Delay of the excited state lasing of 1310 nm InAs/GaAs quantum dot lasers by facet coating

In this letter, we present a facet coating design to delay the excited state (ES) lasing for 1310 nm InAs/GaAs quantum dot lasers. The key point of our design is to ensure that the mirror loss of ES is larger than that of the ground state by decreasing the reflectivity of the ES. In the facet coating design, the central wavelength is at 1480 nm, and the high- and low-index materials are Ta2O5 and SiO2, respectively. Compared with the traditional Si/SiO2 facet coating with a central wavelength of 1310 nm, we have found that with the optimal design the turning temperature of the ES lasing has been delayed from 90 to 100 degrees C for the laser diodes with cavity length of 1.2 mm. Furthermore, the characteristic temperature (T-0) of the laser diodes is also improved.

二元高－k材料研究进展及制备

随着大规模集成电路的发展，需要一种高介质材料来代替传统的SiO2,介绍了可能替代SiO2的几种二元材料的研究现状，主要包括Si3N4,Ta2O5,TiO2,ZrO2,Y2O3,Gd2O3和CeO2几种材料的结构和电学性能，以及制备薄膜的几种方法；蒸发法，化学气相沉积和离子束沉积。

Very low hysteresis organic thin-film transistors

Very low hysteresis vanadyl-phthalocyanine/para-sexiphenyl thin-film transistors (TFTs) have been fabricated using benzocyclobutenone (BCBO) derivatives/tantalum pentoxide (Ta2O5)/BCBO triple gate dielectrics. The field effect mobility, on/off current ratio and threshold voltage of organic TFTs are 0.45 cm(2) V-1 s(-1), 3.5 x 10(4) and -6.8 V, respectively. To clarify the mechanism of hysteresis, devices with different dielectrics have been studied. It is found that the bottom BCBO derivatives (contact with a gate electrode) block the electron injection from a gate electrode to dielectrics.

Organic thin-film transistors having inorganic/organic double gate insulators

Bottom-contact organic thin-film transistors (BC OTFTs) based on inorganic/organic double gate insulators were demonstrated. The double gate insulators consisted of tantalum pentoxide (Ta2O5) with high dielectric constant (kappa) as the first gate insulator and octadecyltrichlorosilane (OTS) with low kappa as the second gate insulator. The devices have carrier mobilities larger than 10(-2) cm(2)/V s, on/off current ratio greater than 10(5), and the threshold voltage of -14 V, which is threefold larger field-effect mobility and an order of magnitude larger on/off current ratio than the OTFTs with a Ta2O5 gate insulator. The leakage current was decreased from 2.4x10(-6) to 7.4x10(-8) A due to the introduction of the OTS second dielectric layer. The results demonstrated that using inorganic/organic double insulator as the gate dielectric layer is an effective method to fabricate OTFTs with improved electric characteristics.

Study on the instability of organic field-effect transistors based on fluorinated copper phthalocyanine

The effects of positive and negative gate-bias stress on organic field-effect transistors (OFET) based on tantalum (Ta)/tantalum pentoxide (Ta2O5)/fluorinated copper phthalocyanine (F16CuPc) structure are investigated as a function of stress time and stress temperature. It is shown that gate-bias stress induces a parallel threshold voltage shift (DeltaV(T)) of OFETs without changes of field-effect mobility mu(EF) and sub-threshold slope (DeltaS). The DeltaV(T) is observed to be logarithmically dependent on time at high gate-bias appropriate to OFET operation. More importantly, the shift is directional, namely, be large shift under positive stress and almost do not move under negative stress. The threshold voltage shift is temperature dependent with activation energy of 0.51 eV We concluded that threshold voltage shift of the OFET with F16CuPc as active layer is due to charge trapping in the insulator in which trapped carriers have redistribution.

On improving the phase stability and thermal expansion coefficients of lanthanum cerium oxide solid solutions

The phase stability of lanthanum cerium oxide (La2Ce2O7), which is stable up to 1400 degrees C, and the thermal expansion coefficient of La2Ce2O7 doped with Ta2O5 or WO3 were studied. The thermal expansion coefficient of La2Ce2O7 below 400 degrees C was increased by adding more CeO2 or doping with either Ta2O5 or WO3.

THE EFFECT OF DOPING WITH TANTALUM ON THE PROPERTIES OF YBA2CU3O7-Y

YBa2Cu3-xTaxO7-y (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) superconductors have been prepared, X-ray diffraction shows that the system remains orthorhombic for all compositions studied but. for x > 0.2, Ta2O5 was detected as an impurity phase. Substitution of Ta5+ for Cu2+ occurs in the Cu(2) sites on the Cu(2)O planes. The introduction of the high-valence element tantalum produces extra free electrons. These electrons recombine with the positive carrier of the system, which causes the mobility and the Hall number of YBa2Cu3-xTaxO7-y to decrease and also results in a depression in T(c).

热带亚热带季风气候条件下表生成矿地球化学－以个旧和老挝Nameung、Boloven地区为例

在前人对热带亚热带季风型气候条件下云南个旧砂矿、老挝Xaymomboun特区Ban Nameung铜多金属矿和Champasak省Boloven高原玄武岩等研究成果基础上，采用典型表生矿床实证解剖思路，选择个旧白云岩风化剖面、锡铅砂矿、锰结核、砂矿重选流程、Ban Nameung硫化氧化矿和Boloven玄武岩风化壳等对象，通过岩矿鉴定、主量微量元素地球化学、稀土元素地球化学、人工重砂、化学物相和微区分析等研究手段，研究这些矿床表生成矿物质来源、成矿机理、矿床地球化学特征和矿物工业可利用性等内容，并探索热带亚热带季风型气候条件下典型矿床表生成矿三个问题：（1）Sn、Pb、Mn、Ag、REE、Nb、Ta、Ga和Cd等元素表生富集成矿（矿化）规律；（2）上述元素成矿机理和工业利用可能性；（3）典型矿床其他20几种元素表生贫化与富集规律。研究获得如下主要认识： 1. 个旧地区燕山期以来持续抬升和亚热带季雨林的表生环境，使个旧地区大面积出露的碳酸盐岩风化形成强烈岩溶地貌，碳酸盐岩风化过程中CaO和MgO大量淋失，为砂矿提供了巨大容矿空间，同时碳酸盐地区碱性环境有利于原生硫化矿分解。含矿或不含矿白云岩、花岗岩、玄武岩、夕卡岩和原生硫化矿石等风化形成粘土矿物和铁锰氧化物，释放出Sn、Pb、Mn、Ga、Cd、Ag、In、Cu和Zn等元素，难风化重矿物如锡石表生残留富集，而粘土矿物和铁锰氧化物对成矿元素吸附是砂矿表生成因机理之一。 2. 个旧地区岩溶型砂矿形成机理为：（1）原生重矿物残留富集成矿，如锡石、磁铁矿。（2）金属硫化物残留成矿，如砂矿中残存大量方铅矿、黄铜矿、黄铁矿，是原生硫化物残留结果。（3）表生矿物富集成矿，如白铅矿、孔雀石、自然铅和自然铜等富集。（4）铁锰氧化物吸附和包裹成矿，如铁锰氧化物吸附Pb和Ga等元素，包裹含Pb和Zn微粒矿物。（5）锰结核吸附包裹成矿，锰结核吸附和包裹Sn、Pb和Cu等元素和微粒矿物。（6）类质同象成矿，如Ga和Al类质同象，Cd和Zn等类质同象成矿。（7）岩溶作用成矿，岩溶落水洞或溶洞内水流冲刷使锡石等重矿物富集成矿。元素表生成矿不仅是单一成矿作用结果，而是综合作用结果，如Pb有表生矿物富集成矿，也有铁锰氧化物吸附成矿。 3. 砂矿中锰结核是锰铁结核，主要成分为Fe2O3 、Al2O3、SiO2和MnO等，包裹了赤铁矿、方解石、云母、石英、蒙脱石、高岭石、白云石、钾长石等和锡石、白铅矿等矿物。锰结核中Mn、Sn、Pb、Ag、Ga、Cd和In富集成矿，Cu和Zn富集矿化，锰结核比砂矿更富集Mn、Pb和REE，其成矿机理应是吸附和包裹成矿元素或矿物使其富集成矿。 4. 个旧表生砂矿共生伴生组分复杂，有用矿物有锡石、方铅矿、白铅矿、黄铜矿、自然铅、自然铜、孔雀石、软锰矿、白钨矿、磁铁矿和褐铁矿等。模拟岩溶作用自然过程中砂矿矿物流向的源兴采选车间砂矿重选流程结果表明，锡铅精矿中Pb、Ga、Mo、Cd、In、Cu和Zn等金属总实收率仅为3.03％～6.44％，绝大部分金属留在了尾矿中。一段床和矿泥床分析中，Ag和Mn回收率低于0.66％～0.29％，Ag富集在硫化物态中，没有富集在铁锰氧化物态中；Mn富集在碳酸盐态中，没有铁锰氧化物态中。整个流程中Pb、Mn、Cu和Zn等富集在碳酸盐态矿物中，没有富集在硫化物态中。选矿流程没有利用具有潜在利用价值矿物如磁铁矿。重选流程解释了岩溶过程能富集Pb、Mn、Cu和Zn的碳酸盐矿物，不能富集这些元素的硫化矿物。 5. 老挝Ban Nameung硫化矿氧化初期，风化产物中Ag、Pb、Zn和Cu淋失，SiO2、K2O和CaO富集，风化后期Ag、Fe和Mn富集。硫化矿风化过程中，Au硫化物态部分变为有机态和铁锰氧化物态；Ag硫化物态部分变为铁锰氧化物态和有机态；Cu硫化物态部分变为铁锰氧化物态和碳酸盐态；Pb硫化物态、吸附态、碳酸盐态和铁锰氧化物态部分变为铁锰氧化物态、碳酸盐态和有机态；Zn硫化物态变为部分铁锰氧化物态、有机态、碳酸盐态和吸附态矿物。随着风化作用加强，上述几种相态比例还会改变。 6. 老挝Boloven新生代亚碱性玄武岩富Nb、Ta和Ga等微量元素，风化壳中REE、Nb、Ta和Ga已富集成矿，∑REE最高775×10-6～1003×10-6，（Nb2O5＋Ta2O5）最高642×10-6~656×10-6，Ga最高81.6 ×10-6。风化壳中达到边界品位的（Nb2O5＋Ta2O5）厚度有2m以上。REE可能存在于含P和Ti矿物中，也可能形成REE独立矿物。Nb、Ta和Ga应赋存在Ti、U、Zr和Th矿物中，其成矿应是重矿物表生残留富集结果，与粘土矿物吸附和三水铝石关系不紧密。

Selective oxidation of a pyrimidine thioether using supported tantalum catalysts

Ta2O5-SiO2 catalysts were prepared by a sol-gel method using tetraethyl orthosilicate (TEOS) and tantalum (V) ethoxide as the sources of silicon and tantalum, and two families of quaternary ammonium salts, [CnH(2n+1)(CH3)(3)N]Br (n = 14, 16, 18) and [(CnH(2n+1))(4)N]Br (n = 10, 12, 16, 18) as surfactants. The catalysts were compared for the selective suffoxidation of 4,6-dimethyl-2-thiomethylpyrimidine using peroxide as an oxidising agent in a range of ionic liquids and organic solvents. The sol-gel catalysts were also compared with tantalum on MCM-41 prepared by grafting. The catalysts were characterized from adsorption-desorption isotherms of N-2, XRD patterns, small-angle X-ray scattering, IR spectra from adsorbed pyridine and CDCl3, XPS spectra, and Si-29 magic angle spinning (MAS) NNIR experiments. The effect of recycling on the catalyst leaching and selectivity/activity was also studied. High activities and selectivities were found in [NTf2](-) based ionic liquids and organic solvents with good recyclability of the catalyst. Tantalum was found in the solution after reaction; however, this was determined to be due to entrapment of catalyst particulates, as opposed to leaching of the active metal. (c) 2005 Elsevier Inc. All rights reserved.

Electrical characterization of metal-oxide-polymer devices for non-volatile memory applications

The objective of this thesis is to study the properties of resistive switching effect based on bistable resistive memory which is fabricated in the form of Al2O3/polymer diodes and to contribute to the elucidation of resistive switching mechanisms. Resistive memories were characterized using a variety of electrical techniques, including current-voltage measurements, small-signal impedance, and electrical noise based techniques. All the measurements were carried out over a large temperature range. Fast voltage ramps were used to elucidate the dynamic response of the memory to rapid varying electric fields. The temperature dependence of the current provided insight into the role of trapped charges in resistive switching. The analysis of fast current fluctuations using electric noise techniques contributed to the elucidation of the kinetics involved in filament formation/rupture, the filament size and correspondent current capabilities. The results reported in this thesis provide insight into a number of issues namely: (i) The fundamental limitations on the speed of operation of a bi-layer resistive memory are the time and voltage dependences of the switch-on mechanism. (ii) The results explain the wide spread in switching times reported in the literature and the apparently anomalous behaviour of the high conductance state namely the disappearance of the negative differential resistance region at high voltage scan rates which is commonly attributed to a “dead time” phenomenon which had remained elusive since it was first reported in the ‘60s. (iii) Assuming that the current is filamentary, Comsol simulations were performed and used to explain the observed dynamic properties of the current-voltage characteristics. Furthermore, the simulations suggest that filaments can interact with each other. (iv) The current-voltage characteristics have been studied as a function of temperature. The findings indicate that creation and annihilation of filaments is controlled by filling and neutralizing traps localized at the oxide/polymer interface. (v) Resistive switching was also studied in small-molecule OLEDs. It was shown that the degradation that leads to a loss of light output during operation is caused by the presence of a resistive switching layer. A diagnostic tool that predicts premature failure of OLEDs was devised and proposed. Resistive switching is a property of oxides. These layers can grow in a number of devices including, organic light emitting diodes (OLEDs), spin-valve transistors and photovoltaic devices fabricated in different types of material. Under strong electric fields the oxides can undergo dielectric breakdown and become resistive switching layers. Resistive switching strongly modifies the charge injection causing a number of deleterious effects and eventually device failure. In this respect the findings in this thesis are relevant to understand reliability issues in devices across a very broad field.

Properties of tantalum oxynitride thin films produced by magnetron sputtering: the influence of processing parameters

The main purpose of this work is to present and to interpret the change of structure and physical properties of tantalum oxynitride (TaNxOy) thin films, produced by dc reactive magnetron sputtering, by varying the processing parameters. A set of TaNxOy films was prepared by varying the reactive gases flow rate, using a N2/O2 gas mixture with a concentration ratio of 17:3. The different films, obtained by this process, exhibited significant differences. The obtained composition and the interpretation of X-ray diffraction results, shows that, depending on the partial pressure of the reactive gases, the films are: essentially dark grey metallic, when the atomic ratio (N + O)/Ta < 0.1, evidencing a tetragonal β-Ta structure; grey-brownish, when 0.1 < (N + O)/Ta < 1, exhibiting a face-centred cubic (fcc) TaN-like structure; and transparent oxide-type, when (N + O)/Ta > 1, evidencing the existence of Ta2O5, but with an amorphous structure. These transparent films exhibit refractive indexes, in the visible region, always higher than 2.0. The wear resistance of the films is relatively good. The best behaviour was obtained for the films with (N + O)/Ta ≈ 0.5 and (N + O)/Ta ≈ 1.3.

Structural and optical properties on thulium-doped LHPG-grown Ta(2)O(5) fibres

Structural, spectroscopic and dielectric properties of thulium-doped laser-heated pedestal Ta(2)O(5) as-grown fibres were studied. Undoped samples grow preferentially with a single crystalline monoclinic structure. The fibre with the lowest thulium content (0.1 at%) also shows predominantly a monoclinic phase and no intra-4f(12) Tm(3+) recombination was observed. For sample with the highest thulium amount (1.0 at%), the appearance of a dominant triclinic phase as well as intraionic optical activation was observed. The dependence of photoluminescence on excitation energy allows identification of different site locations of Tm(3+) ions in the lattice. The absence of recombination between the first and the ground-state multiplets as well as the temperature dependence of the observed transitions was justified by an efficient energy transfer between the Tm(3+) ions. Microwave dielectric properties were investigated using the small perturbation theory. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for thulium-doped Ta(2)O(5) samples it decreases to 18 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. (C) 2008 Elsevier Ltd. All rights reserved.

Effect of Eu(2)O(3) doping on Ta(2)O(5) crystal growth by the laser-heated pedestal technique

High energy band gap hosts doped with lanthanide ions are suitable for optical devices applications To study the potential of Ta(2)O(5) as a host compound pure and Eu(2)O(3)-doped Ta(2)O(5) crystal fibers were grown by the laser-heated pedestal growth technique in diameters ranging from 250 to 2600 pm and in lengths of up to 50 mm The axial temperature gradient at the solid/liquid interface of pure Ta(2)O(5) fibers revealed a critical diameter of 2200 gm above which the fiber cracks X-ray diffraction measurements of the pure Ta(2)O(5) single crystals showed a monoclinic symmetry and a growth direction of [1 (1) over bar 0] An analysis of the pulling rate as a function of the fiber diameter for Eu(2)O(3)-doped Ta(2)O(5) fibers indicated a well defined region in which constitutional supercooling is absent Photoluminescence measurements of pure Ta(2)O(5) crystals using excitation above the band gap (3 8 eV) were dominated by a broad unstructured green band that peaked at 500 nm Three Eu(3+)-related optical centers were identified in the doped samples with nominal concentrations exceeding 1 mol% Two of these centers were consistent with the ion in the monoclinic phase with different oxygen coordinations The third one was visible in the presence of the triclinic phase (C) 2010 Elsevier B V All rights reserved

Revestimentos a base de Ta/Al2O3 produzidos por aspersão térmica sobre substrato metálico

Metal substrates were coated by thermal spraying plasma torch, they were positioned at a distance of 4 and 5 cm from the nozzle exit of the plasma jet. The starting materials were used for deposition of tantalum oxide powder and aluminium. These two materials were mixed and ground into high-energy mill, then immersed in the torch for the production of alumina coating infused with particles of tantalum with nano and micrometric size. The spraying equipment used is a plasma torch arc not transferred, which operating in the range of 250 A and 80 V, was able to produce enough heat to ignite aluminothermic between Ta2O5 and aluminum. Upon reaching the plasma jet, the mixing powders react with the heat of the blaze, which provides sufficient energy for melting aluminum particles. This energy is transferred through mechanisms of self-propagating to the oxide, beginning a reduction reaction, which then hits on the surface of the substrate and forms a coating on which a composite is formed by a junction metal - ceramic (Ta +Al2O3). The phases and quantification of each were obtained respectively by X-ray diffraction and the Rietveld method. Morphology by scanning electron microscopy and chemical analysis by energy dispersive spectroscopy EDS. It was also performed measurements of the substrate roughness, Vickers microhardness measurements in sprays and determination of the electron temperature of the plasma jet by optical emission spectroscopy EEO. The results confirmed the expectation generated around the end product of spraying the mixture Ta2O5 + Al, both in the formation of nano-sized particles and in their final form. The electron excitation temperature was consistent with the purpose of work, in addition, the thermodynamic temperature was efficient for the reduction process of Ta2O5. The electron excitation temperature showed values of 3000, 4500 and 8000 K for flows10, 20 and 30 l / min respectively, these values were taken at the nozzle exit of the plasma jet. The thermodynamic temperature around 1200 ° C, was effective in the reduction process of Ta2O5

Síntese e caracterização de TaC e óxido misto de tântalo e cobre nanoestruturados a partir do precursor oxálico de tântalo através de reações gás-sólido e sólido-sólido a baixa temperatura

The research and development of nanostructured materials have been growing significantly in the last years. These materials have properties that were significantly modified as compared to conventional materials due to the extremely small dimensions of the crystallites. The tantalum carbide (TaC) is an extremely hard material that has high hardness, high melting point, high chemical stability, good resistance to chemical attack and thermal shock and excellent resistance to oxidation and corrosion. The Compounds of Tantalum impregnated with copper also have excellent dielectric and magnetic properties. Therefore, this study aimed to obtain TaC and mixed tantalum oxide and nanostructured copper from the precursor of tris (oxalate) hydrate ammonium oxitantalato, through gas-solid reaction and solid-solid respectively at low temperature (1000 ° C) and short reaction time. The materials obtained were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), Spectroscopy X-Ray Fluorescence (XRF), infrared spectroscopy (IR), thermogravimetric (TG), thermal analysis (DTA) and BET. Through the XRD analyses and the Reitiveld refinement of the TaC with S = 1.1584, we observed the formation of pure tantalum carbide and cubic structure with average crystallite size on the order of 12.5 nanometers. From the synthesis made of mixed oxide of tantalum and copper were formed two distinct phases: CuTa10O26 and Ta2O5, although the latter has been formed in lesser amounts