Electrochemical aspects and structure characterization of VA-VIA compound semiconductor Bi2Te3/Sb2Te3 superlattice thin films via electrochemical atomic layer epitaxy

This paper concerns the electrochemical atom-by-atom growth of VA-VIA compound semiconductor thin film superlattice structures using electrochemical atomic layer epitaxy. The combination of the Bi2Te3 and Sb2Te3 programs and Bi2Te3/Sb2Te3 thin film superlattice with 18 periods, where each period involved 21 cycles of Bi2Te3 followed by 21 cycles of Sb2Te3, is reported here. According to the angular distance between the satellite and the Bragg peak, a period of 23 nm for the superlattice was indicated from the X-ray diffraction (XRD) spectrum. An overall composition of Bi 0.25Sb0.16Te0.58, suggesting the 2:3 stoichiometric ratio of total content of Bi and Sb to Te, as expected for the format of the Bi2Te3/Sb2Te3 compound, was further verified by energy dispersive X-ray quantitative analysis. Both field-emission scanning electron microscopy and XRD data indicated the deposit grows by a complex mechanism involving some 3D nucleation and growth in parallel with underpotential deposition. The optical band gap of the deposited superlattice film was determined as 0.15 eV by Fourier transform infrared spectroscopy and depicts an allowed direct type of transition. Raman spectrum observation with annealed and unannealed superlattice sample showed that the LIF mode has presented, suggesting a perfect AB/CB bonding in the superlattice interface.     

电沉积Bi2Te3基薄膜的电化学阻抗谱研究

以不锈钢为基底,利用电化学沉积方法制备Bi2Te3基薄膜材料,并采用X射线衍射技术、电子探针微观分析等方法对薄膜进行结构和成分表征,通过电化学阻抗谱技术对不锈钢表面Bi2Te3的电化学沉积机理进行了初步探讨.结果表明Bi-Te和Bi-Te-Se体系具有相似的电化学沉积机理,即Bi3+和2HTeO+或H2SeO3首先被还原为Bi单质和Te或Se单质,然后Bi单质与Te或Se单质反应生成Bi2Te3基化合物,而Bi-Sb-Te体系中,2HTeO+首先被还原为Te单质,生成的Te再与Bi3+和Sb(III)反应生成Bi2Te3基化合物,三种体系的沉积都受电化学极化控制.     

Surfactant-mediated electrodeposition of bismuth telluride films and its effect on microstructural properties

We report the synthesis of highly crystallographically textured films of stoichiometric bismuth telluride (Bi(2)Te(3)) in the presence of a surfactant, sodium lignosulfonate (SL), that resulted in the improved alignment of films in the (110) plane and offered good control over the morphology and roughness of the electrodeposited films. SL concentrations in the range 60-80 mg dm(-3) at a deposition potential of -0.1 V vs SCE (saturated calomel electrode) were found to yield the most improved crystallinity and similar or superior thermoelectric properties compared with results reported in the literature.     

添加La的Bi2Te3和Bi0.5Sb1.5Te3热电材料的电磁感应熔炼法制备及其热电性能

在N2气保护下,采用电磁感应法制备了添加La的Bi2Te3和Bi0.5Sb1.5Te3。运用X射线粉末衍射、电感耦合等离子光谱和扫描电子显微镜对材料的物相成分和形貌进行了表征。研究了La对Bi2Te3和Bi0.5Sb1.5Te3热电材料的电导率(σ)、Seebeck系数(S)和热导率(κ)的影响。实验结果表明,添加La明显降低了2种材料的热导率,提高了热电优值(ZT),添加La的Bi0.5Sb1.5Te3的热电优值在室温超过了1。     

Pressure-induced disordered substitution alloy in Sb2Te3

A new type of disordered substitution alloy of Sb and Te at above 15.1 GPa was discovered by performing in situ high-pressure angle-dispersive X-ray diffraction experiments on antimony telluride (Sb(2)Te(3)), a topological insulator and thermoelectric material, at room temperature. In this disordered substitution alloy, Sb(2)Te(3) crystallizes into a monoclinic structure with the space group C2/m, which is different from the corresponding high-pressure phase of the similar isostructural compound Bi(2)Te(3). Above 19.8 GPa, Sb(2)Te(3) adopts a body-centered-cubic structure with the disordered atomic array in the crystal lattice. The in situ high-pressure experiments down to about 13 K show that Sb(2)Te(3) undergoes the same phase-transition sequence with increasing pressure at low temperature, with almost the same phase-transition pressures.     

Large-area Sb2Te3 nanowire arrays

High-density large-area nanowire arrays of thermoelectric material Sb(2)Te(3) have been successfully prepared using electrochemical deposition into the channels of the porous anodic alumina membrane. The morphologies, structure, and composition of the as-prepared Sb(2)Te(3) nanowires have been characterized using field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Individual Sb(2)Te(3) nanowires are single crystalline and continuous with uniform diameters ( approximately 50 nm) throughout the entire length. The atomic ratio of Sb to Te is very close to the 2:3 stoichiometry.     

Formation and characterization of Sb2Te3 nanofilms on Pt by electrochemical atomic layer epitaxy

A nanocrystalline Sb2Te3 VA-VIA group compound thin film was grown via the route of electrochemical atomic layer epitaxy (ECALE) in this work for the first time. The electrochemical behavior of Te and Sb on Pt, Te on Sb-covered Pt, and Sb on Te-covered Pt was studied by methods of cyclic voltammetry, anode potentiodynamic scanning, and coulometry. A steady deposition of the Sb2Te3 compound could be attained after negatively stepped adjusting of the UPD potentials of Sb and Te on Pt in each of the first 40 depositing cycles. The structure of the deposit was proven to be the Sb2Te3 compound by X-ray diffraction. The 2:3 stoichiometric ratio of Sb to Te was verified by EDX quantitative analysis, which is consistent with the result of coulometric analysis. A nanocystalline microstructure was observed for the Sb2Te3 deposits, and the average grain size is about 20 nm. Cross-sectional SEM observation shows an interface layer about 19 nm in thickness sandwiched between the Sb2Te3 nanocrystalline deposit and the Pt substrate surface. The optical band gap of the deposited Sb2Te3 film was determined as 0.42 eV by FTIR spectroscopy and it is blueshifted in comparison with that of the bulk Sb2Te3 single crystal because of its nanocrystalline microstructure.     

Synthesis in ionic liquids: [Bi2Te2Br](AlCl4), a direct gap semiconductor with a cationic framework

The Lewis acidic ionic liquid EMIMBr-AlCl(3) (EMIM = 1-ethyl-3-methylimidazolium) allows a novel synthetic route to the semiconducting layered metal chalcogenides halide [Bi(2)Te(2)Br](AlCl(4)) and its Sb analogue. [Bi(2)Te(2)Br](AlCl(4)) is a direct band gap, strongly anisotropic semiconductor and consists of cationic infinite layers of [Bi(2)Te(2)Br](+) and [AlCl(4)](-) anions inserted between the layers.     

化学蒸气发生-四通道原子荧光光谱法同时测定高纯金中的痕量As,Sb,Bi,Te

采用化学蒸气发生-四通道原子荧光光谱法测定了高纯金中的痕量砷、锑、铋和碲。用乙酸乙脂萃取分离金,水相还原后采用化学蒸气发生-四通道原子荧光光谱法测定高纯金中的痕量砷、锑、铋和碲。在最佳条件下,方法对As,Sb,Bi,Te的检出限分别为0.04,0.05,0.04,0.03 ng/mL(3σ);测定精密度分别为0.98,0.89,0.94,0.99%(对10 ng/mL As,Sb,Bi和Te混合标准,n=7)。方法对实际样品中的As,Sb,Bi,Te进行了同时测定,测定结果与标准方法无明显差异,各元素的加标回收率为95%～105%。     

Acetic acid-confined synthesis of uniform three-dimensional (3D) bismuth telluride nanocrystals consisting of few-quintuple-layer nanoplatelets

High-selectivity, uniform three-dimensional (3D) flower-like bismuth telluride (Bi(2)Te(3)) nanocrystals consisting of few-quintuple-layer nanoplatelets with a thickness down to 4.5 nm were synthesized for the first time by a facile, one-pot polyol method with acetic acid as the structure-director. Micrometre-sized 2D films and honeycomb-like spheres can be obtained using the uniform 3D Bi(2)Te(3) nanocrystals as building blocks.     

Optimization of large area pulsed laser deposition of YBaCuO thin films by SNMS depth profiling and rutherford backscattering

The scaling up of established deposition techniques like pulsed laser deposition (PLD) to larger substrate diameter is a main condition for the technological application of high-T_c superconducting (HTSC) thin films. SNMS depth profiling and RBS have been used to control the homogeneity of film thickness and stoichiometry of Au/YBaCuO/CeO₂ thin film systems deposited on 3-inch sapphire wafers by PLD. A systematic dependence has been found for the relative SNMS sensitivity factors (RSF) on the structural state of YBaCuO. Therefore, a calculation of the composition of the epitaxial YBaCuO thin films is not possible using RSF determined from polycrystalline YBaCuO target material. The interdiffusion of thin films and substrate has been investigated in dependence on the deposition temperature by SNMS depth profiling. The obtained homogeneity of film thickness and stoichiometry over the entire 3-inch diameter proofs the suitability of PLD for in-situ deposition of 3-inch wafers by YBaCuO thin film systems for microwave applications.     

A versatile route to 3-benzoheteroepines containing group 15 and 16 heavier elements involving several novel ring systems, and their thermal stabilities

The C-unsubstituted 3-benzoheteroepines (2a-g) containing group 15 (P, As, Sb, and Bi) and group 16 (S, Se, and Te) heavier elements were prepared by the reaction of the corresponding metal reagents with (Z,Z)-o-bis(beta-lithiovinyl)benzene (5) which was derived in two steps from a common o-phthalaldehyde (3). The heteroepines (2) thus obtained were thermally labile towards heteroatom extrusion, and their half-lives on heating estimated from (1)H-NMR spectral analysis showed that the 3-benzoheteroepines (2) were far less stable than the corresponding 1-benzoheteroepines (1). The 2,4-bis(trimethylsilyl)-3-benzoheteroepines (17) containing Sb, Bi, and Te were also prepared from o-diiodobenzene (9) in 6 steps and were found to be more stable than the corresponding C-unsubstituted heteroepines (2).     

Overview over studies of electrodeposition of Al or Al alloys from low temperature chloroaluminate molten salts

Studies using low-temperature chloroaluminate molten salts are introduced. The physical and chemical properties have been elucidated from around the 1930s, and electrodeposition of Al alloys was reported more recently. Electrodeposition of Bi, Sb, and Te using an AlCl₃-NaCl-KCl molten salt is also introduced as an application of molten salts.     

Electrochemical investigation of the chemical diffusion,partial ionic conductivities,and other kinetic parameters in Li3Sb and Li3Bi

The galvanostatic intermittent titration technique (GITT) has been used to electrochemically determine the chemical and component diffusion coefficients, the electrical and general lithium mobilities, the partial lithium ionic conductivity, the parabolic tarnishing rate constant, and the thermodynamic enhancement factor in “Li₃Sb” and “Li₃Bi” as a function of stoichiometry in the temperature range from 360 to 600°C. LiCl, KCl eutectic mixtures were used as molten salt electrolytes and Al, “LiAl” two-phase mixtures as solid reference and counterelectrodes. The stoichiometric range of the antimony compound is rather small, 7 × 10^?3 at 360°C, whereas the bismuth compound has a range of 0.22 (380°C), mostly on the lithium deficit side of the ideal composition. The thermodynamic enhancement factor in “Li₃Sb” depends strongly on the stoichiometry, and has a peak value of nearly 70 000; for “Li₃Bi” it rises more smoothly to a maximum of 360. The chemical diffusion coefficient for “Li₃Sb” is 2 × 10^?5 cm² sec^?1 at negative deviations from the ideal stoichiometry and increases by about an order of magnitude in the presence of excess lithium at 360°C. The corresponding value for “Li₃Bi” is 10^?4 cm² sec^?1 with high lithium deficit, and increases markedly when approaching ideal stoichiometry. The activation energies are small, 0.1–0.3 eV, depending on the stoichiometry, in both phases. The mobility of lithium in “Li₃Bi” is about 500 times greater than in “Li₃Sb” with a lithium deficit. The ionic conductivity in “Li₃Sb” increases from about 10^?4 Ω^?1 cm^?1 in the vacancy transport region to about 2 × 10^?3 where transport is probably by interstial motion at 360°C. For “Li₃Bi” a practically constant value of nearly 10^?1 Ω^?1 cm^?1 is found at 380°C. The parabolic tarnishing rate constant shows a sharp increase at higher lithium activities in “Li₃Sb” whereas in “Li₃Bi” it has a roughly linear dependence upon the logarithm of the lithium activity. The tarnishing process is about 2 orders of magnitude slower for “Li₃Sb” than for “Li₃Bi.” Because of the fast ionic transport in these mixed conducting materials, “Li₃Sb” and “Li₃Bi” may be called “fast electrodes.”     

Separation of inorganic bromides by adsorption gas chromatography

Gas chromatography has been used to separate the volatile bromides of Zr, Nb, Mo, Te, In, Sn, Sb, Bi, Te and I. SiO(2), NaBr, KBr and CsBr have been used as stationary phases and Br(2)/N(2) and Br(2)/BBr(3)/N(2) as mobile phases. Temperature-programmed as well as isothermal gas chromatographic separations have been carried out.     

Fluorophenyl derivatives of elements II-VI groups

The enthalpies and temperatures of melting of RSi(CH₃)₃, R₄Si, R₃P, R₃As, R₃Sb, R₃Bi, R₂Te and R₂Hg (R=C₆F₅) were obtained by scanning calorimetry measurements. The pressure of the saturated and unsaturated vapors of RSi(CH₃)₃, R₂Si(CH₃)₂, R₄Si, R₃Ga, R₃P, R₃As, R₃Sb, R₃Bi, R₂Te and R₂Hg has been measured by the static method with a membrane-gauge manometer. It was established that all investigated substances proceeded to vapor as monomers. Equations approximating the dependences of saturated vapor pressures on temperature and the enthalpies and entropies of vaporization were obtained. Grafite films with silicon intercalated up to 25 at.% were grown by CVD using R₄Si as a precursor. These films showed semiconductor properties in the temperature interval 80–300 K.     

Development of gas-phase sample-introduction techniques for analytical atomic spectrometry.

For the last 30 years, several types of gas-phase sample-introduction methods in analytical atomic spectrometry, i.e., atomic absorption spectrometry (AAS), atomic emission spectrometry (AES) and atomic fluorescence spectrometry (AFS), have been investigated and developed in the author's laboratory. Their fundamental results are summarized in this review article. The gas-phase sample-introduction techniques developed in the author's laboratory can be roughly divided into four groups: i) hydride generation, ii) cold-vapor generation of mercury, iii) analyte volatilization reactions and iv) miscellaneous. The analytical figures of merit of the gas-phase sample-introduction methods have been described in detail. Hydride generation has been coupled with the AAS of As, Bi, Ge, Pb, Sb, Se, Sn and Te, with the inductively coupled plasma (ICP) AES of As, Bi, Sn, Se and Sb, with the high-power nitrogen microwave-induced plasma (N2-MIP) AES of As, Bi, Pb, Sb, Se, Sn and Te by their single- and multi-element determinations, with the AFS of As, Bi, Pb, Sb, Se, Sn and Te, and with the ICP mass spectrometry (MS) of As and Se. The cold-vapor generation method for Hg has been combined with atmospheric-pressure helium microwave-induced plasma (He- or Ar-MIP)-AES and AFS. Furthermore, analyte volatilization reactions have been employed in the ICP-AES of iodine, in the He-MIP-AES of iodine bromine, chlorine, sulfur and carbon, and in the ICP-MS of sulfur. As a result, when compared with conventional solution nebulization, a great improvement in the sensitivity has been attained in each instance. In addition, the developed techniques coupled with analytical atomic spectrometry have been successfully applied to the determination of trace elements in a variety of practical samples.     

Dual purpose laser ablation-inductively coupled plasma mass spectrometry for pulsed laser deposition and diagnostics of thin film fabrication: Preliminary study

PLD (pulsed laser deposition) is an attractive technique to fabricate thin films with a stoichiometry reflecting that of the target material. Conventional PLD instruments are more or less black boxes in which PLD is performed virtually “blind”, i.e. without having great control on the important PLD parameters. In this preliminary study, for the first time, a 213 nm Nd-YAG commercial laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS) intended for microanalysis work was used for PLD under atmospheric pressure and in and ex situ ICPMS analysis for diagnostics of the thin film fabrication process.A PLD demonstration experiment in a He atmosphere was performed with a Sm_13.8Fe_82.2Ta_4.0 target-Ta-coated silicon wafer substrate (contraption with defined geometry in the laser ablation chamber) to transfer the permanent magnetic properties of the target to the film. Although this paper is not dealing with the magnetic properties of the film, elemental analysis was applied as a means of depicting the PLD process. It was shown that in situ ICPMS monitoring of the ablation plume as a function of the laser fluence, beam diameter and repetition rate may be used to ensure the absence of large particles (normally having a stoichiometry somewhat different from the target). Furthermore, ex situ microanalysis of the deposited particles on the substrate, using the LA-ICPMS as an elemental mapping tool, allowed for the investigation of PLD parameters critical in the fabrication of a thin film with appropriate density, homogeneity and stoichiometry.     

Determination of Te,Bi, Ni,Sb and Au by X-ray fluorescence spectrometry following electroenrichment on a copper cathode

The electrodepositons of Te, Bi, Ni, Sb and Au from aqueous solution of pH = 1 on the cathode surface have been studied for X-ray fluorescence analysis (XRF). A special holder for a copper electrode has been constructed to perform the electrodeposition process on only one side of the electrode. After electrolysis, the copper electrode can be easily removed from the holder; after rinsing it with water and drying it can be analyzed by XRF. The proposed method of sample preparation and preconcentration of Te, Bi, Ni, Sb, Au provides suitable samples which are devoid of the negative and undesirable effects of XRF analysis, such as particle size and matrix effects. The influence of time on the deposition yield has been examined. The method of preconcentration is efficient. The inhomogeneity of the prepared specimens has been studied using internal standard method. The calibration is based on using synthetic standards, certified reference materials and standard addition method. The best results are achieved by the standard addition method. The agreement between results obtained with XRF analysis and certified values is satisfactory and indicates the usefulness of the proposed method for determination of Te, Bi, Ni, Sb and Au in anode slime.