First-principles study of SnS electronic properties using LDA,PBE and HSE06 functionals

Recently, tin sulphide (SnS) has emerged as a promising alternative to conventional CIGS and CZTC for use in solar cells, possessing such properties as non-toxicity, low cost and production stability. SnS has a high theoretically predicted efficiency above 20%, but the experimentally achieved efficiency so far is as low as 4.36%. The reason for the low achieved efficiency is unclear. One of the powerful tools to get deeper insights about the nature of the problem is first-principles calculation approaches. That is why SnS has become an attractive subject for first-principles calculations recently. Previously calculated data, however, show a widespread of such fundamental value as the bandgap varying from 0.26 to 1.26 eV. In order to understand a reason for that, in this work, we concentrate on a systematic study of calculation parameters effects on the resulting electronic structure, with the particular attention paid to the influence of the exchange-correlation functional chosen for calculations. Several exchange-correlation functionals (LDA, PBE and HSE06) were considered. The systematic analysis has shown that the bandgap variation can result from a tensile/compressive hydrostatic pressure introduced by non-equilibrium lattice parameters used for the calculations. The study of the applicability of three functionals has shown that HSE06 gives the best match to both experimentally obtained bandgap and the XPS valence band spectra. LDA underestimates the bandgap but qualitatively reproduces experimentally measured valence DOS similar to that of HSE06 in contrast to PBE. PBE underestimates the bandgap and does not match to the measured XPS spectra.     

Analysis and design of optically transparent antenna on photonic band gap structures

An optically transparent microstrip patch antenna is designed on photonic bandgap structures and its radiation characteristics are computed and analyzed in the visible spectrum region. The proposed antenna consists of indium tin oxide, a transparent conducting material used both as a radiating patch and a ground plane separated by the 5 μm thin glass substrate. The introduction of periodic cylindrical air cavity structures in the glass substrate leads to the formation of photonic band gap. The patch thickness is carefully selected based on the analysis of the optical transmission coefficient with respect to patch thickness. The effective dielectric constant of the photonic band gap loaded glass substrate is computed using the effective medium approach. The refractive index of the proposed antenna is presented and discussed. The radiation efficiency of the antenna is shown to improve significantly due to insertion of proposed photonic band gap structures. The proposed design has yielded a bandwidth of 2–2.3 THz for a return loss (S₁₁) of less than −15dB and achieved a peak gain of 4.97dB at 2.27 THz.     

基于Surfer平台的FLAC3D 复杂三维地质建模研究

复杂三维地质体模型的建立一直是FLAC^3D软件前处理过程中的一个难题。因此,提出以Surfer软件为过渡平台,通过对地表及岩层分界面三维地质信息的提取、转换,并将Surfer输出的数据经由FLAC^3D软件内嵌的Fish语言编制的程序的二次转换,生成FLAC^3D软件可以直接读取的模型数据文件,从而实现了该软件前处理过程中复杂三维地质模型的快速、准确建立。同时结合工程实际,检验了该方法的可行性和仿真效果,结果表明,建模过程简捷、实用,可操作性强,是FLAC^3D软件前处理的一种新方法。     

First-principles study of the interaction of oxygen with the SnO2(1 1 0) surface

First-principles calculations based on density functional theory in the generalised gradient approximation, together with pseudopotentials and plane-wave basis sets, have been used to investigate the energetics of oxygen adsorption on stoichiometric and weakly and strongly reduced SnO₂(1 1 0) surfaces. It is shown that, if the surface species formed by oxygen adsorption are restricted to be charge neutral, then oxygen cannot be exothermically adsorbed from the gas phase on the stoichiometric surface. A variety of molecular and dissociative modes of adsorption are examined on the reduced surface produced by removing all bridging oxygens and on the weakly reduced surface that results from removal of only a fraction of these oxygens, with the adsorbed species being in both the singlet and the triplet states, and we identify a number of modes not discussed before in the literature. We use the calculated adsorption energies to propose a tentative assignment of these adsorption modes to the peaks observed in temperature programmed desorption experiments on the SnO₂ and TiO₂(1 1 0) surfaces.     

Successful location of tin dopant cations on surface sites of anatase-type TiO2 crystallites evidenced by 119Sn Mössbauer spectroscopic probe and XPS techniques

The present study provides the first experimental evidence for the stabilization of tin dopant cations immediately on the surface of an oxide having a tetragonal structure. ¹¹⁹Sn Mössbauer spectra of the dopant, introduced by air annealing into the bulk of anatase microcrystals, showed that it was located, in the tetravalent state, in somewhat distorted octahedral sites of a unique type. On the contrary, the reduced tin species, formed upon subsequent hydrogen annealing the Sn⁴⁺-doped samples, are found to occupy different sites being characterized by two sets of the isomer shift δ and quadrupole splitting ΔE_Q values (δ_I = 3.25 mm s⁻¹, ΔE_QI = 1.75 mm s⁻¹; and δ_II = 2.85 mm s⁻¹, ΔE_QII = 1.71 mm s⁻¹). Either of them implies both the divalent state of tin atoms and their presence at low-coordination sites that can be assigned to the surface of crystallites. Mössbauer spectra of Sn^4+←2+ daughter ions, formed upon contact with air of Sn²⁺, consist of a symmetrically broadened peak characterized by only slightly different average values of both the isomer shift (<δ> = 0.07 mm s⁻¹) and quadrupole splitting (<ΔE_Q> = 0.50 mm s⁻¹), as compared to the δ and ΔE_Q values for the bulk-located Sn⁴⁺. However, considerable broadening of Sn^4+←2+ doublet components (Γ = 0.97 mm s⁻¹) allows one to suggest that these secondary formed ions remain distributed over the non equivalent sites inherited from their Sn²⁺ precursors. The occurrence of Sn^4+←2+ at surface sites is independently proven by XPS measurements that revealed a greater than 10-fold enrichment with tin of 3–5 nm thick surface layers.     

氢化物发生-原子荧光光谱法测定海水中的痕量锡

对氢化物发生-原子荧光光谱仪的仪器条件和氢化反应条件进行了研究,建立了测定海水中痕量锡的方法,方法检出限为0.012μg/L,线性范围0.012-20 μg/L,精密度为5.5%.     

Preparation and properties of SnS film grown by two-stage process

SnS films have been prepared by a novel two-stage process. It involved sputtering of Sn film on glass substrate and sulfurization of the thin metallic tin precursor layers in a vacuum furnace. The X-ray diffraction results showed that the SnS layers had orthorhombic structure and (0 4 0) preferential growth is more and more obvious with the increase of sulfurization time. The SnS film obtained by this work shows high optical absorption efficiency, and the film has a direct optical band gap of about 1.3 eV. The films show p-type conductivity and the resistivity of SnS film decreased obviously under illumination.     

Sonochemical synthesis of carbon supported Sn nanoparticles and its electrochemical application

A sonochemical approach was employed to prepare Vulcan carbon XC-72R supported by Sn nanoparticles at room temperature in the presence of ethylene glycol. The reduction of metallic Sn ion and ethylene glycol takes place and in turn the glycolate ion as formed acts as a stabilizing agent. Transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy have illustrated that the metallic Sn nanoparticles are successfully embedded on the carbon. The significantly observed reduction over potential for oxygen reduction reaction displays a higher catalytic activity of carbon supported by Sn nanoparticles due to the large surface area of the modified electrode.     

Surface and catalytic properties of doped tin oxide nanoparticles

Mixed oxides composed of Zn-Sn, Ti-Sn and V-Sn were prepared by a co-precipitation method and evaluated as catalysts for methanol oxidation in an ambient fixed-bed reactor. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed an electronic interaction between dopant and Sn atoms in the oxide structure and showed the formation of surface states associated with the dopants. Oxygen vacancies were present on the Zn-doped oxide, and the oxidation of methanol to carbon oxides was favored. The Ti-doped oxide exhibited a favorable selectivity to dimethyl ether, related to the oxygen anions near Ti centers. Vanadium dopants not only dramatically increased the catalytic activity but also promoted the partial oxidation of methanol to formaldehyde. Results demonstrate that the bridging dopant-O-Sn bond acts as active sites and influences product distribution.