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.     

Theoretical investigation of the electronic structure of a ferroelectric SbSI cluster at a phase transition

This paper presents the theoretical investigation of energy levels of valence bands (VB) and core levels (CL) of the ferroelectric SbSl single crystals in antiferroelectric and ferroelectric phases. Since the best approximation for the deep VB levels is a calculation by the Hartree-Fock method, the molecular model of a SbSI crystal was used for calculations. This model of the crystal was also used for calculations of the total density of states. It was found that the VB and CL of this ferroelectric semiconductor are sensitive to the small lattice distortion at the phase transition, and that an average of the total density of states, when all atoms participate in oscillations of all normal modes, are more similar to the experimental X-ray photoelectron spectra (XPS). The experimental splitting of CL obtained by XPS was compared with the theoretically calculated one by two different methods. The cluster model calculations showed that the splitting of the CL in SbSI might be caused by photoelectron emission from the atoms, which have different valence state, at the surface.     

铁电半导体碘硫化锑量子点复合材料及其光学性能的研究

用溶胶-凝胶法成功地制备了铁电半导体碘硫化锑(SbSI)微晶掺杂有机改性的TiO_2薄膜及块状凝胶。铁电SbSI晶体在C轴具有非常大的介电常数,非常高的电-光系数,较大的光电导系数,同时又是一种本征半导体材料。将SbSI掺杂到非晶态的基质中,通过热处理及气氛保护的方法控制微晶的生长。通过X射线衍射光谱与高分辨透射电子显微镜观察到微晶的存在以及晶体尺寸和分布情况。使用简并的四波混频的方法测得了薄膜样品的三阶非线性极化率,并在块状样品中发现了复合材料中存在的电控双折射效应,测得样品的有效电光系数为2.42×10~(-3)nm/V。     

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.      

The thermodynamic functions of ferroelectric and paraelectric SbSI

A first-principle method is used to calculate phonon density of states, Helmholtz free energy, internal energy, and entropy for ferroelectric and paraelectric SbSI. Theoretical phase transition temperature was obtained using the difference of the Helmholtz free energy, internal energy, and entropy term between ferroelectric and paraelectric phases on temperature. The obtained value is in reasonable agreement with the experimental second-order phase transition temperature T_c2 = 233 K.     

Influence of the solvent on ultrasonically produced SbSI nanowires

The influence of the substitution of methanol in place of ethanol during the ultrasonic production of antimony sulfoiodide (SbSI) nanowires is presented. The new technology is faster and more efficient at temperatures greater than 314 K. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), optical diffuse reflection spectroscopy (DRS) and IR spectroscopy. The coexistence of Pna2₁ (ferroelectric) and Pnam (paraelectric) phases at 298 K was observed in the SbSI nanowires produced in methanol. The methanol decomposes during the sonication or due to the adsorption process on SbSI nanowires.     

Using of sonochemically prepared SbSI for electrospun nanofibers

A novel polymeric, polyacrylonitrile (PAN) nanofibers containing ferroelectric and semiconducting antimony sulfoiodide (SbSI) have been made by electrospinning. SbSI nanowires, used as the filler, have been prepared sonochemically from antimony sulphide (Sb₂S₃) and antimony tri-iodide (SbI₃) for the first time. Nanocrystalline SbSI has been fabricated in ethanol under ultrasonic irradiation (20 kHz, 565 W/cm²) at 323 K within 2 h. The products have been 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 as well as transmission spectroscopy. The good quality of the nanocrystals and their dispersion in the nanofiber’s volume is important because this material is attractive for nanogenerators due to its ferroelectric and piezoelectric properties. The amplitude of the voltage pulse, generated under shock pressure of 3.0 MPa, has reached 180 V in the prototype PAN/SbSI piezoelectric nanogenerator. The peak output voltage of about 0.2 V was measured in bending/releasing conditions with the deformation frequency of 1 Hz.     

Laser-modulated reflectance of SbSI near Tc

Reflectance modulation spectra of the semiconducting ferroelectric compound SbSI, at wavelengths near the fundamental edge and at temperatures around the phase-transition are reported. Modulation was obtained by the periodical injection of free carriers produced by a laser beam chopped at 10.18 Hz. In order to explain the mechanism of photoreflectance in SbSI, a comparison of the experimental data has been made both with electroreflectance spectra and eith the theoretical curve expected under the assumption of a periodical change of free carriers density.     

Sonochemical preparation of SbSI gel

A novel sonochemical method for direct preparation of nanocrystalline antimony sulfoiodide (SbSI) has been established. The SbSI gel was synthesized using elemental Sb, S and I in the presence of ethanol under ultrasonic irradiation (35 kHz, 2 W/cm²) at 50 °C for 2 h. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and optical diffuse reflection spectroscopy (DRS). The SEM and HRTEM investigations exhibit that the as-prepared samples are made up of large quantity nanowires with diameters of about 10–50 nm and lengths reaching up to several micrometers and single-crystalline in nature.     

Synthesis technique for and certain properties of AsxSb1-xSI crystals

A technique for synthesizing As_xSb_1-xSI is described. The system is shown to form crystals of a limited solid solution. In the region in which a solid solution is formed, the crystals are ferroelectric photoconductors. An arsenic admixture reduces the Curie point from 295°K (SbSI) to 243 °K (As_0.1(Sb_0.9SI). A study of the basic electrophysical properties of these crystals is reported.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 28–33, September, 1969.In conclusion the authors thank professor V. M. Fridkin for interest in the study and for participation in discussion of the results.     

Coulomb microexplosions of ferroelectric ceramics

Energetic neutral and extreme ultraviolet emission initiated by the dense plasma propagation along a ferroelectric surface has been found. It was shown that the emission of neutrals is characterized by a large divergence and velocities up to 7 x 10(7) cm/s. This phenomenon is explained by an extremely large electric field with amplitude > or =10(6) V/cm and rise time approximately 10(-10) s which appears at the plasma front due to the fast fall in the driving pulse. This electric field causes microexplosions of the ferroelectric surface due to inertia in the ion polarization response.     

Ferroelectric phase transition in SbSI type crystals

In this work Lorenz field coefficients F for SbSI type crystals are estimated. Also transverse and longitudinal frequencies (ω _T and ω _l) of optical vibrations are determined. From a study of these quantities it was concluded that a combination of F is an inadequate condition for ferroelectric phase transitions to take place. Taking the electronic structure, chemical bond model, electronic potential and condition ω _T—>0 into account, the phase transition in SbSI type crystals was investigated. The dependence of the electronic potential upon the composition of V-VI-VII crystals and mixed crystals has revealed the factors that change the phase transition temperature T _c and the dynamics of the soft mode.     

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.     

Sonochemical growth of antimony sulfoiodide in multiwalled carbon nanotube

This paper presents for the first time the nanocrystalline, semiconducting ferroelectrics antimony sulfoiodide (SbSI) grown in multiwalled carbon nanotubes (CNTs). It was prepared sonochemically using elemental Sb, S and I in the presence of methanol under ultrasonic irradiation (35 kHz, 2.6 W/cm²) at 323 K for 3 h. The CNTs filled with SbSI 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 SbSI filling the CNTs is single crystalline in nature and in the form of nanowires. It has indirect forbidden energy band gap E_gIf = 1.871(1) eV.     

Electronic polarization in SbSI near electrodes

An experimental study has been made of the residual-polarization charge [q] at various temperatures in darkness and with illumination. Illumination of the anode has the greatest effect on the q = f(E) dependence. The potential distribution in the sample and the q = f(T) dependences reveal a high electron density near the anode, giving rise to polarization charge of up to 10^-5 C/cm², in SbSI with In-Ga electrodes. The time dependence of the discharge current reveals three slow-relaxation components, with relaxation times of 1.4 · 10², 1.1·10³, and 2.1·10³ sec.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 45–49, December, 1969.The authors thank M. S. Kosman and V. A. Izvozchikov for discussion of these results.     

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.     

Supersymmetric Yang-Mills theories in D ⩾ 12

We present supersymmetric Yang-Mills theories in arbitrary even dimensions with the signature (9+m, 1 +m) where m = 0, 1, 2,… beyond ten dimensions up to infinity. This formulation utilizes null-vectors and is a generalization of our previous work in 10+2 dimensions to arbitrary even dimensions with the above signature. We have overcome the previously observed obstruction beyond 11+3 dimensions, by the aid of projection operators. Both component and superspace formulations are presented. This also suggests the possibility of consistent supergravity theories in any even dimensions beyond 10+1 dimensions.     

Phase transitions in SbSI

In ferroelectric SbSI the phase transitions are studied by means of precise birefringence measurement. It is observed that the transition from D^162h phase to C⁹_2v phase occurs at 15.70°C. At ? 36.61°C, the second order transition from C⁹_2v phase to C¹_s or C²_s phase is observed. From the behavior of birefringence near the second order transition point, the mechanism of the phase transition in SbSI is considered.     

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.     

Deposition of SbSI and BiSeI films in quasi-equilibrium conditions

The problem of obtaining structurally perfect SbSI and BiSeI films in quasi-equilibrium conditions is examined. A stoichiometric composition of the gas phase leads to the formation of acicular single crystals of SbSI and BiSeI, while an excess of Sb during the deposition of SbSI leads to films with lamellar crystallites and the C axis perpendicular to the substrate. Some of the electrical and optical properties of the SbSI films are compared with the properties of similar films obtained by discrete evaporation.