Reorientation effect measurements of 122Te and 130Te

Coulomb excitation probabilities of the first 2 ⁺ states of ¹²²Te and ¹³⁰Te have been determined. The measurement was performed by resolving the inelastically and elastically scattered ⁴He and ¹⁶O projectiles using eight surface barrier detectors between 44° and 173°. Quadrupole moments Q₂⁺ as well as B(E2, 0⁺ → 2⁺) values were deduced. The Q₂⁺ found for the positive sign of the 2₂⁺ interference term are ?0.46±0.05 e · b and ?0.15±0.10 e · b for ¹²²Te and ¹³⁰Te respectively.     

Theoretical and experimental investigations of the properties of Ge2Sb2Te5 and indium-doped Ge2Sb2Te5 phase change material

We have carried out comprehensive computational and experimental study on the face-centered cubic Ge₂Sb₂Te₅ (GST) and indium (In)-doped GST phase change materials. Structural calculations, total density of states and crystal orbital Hamilton population have been calculated using first-principle calculation. 5 at.% doping of In weakens the Ge–Te, Sb–Te and Te–Te bond lengths. In element substitutes Sb to form In–Te-like structure in the GST system. In–Te has a weaker bond strength compared with the Sb–Te bond. However, both GST and doped alloy remain in rock salt structure. It is more favorable to replace Sb with In than with any other atomic position. X-ray diffraction (XRD) analysis has been carried out on thin film of In-doped GST phase change materials. XRD graph reveals that In-doped phase change materials have rock salt structure with the formation of In₂Te₃ crystallites in the material. Temperature dependence of impedance spectra has been calculated for thin films of GST and doped material. Thickness of the as-deposited films is calculated from Swanepoel method. Absorption coefficient (α) has been calculated for amorphous and crystalline thin films of the alloys. The optical gap (indirect band gap) energy of the amorphous and crystalline thin films has also been calculated by the equation \( \alpha h\nu = \beta (h\nu - E_{\text{g }} )^{2} \) . Optical contrast (C) of pure and doped phase change materials have also been calculated. Sufficient optical contrast has been found for pure and doped phase change materials.     

Ferromagnetism modulation by phase change in Mn-doped GeTe chalcogenide magnetic materials

In this work, an effective method to modulate the ferromagnetic properties of Mn-doped GeTe chalcogenide-based phase change materials is presented. The microstructure of the phase change magnetic material Ge_1?x Mn _x Te thin films was studied. The X-ray diffraction results demonstrate that the as-deposited films are amorphous, and the crystalline films are formed after annealing at 350 °C for 10 min. Crystallographic structure investigation shows the existence of some secondary magnetic phases. The lattice parameters of Ge_1?x Mn _x Te (x = 0.04, 0.12 and 0.15) thin films are found to be slightly different with changes of Mn compositions. The structural analysis clearly indicates that all the films have a stable rhombohedral face-centered cubic polycrystalline structure. The magnetic properties of the amorphous and crystalline Ge_0.96Mn_0.04Te were investigated. The measurements of magnetization (M) as a function of the magnetic field (H) show that both amorphous and crystalline phases of Ge_0.96Mn_0.04Te thin film are ferromagnetic and there is drastic variation between amorphous and crystalline states. The temperature (T) dependence of magnetizations at zero field cooling (ZFC) and field cooling (FC) conditions of the crystalline Ge_0.96Mn_0.04Te thin film under different applied magnetic fields were performed. The measured data at 100 and 300 Oe applied magnetic fields show large bifurcations in the ZFC and FC curves while on the 5,000 Oe magnetic field there is no deviation.     

Synthesis of α-In 2 Te 3 thin films from In/Te bilayer by Si ion irradiation

In this work, In/Te bilayer thin films were prepared using sequential thermal evaporation method and subsequently irradiated using swift heavy ions (SHIs) of 100 MeV silicon (Si) with different fluences (1×10¹³ to 5×10¹³/cm²). The inter-diffusion of In and Te layers was highly controlled by SHI irradiation and the In₂Te₃ formation capability was compared with that of the conventional annealing method. The structural as well as optical properties of a post-sintered SHI-irradiated In/Te bilayer were investigated using X-ray diffraction (XRD) measurements and UV–visible spectroscopy, respectively. We found that irradiated samples showed single-phase In₂Te₃ under post-annealed conditions at 150 °C unlike that prepared using the conventional thermal annealing method, which showed mixed phases under similar conditions. This confirms the effective inter-diffusion in bilayer films by SHI irradiation toward the formation of single-phase In₂Te₃. The estimated optical band gap energy was found to be 1.1±0.5 eV and strongly corroborated the XRD results. In addition, the estimated refractive index (n) value of the SHI-irradiated sample (～3.3) was higher than that of the sample obtained through the conventional annealing method (～2.8). This proves that SHI offers a highly compact nature even at low temperatures. This work has a wide scope for achieving single-phase alloyed films through bilayer mixing by SHI irradiation.     

Lattice site location and electronic structure of Te in GaAs

High purity <100> wafers of GaAs were implanted with radioactive^129mTe and stable¹²⁸Te at 110 keV to total doses of 2×10¹⁴ and 2×10¹⁵ Te/cm² respectively and studied with RBS/ channeling and Mössbauer spectroscopy on the 27.8 keV level of¹²⁹I. After implantation and/or annealing at temperatures between 200–300°C the Mössbauer spectra are dominated by a single line. Channeling reveals an appreciable residual damage in the host lattice, but also points to a substitutional position of the Te atoms. After annealing above ≌500°C, where nearly complete lattice damage recovery is obtained, the Te atoms become defect-associated. The results clearly point to the formation of Te_As?V_Ga complexes.     

Evidence for insulator–metal transition in amorphous chalcogenide Se–Ge–Te films

The temperature dependence of the dc conductivity and thermoelectric power was determined for five different amorphous chalcogenide Se–Ge–Te films, with Ge?=?3.0–22?at.%, Se?=?0–97?at.% and Te?=?0–97?at.%. The films were prepared by thermal evaporation of GeSe₄, GeTe₄ and GeSe₂Te₂ quenched bulk materials. Values of the activation energy calculated from the temperature dependence of both electrical conductivity and thermoelectric power showed a decrease with increasing Ge content in the Se–Ge films as well as with replacement of Te for Se in the Se–Ge–Te films. The results showed an Anderson transition, with the conductivity showing insulating behaviour on the Ge–Se side to metallic behaviour at the binary composition Ge–Te. The radius of localization was obtained for the different compositions investigated. The wave function associated with the charge carriers at the composition Ge_3.3Te_96.7 is non-localized. A minimum metallic conductivity of 237?±?5?(Ω?cm)^?1 was found.     

Enhanced thermoelectric properties of PEDOT/PSS/Te composite films treated with H<Subscript>2</Subscript>SO<Subscript>4</Subscript>

Firstly, tellurium (Te) nanorods with a high Seebeck coefficient have been integrated into a conducting polymer PEDOT/PSS to form PEDOT/PSS/Te composite films. The Seebeck coefficient of the PEDOT/PSS/Te (90 wt.%) composite films is ~191 μV/K, which is about 13 times greater than that of pristine PEDOT/PSS. Then, H₂SO₄ treatment has been used to further tune the thermoelectric properties of the composite films by adjusting the doping level and increasing the carrier concentration. After the acid treatment, the electrical conductivity of the composite films has increased from 0.22 to 1613 S/cm due to the removal of insulating PSS and the structural rearrangement of PEDOT. An optimized power factor of 42.1 μW/mK² has been obtained at room temperature for a PEDOT/PSS/Te (80 wt.%) sample, which is about ten times larger than that of the untreated PEDOT/PSS/Te composite film.     

Cd1－xZnxTe晶体的In气氛扩散热处理研究

为了满足辐射探测器件的需要，将生长得到的Cd_1-xZn_xTe晶体在In 气氛下进行退火处理能有效提高晶体的电阻率等性能. 退火处理过程的实质是一个扩散过程 ，因此研究扩散系数与Cd_1-xZn_xTe晶体的性能特别是电阻率变化之 间的关系具有重要的意义. 建立了退火处理过程中Cd_1-xZn_xTe晶体 材料电阻率及导电类型变化与杂质的扩散系数之间关系的模型.结合实验数据，获得了10 关键词： CdZnTe 热处理 In气氛 扩散系数     

Fast and wide-band response infrared detector using porous PZT pyroelectric thick film

Porous lead zirconate titanate (PbZr_0.3Ti_0.7O₃, PZT30/70) thick films and detectors for pyroelectric applications have been fabricated on alumina substrates by screen-printing technology. Low temperature sintering of PZT thick films have been achieved at 850 °C by using Li₂CO₃ and Bi₂O₃ sintering aids. The microstructure of PZT thick film has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dielectric properties were measured using HP 4284 at 1 kHz under 25 °C. The permittivity and loss tangent of the thick films were 94 and 0.017, respectively. Curie temperature of PZT thick film was 425 °C as revealed by dielectric constant temperature measurement. The pyroelectric coefficient was determined to be 0.9 × 10⁻⁸ Ccm⁻² K⁻¹ by dynamic current measurement. Infrared detector sensitive element of dual capacitance was fabricated by laser directly write technology. Detectivity of the detectors were measured using mechanically chopped blackbody radiation. Detectivity ranging from 1.23 × 10⁸ to 1.75 × 10⁸ (cm Hz^1/2 W⁻¹) was derived at frequency range from 175.5 Hz to 1367 Hz, and D^*’s −3 dB cut-off frequency bandwidth was 1.2 kHz. The results indicate that the infrared detectors based on porous thick films have great potential applications in fast and wide-band frequency response conditions.     

Te/TeO2-SiO2复合薄膜的吸收和非线性光学特性研究

应用分光光度计测量Te/TeO₂-SiO₂复合薄膜的透射光谱和吸收光谱, 在480nm附近观察到Te颗粒引起的等离子体共振吸收峰; 采用Z扫描技术研究了共振(激发波长为532 nm)和非共振情况下(激发波长1064 nm) 不同电位制备薄膜的Te颗粒状态与复合薄膜的三阶非线性极化率的关系. 基于有效介质理论对复合薄膜的三阶非线性效应进行分析, 研究Te颗粒大小对Te/TeO₂-SiO₂复合薄膜的非线性光学性质的影响及其产生机理. 结果表明薄膜制备过电位增大, Te的粒径减小, 颗粒数量多, 颗粒分布趋于均匀, 使得金属颗粒的表面等离子体共振峰红移, 吸收强度增强, 导致三阶非线性光学效应增强, χ⁽³⁾由1064 nm的5.12×10^-7 esu增大为532 nm的8.11×10^-7 esu. 关键词： 碲 二氧化碲 复合薄膜 三阶非线性     

125Te NMR chemical-shift trends in PbTe–GeTe and PbTe–SnTe alloys

Complex tellurides, such as doped PbTe, GeTe, and their alloys, are among the best thermoelectric materials. Knowledge of the change in ¹²⁵Te NMR chemical shift due to bonding to dopant or “solute” atoms is useful for determination of phase composition, peak assignment, and analysis of local bonding. We have measured the ¹²⁵Te NMR chemical shifts in PbTe-based alloys, Pb_1−xGe_xTe and Pb_1−xSn_xTe, which have a rocksalt-like structure, and analyzed their trends. For low x, several peaks are resolved in the 22-kHz MAS ¹²⁵Te NMR spectra. A simple linear trend in chemical shifts with the number of Pb neighbors is observed. No evidence of a proposed ferroelectric displacement of Ge atoms in a cubic PbTe matrix is detected at low Ge concentrations. The observed chemical shift trends are compared with the results of DFT calculations, which confirm the linear dependence on the composition of the first-neighbor shell. The data enable determination of the composition of various phases in multiphase telluride materials. They also provide estimates of the ¹²⁵Te chemical shifts of GeTe and SnTe (+970 and +400±150 ppm, respectively, from PbTe), which are otherwise difficult to access due to Knight shifts of many hundreds of ppm in neat GeTe and SnTe.     

Pulsed laser deposition conditions and superconductivity of FeSe thin films

We report the effects of growth conditions on the superconducting properties of FeSe films epitaxially grown on LaAlO₃ substrates by pulsed laser deposition (PLD). Customary materials characterization techniques [X-ray diffraction (XRD), in-situ X-ray photoelectron spectroscopy (XPS), in-situ ultra-violet photoelectron spectroscopy (UPS), and scanning electron microscopy (SEM)] revealed the films had a c-axis oriented tetragonal structure with lattice constants dependent on the growth temperature (varied from 100 to 600°C). The standard four-point probe method was used to measure the resistivity and superconducting transitions. Films grown at 400–550°C showed a clear superconducting onset but no zero resistance down to 2 K. The highest superconducting onset temperature (T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}) of 8 K was observed in films grown at 500°C and the onset temperature was clearly correlated to the ratio of the lattice constants (c/a). As the thickness of the FeSe films increased from 27 nm to 480 nm, T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}} also increased as the strain in the system was relaxed.     

Structuring effect of heteroepitaxial CdHgTe/CdZnTe systems under irradiation with silver ions

The characteristics of a damaged layer of p-Cd _x Hg_{1 ? x} Te/CdZnTe (x ～ 0.223) heterostructures after implantation by 100-keV silver ions with the implantation dose Q = 3.0 × 10¹³ cm^?2 have been obtained using X-ray diffraction, atomic force microscopy, and electron microscopy. It has been found that, as a result of the ion implantation and subsequent annealing (75°C), a uniform array of nanostructures is formed on the surface of Hg(Cd)Te/Zn(Cd)Te samples. The X-ray diffraction patterns of the structurized Hg(Cd)Te/Zn(Cd)Te sample indicate the formation of polycrystalline Hg(Cd)Te phases of cubic structure with a composition x ～ 0.20 and also oxide Ag₂O in the subsurface (<100 nm) region of the host material. The observed effects of transformation of the defect-impurity system and structuring of the surface of the heteroepitaxial film of the low-energy-gap semiconductor have been explained using a deformation model.     

Evolution of thermal conductivity of In3Sbβ Teγ thin films up to 550 °C

The temperature dependent thermal conductivity of In–Sb–Te thin films has been measured by modulated photothermal radiometry in the 20–550 °C range for samples with different Te content. Significant changes with temperature are observed and ascribed to a sequence of structural transformations on the basis of in‐situ Raman spectra. The data suggest that the as‐deposited material consisting of a mixture of polycrystalline InSb_0.8Te_0.2and amorphous Te first undergoes a progressive crystallization of the amorphous part, mostly above 300 °C. Further increase in temperature above 460 °C leads, for higher Te content in the alloy, to the formation of crystalline In₃SbTe₂, intertwined with a less conductive compound, possibly InTe and/or InSb. Upon cooling to room temperature, the initial polycrystalline InSb_0.8Te_0.2phase is mostly recovered along with other compounds, with a slightly higher thermal conductivity than that of the as deposited material. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Studies on Structural,Morphological and Optical Properties of Chemically Deposited CdS<Subscript>1-x</Subscript>Se<Subscript>x</Subscript> Thin Films

The thin films of CdS_1-xSe_x were successfully deposited over glass substrates by chemical bath deposition technique. Cadmium acetate, thiourea and sodium selenosulfate were used as source materials for Cd²⁺, S^2? and Se^2? ions, while 2-mercaptoethanol was used as capping agent. The various deposition conditions such as precursor concentration, deposition temperature, pH and deposition time were optimized for the deposition of CdS_1-xSe_x thin films of good quality and the films were annealed at 200° and 300 °C. The structural, morphological, chemical and optical properties were examined by various characterization techniques and discussed in detail. The optical band gap of CdS_1-xSe_x thin film samples were estimated and found in the range from 2.11 to 1.79 eV for as-deposited and annealed thin films.     

Electro-Optic Coefficient Measurements for Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript> Te Single Crystals at 1550 nm Wavelength

Nonlinear optical materials of the type Zn _x Cd_1-x Te single crystals, where x = 0.0, 0.2, 0.4, 0.6, 0.7, 0.8, and 1.0, have been grown by the Bridgman method, using a vertical furnace. We have investigated the electro-optic (E-O) coefficient and refractive index of Zn _x Cd_1-x Te single crystals at optical communication wavelength (1550 nm). In the case of CdTe crystal, the E-O coefficient was 15.5 × 10^-12 m/V, which is the biggest among the E-O coefficients of Zn _x Cd_1-x Te crystals. The E-O modulation signal was very big in low frequency range (DC-100kHz), but the signal amplitude became smaller as we increased frequency above 100 kHz. We also found the acousto-optic modulation at CdTe single crystals.     

Impurity lattice sites after implantation of Te and Sb in GaAs: Search for the DX centre

¹¹⁹Sn Mössbauer Spectroscopy has been applied to study the nearest environment of radioactive^119mTe and¹¹⁹Sb atoms implanted into GaAs. After a low-dose implantation and annealing above 300°C the impurity atoms are found at As sites. High-dose implantation and annealing above 600°C results in the population of at least two additional sites; these are clearly different for Te and Sb. No evidence is found for the population of DX-centres. A likely possibility is the formation of coherent Ga₂Te₃ precipitates.     

Bi-Sb-Te基热电薄膜温差电池离子束溅射制备与表征

本文采用离子束溅射Bi/Te和Sb/Te二元复合靶,直接制备n型Bi₂Te₃热电薄膜和p型Sb₂Te₃热电薄膜.在退火时间同为1 h的条件下,对所制备的Bi₂Te₃薄膜和Sb₂Te₃薄膜进行不同温度的退火处理,并对其热电性能进行表征.结果表明,在退火温度为150 ℃时,制备的n型Bi₂Te₃关键词： 薄膜温差电池 2Te₃薄膜')" href="#">Sb₂Te₃薄膜 2Te₃薄膜')" href="#">Bi₂Te₃薄膜 离子束溅射     

Optical characterization of nano-structured Cu2ZnSnS4 thin films deposited by GLAD technique

In this paper, Cu₂ZnSnS₄ (CZTS) thin films were elaborated at room temperature by thermal evaporation method using Glancing Angle Deposition (GLAD) technique at different incident angles γ = 00°, 20°, 40°, 60°, 75° and 85°. XRD, Raman scattering analysis, (SEM) and UV-Visible-NIR spectroscopy were used to characterize the crystalline structure, morphology and optical properties of CZTS samples. The results have showed that the ellipsometric analysis leaded to an optical anisotropy due to the structural anisotropy for CZTS samples deposited at γ = 85°. All Cu₂ZnSnS₄ samples exhibited a high absorption coefficient (α > 10⁴ cm⁻¹) and a direct optical transition varied between 1.48 eV and 2.05 eV for CZTS thin films deposited at γ = 00° and 85°, respectively. The value of the Urbach energy increased with incident angle, indeed, its value increased from 58 meV (γ = 00°) to 604 meV (γ = 75°) and decrease to be 368 meV for γ = 85°. This result is correlated with the Raman analysis. From transmittance data of CZTS thin films deposited at γ = 00°, 20° and 40° Swanepoel's method was used, to estimate the refractive index n. It allows us, using the Wemple-DiDomenico and Spitzer-Fan models, to calculate other optical parameters such as the oscillator energy E₀, dispersion energy E_d, zero frequency refractive index n₀, high frequency dielectric constant ε_∞ and the electric susceptibility χ_e. On the other hand, to have an idea about the evolution of the nonlinear optical character, the nonlinear susceptibility χ⁽³⁾ and the nonlinear refractive index n₂ of CZTS thin films deposited at γ = 00°, 20° and 40° were investigated. Ellipsometric measurements of CZTS thin films has leaded to an optical anisotropy for γ = 85°. In addition, the generalized ellipsometry in Jones formalism have proved this property, which can be related to the nano-columnar slanted structure as revealed by (SEM) analysis.