Forming of CdZnTe thin films grown by hot wall epitaxy and their properties

In this work morphological, X-ray structural and optical studies of CdZnTe films grown by hot wall epitaxy method at relatively low substrate temperatures were performed. Possible mechanisms and processes of self-organization that occur during the growth of such structures are considered. It is shown that at thickness of film more than 130 nm on the surface, large (lateral size 150 - 200 nm, height - up to 10 nm) and small crystals are observed. The thicknesses and energy of the band gap width of the CdZnTe films grown at different growth times were determined. It is shown that the film absorption edge in the transmission spectra depends on the film thickness and the reasons for the shift of the film absorption edge are discussed.

Ab initio calculation of the electronic structure of a solid solution of strontium-bismuth molybdat

Scheelite-like compounds based on SrMoO4 have been studied. Based on X–ray structural data, models of Sr1-3xBi2xMoO4 structures (x=0.2125) are constructed, at x≧0.175, a superstructural ordering is observed associated with the location of cationic vacancies. From the first principles, calculations of the density of states in the vicinity of the forbidden zone are performed. The calculated values of the band gap width were compared with the values obtained from the reflection spectra.

Resistive switching and optical properties of strontium ferrate titanate thin film prepared via chemical solution deposition

The polycrystalline strontium ferrate titanate (SrFe0.1Ti0.9O3, SFTO) thin films have been successfully prepared by chemical solution method. By analyzing the current-voltage (I–V) characteristics, we discuss the conduction mechanism of SFTO. It is found that the number of oxygen vacancy defects is increased by Fe ion doping, making SFTO be with better resistive switching property. Fe ion doping can also enhance the absorption of strontium titanate to be exposed to visible light, which is associated with the change of energy band. The band gap width (2.84 eV) of SFTO films is figured out, which is less than that of pure strontium titanate. Due to more oxygen vacancy defects caused by Fe ion doping, the band gap width of strontium titanate was reduced slightly. The defect types of SFTO thin films can be determined by electron paramagnetic resonance spectroscopy. In addition, we analyzed the energy band and state density of SFTO by first-principles calculation based on density functional theory, and found that Fe ion doping can reduce the band gap width of strontium titanate with micro-regulation on the band structure. A chemical state of SFTO was analyzed by X-ray photo electron spectroscopy. At the same time, the structure and morphology of SFTO were characterized by X-ray diffraction and scanning electron microscope. This study deepens further understanding of the influence of Fe ion doping on the structure and properties of strontium ferrate titanate, which is expected to be a functional thin film material for memristor devices.

"Зародышевые" трещины на поверхности кристалла кремния

The surface (100) of a silicon crystal after cutting the workpiece with a diamond disk and subsequent polishing was studied by the methods of white light interference profilometry and photoluminescence spectroscopy (PL). It was found that it is covered by "grooves". Their length is 10-40 µm, and the depth is quantized. It has values-1, 2.6, 3.6 and 4.5 nm. Four bands (1.63, 1.62, 1.68 and 2.25 eV) were observed in the PL spectra. They arise due to confinement, i.e., an increasing on the band gap width and a violation of momentum of the conservation law in nanocrystals. The sizes of nanocrystals are determined from the energy of the maxima of these bands. They are equal about 2, 2.3, 3 and 4 nm. When cutting silicon or striking it with a striker, fractoluminescence (FL) signals containing 4 maxima were observed. Signals are formed when dislocations break through barriers that occur at intersections.

Resistive switching and optical properties of strontium ferrate titanate thin film prepared via chemical solution deposition

The polycrystalline strontium ferrate titanate (SrFe0.1Ti0.9O3, abbreviated to SFTO) thin films have been successfully prepared by chemical solution method. By analyzing the current-voltage (I-V) characteristics, we discuss the conduction mechanism of SFTO. It is found that the number of oxygen vacancy defects is increased by Fe ions doping, making SFTO be with better resistive switching property. Fe ions doping can also enhance the absorption of strontium titanate to be exposed to visible light, which is associated with the change of energy band. The band gap width (2.84 eV) of SFTO films is figured out, which is less than that of pure strontium titanate. Due to more oxygen vacancy defects caused by Fe ions doping, the band gap width of strontium titanate was reduced slightly. The defect types of SFTO thin films can be determined by electron paramagnetic resonance spectroscopy. In addition, we analyzed the energy band and state density of SFTO by first-principle calculation based on density functional theory, and found that Fe ions doping can reduce the band gap width of strontium titanate with micro-regulation on the band structure. A chemical state of SFTO was analyzed by X-ray photo electron spectroscopy. At the same time, the structure and morphology of SFTO were characterized by X-ray diffraction and scanning electron microscope. This study deepened the understanding of the influence of Fe ions doping on the structure and properties of strontium ferrate titanate, which is expected to be a functional thin film material for memristor devices.

Active tuning of the vibration band gap characteristics of periodic laminated composite metamaterial beams

A novel strategy is proposed to investigate the vibration band-gap and active tuning characteristics of the laminated composite metamaterial beams. The piezoelectric actuator/sensor pairs are periodically placed along the laminated composite beam axis so that the vibration frequency band-gap and active tuning characteristics can be induced. The dynamic equations of the laminated composite metamaterial beams bonded by the piezoelectric actuator/sensor pairs are established based on the Euler–Bernoulli beam theory. The negative proportional feedback control strategy is employed to provide the positive active control stiffness for the piezoelectric actuator/sensor patches. The spectral element method is used to calculate the dynamic responses of the laminated composite metamaterial beams with the periodically placed piezoelectric patches, and the calculation accuracy for the dynamic responses is validated by the finite element method. The results demonstrating the high-performance vibration band-gap properties in the low-frequency ranges can be achieved by properly designing the sizes and the number of the piezoelectric patches. Moreover, the vibration band-gap characteristics, especially the band-gap width and the normalized band-gap width with respect to the considered excitation frequency range, can be significantly changed by tuning the structural parameters of the piezoelectric actuators and sensors. In addition, the cross-ply angle of the laminated composite metamaterial beams has significant influences on the band-gap characteristics and the vibration reduction performance of the laminated composite beam structures.

Structural and Electronic Properties of Qatranaite

The present work addresses the atomic structure and electronic properties of a recently discovered mineral qatranaite (CaZn2(OH)6·2H2O). The present study was performed theoretically by means of density functional theory- (DFT-) based calculations within the frame of local density approximation (LDA) and general gradient approximation (GGA). To determine the energy band gap width, we carried out the ultraviolet-visible spectroscopy (UV-Vis) measurements. The structure relaxation performed with use of LDA and GGA provides results matching the experimentally determined crystal parameters. Interestingly, in contrast to existing interpretation of experimental data, our DFT calculations revealed energy gap of direct characteristics. Accordingly, our UV-Vis experiments yield the band gap width of 3.9 eV.

Влияние рентгеновского излучения на оптические свойства фоторефрактивных кристаллов силиката висмута

The results of investigations of the optical-absorption spectra of bismuth-silicate (Bi_12SiO_20) single crystals are presented. The band-gap width and the characteristic Urbach energy are determined. The effect of preliminary X -ray irradiation on the behavior of the experimental spectral dependences and the values of the characteristic parameters induced by the bismuth-silicate defect structure is established.