Wavelength modulation spectra of SbSI and its electronic band structure

The reflectivities of SbSI and their logarithmic derivatives between 1.8 and 4.5 eV have been measured at different temperatures. The structures in the reflectivities are compared with those calculated independently by the empirical pseudopotential method (EPM), using the pseudopotential form factors scaled from previous band structure calculations of other crystals. The large optical anisotropy of SbSI is explained. A preliminary band structure for SbSI is presented.     

Preparation and photoelectric properties of antimony selenium iodide

The dependence of the photoelectric current on the wave-length was measured on SbSeI crystals in the temperature range of 83–293°K. The maximum of the internal photoeffect was found in the region of 720–740 nm for various crystals at room temperature. The temperature dependence of the forbidden band width of SbSeI crystals was deduced from the shift of the photoeffect maximum. The results were compared with the properties of homological compounds SbSI and BiSI.     

Birefringence of SbSI and SbSeI crystals at the region of antiferroelectric phase transition

Anomalous behavior has been observed in the temperature range of T = 140–145 °C. The electric current I(T) of SbSI and SbSeI crystals along the c(z) axis changes significantly at the region of the antiferroelectric phase transition when DC voltage is applied. The peak positions are observed at 140 °C and 145 °C for SbSI and SbSeI, respectively. The birefringence spectra show temperature-dependent changes upon retardation m, confirming the antiferroelectric phase transition for both crystals. The peak positions observed from the optical measurements do not differ from the electrical measurements, showing the transition point at 140?°C and 145?°C for SbSI and SbSeI, respectively.     

A simple model for the optical Bu modes inAV-BVI-CVII compounds

The eigenvalues of the optical modes of theAV-BVI-CVII compounds SbSI, SbSeI, BiSI, BiSeI, BiSBr, BiSeBr, and SbSBr in the paraelectric phase and the polarizationE c are calculated by use of a simple model fitted by the observed transverse mode frequencies. For the low-frequency mode theAV and theBVI ions are shown to vibrate simultaneously against theCVII ions. For the high-frequency mode the motion of theCVII ions is almost absent and theAV ions vibrate against theBVI ions.     

Synchrotron radiation measurements and calculation of core to conduction level transitions in lead chalcogenides

New high resolution reflectivity measurements on PbSe and PbTe using synchrotron radiation (18–26 eV) are studied using an OPW formalism based on recent improved EPM band structure models to determine the angular momentum character of the final conduction band states. Detailed analysis reveals that the reflectivity threshold is shifted to lower energies by 0.8 eV compared to results derived from photoemission and low energy reflectivity data. Electron-hole interactions are suggested as a possible explanation for this shift.     

Band structure and optical properties of antimony-sulfobromide: density functional calculation

The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.      

Optical spectra of CsI,CsBr, ZuGeP2, and SbSI

We report here the study of the normal reflectivity spectra R and the corresponding derivative spectra (1/R) dR/dE of SbSI between 2 and 6 eV. The spectra show very strong anisotropy. We have also tried to use the change of the wavelength modulation spectrum to monitor the change in the band structure of SbSI due to the phase transition at 292 °C (D_2h¹⁶→C_2v⁹). Careful examination of the spectra at various temperatures around T_c shows no observable change. We report also the wavelength-modulated reflectivity spectra of the chalcopyrite crystal ZnGeP₂ at 5 K between 2 and 6 eV, for E∥ C and E⊥ C. The experimental results are compared with the theoretical band structure calculation by de Alvarez and Cohen. We also present measurements on CsBr, CsI in the vacuum uv (between 5 and 8 eV) at 1.8K, showing noticeable difference with previous reflectivity measurements at 77 K.     

XPS analysis of sonochemically prepared SbSI ethanogel

This paper, for the first time, presents the results of the X-ray photoelectron spectroscopy (XPS) of the valence band and core levels in sonochemically prepared SbSI ethanogel consisting of nanowires. The XPS spectra were measured with monochromatized Al K_α radiation in the energy range of 0-1400 eV at room temperature. It was found that the sonochemically prepared SbSI ethanogel is a p-type semiconductor. The XPS determined composition of this material suggests the existence of antimony subiodide at surfaces of SbSI nanowires. The chemical shifts in SbSI ethanogel for the Sb, I and S states are reported. Experimentally obtained binding energies are compared with the results reported for single crystals of SbSI.     

Thermoreflectance spectra of the ferroelectric phase of semiconducting SbSI

Thermoreflectance measurements on SbSI between 2.2 and 3.0 eV are reported at 110°K. Strong polarization effects have been found to depend on the orientation of the electric vector with respect to the c-axis. Correlations, between present results and previously reported reflectivity and its logarithmic derivative results are presented.     

Ab-initio calculation of band structure and linear optical properties of SbSI in para- and ferroelectric phases

An ab-initio pseudopotential calculation has been performed by using density functional methods within the local density approximation (LDA) to investigate the band structure and optical properties of the ferroelectric-semiconductor SbSI in the para- and ferroelectric phases. It has been shown that SbSI has an indirect gap in both phases (1.45 eV and 1.49 eV in the para- and ferroelectric phases respectively) and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV and 1.58 eV in the para- and ferroelectric phases respectively). Furthermore, it is shown that first-order phase transition, from the paraelectric phase to the ferroelectric phase (the transiton temperature is about 22 °C), does not change the nature of the band gap. Moreover, the linear frequency dependent dielectric function, including self-energy effects, has been calculated along the c-polar axis in the para- and ferroelectric phases.      

Low field microwave absorption and magnetization process in CoFeNi electroplated wires

Ferromagnetic resonance （FMR）, Ferromagnetic antirresonance （FMAR） and low field magnetoimpedance （MI） are the characteristic features of high frequency losses in applied fields. While some results on FMR and FMAR in CoFeNi electroplated wires were reported earlier, here we present microwave absorption in CuBe wires electroplated by 1 μm FeCoNi magnetic layer at very low fields. These data are comparatively analysed together with longitudinal hysteresis loops in order to reveal the correlation between power absorption and magnetization processes. Microwave studies are made by using the cavity perturbation method at 9.65 GHz for a DC field parallel to the sample axis, and with microwave magnetic field hrf parallel or perpendicular to the wire axis. Two peaks have been observed in all samples, one is due to FMR, and the other is, at very low fields, related to MI. The MI peaks represent minima in power absorption. By comparing with the hysteresis loop we remark the close correspondence between the MI phenomena in the axial mode and the concomitant magnetization process.     

Electronic structure of BiSeI clusters

The valence band (VB) energy levels of BiSeI crystals have been calculated and compared to the X-ray photoelectron spectra of SbSI crystals. A molecular cluster consisting of 20 molecules of BiSeI has been used to calculate the total VB density of states by the density functional theory (DFT) method. The spectrum of total VB density of states of the (BiSeI)₂₀ cluster weighted by atomic photoemission cross-sections has been compared with the experimental X-ray photoelectron VB spectrum of SbSI type crystals. The cluster model calculation has showed that the core level energy splitting depends on the difference of ionic charges of the same atoms at the edges of the (BiSeI)₂₀ cluster.     

Anisotropy of reflection spectrum and band structure of SbSI

Anisotropy of the SbSI reflection spectra at various temperatures (300, 273, and 90 °K) is studied. Selection rules are examined for matrix transition elements at extreme points for crystals with symmetry D _2h ¹⁶ , C _2v ⁹ , and C ₂ ² corresponding to different states of SbSI during phase transitions. A comparison of experimental data with theoretical and group-theoretical analysis results made possible a conclusion on the character of the band spectrum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 13–19, August, 1971.     

Structural,electronic, optical and bonding properties of strontianite,SrCO3: First-principles calculations

The first-principles calculations are performed within the density functional theory to investigate the crystal structure, energy band structure, density of states, optical properties, and bonding properties of strontianite. The optimized structure parameters and bonding results with the generalized gradient approximation (GGA) functional and the localized density approximation (LDA) functional are in good agreement with the earlier experimental data. The band structure, density of states and chemical bonding of strontianite have been calculated and analyzed. The indirect band gap of strontianite is estimated to be ~4.45 eV (GGA) or ~4.24 eV (LDA). The absorption, reflectivity, refractive index and extinction coefficient have been calculated using the imaginary part of the dielectric function. The calculated results of the optical properties show that strontianite has an optical anisotropy along [100] (or [010]) and [010] polarization directions of incoming light. Furthermore, the calculated results of the density of states and Mulliken population indicate that the interactions among atoms are both ionic and covalent bonding in strontianite.     

Infrared free carrier reflectivity of p-type PbTe

Some of the existing experimental data on free carrier reflectivity of p-type PbTe is reanalysed using the analytical procedure of the author. Contrary to earlier conclusions, the new results are consistent with the results of other measurement techniques in predicting a two valence band model for PbTe. The results of the present analysis also suggest that the use of the new analytical procedure in surface characterization should be preferable as compared to the independent methods of surface characterization in plasma reflectivity studies.     

Dielectric Response and Broadband Microwave Absorption Properties of Three-Layer Graded ZnO Nanowhisker/Polyester Composites

We design and prepare three-layer graded ZnO nanowhisker/polyester composites. The dispersion configuration of ZnO nanowhiskers in the polyester is investigated, and their microwave reflectivity curves are also measured. Experimental results have shown that the graded dispersion with ZnO nanowhiskers contributes to broadband microwave absorption. In other words, the absorption band depends on the graded dispersion configuration of ZnO nanowhiskers in polyester matrix.     

Theoretical study on the band structure and optical properties of 4H-SiC

We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers－Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated. We found the theoretical results are in good agreement with the experimental data.     

Sonochemical growth of antimony selenoiodide in multiwalled carbon nanotube

This paper presents, for the first time, the nanocrystalline, semiconducting antimony selenoiodide (SbSeI) grown in multi-walled carbon nanotubes (CNTs). It was prepared sonochemically using elemental Sb, Se, and I in the presence of ethanol under ultrasonic irradiation (35 kHz, 2.6 W/cm²) at 323 K for 3 h. The CNTs filled with SbSeI were characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, and optical diffuse reflection spectroscopy. These investigations exhibit that the SbSeI filling the CNTs is single crystalline in nature and in the form of nanowires. It has indirect allowed energy band gap E_gIf = 1.61(6) eV.     

Chemical bond approach to the dielectric constant of SbSI

The electronic band structure of SbSI crystal was calculated by Mulliken-Wolfsberg-Helmholtz (MWH) method. The semiempirical evaluation of dipole moments for band-to-band transitions was discussed. It was shown the interatomic transitions contribute mainly to the static dielectric constant ϵ₁(0). The interchain interactions should be taken in consideration to describe the dielectric constant. The chemical bonding of SbSI is discussed.     

Active microwave radiometry and its applications

Summary In microwave bands, attenuation and reflectivity of objects are usually determined by locating the objects between two antennas, connected to a generator and a detector. If a narrowband signal is used, the radiators and an object should be adequately separated as otherwise so-called near field exists around the radiators; due to interfering wave fronts, space is filled by interference maxima and minima that prevent a reasonable measurement from being done.The described method employs wideband noise instead of a narrowband or CW (continuous wave) signal. Therefore a radiometer is used as detector and a noise generator as source.By creating a random field in the space between radiators, interesting phenomena have been observed which can find also a practical use even though no ready-to-use theory apparently exists to describe such phenomena.