Mössbauer analysis on the magnetic properties of Fe–Co nanoparticles synthesized by chemical vapor condensation process

The magnetic properties of Fe–Co nanoparticles synthesized by chemical vapor condensation (CVC) process were investigated. Effect of CVC processing variables on the magnetic properties was analyzed in detail, using Mössbauer spectroscopy, XRD, BET and HRTEM. The synthesized particles were nearly spherical, and their surfaces were identified to be -FeOOH, γ-FeOOH and Fe₃O₄, but not -Fe₂O₃. The magnetic properties were strongly influenced by CVC processing parameters. The increase of cobalt content had changed the magnetic property of the sample. However, when the decomposition temperature and the oxygen content in the carrier gas (Ar) were increased, the magnetic property reduced with decreasing the average particle size. Increasing the vacuum pressure in the chamber resulted in that the magnetic field reinforced with the increase of average particle size.     

Fixed charge and interface traps at heterovalent interfaces between Si(1 0 0) and non-crystalline Al2O3–Ta2O5 alloys

Characterization by Auger electron spectroscopy (AES) and Fourier transformation infrared spectroscopy (FTIR) confirms (Ta₂O₅)_x(Al₂O₃)_1−x alloys are homogeneous pseudo-binary alloys with increased thermal stability with respect to end member oxides, Ta₂O₅ and Al₂O₃. Capacitance–voltage (C–V) and current density–voltage (J–V) data as a function of temperate show that the Ta d-states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta₂O₅ with respect to Si.     

蓝光激发的Y2.93Al5O12∶0.07Ce3+黄色荧光粉的制备及光致发光

以Al₂(SO₄)₃·18H₂O、尿素为原料,采用水热-热解法制备了球形α-Al₂O₃粉体。以自制α-Al₂O₃、Y₂O₃及CeO₂为原料,固相法制备了白光LED用Y_2.93Al₅O₁₂∶0.07Ce3+黄色荧光粉,通过X射线衍射（XRD）、扫描电镜（SEM）、X射线能谱（EDS）及荧光光谱（PL）等对产物的物相、形貌及光致发光性能进行了表征。结果表明：水热-热解法制备出了物相纯净、分散性良好的球形α-Al₂O₃粉体,以该α-Al₂O₃为原料,合成出可被460 nm蓝光有效激发,发射光谱为峰值在550 nm宽带的Y_2.93Al₅O₁₂∶0.07Ce3+荧光粉,色坐标为（0.453,0.531 9）,采用GSAS软件对Y_2.93Al₅O₁₂∶0.07Ce3+荧光粉的XRD图进行了Rietveld结构精修,精修图与XRD测试图完全吻合,Y,Al,Ce,O四元素均匀地分布在黄色荧光粉产物中,Y_2.93Al₅O₁₂∶0.07Ce3+黄色荧光粉的激发光谱由两个部分组成,在340和460 nm处有两个非常明显的吸收峰,Ce3+的4f能级由于自旋-耦合而劈裂为两个光谱支项2F_7/2和2F_5/2,其中2F_5/2为基谱项。340 nm的激发峰对应于2F_5/2→5D_5/2的跃迁,460 nm的激发峰属于2F_7/2→5D_3/2的跃迁,并且460 nm处的激发强度强于340 nm处激发强度。以460 nm为监测波长得到的发射光谱,最强发射峰位于550 nm,Y_2.93Al₅O₁₂∶0.07Ce3+荧光粉是一种适用于白光LED的高性能黄色荧光粉。     

The interaction of Cu and S2 with aluminum and alumina surfaces: a comparative study

The bonding interactions between Cu and Al are much stronger than those between Cu and Al₂O₃. Cu atoms supported on alumina show a narrow 3d band with a centroid shifted 0.35 eV with respect to that of the 3d band in bulk metallic Cu. In contrast, Cu atoms deposited on aluminum exhibit shifts of 1.3–1.6 eV in the centroid of the 3d band. Similar differences are observed when comparing the behavior of Ag and Pt overlayers on alumina and aluminum. The d band shifts on the oxide substrate are in the order of 0.3–0.4 eV, whereas on the metal substrate they vary from 0.8 to 2.0 eV. These trends are explained in terms of a simple model that takes into account changes in the energy of the Al(3s, 3p) bands when going from metallic aluminum to alumina. The sticking coefficient of S₂ on alumina surfaces is at least one order of magnitude smaller than on aluminum, a difference that also reflects variations in the position of the Al(3s,3p) bands. Submonolayer coverages of Cu do not produce significant changes in the electronic properties of Al₂O₃. In contrast, the deposition of small amounts of sulfur (0.1 ML) induces a substantial reduction (0.4–0.5 eV) in the binding energies of the O KVV, O 1s and Al 2p features of alumina. This is consistent with a transfer of electrons from alumina into the S atoms that produces a transformation similar to a change from n-type to p-type semiconductors. The reactivity of Cu/Al₂O₃ surfaces toward sulfur is much larger than that of pure Al₂O₃ surfaces. Cu clusters supported on alumina react with S₂ to form CuS_x compounds that decompose at temperatures between 850 and 1100 K.     

Influence of the transparency of tunnel barriers in Nb/Al2O3/Al/Al2O3/Nb junctions on transport properties

The transparency of the tunnel barriers in double-barrier junctions influences the critical current density and the form of the current–voltage characteristics (IVC). Moreover, the barrier asymmetry is an important parameter, which has to be controlled in the technological process. We have performed a systematic study of the influence of the barrier transparency on critical current, I_C, and normal resistance, R_N, by preparing SIS and SINIS junctions under identical technological conditions and comparing their transport properties. We have fabricated Nb/Al₂O₃/Nb and Nb/Al₂O₃/Al/Al₂O₃/Nb devices with different current densities using a conventional fabrication process, varying pressure and oxidation time. The thickness of the Al middle electrode in all Nb/Al₂O₃/Al/Al₂O₃/Nb junctions was 6 nm. Patterning of the multilayers was done using conventional photolithography and the selective niobium etching process. The current density of SIS junctions was changed in the range from 0.5 to 10 kA/cm². At the same conditions the current density of SINIS devices revealed 1–100 A/cm² with non-hysteretic IVC and characteristic voltages, I_CR_N, of up to 200 μV. By comparing the experimental and theoretical temperature dependence of the I_CR_N product we estimated the barrier transparency and its asymmetry. The comparison shows a good agreement of experimental data with the theoretical model of tunneling through double-barrier structures in the dirty limit and provides the effective barrier transparency parameter γ_eff≈300. A theoretical framework is developed to study the influence of the barrier asymmetry on the current–phase relationship and it is proposed to determine the asymmetry parameter by measuring the critical current suppression as function of applied microwave power. The theoretical approach to determine the non-stationary properties of double-barrier junctions in the adiabatic regime is formulated and the results of calculations of the I–V characteristics are given in relevant limits. The existence and the magnitude of a current deficit are predicted as function of the barrier asymmetry.     

Influences of annealing on structural and compositional properties of Al_2O_3 thin films grown on 4H–SiC by atomic layer deposition

Annealing effects on structural and compositional performances of Al_2O_3 thin films on 4H–Si C substrates are studied comprehensively. The Al_2O_3 films are grown by atomic layer deposition through using trimethylaluminum and H_2 O as precursors at 300?C, and annealed at various temperatures in ambient N_2 for 1 min. The Al_2O_3 film transits from amorphous phase to crystalline phase as annealing temperature increases from 750?C to 768?C. The refractive index increases with annealing temperature rising, which indicates that densification occurs during annealing. The densification and grain formation of the film upon annealing are due to crystallization which is relative with second-nearest-neighbor coordination variation according to the x-ray photoelectron spectroscopy(XPS). Although the binding energies of Al 2p and O 1s increase together during crystallization, separations between Al 2p and O 1s are identical between as-deposited and annealed sample, which suggests that the nearest-neighbour coordination is similar.     

Deposition of Co nano-particles in a CoO/Al2O3 matrix by magnetron sputtering

We have explored the use of sequential sputtering as an alternative way of growing Co clusters inside an antiferromagnetic matrix of CoO. The samples are composed of 10 bi- or tri-layers and have been deposited by direct magnetron sputtering of Co, CoO and Al₂O₃ targets. Transmission electron microscopy and impedance spectroscopy measurements show that the direct deposition of Co over CoO does not favor the Volmer–Weber tridimensional mode in the tested range of Co nominal thicknesses. In the samples where an Al₂O₃ layer is formed prior to the Co deposition, Co aggregates of nano-size are formed and retained when the empty space is filled by CoO. Some preliminary results of the magnetization as a function of temperature are presented and discussed.     

Study of the interfacial structure and chemistry of CVD κ-Al2O3/TiC multilayer coatings

This article describes the interfacial regions in CVD grown TiC/κ-Al₂O₃ multilayers. A number of microanalytical techniques were used including HREM, EDX and EELS. Occasionally, the first 50 nm of the alumina layers deposited on the intermediate TiC layers grew as a cubic alumina, heavily faulted, containing small amounts of sulphur (S), maybe as a stabiliser. The presence of slightly rounded TiC (111) facets may act as preferred nucleation sites for the cubic Al₂O₃ phase, with a ‘cube on cube’ orientation relationship. In this way the nucleation of κ-Al₂O₃ is less favourable. After some tens of nanometres the cubic phase cannot be stabilised any longer and the layer continues to grow as κ-Al₂O₃. A number of observations point towards the reaction zone (RZ) being η- and/or γ-Al₂O₃. The diffraction work and the FFT analysis of the HREM images show that the RZ is an fcc phase with a=7.9 Å, which matches with η- and γ-Al₂O₃. The EELS Al fine structure indicate more tetrahedral Al ions than in κ-Al₂O₃, as in η- and γ-Al₂O₃. The RZ contains small amounts of S, as has been reported for γ-Al₂O₃. Due to the structural similarities between η- and γ-Al₂O₃ it was not possible to determine which of these cubic phases is present in the RZ.     

原子层沉积方法制备核-壳型纳米材料研究

采用原子层沉积方法在碳黑纳米颗粒表面分别沉积Al₂O₃, ZnO, TiO₂和Pt, 成功制备出核-壳型纳米材料. 通过高分辨率透射电子显微镜、X射线光电子能谱仪、 能谱仪对材料的表面形貌、晶体结构、薄膜成分进行了表征和分析. 结果表明, 原子层沉积方法是制备核壳型纳米材料的理想方法. 此外, 还分析了采用原子层沉积方法沉积不同材料, 所生长的薄膜材料有单晶、多晶、非晶等多种存在形式的形成原因. 关键词： 原子层沉积 核-壳型纳米材料 碳黑纳米颗粒     

磁控溅射沉积铝/贫铀与金/贫铀镀层的界面研究

采用磁控溅射技术沉积制铝/贫铀/铝(Al/DU/Al)、金/贫铀/金(Au/DU/Au) "三明治" 薄膜样品. 利用高分辨扫描电镜、 X射线衍射仪、X射线光电子能谱仪、 扫描俄歇微探针对Al/DU/Al, Au/DU/Au样品的Al/DU, Au/DU界面行为进行表征与研究. 结果表明: 沉积态DU层以柱状晶生长; Al/DU界面扩散明显, 物理扩散过程中伴随着Al, DU化学反应形成Al₂U, Al₃U金属化合物; 金属化合物的形成导致界面处Al 2p电子结合能向高能端移动, U 4f电子向低能端移动; 微量O在Al/DU界面处以Al₂O₃及铀氧化物形式存在; DU镀层中以铀氧化形式存在; 沉积态的Au/DU界面扩散为简单的物理扩散, 团簇效应导致Au/DU界面处Al 2p, U 4f电子结合能均向高能端移动; 在Au/DU界面及DU镀层中, 微量O以铀氧化物形式存在; Al/DU界面扩散强于Au/DU; 相同厚度的Al, Au保护镀层, Al镀层保护效果优于Au镀层. 关键词： Al/DU界面 Au/DU界面 磁控溅射 界面扩散     

Atomic-layer-deposited Al_2O_3 and HfO_2 on InAlAs: A comparative study of interfacial and electrical characteristics

Al_2O_3 and HfO_2 thin films are separately deposited on n-type InAlAs epitaxial layers by using atomic layer deposition(ALD).The interfacial properties are revealed by angle-resolved x-ray photoelectron spectroscopy(AR-XPS).It is demonstrated that the Al_2O_3 layer can reduce interfacial oxidation and trap charge formation.The gate leakage current densities are 1.37×10~6 A/cm~2 and 3.22×10~6 A/cm~2 at+1V for the Al_2O_3/InAlAs and HfO_2/InAlAs MOS capacitors respectively.Compared with the HfO_2/InAlAs metal-oxide-semiconductor(MOS) capacitor,the Al_2O_3/InAlAS MOS capacitor exhibits good electrical properties in reducing gate leakage current,narrowing down the hysteresis loop,shrinking stretch-out of the C-V characteristics,and significantly reducing the oxide trapped charge(Q_(ot)) value and the interface state density(D_(it)).     

不同退火温度的Al_2O_3:C薄膜热释光和光释光性能

α-Al_2O_3:C晶体的热释光和光释光性能优越,但其制备要求高,需高温和高还原气氛.与α-Al_2O_3:C晶体性能接近的α-Al_2O_3:C陶瓷,热释光峰不单一.本文采用两次阳极氧化法在0.5 mol/L的草酸溶液中5℃恒温制备高度均匀有序的多孔Al_2O_3:C薄膜,主要研究不同退火温度对其热释光和光释光特性的影响.结果表明,经不同温度退火后的Al_2O_3:C薄膜均为非晶结构;不同退火温度的Al_2O_3:C薄膜热释光的主发光峰约在310℃左右,符合通用级动力学模型.600℃退火后的Al_2O_3:C薄膜热释光灵敏度最强,其热释光剂量曲线在1-10 Gy范围内具有很好的线性响应,在剂量10-120 Gy范围内出现超线性响应;在相同的辐照剂量下,随着退火温度的升高(≤600℃)光释光的初始发光强度逐渐增强.不同退火温度的Al_2O_3:C薄膜光释光衰减曲线都呈典型的指数衰减且快衰减速率相比α-Al_2O_3:C晶体显著加快.600℃退火后的Al_2O_3:C薄膜光释光灵敏度最强,其光释光剂量响应曲线在1-200 Gy整体上都具有很好的剂量线性关系.与热释光相比,Al_2O_3:C薄膜的光释光具有更宽的线性剂量响应范围.此研究为Al_2O_3:C薄膜作为光释光辐射剂量材料做出了有益的探索.     

Synthesis and electron storage characteristics of isolated silver nanodots on/embedded in Al2O3 gate dielectric

Monolayer-isolated silver (Ag) nanodots with the average diameter down to 7 nm are synthesized on Al₂O₃/Si substrate by vacuum electron-beam evaporation followed by annealing at 400 °C in N₂ ambient. Metal–insulator-silicon (MIS) structures with Ag nanodots embedded in Al₂O₃ gate dielectric are fabricated. Clear electron storage effect with the flatband voltage shift of 1.3 eV is observed through capacitance–conductance and conductance–voltage measurements. Our results demonstrate the feasibility of applying Ag nanodots for nanocrystal floating-gate memory devices.     

高铁车轮中复合夹杂物的火花光谱原位分析

火花发射光谱分析钢中单一夹杂物的研究已有文献报导,但用火花光谱分析钢中复合夹杂物一直是个难题.钢中复合夹杂物是一种单一夹杂物包裹另外一种单一夹杂物组成的复合体,或由两个及以上单一夹杂物紧密相邻结合体.如何区分材料中同时存在但不相邻的两种单一夹杂物和二者复合夹杂物,用火花发射光谱技术难于实现.该工作采用火花光谱原位统计分...     

Preparation and characterization of Y1−xPrxBa2Cu3O7−δ single crystals

We present a reliable method for growing single crystals of Y_1−xPr_xBa₂Cu₃O_7−δ high-T_c superconductors in ZrO₂ crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al₂O₃ crucibles. We describe techniques for crystal growth in both Al₂O₃ and ZrO₂ crucibles using an excess of BaCo₃ and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant.     

Structural evolution of Sc-containing zirconia electrolytes

A powder of nominal composition (ZrO₂)_0.886(Sc₂O₃)_0.104(Al₂O₃)_0.01 was synthesized by spray drying with the purpose of testing the performance of solid oxide fuel cells containing scandia-stabilized zirconia (ScSZ) as electrolyte. The phases resulting from calcination and sintering at different temperatures were investigated by XRD, impedance and Raman spectroscopy. At sintering temperatures of 1200–1400 °C nearly equal amounts of cubic and rhombohedral ScSZ were detected, whereas heat treatment higher than 1500 °C led to a cubic single-phase material. A preliminary reaction mechanism of phase formation is proposed with respect to the various results depending on heat treatment.     

Dramatic reduction in dark current of β-Ga2O3 ultraviolet photodectors via β-(Al0.25Ga0.75)2O3 surface passivation

Solar-blind ultraviolet photodetectors with metal-semiconductor-metal structure were fabricated based on β -(Al_0.25Ga_0.75)₂O₃/β -Ga₂O₃ film grown by metal-organic chemical vapor deposition. It was known that various surface states increase dark current and a large number of defects can hinder the transport of carriers, resulting in low switching ratio and low responsivity of the device. In this work, β -(Al_0.25Ga_0.75)₂O₃ films are used as surface passivation materials. Owning to its wide band gap, we obtain excellent light transmission and high lattice matching with β -Ga₂O₃. We explore the change and mechanism of the detection performance of the β -Ga₂O₃ detector after β -(Al_0.25Ga_0.75)₂O₃ surface passivation. It is found that under the illumination with 254 nm light at bias 5 V, the β -(Al_0.25Ga_0.75)₂O₃/β -Ga₂O₃ photodetectors show dark current of just 18 pA and high current on/off ratio of 2.16×10⁵. The dark current is sharply reduced about 50 times after passivation of the β -Ga₂O₃ surface, and current on/off ratio increases by approximately 2 times. It is obvious that β -Ga₂O₃ detectors with β -(Al_0.25Ga_0.75)₂O₃ surface passivation can offer superior detector performance.     

Enhanced luminescence from transparent Ni-doped MgO–Al2O3–SiO2 glass ceramics by Ga2O3 addition

Transparent Ni²⁺-doped MgO–Al₂O₃–SiO₂ glass ceramics without and with Ga₂O₃ were synthetized. The precipitation of spinel nanocrystals, which was identified as solid solutions in the glass ceramics, could be favored by Ga₂O₃ addition and their sizes were about 7.6 nm in diameter. The luminescent intensity of the Ni²⁺-doped glass ceramics was largely enhanced by Ga₂O₃ addition which could mainly be caused by increasing of Ni²⁺ in the octahedral sites and the reduction of the mean frequency of phonon density of states in the spinel nanocrystals of solid solutions. The full width at half maximum (FWHM) of emissions for the glass ceramics with different Ga₂O₃ content was all more than 200 nm. The emission lifetime increased with the Ga₂O₃ content and the longest lifetime is about 250 μs. The Ni²⁺-doped transparent glass ceramics with Ga₂O₃ addition have potential application as broadband optical amplifier and laser materials.     

空位缺陷和相变对冲击压缩下蓝宝石光学性质的影响

为了探究冲击压缩下蓝宝石光学性质的变化行为,本文采用第一性原理方法,在180 GPa的压力范围内计算了蓝宝石理想晶体和含空位点缺陷晶体的光学性质.吸收光谱数据表明,仅考虑压力和温度因素不能解释冲击消光实验的结果,而冲击诱导的氧离子空位点缺陷应该是导致该结果的一个重要原因.波长在532 nm处的折射率数据表明:1)蓝宝石的两个高压结构相变将导致其折射率明显上升;在Corundum和Rh_2O_3相区,其折射率将随冲击压力增大而降低;在CalrO_3相区,压力小于172 GPa时,其折射率随冲击压力增大而缓慢地降低,但172 GPa以上时折射率却随冲击压力增大而逐渐增大;2)空位点缺陷对折射率随冲击压力的变化规律有明显的影响.本文结果不仅有助于增强用空位点缺陷的物理机理来解释蓝宝石冲击透明性损伤现象的可靠性,而且对未来进一步的实验研究以及发展新型窗口材料有重要的参考作用.     

石榴子石热红外波谱特征研究

近年来短波红外高光谱技术已成功应用于含水含羟基蚀变矿物及矿床学研究,但是对于不含水不含羟基矿物探测效果不好,而热红外高光谱技术可以弥补这一技术缺陷,对于含Si_nO_k,SO₄,CO₃和PO₄等原子基团的矿物具有良好的应用前景。石榴子石是一种重要的含Si_nO_k 基团的岛状结构硅酸盐矿物,根据成分可分为钙铝榴石、钙铁榴石、镁铝榴石、铁铝榴石及锰铝榴石等不同端元,石榴子石成分对成矿温压环境及成矿中心预测具有重要的研究意义。目前针对石榴子石热红外波谱特征研究非常欠缺。故采集不同成分、不同颜色石榴子石样品16件,创新性地运用美国Agilent4300热红外波谱仪开展热红外波谱特征研究,同时运用美国Niton手持式XRF分析仪开展石榴子石同一测量位置的SiO₂,MgO,Al₂O₃,K₂O,CaO和Fe₂O₃等主量元素含量测试,并分析波谱吸收位置与主量元素含量之间的关系。结果表明石榴子石在热红外波段10~13 μm具有左高右低的双峰式诊断性波谱特征,在11.5 μm附近呈现一个主吸收谷,在12 μm附近有一个次级吸收谷,且主吸收谷及次级吸收谷波长位置与石榴子石Al₂O₃和Fe₂O₃含量具有良好的相关性,相关系数大于0.9,即波谱吸收谷的波长位置与Al₂O₃含量具有线性负相关关系,与Fe₂O₃含量具有线性正相关关系。据此研究结果,可以快速开展石榴子石矿物成分的野外鉴定,还可以快速开展矽卡岩矿床野外蚀变分带研究,进而指导找矿勘查。揭示了不同成分石榴子石矿物的热红外波谱特征,对其他架状硅酸盐、岛状硅酸盐、单链状硅酸盐、碳酸盐、硫酸盐矿物的热红外波谱特征研究具有重要的指导意义。