Scanning tunneling microscope light emission spectra of polycrystalline Ge2Sb2Te5 and Sb2Te3

We have observed scanning tunneling microscope light emission (STM-LE) spectra of Ge₂Sb₂Te₅ and Sb₂Te₃. Although these chalcogenide alloys exhibit band gaps less than 0.5 eV, the STM-LE was observed with a narrow spectral width at a photon energy of 1.5 eV for both materials. By analyzing its bias voltage, polarity, and temperature dependencies combined with recently reported theoretical electronic structures, we concluded that the STM-LE is excited by electronic transitions taking place in the local electronic structure having a direct gap-like shape with a band gap of 1.5 eV, commonly found in the electronic structures of both materials.     

X-ray Photoelectron Spectroscopy of Sb2S3 Crystals

The paper presents the X-ray photoelectron spectra (XPS) of the valence band and core levels of semiconductor ferroelectric Sb₂S₃ single crystals, which show weak phase transitions and anomalies of various physical properties. The XPS were measured with monochromatized Al K _α radiation in the energy range 0-1450 eV and the temperature range 160-450 K. The valence band is located 0.8-7.5 eV below the Fermi level. Experimental results of the valence band and core levels are compared with the results of theoretical ab initio calculations of the molecular model of Sb₂S₃ crystal. The chemical shifts in Sb₂S₃ crystal for the Sb and S states are obtained. Results revealed that the small structural rearrangements at the phase transition T _c1 = 300 K shift the Fermi level and all electronic spectrum. Also, temperature dependence of a spontaneous polarisation shifts the electronic spectra of the valence band and core levels. Specific temperature-dependent excitations in Sb 3d core levels are also revealed.     

相变存储材料Ge1Sb2Te4和Ge2Sb2Te5薄膜的结构和电学特性研究

采用射频磁控溅射方法制备了两种用于相变存储器的Ge₁Sb₂Te₄和Ge₂Sb₂Te₅相变薄膜材料,对其结构、电学输运性质和恒温下电阻随时间的变化关系进行了比较和分析.X射线衍射(XRD)和原子力显微镜(AFM)的结果表明:随着退火温度的升高,Ge₁Sb₂Te₄薄膜逐步晶化,由非晶态转变为多晶态,表面出现均匀的、 关键词： 硫系相变材料 1Sb₂Te₄')" href="#">Ge₁Sb₂Te₄ 2Sb₂Te₅')" href="#">Ge₂Sb₂Te₅     

Effects of micro-additions on structures and properties of rapidly solidified Sn-10% Sb alloy

Structure, electrical resistivity, hardness, internal friction and elastic modulus of Sn-10% Sb and Sn₈₉Sb₁₀M₁ (M₁ = Ag, Cu, Zn and Pb) alloys have been investigated. No obvious change on the electrical resistivity value was found at 293 °K of a Sn-10% Sb alloy by adding Zn and Cu, but extreme changes occurred after adding Ag and Pb. The elastic modulus, internal friction, hardness and thermal diffusivity values are greatly affected by adding the micro-additions to a Sn-10% Sb rapidly solidified alloy. It is also interesting to note that Ledbetter's theoretical values of μ/E are in good agreement with the experimental results. The rapidly solidified alloys Sn₉₀Sb₁₀ and Sn₈₉Sb₁₀Ag₁ have good properties as toxic-free lead solder alloys for high-temperature applications and good mechanical properties such as under the hood in the automobile and avionics systems. Also, the rapidly solidified alloys Sn₈₉Sb₁₀Zn₁, Sn₈₉Sb₁₀Cu₁ and Sn₈₉Sb₁₀Pb₁ have good properties as bearing materials.     

Sb2Te3 纳米结构的制备与表征

以室温热电性能优异的传统热电材料Sb₂Te₃为研究对象,利用化学气相沉积法制备Sb₂Te₃单晶纳米结构,并研究其生长机理.实验结果表明,不加催化剂时Sb₂Te₃易生长成六方纳米盘,在金催化剂条件下定向生长成纳米线.Sb₂Te₃的形貌与其晶体结构和生长机理有关.Sb₂Te₃为三角结构,Sb和     

应用于相变存储器的Cu-Ge3Sb2Te5薄膜的结构及相变特性研究

采用磁控溅射法制备了不同Cu含量的Cu-Ge₃Sb₂Te₅薄膜, 原位测试了薄膜电阻与温度的关系, 并利用X射线衍射仪、透射电镜、透过和拉曼光谱仪分别研究了 Cu-Ge₃Sb₂Te₅薄膜的晶体结构、微结构、禁带宽度及成键情况. 结果表明, Cu-Ge₃Sb₂Te₅薄膜的结晶温度和结晶活化能随着Cu含量的增加而增大, Cu的加入有效改善Ge₃Sb₂Te₅薄膜的热稳定性和10年数据保持力. 随着Cu含量的增加, 非晶态Cu-Ge₃Sb₂Te₅薄膜的禁带宽度逐渐减小. 同时, 拉曼峰从129 cm^-1向127 cm^-1处移动, 这是由于Cu–Te极性键振动增强的缘故. Cu-Ge₃Sb₂Te₅结晶为均匀、相互嵌套的六方Cu₂Te和Ge₂Sb₂Te₅相.     

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.     

The effect of quenching from different temperatures on Bi0.88Sb0.12 alloy

Structural, thermal, resistive and magnetic properties of melt quenched Bi_0.88Sb_0.12 alloys are reported. The samples are heated at three different temperatures, followed by rapid quenching in liquid nitrogen. Large temperature difference between liquidus and solidus lines, led to microscopic in-homogeneity in the alloy. The effect of quenching from different temperatures in polycrystalline Bi_0.88Sb_0.12 alloy has been studied. The parameters such as strain, unit cell volume, and resistivity are found to increase with temperature. Thermal variation of resistivity depicts non-monotonic temperature dependence. The total negative susceptibility increases and band gap of semiconducting Bi_0.88Sb_0.12 samples decreases with increasing temperature.     

Process-parameter optimization of Sb2O3 films in the ultraviolet and visible region for interferometric applications

The influence of different evaporation process parameters on the optical properties and constants of thin Sb₂O₃ films in the ultraviolet and visible region from 250 to 800 nm has been investigated. The most dominant parameters, namely the substrate temperature, rate of evaporation, and ambient oxygen pressure used during the deposition process and the post-annealing temperatures were optimised which resulted in low loss, dense and homogeneous Sb₂O₃ films. The optical constants and band gaps of these films were evaluated using their interference modulated transmittance spectra in case of both homogeneous and inhomogeneous conditions. Optimized films have been successfully used in developing multilayer high reflecting coatings for Fabry-Perot etalons along with the cryolite (Na₃AlF₆) films.     

Complete characterization of an (Sb2O3)n/SWNT inclusion composite

The detailed inclusion crystallography of a one-dimensional valentinite Sb₂O₃ crystal incorporated within a helical (21, ?8) single-walled carbon nanotube (SWNT) was identified from a phase image that was recovered via a modified object wave restoration scheme. A detailed analysis of asymmetric fringe contrast in the tube walls provided strong evidence for the chiral sense of the tube itself. Due to the good agreement of the observed wall periodicity with the determined absolute focus values and power spectra obtained from single-pixel line traces along both tube walls, we were able to determine the chiral sense of the SWNT and the tilt angle of the Sb₂O₃/SWNT composite relative to the electron beam. The angle between the optimum $\left\langle {10\bar 1} \right\rangle $ viewing direction of the crystal fraction and the tube axis, which is aligned with the $\left\langle {4\bar 12} \right\rangle $ direction of the Sb₂O₃ crystal, is 78.3°. Since small deviations from this viewing direction make an insignificant difference to the observed contrast, a tube inclination of 15° is plausible for both the Sb₂O₃ crystal and the assigned (21, ?8) SWNT, which is the mirror image of a (13, 8) SWNT.     

Structural phase transitions in the Cs3Sb2I9 crystal

A sequence of two phase transitions at 85.3±0.6 K and 72.6±0.4 K is observed in hexagonal Cs₃Sb₂I₉. The NQR spectra of ¹²⁷I are analyzed, optical polarization studies are made, and the thermal properties, linear expansion coefficients, and stiffness constants are measured over a broad range of temperatures below room temperature. Fiz. Tverd. Tela (St. Petersburg) 39, 946–948 (May 1997)     

Local atomic structure in molten Si3Sb2Te3 phase change material

By means of ab initio molecular dynamics calculations, we have studied the local structures of liquid and amorphous Si₃Sb₂Te₃. The results show that all the constitute elements in liquid Si₃Sb₂Te₃ are octahedrally coordinated. While in amorphous state, Sb and Te atoms are mainly octahedrally coordinated and Si atoms are mainly tetrahedrally coordinated. In both states, Si is mainly homo-bonded by Si. Finally, we proposed a phase separation model for liquid and amorphous Si₃Sb₂Te₃, which is responsible for the good performance of Si₃Sb₂Te₃ alloy as a phase change material.     

The effect of doping by IV-family elements on the electronic structure and electrical characteristics of Sb2O5

The electronic structures of doped Sb₂O₅ by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results showed that the substituted IV-family elements act as acceptors in Sb₂O₅. Partial DOSs indicates that by substituting Ge(Ge _Sb ) or Sn(Sn _Sb ), there may be a larger contribution to the total DOSs near E _F than by substituting Si, which suggests that doping Ge or Sn in Sb₂O₅ produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely to exist in the substituted position rather than in the interstitial position in Sb₂O₅, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb₂O₅. Ionization energy results show that Ge _Sb or SnSb, two among the three impurities considered, act as shallow acceptors in Sb₂O₅, thus producing a higher concentration of holes.      

Effective Mass Enhancement and Thermal Conductivity Reduction for Improving the Thermoelectric Properties of Pseudo-Binary Ge2Sb2Te5

Ge₂Sb₂Te₅ is a famous phase-change memory material for rewriteable optical storage, which is widely applied in the information storage field. The stable trigonal phase of Ge₂Sb₂Te₅ shows potential as a thermoelectric material as well, due to its tunable electrical transport properties and low lattice thermal conductivity. In this work, the carrier concentration and effective mass of Ge₂Sb₂Te₅ are modulated by substituting Te with Se. Meanwhile, the thermal conductivity reduces from 2.48 W m⁻¹ K⁻¹ for Ge₂Sb₂Te₅ to 1.37 W m⁻¹ K⁻¹ for Ge₂Sb₂Te_3.5Se_1.5 at 703 K. Therefore, the thermoelectric figure of merit zT increases from 0.24 for Ge₂Sb₂Te₅ to 0.41 for Ge₂Sb₂Te_3.5Se_1.5 at 703 K. This study reveals that Se alloying is an effective way to enhance the thermoelectric properties of Ge₂Sb₂Te₅.     

Investigation of Sb-rich Si2Sb2+x Te6 material for phase change random access memory application

Sb-rich Si₂Sb_2+x Te₆ (x=0, 1.4, 10) thin films are proposed to present the feasibility for electronic phase change memory application. The crystallization behavior is improved by adding Sb into the material. The crystallization temperature is about 506, 502, and 450 K for Si₂Sb₂Te₆, Si₂Sb_3.4Te₆, and Si₂Sb₁₂Te₆ films, respectively, and the corresponding activation energy is in the range from 2.70 to 1.69 eV, which is expected for a low-power and high-speed SET operation. In addition, maximum temperature for a 10 year data lifetime is estimated to be 133, 127, and 98°C, respectively. The memory devices are successfully fabricated employing these films, promising that the stability of the low-resistance crystalline state is improved by adding Sb into the stoichiometric Si₂Sb₂Te₆ material, and the reversibility of the device is also realized for the Si₂Sb₁₂Te₆-based cell.     

Study of aluminium-modified Ge2Sb2Te5 thin films for the applicability as phase-change storage device material

Electrical and optical studies have been carried out on aluminium-modified Ge₂Sb₂Te₅ thin films to check its applicability as an active material in optical and electrical memory storage devices. Five polycrystalline bulk samples were prepared with compositions: Al_x(Ge₂Sb₂Te₅)_1?x; x = 0, 0.08, 0.14, 0.21, 0.25. Amorphous thin films were deposited from the polycrystalline bulk by thermal evaporation. Temperature-dependent resistance shows the increase in crystallization temperature of Ge–Sb–Te films on aluminium addition. Activation energy for conduction, conductivity, optical band gap, coefficient of refraction and extinction coefficient are studied with respect to Al content in both amorphous and crystalline phases of Ge–Sb–Te alloy films.     

Thermoelectric properties of Bi2Se3/Bi2Te3/Bi2Se3 and Sb2Te3/Bi2Te3/Sb2Te3 quantum well systems

In this work, we develop a theory of thermoelectric transport properties in two-dimensional semiconducting quantum well structures. Calculations are performed for n-type 0.1 wt.% CuBr-doped Bi₂Se₃/Bi₂Te₃/Bi₂Se₃ and p-type 3 wt.% Te-doped Sb₂Te₃/Bi₂Te₃/Sb₂Te₃ quantum well systems in the temperature range 50–600 K. It is found that reducing the well thickness has a pronounced effect on enhancing the thermoelectric figure of merit (ZT). For the n-type Bi₂Se₃/Bi₂Te₃/Bi₂Se₃ with 7 nm well width, the maximum value of ZT is estimated to be 0.97 at 350 K and for the p-type Sb₂Te₃/Bi₂Te₃/Sb₂Te₃ with well width 10 nm the highest value of the ZT is found to be 1.945 at 440 K. An explanation is provided for the resulting higher ZT value of the p-type system compared to the n-type system.     

The heterostructure and electrical properties of Sb2Se3/Bi2Se3 grown by molecular beam epitaxy

We report the growth and characterization of Sb₂Se₃/Bi₂Se₃ bilayer films fabricated by molecular beam epitaxy. High quality heterostructures are obtained as evidenced from the X-ray diffraction (XRD), atomic force microscopy and high-resolution transmission electron microscopic (HRTEM) analysis. Interestingly, Sb₂Se₃ grows as a (120) hexacrystal film in orthorhombic phase on rhombohedral Bi₂Se₃ (0001) plane, as verified by the out-of-plane and in-plane XRD scans. The cross-sectional TEM studies indicate a sharp interface between Sb₂Se₃ and Bi₂Se₃, which is important for the protection of surface states Bi₂Se₃. The ultraviolet photoelectron spectroscopy indicates that the Fermi level located 0.95 eV above the valence band maximum in Sb₂Se₃. The insulating nature of Sb₂Se₃ is confirmed by the nonlinear current-voltage curve via the vertical junction electrical measurement. By four point probe measurements, we confirm the charge transfer effect from Sb₂Se₃ into Bi₂Se₃, and such effect can be reduced in the Sb₂Se₃/(Bi_0.7Sb_0.3)₂Se₃ bilayer. This work opens a new avenue for the synthesis of multilayers consisting of topological insulators and ordinary insulator, which is important for harvesting of the multiple surface states for advanced electronic and spintronic applications.     

Topotaxy in the oxidation of valentinite,Sb2O3, to cervantite,Sb2O4

The oxidation of orthorhombic Sb₂O₃, valentinite, to orthorhombic Sb₂O₄, cervantite, has been shown by single crystal x-ray diffraction techniques to be a topotactic reaction. The orientation relationships between the two lattices have been determined by making use of a hybrid crystal. It has been found that the individual axes in the two oxides are parallel. The two crystal structures have been compared in the appropriate orientation and their close similarity has been established. The shifts of the individual atoms in valentinite during the process of oxidation have been calculated to be not more than 0·6 Å. It has been established that the reduction of cervantite to valentinite also takes place topotactically.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]3Sb2Br9

The crystal structure of [C(NH₂)₃]₃Sb₂Br₉ was determined at 143 K: monoclinic, space group C2/c, Z = 4, a = 15.695 (3), b = 9.039(2), c = 18.364(3) Å, β = 96.94(1)°. The structure consists of two crystallographically independent guanidinium ions and two-dimensional corrugated sheets of (Sb₂Br₉ ^3?) _n , in which SbBr₆ octahedra are connected through three bridging Br atoms each other. One of the cations situates in a cavity of the (Sb₂Br₉ ^3?) _n layer with statistical disorder, while the other situates between the layers without disorder. Three ⁸¹Br NQR resonance lines were assignable to terminal Br atoms, while only one line was found for two inequivalent bridging Br atoms. All the ⁸¹Br NQR resonance lines were subjected to fade-out at low temperatures. The temperature dependence curve of ¹H NMR T ₁ showed well defined two minima, which were explained by postulating the C₃ reorientations of two types of cations with very different activation energies. The DTA (DSC) measurement revealed a phase transition of a first-order type at 444 K.