotational contributions to T^?1 ₁. In the smectic C* phase the main rate determining contribution are order fluctuations with a T^?1 ₁ ∝ ν^?1/2 _L frequency dependence, whereas in the smectic H* phase the translational diffusion, which is slower than in the smectic H* phase, determines the dispersion of T^?1 ₁.     

退火温度对纳米晶ZrO2发光和ZrO2:Pr3+能量传递的影响

利用共沉淀法制备了纳米晶ZrO2和ZrO2:Pr3+,通过XRD对材料的晶体结构、颗粒尺寸进行了表征,研究了退火温度对纳米晶ZrO2发光性质的影响,探讨了ZrO2的发光机制,研究了退火温度对ZrO2∶ Pr3+能量传递的影响,给出了基质ZrO2与Pr3+离子间的能量传递模型.结果表明:随着退火温度的提高,纳米晶ZrO2由四方相转变为单斜相,颗粒尺寸增大;ZrO2的发射谱是一个中心位于470 nm的宽带,发光强度随退火温度升高而增强;基质ZrO2向激活离子Pr3+的能量传递方式为无辐射过程,高温退火有利于基质向Pr3+离子的能量传递,这种现象与退火温度对纳米晶ZrO2发光性质的影响有关.     

Basic Processes of Creep and their Investigation in the EM

The experimental data on the dislocation structure, its evolution and the mechanical behavior of the materials are considered at “moderate” and “elevated” temperatures. Possible schemes of the processes are represented.     

Modelling of the Transport Processes in Bridgman grown Gallium Antimonide

In this work the thermal, velocity and species fields in the melt during the crystal growth by the vertical Bridgman method, has been studied. The simulations were focused on the special case of GaSb, which is a semiconductor of high technological importance. The simulations have been carried out both in 2 and 3‐D. In both cases the momentum (Navier‐Stockes), energy and mass transport equations were solved. The wall‐to‐wall radiation has also been included. In the two‐dimensional case an axisymmetric global model was developed taking into account the different elements present inside the real Bridgman growth system. In order to study the transport processes in the whole system during a complete growth process, the time dependence has also been considered. In the three‐dimensional case, the mathematical domain is restricted to the melt. These simulations were developed in order to study the influence of the ampoule tilting on the dopant distribution in the melt.     

Relaxation of bubbles in the leucosapphire melt during crystal growth through lateral directed crystallization

The influence of the porosity of the feed material on the formation of micropores in the structure of leucosapphire crystals during crystal growth through the lateral directed crystallization is discussed.     

不同参数声子晶体第一完全带隙影响因素研究

基于时域有限差分法研究了二维声子晶体的第一完全带隙,数值计算了不同基体和散射体参数下XY模式的带隙特性.结果表明随着散射体与基体密度比的增大,第一完全带隙增宽.同时研究了不同晶格结构参数和填充率参数对第一完全带隙的影响,三角晶格的填充率高于正方晶格,较宽的带隙范围.研究结论为声子晶体器件的设计提供理论依据.     

Crystal-Chemical Approach to the Determination of Oxo-Centered Complexes in Divalent Lead Silicates

Crystallography Reports - The crystal-chemical analysis of seven structures of synthetic and natural lead silicates with formulas Pb2SiO4, Pb11Si3O17, Pb3Si2O7,...     

On the Influence of Twinning Processes on Columnar Crystallite Growth in Electrodeposited Films

An investigation of columnar crystallite growth during the electrodeposition of fcc Ni and hcp Co-W films has been made. It has been shown that the twinning processes not only promote the transformation of the initial orientation to the growth texture, but also lead to the change of the orientation of long columnar axes, the twinning processes in the fcc metal films exerting more significant influence on the columnar growth character than in the hcp ones.     

具有完全带隙的异质结构声子晶体的声波导特性

利用正方形和三角形结构声子晶体具有范围较大完全带隙的特性,设计了新型正方形晶格和三角形晶格构成的声子晶体异质结.采用平面波展开和超原胞相结合的方法研究了该异质结的能带结构特性.给出异质结的结构和相应的能带图,分析了异质结界面传导模,研究两侧结构作横向拉开和侧向滑移时对传导模的影响,讨论这些结构的实际可行性.计算结果表明,没有任何晶格移动,该结构异质结在完全带隙中就有传导模存在,界面两侧发生相对移动时,带隙内传导模的数量及位置都发生变化.     

The Temperature Dependence of Electron Spin-Lattice Relaxation Data in Trans-Polyacetylene and the Evidence for a Soliton-Phonon Interaction

Abstract

The temperature and frequency dependence of the electron spin-lattice relaxation rate Rj for the paramagnetic defects in pristine transpolyacetylene is analyzed in terms of a model in which the electron-electron dipolar interaction between spins is modulated by one-dimensional diffusion induced by phonon scattering of the spins. According to this model, at room temperatures R₁ has a T¹/² temperature dependence; at low temperatures R₁ has a T² or T⁵/² temperature dependence. R₁ is described by a ω^?1/² frequency dependence. The model shows the symmetry between moving and stationary solitons scattered by phonons. The soliton wave function obtained from experimental ENDOR data is used to obtain analytical results. We discuss the possible temperature and frequency limitations of this model.     

Molecular Recognition and Chemical Reactions in Lattice Inclusion Complexes of the Natural Product Gossypol

Abstract

Two level recognition by gossypol of the organic substances during complexation is discussed. Reactions in lattice inclusion compounds of gossypol are considered.     

Relaxation process of the I13/2 level of Er in a borosilicate glass

Relaxation of 1.54 μm emission of the erbium doped borosilicate glasses with high rare earth solubility was investigated. When the erbium content is less than 0.2 wt%, multi-phonon relaxation is the predominant process of non-radiative relaxation. It is difficult to increase the quantum efficiency higher than 70% for erbium ions in this glass due to multi-phonon relaxation. Because of the good glass-formation ability and high rare earth solubility, this glass will be suitable as a host for rare earth ions with a large energy gap, such as Yb³⁺, Eu³⁺ or Tb³⁺.