Synthesis of rod and lath-shaped CuSe and tremella-shaped Cu<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>Se nanostructures at room temperature,and their optical properties

The research for tunable synthesis and characterization techniques is important for the investigation of nanomaterials. Herein we developed old precipitation reaction for the morphology- and phase-tunable synthesis of copper selenides nanostructures at room temperature, avoiding tedious preparation of selenium precursors, such as selenite or selenosulfate. The molar ratio of Cu²⁺ and Se sources served the function of a switch for selectively synthesis of stoichiometric CuSe and non-stoichiometric Cu_2−x Se. Nanorod and lath-like CuSe formed with excess of selenium source, while tremella-shaped Cu_2−x Se responded to the 1:1 of Cu²⁺/Se or excess of copper source. The structures of nanocrystals, especially the lifelike surface, were characterized in detail by electron microscopy techniques, such as STEM. Novel nanostructures put up the excellent absorption properties in the visible light region, respectively, and could bear potential applications in solar cell devices in the future. This strategy offered a convenient, mild and energy-efficient route for the preparation of other mental chalcogenides nanocrystals with different morphologies or tunable phases.     

Oleylamine‐Assisted Phase‐Selective Synthesis of Cu2−xS Nanocrystals and the Mechanism of Phase Control

Environmentally friendly Cu_2?x S compounds exist in many different mixed phases in nature, while their nanoscale counterparts can be pure phase with interesting localized surface plasmon resonance properties. Because of the complexity of composition and phase, controllable synthesis of Cu_2?x S nanocrystals becomes an important scientific issue in colloidal chemistry. In this work, a hot‐injection method is developed to synthesize Cu_2?x S nanocrystals by injecting a sulfur precursor into a copper precursor using oleylamine and octadecene as solvents. By varying the reaction parameters (temperature, volume ratio of oleylamine/octadecene, molar ratio of Cu/S in the precursors), hexagonal CuS, monoclinic Cu_1.75S, and rhombohedral Cu_1.8S, nanocrystals can be selectively synthesized, providing a platform to illustrate the mechanism of crystal phase control. The crystal phase control of Cu_2?x S nanocrystals is oleylamine‐determined by controlling the molar ratio of Cu/S in the reaction precursors as well as the ratio of Cu_2?x S clusters/Cu⁺ in the subsequent reaction. More importantly, temperature plays an important role in varying the molar ratio of Cu/S and Cu_2?x S clusters/Cu⁺ in the reaction system, which significantly influences the crystal phase of the resulting Cu_2?x S nanocrystals. The understanding into crystal control provides a guideline to realize reproducible phase‐selective synthesis and obtain well‐defined high‐quality materials with precise control.     

Cu2ZnSn(S1–xSex)4 thin film solar cells prepared by water‐based solution process

The kesterite Cu₂ZnSn(S_1–xSe_x)₄ (CZTSSe) thin film solar cell has been developed rapidly due to its excellence in structural and optical properties and its abundance in raw materials. Both vacuum‐based and solution‐based methods have been successfully employed to fabricate CZTSSe thin film solar cells. In this Letter, we report an environmentally friendly, water‐based, solution process for fabrication of high‐efficiency CZTSSe thin film solar cells. High quality CZTSSe thin film is obtained by selenization under high temperature and Se vapor. An efficiency of 6.2% is achieved on CZTSSe thin film solar cell fabricated by such water‐based solution process. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photo‐enhanced catalytic activity of spray‐coated Cu2SnSe3 nanoparticle counter electrode for dye‐sensitised solar cells

Cu₂SnSe₃ nanoparticles are synthesised using oleylamine as both a solvent and capping agent and spray coated to form dye‐sensitised solar cell (DSSC) counter electrodes (CEs) using earth‐abundant elements. The film requires annealing at only 400 °C in nitrogen, which is a lower temperature than previous reports of both Cu₂SnSe₃and Cu₂ZnSnSe₄ films, also avoiding the use of Se gas. The composition and phase of the material is confirmed to be kesterite Cu₂SnSe₃. DSSCs using Cu₂SnSe₃ CEs give a power conversion efficiency of 4.87%, compared to 5.35% when using Pt. Electrochemical impedance spectroscopy indicates that the performance of the Cu₂SnSe₃ CE is enhanced under illumination, leading to a drop in the charge transfer resistance. This illumination‐induced enhancement of the catalytic activity provides a novel mechanism for the enhancement of CE performance in DSSCs.

     

In situ investigation of the formation of Cu(In,Ga)Se2 from selenised metallic precursors by X-ray diffraction—The impact of Gallium, Sodium and Selenium excess

The chemical reactions during rapid thermal processing of stacked elemental layers were investigated by angle-dispersive in situ X-ray diffraction. With a time resolution of 5 diffractograms per minute four different solid state reactions resulting in ternary chalcopyrites were identified: (A) CuSe+InSe→CuInSe₂, (B) Cu₂Se+2InSe+Se→2CuInSe₂, (C) Cu₂Se+In2Se₃→2CuInSe₂, (D) Cu₂Se+Ga2Se₃→2CuGaSe₂. All these reactions form pure tenary chalcopyrites. The reaction resulting in the mixed crystal Cu(In,Ga)Se₂ starts not before (B) has begun. The reaction speed of (A) and the fraction of CuInSe₂ formed by (B) depend on Na-doping and Se-pressure, (C) takes place only, if the reaction paths (A) and (B) are suppressed. Reaction (D) is observed only, if 25% In is replaced by Ga in the precursor. The diffractograms were evaluated by Rietveld refinement to give the phase contents of the samples as a function of reaction time.     

Fe39.4－xCo40Si9B9Nb2.6Cux纳米晶合金的有效磁各向异性研究

采用多晶材料趋近饱和定律研究了非晶Fe_39.4-xCo₄₀Si₉B₉Nb_2.6Cu_x(x=0.5,1,1.5) 合金在不同温度纳米晶化后的有效磁各向异性常数〈K〉.结果表明， Cu含量较低(x=0.5)时，纳米晶粒较大并且在较低的退火温度(550℃)下析出硬磁相，〈K〉随退火温度T_a升高显著增加；随着Cu含量的增加，有效地细化了晶粒，并且抑制了硼化物的析出，〈K〉明显减小.讨论了〈K〉与晶粒尺寸D及初始磁导率的关系. 关键词： 纳米晶 有效磁各向异性 磁导率 FeCo基合金     

Sonochemical synthesis of silver, copper and lead selenides

Ag₂Se, CuSe and PbSe were prepared by irradiating the mixtures of AgNO₃, CuI or PbCl₂ with selenium in ethylenediamine (en) with ultrasound at 18 kHz, using a commercial ultrasonic cleaner, respectively. X-ray powder diffraction (XRD) patterns and transmission electron microscope (TEM) images show that the products are orthorhombic Ag₂Se, hexagonal CuSe and cubic PbSe, respectively, and all are well crystallized in nanometers.     

Simple solar cells of 3.5% efficiency with antimony sulfide‐selenide thin films

Thin films of antimony sulfide‐selenide solid solutions (Sb₂S_x Se_3–x) were prepared by chemical bath deposition and thermal evaporation to constitute solar cells of a transparent conductive oxide (FTO)/CdS/Sb₂S_x Se_3–x/C–Ag. The cell parameters vary depending on the sulfide‐selenide composition in the films. The best solar cell efficiency of 3.6% was obtained with a solid solution Sb₂S_1.5Se_1.5 prepared by thermal evaporation of the precipitate for which the open circuit voltage is 0.52 V and short circuit current density, 15.7 mA/cm²under AM 1.5G (1000 W/m²) solar radiation. For all‐chemically deposited solar cells of Sb₂S_1.1Se_1.9 absorber, these values are: 2.7%, 0.44 V, and 15.8 mA/cm², and for Sb₂S_0.8Se_2.2, they are: 2.5%, 0.38 V and 18 mA/cm². (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Phase transition and high temperature thermoelectric properties of copper selenide Cu2-x Se （0 ≤ x ≤ 0.25）

With good electrical properties and an inherently complex crystal structure, Cu_2-xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu_2-xSe (0 ≤ x ≤ 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu_2-xSe were investigated in the temperature range of 300 K—750 K. The results of X-ray diffraction at room temperature show that Cu_2-xSe compounds possess a cubic structure with a space group of Fm3m (#225) when 0.15 < x le 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤ x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu₂Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.     

Structural,thermal and electrical properties of the semiconductor system Ag(1−x)CuxInSe2

This paper presents a study of bulk samples synthesized of the Ag_1−xCu_xInSe₂ semiconductor system. Structural, thermal and electrical properties, as a function of the nominal composition (Cu content) x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 were studied. The influence of x on parameters such as melting temperature, solid phase transition temperature, lattice parameters, bond lengths, crystallite size t (coherent domain), electrical resistivity, electrical mobility and majority carrier concentration was analyzed. The electrical parameters are analyzed at room temperature. In general, it is observed that the properties of the Ag_1−xCu_xInSe₂ system for x≤0.4 are dominated by n-AgInSe₂, while for x>0.4, these are in the domain of p-CuInSe₂. The crystallite size t in the whole composition range (x) is of the order of the nanoparticles. Secondary phases (CuSe, Ag₂Se and InSe) in small proportion were identified by XRD and DTA.     

多晶Mn1-xCux(0.1≤x≤0.3)合金的磁诱发应变

采用X射线衍射分析、显微形貌观察、差示扫描量热法、标准电阻应变计法等实验方法,研究了室温下多晶Mn_1-xCu_x(0.1≤x≤0.3,原子分数)合金在低磁场中的磁诱发应变性能.结果表明,Mn_1-xCu_x合金经过长时间的固溶处理,在冷却过程中会出现fcc(γ)→fct(γ’)马氏体相变,形成(γ+γ 关键词： 磁诱发应变 MnCu合金 马氏体相变     

CoxCu1-x复相纳米线阵列的制备及其磁性的研究

利用电化学沉积方法在同一种富Co²⁺溶液Co²⁺/Cu²⁺=10∶1中,利用不同的沉积电位成功地制备了一系列不同成分(x=0.38—0.87)和复合相结构的Co_xCu_1-x纳米线阵列.发现随着纳米线中Cu含量的变化,Co_xCu_1-x纳米线的复相结构随之发生规律的变化,最终导致纳米线的磁性也随之规律的变化.随着纳米线中Cu含量的不断增加,一部分Cu与Co形成面心立方结构(fcc)的CoCu固溶体,减弱了磁晶各向异性与形状各向异性的竞争,从而提高样品的方形度;一部分Cu以fcc结构的Cu单质的形式存在于纳米线中,并随着Cu颗粒大小的不同分别起到破坏磁晶各向异性和钉扎畴壁的作用,从而增加纳米线的方形度和矫顽力.对比不同成分的样品,发现Co_xCu_1-x纳米线的方形度和矫顽力的最大值分别出现在Co₇₅Cu₂₅和Co₆₀Cu₄₀中,并且由于其特殊的复相结构致使它们的值要好于相同直径的单相结构的结果. 关键词： 纳米线 电化学沉积 磁性     

Cationic Polyelectrolyte Mediated Synthesis of MnO2‐Based Core–Shell Structures as Activatable MRI Theranostic Platform for Tumor Cell Ablation

Improving nanomaterial imaging contrast is critical for disease diagnosis and treatment monitoring. Designing activatable imaging agents has the extra benefit of improving signal‐to‐background ratios, as well as reporting local environmental cues. MnO₂, sensitive to local pH and redox state, is used to modulate the tumor microenvironment and can serve as a potential activatable magnetic resonance imaging (MRI) agent. However, the intrinsic 2D form may limit their applications in nanomedicine. Here, a novel facile aqueous route to synthesize MnO₂ nanoshells on various core nanomaterials, regardless of their chemical nature and morphology, is reported. Cationic polyelectrolyte is discovered to be the key to obtain a universal method of coatingMnO₂ on nanomaterials. Taking Cu_2−xSe@MnO₂ as an example, a remarkable three times enhanced T₁‐MRI contrast in a tumor reducing environment is demonstrated. Combined with large optical absorbance of inner Cu_2−xSe cores, they can be applied for efficient redox‐activated MRI‐guided photothermal therapy in the NIR‐II window in vitro and in vivo.     

Contact passivation in silicon solar cells using atomic‐layer‐deposited aluminum oxide layers

Atomic‐layer‐deposited aluminum oxide (AlO_x) layers are implemented between the phosphorous‐diffused n⁺‐emitter and the Al contact of passivated emitter and rear silicon solar cells. The increase in open‐circuit voltage V_oc of 12 mV for solar cells with the Al/AlO_x/n⁺‐Si tunnel contact compared to contacts without AlO_x layer indicates contact passivation by the implemented AlO_x. For the optimal AlO_x layer thickness of 0.24 nm we achieve an independently confirmed energy conversion efficiency of 21.7% and a V_oc of 673 mV. For AlO_x thicknesses larger than 0.24 nm the tunnel probability decreases, resulting in a larger series resistance. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nanoscale C‐Rich SixC1−x Bus/Ring Waveguide Based Cross‐Wavelength Data Converter

The carbon‐rich silicon carbide (C‐rich Si_xC_1?x) micro‐ring channel waveguide with asymmetric core aspect is demonstrated for all‐optical cross‐wavelength pulsed return‐to‐zero on‐off keying (PRZ‐OOK) data conversion. Enhanced nonlinear optical Kerr switching enables 12‐Gbit per second data processing with optimized modulation depth. The inverse tapered waveguide at end‐face further enlarges the edge‐coupling efficiency, and the asymmetric channel waveguide distinguishes the polarization modes. To prevent data shape distortion, the bus/ring gap spacing is adjusted to control the quality factor (Q‐factor) of the micro‐ring. Designing the waveguide cross section at 500 × 350 nm² provides the C‐rich Si_xC_1?x channel waveguide to induce strong transverse electric mode (TE‐mode) confinement with a large Kerr nonlinearity of 2.44 × 10^?12 cm² W^?1. Owing to the trade‐off between the Q‐factor and the on/off extinction ratio, the optimized bus/ring gap spacing of 1400 nm is selected to provide a coupling ratio at 5–6% for compromising the modulation depth and the switching throughput. Such a C‐rich Si_xC_1?x micro‐ring with asymmetric channel waveguide greatly enhances the cross‐wavelength data conversion efficiency to favor its on‐chip all‐optical data processing applications for future optoelectronic interconnect circuits.     

dc ionic conductivity measurements on the mixed conductor Cu2−xSe

A brief review and some remarks on the theory and practice of the four point dc ionic conductivity measurement in a mixed conductor are presented. Measurements were made on Cu_2?xSe which has the electronic to ionic conductivity ratio of 2×10³–2×10⁵. The transients which appear on the voltage probes when a constant current is sent through the sample were found in complete agreement with the dependence predicted from the solution of the diffusion equation. Temperature dependence of σ_i of Cu_1.99Se in the range between 40°C and 180°C confirms the expected behaviour in the low- and high-temperature and intermediate phase. Composition dependence of σ_i of Cu_2?xSe in the high-temperature phase is not linear in x.     

Band gap tunable and improved microstructure characteristics of Cu2ZnSn(S1−x,Sex)4 thin films by annealing under atmosphere containing S and Se

Cu₂ZnSn(S_xS_1?x)₄ (CZTSSe) thin films were prepared by annealing a stacked precursor prepared on Mo coated glass substrates by the sputtering technique. The stacked precursor thin films were prepared from Cu, SnS₂, and ZnS targets at room temperature with stacking orders of Cu/SnS₂/ZnS. The stacked precursor thin films were annealed using a tubular two zone furnace system under a mixed N₂ (95%) + H₂S (5%) + Se vaporization atmosphere at 580 °C for 2 h. The effects of different Se vaporization temperature from 250 °C to 500 °C on the structural, morphological, chemical, and optical properties of the CZTSSe thin films were investigated. X-ray diffraction patterns, Raman spectroscopy, and X-ray photoelectron spectroscopy results showed that the annealed thin films had a single kesterite crystal structure without a secondary phase. The 2θ angle position for the peaks from the (112) plane in the annealed thin films decreased with increasing Se vaporization temperature. Energy dispersive X-ray results showed that the presence of Se in annealed thin films increased from 0 at% to 42.7 at% with increasing Se vaporization temperatures. UV–VIS spectroscopy results showed that the absorption coefficient of all the annealed thin films was over 10⁴ cm^?1 and that the optical band gap energy decreased from 1.5 eV to 1.05 eV with increasing Se vaporization temperature.     

A new green synthesis method of CuInS<Subscript>2</Subscript> and CuInSe<Subscript>2</Subscript> nanoparticles and their integration into thin films

A new preparation method for CuInS₂ and CuInSe₂ nanoparticles synthesis is described without using any organic solvent. Heating Cu, In, and S/Se precursors dissolved in water for 30 min in a microwave oven in the presence of mercapto-acetic acid leads to monodispersed chalcopyrite nanoparticles. No precipitation of these nanoparticles is observed after several months at room temperature. These new materials have been thoroughly characterized to confirm their compositions, sizes, and structure without any filtration. Transmission electron microscopy (TEM) confirmed particle sizes below 5 nm. Energy dispersive X-ray analysis (EDXA) confirmed the chemical composition of these samples. X-ray diffraction (XRD) showed a chalcopyrite-type structure with crystallite size of about 2 nm. No difference has been observed between batch and continuous synthesis processes. Cu _x InS₂ and Cu _x InSe₂ nanoparticles, with x < 1, have been also synthesized and identified. Simulation using a commercial software confirmed the difference between copper poor (Cu _x InS₂) and copper rich (CuInS₂) chalcopyrite structures. Conventional spray deposition techniques have been used to form relatively thin films on solid substrates.     

Band alignment at sputtered ZnSx O1–x/Cu(In,Ga)(Se,S)2 heterojunctions

Valence band offsets ΔE_VBM at ZnS_x O_1–x/Cu(In,Ga)(Se,S)₂ (CIGSSe) heterojunctions have been studied by photoemission spectroscopy (XPS, UPS) as a function of composition x in sputtered ZnS_x O_1–x films. In the composition range from ZnO to ZnS we found ΔE_VBM between –(2.1 ± 0.3) eV and –(0.8 ± 0.4) eV, respectively. Considering the optical band gaps, the conduction band offsets ΔE_CBM range from –(0.1 ± 0.3) eV to +(1.4 ± 0.4) eV. These results suggest that sputtered ZnS_x O_1–x is suitable as substitution for the CdS buffer and ZnO window layers in standard chalcopyrite‐based solar cells. Current–voltage characteristics of the solar cells have been investigated as a function of the composition x. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reaction-diffusion-induced explosive crystallization in a metal–selenium nanometer film structure

Experimental data for reaction-diffusion-induced explosive crystallization in a nanodimensional metal (Cu, Ag)/selenium structure are presented. It is found that after the metal layer has completely diffused into the amorphous Se film, the electrical potential rises from 0.14 to 1.21 V in the Cu(30 nm)/Se(140 nm) heterolayer and from 0.01 to 1.17 V in the Ag(30 nm)/Se(140 nm) heterolayer. The metals diffusing into the amorphous Se layer interact with Se, forming nuclei of a new phase (CuSe or Ag₂Se). The intense growth of the CuSe and Ag₂Se crystallization centers results in a considerable liberation of latent energy in the form of phase transformation heat and in explosive growth of CuSe and Ag₂Se nanocrystalline particles. The mean size of CuSe and Ag₂Se crystallites equals 25 and 50 nm, respectively.