Electrical properties and valence band structure of GeSexTe1−x single crystals

The anomalous composition dependence of the carrier transport properties of Ge_1?y(Se_0.2Te_0.8)_y in the range y=0.495 ? 0.510 has been analyzed at room temperature by means of a two-carrier model. The close agreement between the experimental and computational results confirms the existence of two valence bands in α-GeSe_xTe_1?x which are produced by the rhombohedral distortion of the lattice at low temperature.     

First principles study on the structure and electronic properties of 2‐nitrimino‐1‐nitroimidazolidine

The properties of 2‐Nitrimino‐1‐nitroimidazolidine are calculated by using SIESTA code, which adopts the standard Kohn‐Sham self‐consistent density functional method in the local density approximation. The structures and electronic properties are analyzed, and the factors that affect the impact sensitivity are discussed based on the crystal structure, band energy, and projected density of state. The reason for the smaller impact sensitivity compared to RDX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine) is also explored from several respects such as the weakest bond dissociation energy in single molecule, and hydrogen bond, band gap in the crystal. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Vacancy‐Rich Monolayer BiO2−x as a Highly Efficient UV,Visible, and Near‐Infrared Responsive Photocatalyst

Vacancy‐rich layered materials with good electron‐transfer property are of great interest. Herein, a full‐spectrum responsive vacancy‐rich monolayer BiO_2?x has been synthesized. The increased density of states at the conduction band (CB) minimum in the monolayer BiO_2?x is responsible for the enhanced photon response and photo‐absorption, which were confirmed by UV/Vis‐NIR diffuse reflectance spectra (DRS) and photocurrent measurements. Compared to bulk BiO_2?x, monolayer BiO_2?x has exhibited enhanced photocatalytic performance for rhodamine B and phenol removal under UV, visible, and near‐infrared light (NIR) irradiation, which can be attributed to the vacancy V_Bi‐O′′′ as confirmed by the positron annihilation spectra. The presence of V_Bi‐O′′′ defects in monolayer BiO_2?x promoted the separation of electrons and holes. This finding provides an atomic level understanding for developing highly efficient UV, visible, and NIR light responsive photocatalysts.     

Ion induced controlled modifications in structural and optical properties of indium oxide thin films – studies with 25‐keV Co− and N+ beam implantations

Two sets of indium oxide thin films (~150 nm) grown on quartz substrates using thermal evaporation technique were processed separately with 25‐keV Co^? and N⁺ ions with several fluences ranging from 1.0 × 10¹⁵ to 1.0 × 10¹⁶ ions/cm². The pristine and the ion implanted films were characterized by Rutherford backscattering spectroscopy (RBS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–Vis spectrometry. The RBS spectra reveal signature of only cobalt and nitrogen in accordance to their fluences confirming absence of any contamination arising due to ion implantation. An increase in the average crystallite size (from 13.7 to 15.3 nm) of Co^? ions implanted films was confirmed by XRD. On the other hand, the films implanted with N⁺ ions showed a decrease in the average crystallite size from 20.1 to 13.7 nm. The XRD results were further verified by SEM micrographs. As seen in AFM images, the RMS surface roughness of the samples processed by both ion beams was found to decrease a bit (29.4 to 22.2 nm in Co^? implanted samples and 24.2 to 23.3 nm in N⁺ implanted samples) with increasing fluence. The Tauc's plot deduced from UV–visible spectroscopy showed that the band gap decreases from 3.54 to 3.27 eV in Co^? implanted films and increases from 3.38 to 3.58 eV for films implanted with N⁺ ions. The experimental results suggest that the modifications in structural and optical properties of indium oxide films can be controlled by optimizing the implantation conditions. Copyright © 2017 John Wiley & Sons, Ltd.     

Bandgap engineering and optoelectronic properties of all-inorganic lead-free Pd-based double perovskites

The various physical properties of lead-free double perovskites A₂PdX₆ (A = K, Rb, Cs; X  = Cl, Br, I) are revealed for the first time. The calculated structural parameters of these Pd-based compounds are consistent with the experimental data. It is likely to possess a tetragonal structure for K₂PdI₆ at room temperature. Cs₂PdBr₆ is dynamically stable when the pressure is in the range of 0–6.95 GPa. The mechanical properties are analysed and all the compounds are mechanically stable. The band gap trend of the A₂PdX₆ compound is identified when the A-site cation and halide anion are varied. Three A₂PdBr₆ compounds exhibit suitable band gaps for photovoltaic applications. An optimum band gap can be achieved for Cs₂PdBr₆ when the moderate pressure is applied. In addition, the electron shows better mobility than that of the hole for three A₂PdBr₆ compounds. The optical absorption coefficient of the A₂PdBr₆ compound is improved when the A-site cation changes from Cs to Rb to K. Applying pressure is beneficial to enhance light absorption capacity of Cs₂PdBr₆. The findings of this work can provide guidance for the design of potential A₂PdBr₆ compounds for photovoltaic applications.     

Theoretical studies on the structures and electronic spectra of C75B−

Intermediate neglect of differential overlap (INDO) calculations were used to study the structure of C₇₅B^?—the isoelectronic molecule of C₇₆. It was found that the boron atom mainly substitutes the second carbon atom (there are 19 types of carbon atoms in C₇₆). The electronic spectra of all the possible isomers of C₇₅B^? were calculated based on the optimized geometries. It was shown that the UV‐Vis spectra of C₇₅B^? and C₇₆ resemble each other in many ways with the exception of the absorptions beyond 700 nm. The red shift of the absorptions was rationalized and nature of transition of the peaks discussed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Composition optimization and UV‐annealing dependence on the electrical properties of Hf1−xSixO2/Si gate stacks

Hf_1?xSi_xO₂ gate dielectrics grown by UV‐photo‐induced chemical vapor deposition (UV‐CVD) using Hf(OBu^t)₂(mmp)₂ and tetraethoxysilane as precursors have been deposited on Si substrate. Composition dependence of the interfacial microstructure of the Hf_1?xSi_xO₂/Si gate stacks has been investigated via Fourier transform infrared spectroscopy (FTIR) systematically. It has been indicated that the physical properties of the Hf_1?xSi_xO₂ films can be effectively optimized by adjusting the silicon contents incorporated in the films. In order to evaluate its potential implementation as an alternative dielectric in future devices, detailed electrical characterization of Au/Hf_1?xSi_xO₂/Si capacitor has been performed as functions of the silicon contents and the UV‐annealing time. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and properties of acceptor-donor-acceptor molecules based on oligothiophenes with tunable and low band gap

A series of acceptor-donor-acceptor molecules (DCN3T, DCN5T and DCN7T) based on oligothiophenes with low band gap are synthesized. The UV-vis absorption spectra of solution show that the introduction of electron-accepting groups results in a shift of the absorption onset towards longer wavelengths. Moreover, the optical spectra of their films show a large bathochromic shift and broadening of the bands with respect to the spectra in solution. The optical band gaps of film of these A-D-A molecules are 1.90, 1.74 and 1.68 eV, respectively. Cyclic voltammetry shows that all these compounds present a reversible first oxidation process whose potential decreases with the lengthening of oligothiophene cores. Electrochemical band gaps are 2.14, 1.88 and 1.71 eV, respectively.     

Formation of CdS x Se1−x microcrystals in sol-gel derived glasses

Sol-gel method was applied to prepare CdS _x Se_1–x microcrystals doped glasses. Gels were synthesized through the hydrolysis of Si(OC₂H₅)₄, CdSeO₄, and NH₄SCN, and then heated in H₂-N₂ gas atmosphere to precipitate CdS _x Se_1–x microcrystals in the glasses. The composition of crystals was preliminarily determined during the synthesis of the gels. The optical band gap energies were blue shifted compared with those of the bulk crystals due to the quantum-sized confinement effect.     

Theoretical studies of physicochemical properties of aniline oligomers: analysis of counterion influence

We present some semiempirical quantum chemistry calculations, geometric structures, charge distribution, gap energy, and enthalpy of formation (H _f ) for aniline oligomers in the different oxidation states using the AM1 method. A linear relationship between calculated optical transition values and the experimental reported ones was found. The effect of the interaction between the chloride counterion and these molecules was analyzed and indicates a decrease both in H _f of the aniline oligomers in the radical cation state and in E(SOMO-LUMO). The withdrawal of one electron from the reduced aniline tetramer to form a radical cation in the presence of chloride (Cl^–) yields to the radical cation band, similar to the polaron band in the polyaniline case. Contrary to the expected results, our calculations show that Cl^– was able to transfer about 80% of its charge to the oligomers.     

Complex investigation of multilayer nanostructure of a‐Si/SiO1.9 by probe and spectroscopic analysis techniques. Visualization of the band structure. Studying of the band structure of the suboxide border layers

This article describes an integrated approach to the study of multilayer nanostructures of a‐Si/SiO_1.9 as a potential model to study the influence of the effects arising at the interface of Si/SiO₂ under the influence of ionizing radiation. The results of the functional layers of amorphous silicon and silicon dioxide surface topology investigation have been disclosed. The possibility of application of a band gap contrast in electron probe studies by means of electron energy filtering during the detection process has been demonstrated. Changes in valence band and band gap through depth of the a‐Si/SiO_1.9 nanostructure have been registered. As part of the study, density of states of the a‐Si/SiO_1.9 multilayer nanostructures and depth distribution of surface suboxide layers of native oxide of amorphous silicon have been reconstructed using the determination of an effective mean free path of the electrons by the TPP2M algorithm in conjunction with PARXPS and REELS measurements. Copyright © 2015 John Wiley & Sons, Ltd.     

Pr10[Si10−xAlxO9+xN17−x]Cl with x ≈ 1 – an Oxonitridoaluminosilicate Chloride

The oxonitridoaluminosilicate chloride Pr₁₀[Si_10?xAl_xO_9+xN_17?x]Cl was obtained by the reaction of praseodymium metal, the respective chloride, AlN and Al(OH)₃ with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1900 °C. The crystal structure was determined by single‐crystal X‐ray diffraction (Pbam, no. 55, Z = 2,a = 10.5973(8) Å, b = 11.1687(6) Å, c = 11.6179(7) Å, R1 = 0.0337). The sialon crystallizes isotypically to the oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl, which represent a new layered structure type. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/Noccupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The Si and Al atoms were refined equally distributed on their three crystallographic sites, due to their poor distinguishability by X‐ray analysis. The tetrahedra layers of the structure consist of condensed [(Si,Al)N₂(O,N)₂] and [(Si,Al)N₃(O,N)] tetrahedra of Q² and Q³ type. The chemical composition of the compound was derived from electron probe micro analyses (EPMA).     

Synthesis of BiOClxBr1−x Nanoplate Solid Solutions as a Robust Photocatalyst with Tunable Band Structure

The use of bismuth oxyhalides as photocatalysts has received extensive interest because of their high photocatalytic activity and stability. However, available methods for the synthesis of bismuth oxyhalides with tailored morphologies, well‐defined facets, and tunable band gaps are still lacking. In this work, two‐dimensional BiOCl_xBr_1?x solid solution with exposed {001} facets and tunable band gaps were synthesized by using solvothermal methods. The BiOCl_xBr_1?x solid solution nanoplates crystallized in a homogeneous crystal structure but possessed continuously tuned band gaps from 3.39 to 2.78 eV by decreasing the ratio of Cl/Br. Among the synthesized nanoplates, the BiOCl_0.5Br_0.5 sample exhibited the highest photocatalytic activity for degrading Rhodamine B (RhB), a typical organic pollutant, under visible light. The highest photoactivity of the BiOCl_0.5Br_0.5 sample was attributed to a synergetic effect of higher surface area, facets exposed, and optimized band structure. The results are of profound significance for the design of novel photocatalyst materials.     

[1,2,5]thiadiazolo[3,4‐g]quinoxaline acceptor‐based donor–acceptor–donor‐type polymers: Effect of strength and size of donors on the band gap

Electrochromic polymers based on [1,2,5]thiadiazolo[3,4‐g]quinoxaline acceptor and thiophene, 3,4‐ethylenedioxythiophene and 3,3‐didecyl‐3,4‐proylenedioxythiophene donors, namely poly(6,7‐diphenyl‐4,9‐di(thiophen‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) ( P1 ), poly(4‐(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)‐9‐(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐7‐yl)‐6,7‐diphenyl‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) ( P2 ), and poly(4‐(3,3‐didecyl‐3,4‐dihydro‐2H‐thieno[3,4‐b][1,4]dioxepin‐6‐yl)‐9‐(3,3‐didecyl‐3,4‐dihydro‐2H‐thieno[3,4‐b][1,4]dioxepin‐8‐yl)‐6,7‐diphenyl‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) ( P3 ), respectively, were electrochemically and/or chemically synthesized and characterized. Electrochemical and optical properties of the polymers were then investigated. The results, which were obtained electrochemically and optically, indicate that the polymers bearing the same acceptor and different donor units have a band gap range of 0.59–1.24 eV depending on the strength and size of the donor units and band gap determination method. A significant finding in this study was the phenomenon that when the acceptor is physically huge, the general rule that a weak donor would have a high band gap whereas a strong donor would have low band gap can be broken due to the torsional angles/steric hindrances involved with physically large donor molecules. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3483–3493     

Segregation and Stability in Surface Alloys: PdxRu1−x/Ru(0001) and PtxRu1−x/Ru(0001)

The stability of PdRu/Ru(0001) and PtRu/Ru(0001) surface alloys and the tendency for surface segregation of Pd and Pt subsurface guest metals in these surface alloys is studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Atomic resolution STM imaging and AES measurements reveal that upon overgrowing the surface alloys with a 1–2 monolayer Ru film and subsequent annealing to the temperatures required for initial surface alloy formation, the Ru‐covered Pd (Pt) atoms float back to the outermost layer. The lateral distribution of these species is also essentially identical to that of the initial surface alloys, before overgrowth by Ru. In combination, this clearly demonstrates that the surface alloys represent stable surface configurations, metastable only towards entropically favored bulk dissolution, and that there is a distinct driving force for surface segregation of these species. Consequences of these data on the mechanism for surface alloy formation are discussed.     

Preparation and electrical and magnetic properties of Sr2−xNaxCuO3 (0 ≤ x ≤ 1) solid solutions

Mixed-valence copper(II/III) oxide solid solutions Sr_2?xNa_xCuO₃ (0 ≤ x ≤ 1) have been prepared by solid-state reactions in oxygen atmosphere. All solid solutions exhibit the structure of Sr₂CuO₃ (S.G. Immm). Electrical conductivity and thermoelectric power measurements show a semiconducting behavior in the whole composition range. The electronic structure of Sr₂CuO₃ is compared with that of La₂CuO₄ on the basis of an iono-covalent model. Interpretation of transport properties suggests the formation of small polarons. Magnetic susceptibility and EPR measurements show that the antiferromagnetic ordering of Sr₂CuO₃ tends to vanish as x increases, however magnetic interactions are still strong for a concentration of Cu²⁺ ions corresponding to x = 0.8.     

Theoretical investigation on the photophysical properties of N‐heterocyclic carbene iridium (III) complexes (fpmb)xIr(bptz)3‐x (x = 1−2)

In the search for efficiently phosphorescent materials, this article presents a rational design and theoretical comparative study of some photophysical properties in the (fpmb)_xIr(bptz)_3‐x (x = 1–2), which involve the usage of two 2‐pyridyl triazolate ( bptz ) chromophores and a strong‐field ligand fpmb ( fpmb = 1‐(4‐difluorobenzyl)‐3‐methylbenzimidazolium). The first principle theoretical analysis under the framework of the time‐dependent density functional theory approach is implemented in this article to investigate the electronic structures, absorption and phosphorescence spectra. It is intriguing to note that 1 and 2 exhibit theirs blue phosphorescent emissions with maxima at 504 and 516 nm, respectively. Furthermore, to obtain the mechanism of low phosphorescence yield in 1 and estimate the radiative rate constant k_r for 2 , we approximately measure the radiative rate constant k_r, the spin‐orbital coupling (SOC) value, ΔE (S ? T), and the square of the SOC matrix element (<Ψ_S1.H_SO.Ψ_T1>²) for 1 and 2 . Finally, we tentatively come to conclusion that the switch of the cyclometalated ligand from the main to ancillary chelate seems to lower the splitting ΔE (S ? T) in the current system. © 2012 Wiley Periodicals, Inc. J Comput Chem, 2012     

Origin and Location of Electrons and Protons during the Formation of Intermetalloid Clusters [Sm@Ga3−xH3−2xBi10+x]3− (x=0, 1)

Reaction of [GaBi₃]^2? with [Sm(C₅Me₄H)₃] yielded the first protonated ternary intermetalloid clusters [Sm@Ga_3?xH_3?2xBi_10+x]^3? ( 1 ; x=0,1). The presence of the Ga? H bonds and the transfer of electrons and protons during the formation of 1 were elucidated by a combination of experimental and quantum chemical methods, thereby rationalizing the role of the solvent ethane‐1,2‐diamine as a Brønsted acid. As an organic by‐product, we observed the previously unknown octamethylfulvene ( 2 ) upon C? C coupling of (C₅Me₄H)^?.