磁控溅射沉积制备SnSe薄膜及其热电性能研究

因为晶体结构以及热电性能各向异性,硒化锡(SnSe)沿b轴方向表现出优异的热电性能,受到业内的广泛关注.但关于SnSe薄膜研究的报道较少.本研究利用磁控溅射技术,将SnSe沉积到Si/SiO2基底得到SnSe薄膜,分析了沉积温度对SnSe薄膜结构和热电性能的影响.结果显示:沉积温度升高,晶粒尺寸相应增加,薄膜的结晶质量...     

Al掺杂ZnO薄膜的结构和热电性质研究

用直流反应磁控溅射方法在透明平面玻璃上制备出Al掺杂ZnO薄膜,并对其结构和温差电动势率进行研究.实验结果表明,所制备样品具有C轴择优取向的多晶结构,温差电动势随着温差(△T)的增大而呈线性增加.并且样品的电阻越大,温差电动势率越小.在室温附近的环境温度对温差电动势率几乎无影响.退火处理后,温差电动势率增大.实验还发现,在外加磁场时,温差电动势率稍微减小.     

Structural and thermoelectric properties of HfNiSn half-Heusler thin films

The bulk thermoelectric properties of half-Heusler alloys have recently been extensively studied due to their potential as thermoelectric materials. However, only a few publications have been addressed on thin film systems. The present study investigated the structural and thermoelectric properties of HfNiSn half-Heusler alloy thin films grown at different substrate temperatures: 25 °C, 200 °C, and 400 °C. The crystalline phase and structural variation of the films were determined by X-ray diffraction and scanning electron microscopy. Polycrystalline thin films were obtained for utilizing lower substrate temperatures. The HfNiSn thin films exhibited preferred (111) orientation when substrate temperature was higher than 400 °C. The in-plane Seebeck coefficient and resistivity of HfNiSn thin films with preferred orientation were much lower than those of films without orientation. This implies the thermoelectric properties of HfNiSn alloy may exhibit anisotropic characteristics. The best Seebeck coefficient and power factor of HfNiSn thin films obtained in this work are −68 μV/K and 1.3 μW/K²cm, respectively, measured at room temperature. The effects of partial substitution of Sn by Sb on thermoelectric properties of HfNiSn thin films were also studied with a “pseudo-combinatorial” approach.     

Photoconductive relaxation studies of SnSe thin films

The compound tin selenide was prepared from the constituent elements (Sn and Se) using the standard fusing technique and from X-ray diffraction studies it was identified as tin selenide. Thin films of SnSe were obtained on thoroughly cleaned glass substrates by vacuum sublimation on substrates maintained at 301 K. The photoconductive relaxation of these films was studied with oxidation. The results have been explained with the help of grain boundary potential barrier model.     

Effect of thickness on the thermoelectric properties of PbS thin films

A non-monotonic dependence of the thermoelectric properties of PbS epitaxial films grown on (001)KCl substrates and covered with an EuS protective layer on the PbS layer thickness (d=2-200 nm) was detected at room temperature. The complex character of the dependence on d is attributed to a competition between percolation phenomena and size quantization. Within the framework of percolation theory on the basis of experimental data, the critical exponent for the electrical conductivity was determined. Oscillations in the thickness dependence of the kinetic coefficients are attributed to quantum size effects occurring in thin layers.     

Optimization of growth conditions for SnSe2 thin films

Bulk SnSe₂ was prepared by melting the constituents in stoichiometric proportions and thin films of this material were grown by a flash evaporation technique. X-ray and electron diffraction methods were used for characterization of the bulk material and the films. The effect of substrate temperature on the structural properties, composition and electrical resistivity of the films have been studied. It was found that single-phase polycrystalline stoichiometric films of SnSe₂ can be grown in the substrate temperature range 398 to 623 K. The films deposited at 523 K had the minimum electrical resistivity.     

Optical properties of pulse plated SnSe films

SnSe films were pulse electrodeposited on tin oxide coated glass substrates at different duty cycles. The films were single phase with orthorhombic structure. Optical absorption measurements indicated a band gap in the range of 1.28–1.50 eV with decrease of duty cycle. Transmission spectra exhibited interference fringes. Using the envelope method, refractive index was calculated. From the refractive index and extinction coefficient data, real and imaginary part of dielectric constant were estimated. Optical conductivity was evaluated from the absorption coefficient and refractive index data. Optical data were analysed by the single-effective oscillator model.     

Bi-Te-Se热电薄膜的电化学沉积

在含有Bi 3＋、HTeO2＋、Se4＋离子的水溶液中通过电化学方法实现了Bi2Te3-ySey热电薄膜沉积,研究了电沉积Bi2Te3-ySey的阴极极化曲线及热电薄膜的生长过程,通过电子显微镜（SEM）和能谱仪（EDS）等手段对热电薄膜进行了形貌、成分分析。结果表明电解液的离子组成、沉积电位对薄膜成分、形貌有较大影响。在-0.07V沉积电位下制备的热电薄膜Bi2Te2.75Se0.95晶粒大小均匀,结构致密。     

Realizing enhanced thermoelectric properties in Cu2S-alloyed SnSe based composites produced via solution synthesis and sintering

SnSe emerges as one of the most promising Te-free thermoelectric materials due to its strong anharmonic-ity and multiple valence bands structure.Recently,compositing has been proven effective in optimizing thermoelectric performance of various metal chalcogenides.Herein,a series of SnSe-xCu2S(x=0,0.5％,1％,3％,5％)materials have been fabricated via solution synthesis,particle blending,and spark plasma sinter-ing in sequence.After incorporating Cu2S,the materials become SnSe based composites with Cu doping,S substitution and Cu2SnSe3 secondary phase.We elucidate that the power factor of polycrystalline SnSe can be tuned and enhanced at varied temperature ranges through adjusting the addition amount of Cu2S.Additionally,the composites achieve suppressed lattice thermal conductivity when compared to SnSe itself,as the introduced point defects and SnSe/Cu2SnSe3 interfaces intensify phonon scattering.Conse-quently,SnSe-0.5％Cu2S and SnSe-3％Cu2S achieve a peak zT of 0.70 at 830 K(intermediate temperature range)and a highly increased zT of 0.28 at 473 K(low temperature range),respectively,which are～130％and 200％of values reached by SnSe at the corresponding temperatures.The study demonstrates that our approach,which combines compositing with elemental doping and substitution,is effective in optimizing the thermoelectric performance of SnSe at varied temperature ranges.     

Microstructure and thermoelectric properties of p-type Bi-Sb-Te-Se thin films prepared by electrodeposition method

P-type Bi-Sb-Te-Se thermoelectric thin films with thickness of 8 μm have been prepared by cathodic electrodeposition technique on Au substrate from nitric acid solution system at room temperature. Cyclic voltammetry was used for determination of the deposition potentials of the thin films. In order to enhance the crystallinity, as well as the thermoelectric properties of the deposited films, they were annealed at 523 K for 2 h under nitrogen atmospheric pressure condition. X-ray diffraction (XRD), environmental scanning electron microscopy, and energy-dispersive spectroscopy (EDS) were employed to characterize the thin films. Seebeck coefficients and resistivities of the films were also evaluated. The results revealed that Bi, Sb, Te and Se could be co-deposited to form Bi-Sb-Te-Se semiconductor compound in the solution containing Bi^III, Sb^III, Te^IV and Se^IV and the compositions of the films were sensitive to the electrodepositing potentials. The XRD results suggested that the crystal structure of the thin films were changed from amorphous state to polycrystalline after annealing. The EDS data indicated that the composition of the films was consistent with XRD results. The annealed Bi-Sb-Te-Se thin films exhibited the Seebeck coefficients of 116-133 μV/K and a maximum power factor of 0.62 mW·K^− 2·m^− 1.     

Synthesis and characterization of low particle size nanocrystalline SnSe thin films

Tin selenide (SnSe) nanocrystalline thin films of different thickness from 15 to 70 nm were prepared by inert gas condensation technique. Argon gas flow and substrate temperature were kept constant during deposition process at 2 × 10^?3 Torr and 27 °C respectively. Polycrystalline orthorhombic phase structured was deduced for the prepared SnSe ingot powder by X-ray diffraction pattern. The grazing incident in-plane X-ray diffraction (GIIXD) pattern showed nanocrystalline orthorhombic structure for deposited SnSe thin film. The TEM micrographs showed that thin films were nanocrystalline with particle size in the range from 2 to 5.7 nm. The optical band gap E_g of the thin films due to direct allowed transition have values ranging from 2.5 to 2.13 eV as the particle size increases from 2 to 5.7 nm. The photoconductivity spectra of the nanostructured SnSe thin films of different particle size showed transitions at 2.45, 2.34 and 2.21 eV for films of different particle size.     

Cu/Sn比率对Cu2SnSe3薄膜若干物理性质的影响

利用射频(RF)磁控溅射在玻璃基片上共溅射沉积Cu-Sn预制膜。采用固态硒化法,制备Cu/Sn化学计量比在1.87～2.22之间的Cu2SnSe3薄膜。研究了Cu/Sn比率对Cu2SnSe3薄膜的晶体结构、微结构、光学性能以及电学性能的影响。X射线衍射(XRD)结果表明,所制备的Cu2SnSe3薄膜为立方晶体结构,具有(111)择优取向;贫铜的Cu2SnSe3薄膜光学带隙Eg随着Cu/Sn比率增大而增大;富铜的Cu2SnSe3薄膜光学带隙Eg随着Cu/Sn比率增大而不变。薄膜电阻率为1.67～4.62mΩ.cm。     

Influence of heat treatment on electrical properties of thermally evaporated tin diselenide (SnSe2) thin films

SnSe₂ thin films were prepared on glass substrate by thermal evaporation method. The resistivity of the films were measured in the temperature range 30–200 °C. It is observed that the as grown films are highly resistive and on heating the resistance abruptly changes. The heating and cooling curves of log of resistance versus temperature are not reproducible till the third cycle and this reproducible curve is similar to that for the films annealed at 200 °C for 3 hours.     

Effect of oxidation on thickness dependencies of thermoelectric properties in PbTe/mica thin films

The dependencies of the Hall coefficient R_H and Seebeck coefficient S at room temperature on the thickness (d=10-550 nm) of thin PbTe films prepared by the thermal evaporation in vacuum of n-type PbTe crystals with various charge carrier concentrations (10¹⁷-10¹⁹ cm⁻³) and their deposition on mica substrates were obtained. It was established that, with decreasing thickness of PbTe films, a transition from an electron to a hole conductivity occurs, and the inversion point shifts to smaller d values as the electron concentration in the target material increases. The experimental R_H(d) and S(d) dependencies are interpreted in terms of the acceptor states created by oxygen on the film surface. These dependencies were also calculated theoretically, taking into account the existence of two types of charge carriers (electrons and holes). The theoretical curves are found to be in good agreement with the experimental data.     

Homoepitaxial growth of ZnO films via low-temperature liquid-phase epitaxy

Homoepitaxial ZnO films have been grown via liquid-phase epitaxy (LPE) on (0001) oriented ZnO substrates. X-ray rocking curve revealed the high quality of the ZnO films with a FWHM of 40 arc sec. Films of thickness about 20 μm were grown in the temperature range 700–720 °C. The growth rate of ZnO films was estimated to be 0.3 μm h^− 1. Atomic force microscope analysis showed that the surface roughness of ZnO films was very low, which further confirmed the high crystallinity of ZnO films.     

A facile approach to the synthesis of graphene nanosheets under ultra-low exfoliation temperature

High specific surface area graphene nanosheets have been obtained from graphite oxide by using an effective modified exfoliation method under vacuum, the exfoliation temperature (135 degrees C) is much lower than that conventionally applied (1050 degrees C) to obtain monolayer graphene sheets via rapid thermal shock. These products have fluffy and highly porous structure and with a lateral size typically of a few micrometers. Transmission electron microscopy (TEM) observation shows that it looks like a wrinkled transparent ultrathin film consisting of single or few-layer graphene sheets, and their Brunauer-Emmett-Teller surface area is as large as 750 m2/g. Simultaneously, X-ray photoelectron spectroscopy analysis revealed that considerable amount of oxygen-containing groups (C/O ratio, 5:1) retained on the graphene sheets after exfoliation process, which would provide convenience for further modification of the surface properties and chemistry of graphene sheets. This work offers a facile and scalable approach to fabricate graphene oxide and opens up a new vista of various potential applications electronics and composite materials.     

Electrical characterization of nanocrystalline SnSe and ZnSe thin films: effect of annealing

In this paper, experimental data on the electrical properties of as deposited and annealed nanocrystalline SnSe and ZnSe thin films are reported. The thin films of SnSe and ZnSe are deposited on glass substrate by chemical bath deposition method. The films are studied before and after thermal annealing at temperatures 473 K for 1 h. This annealing is done in vacuum of 2?×?10^?3 mbar. The various electrical parameters like dark conductivity, photoconductivity, activation energy, photosensitivity and carrier life time have been measured on these films before and after annealing.