薄膜沉积过程中TiO_2的金红石相向锐钛矿相转变

用ＲＦ磁控放电方法以纯金属钛做靶材在氩氧混合气体中制备了ＴｉＯ２薄膜,Ｒａｍａｎ光谱测量表明,在２Ｐａ工作气压下制备的ＴｉＯ２薄膜为锐钛矿结构,而在０２Ｐａ工作气压下制备的是金红石结构。工作气压的改变引起了ＴｉＯ２薄膜沉积中的相转变。     

Hyperfine interactions in intermetallic rare earth-gallium compounds studied by 111 Cd PAC

Magnetic and electric hyperfine interaction of the nuclear probe ¹¹¹In/¹¹¹Cd in intermetallic compounds of the rare earth-gallium system have been investigated by perturbed angular correlation (PAC) spectroscopy. The PAC measurements, supported by X-ray diffraction, provide evidence for a marked phase preference of ¹¹¹In for hexagonal RGa₂ over orthorhombic RGa and of RGa₃ with the L12 structure over RGa₂. In the case of SmGa₂, the magnetic hyperfine field B_hf, the electric quadrupole interaction and the angle β between B_hf and the symmetry axis of the electric field gradient have been determined as a function of temperature. The angle β?=?0 is consistent with the results of previous magnetization studies. Up to T?≤?17 K the magnetic hyperfine field has a constant value of B_hf?=?3.0(2) T. The rapid decrease at higher T gives the impression of a first-order transition with an order temperature of T_N?=?19.5 K. In the RKKY model of indirect 4f interaction the ratio T_C/B_hf(0) is a measure of the coupling constant. For ¹¹¹Cd:SmGa₂ (T_C/B_hf(0)~6.5 K/T) this ratio is significantly smaller than for the same probe in other R intermetallics (SmAl₂ ~9.5 K/T, Sm₂In ~13.5 K/T).     

Level crossing in hyperfine interactions studied by perturbed γ-γ angular correlations

The technique of differential γ-γ angular correlation measurements has been applied to an investigation of the hyperfine interactions in the 482 keV level of¹⁸¹Ta. The activity was embedded in the lattice of a hafnium single crystal. The investigation of the quadrupole interaction gave for the electric interaction frequencyω ₀=(313±4) MHz. The electric field gradient was found to be axially symmetric, the asymmetry parameter beingη<0.1. Furthermore the combined collinear magnetic dipole and electric quadrupole interaction was studied. The angular correlation was investigated as a function of the strength of the external magnetic field by integral as well as time differential measurements. The integral anisotropy as function of the magnetic field has the shape of a resonance curve. The maximum was observed at a magnetic field ofB _res=(24.2±0.5)kG.     

Hyperfine interactions of111Cd impurities in Cr2O3

The electric and (antiferro-)magnetic hyperfine interaction of¹¹¹Cd in α-Cr₂O₃ after¹¹¹In implantation was studied via PAC. Two fractions with axially symmetric electric field gradients were observed having antishielding factors of V_zz/V_zz ^pc=79(12) and 106(16), respectively. From the line broadening of the Fourier components of the first fraction its supertransferred magnetic field was estimated as B_loc (20 K)≤0.41 T, about two orders of magnitude smaller than for substitutional¹¹¹Cd in NiO and CoO.     

高压下金红石的拉曼光谱分析

常温下利用金刚石压腔装置(DAC)对金红石加压至40GPa,进行拉曼光谱的原位分析.发现压力约为13GPa时,金红石结构转变为斜锆石结构(ZrO2).21.1GPa相变完全.直至实验最高压力,没有进一步相变出现.在卸压中,斜锆石结构转变为α-PbO2结构.实验压力通过红宝石用拉曼光谱测压的计算方法确定,快速方便.     

Lattice defects in ion-implanted aluminium studied by means of perturbed angular correlations

Migration and clustering of lattice defects after implantation of¹¹¹In in Al and subsequent annealing at temperatures in the range from 80 to 800 K were investigated applying the DPAC technique. The effects of implantation dose, implantation temperature, laser irradiation, and plastic deformation were studied. The measurements on plastically deformed Al were complemented by positron lifetime measurements. We observed four In-defect clusters that can be flagged by well-defined hyperfine interaction parameters, and we determined their symmetry properties by using single-crystal samples. Important conclusions are: (i) monovacancies are not trapped by In-atoms, (ii) small In-defect clusters are formed by direct trapping of divacancies and/or trivacancies, and (iii) extended In-defect clusters are very stable and anneal in the temperature range 600–700 K. Consequences for the interpretation of other measurements on dilute Al(In) alloys are discussed.On leave from Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India.     

Hyperfine interactions of111In→111Cd probe atoms on GaAs (111)B reconstructed surfaces

Hyperfine Interactions - We have used111In→111Cd perturbed-angular-correlation (PAC) spectroscopy to measure hyperfine interactions at surface sites on two molecular-beam-epitaxy-grown GaAs...     

Charge transport in anodic TiO2 nanotubes studied by terahertz spectroscopy

We report on the photoelectrochemical and terahertz measurements, of the charge transport properties of 1 μm thick self‐organized TiO₂ nanotube layers, prepared by the anodization of titanium. We provide evidence regarding the complexity of electron transport, and dynamics in the nanotubes. Shortly after photoexcitation, charge mobilites in amorphous and crystalline nanotubes are similar, but still lower compared to the bulk anatase. The mobility subsequently decreases due to trapping‐detrapping processes. The recombination rate in anatase nanotubes is much slower than in the amorphous ones, enabling the material to reach an internal photon to electron conversion efficiency exceeding 60%.     

以Eu_2(CA)_3(phen)_2为掺杂剂的Eu~(3+)/TiO_2纳米粉体的制备及其谱学性能研究

采用溶胶-凝胶法制备了分别以Eu(NO3)3和Eu2(CA)3(phen)2(CA:樟脑酸;phen:1,10-菲咯啉)为前驱体,掺杂量为1%(原子摩尔比)的Eu3+/TiO2纳米粉体,通过差热-热重(TG-DTA)、X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(FTIR)、紫外-可见漫反射吸收光谱(UV-Vis)和荧光光谱等分析手段,对样品的结构和谱学性能进行了对比研究。研究表明,稀土Eu3+以有机配合物Eu2(CA)3(phen)2为前躯体掺杂时,能更有效抑制TiO2纳米粉体的颗粒度增长和晶相转变温度;且UV-Vis吸收峰有一定的红移现象。2种样品中均产生了Eu3+578nm(5D0→7F0),590nm(5D0→7F1)和612nm(5D0→7F2)处的特征发射光谱峰,612nm处最强发射峰为Eu3+特征红色发射峰。当稀土Eu3+含量相同时,以有机配合物Eu2(CA)3(phen)2为前躯体制备的纳米粉体发光强度更大。     

甲醛在金红石型TiO2(100)-(1×1)表面的光解离

We have investigated the photoinduced decomposition of formaldehyde (CH₂O) on a rutile TiO₂(100)-(1×1) surface at 355 nm using temperature-programmed desorption. Products, formate (HCOO^-), methyl radical (CH₃·), ethylene (C₂H₄), and methanol (CH₃OH) have been detected. The initial step in the decomposition of CH₂O on the rutile TiO₂(100)-(1×1) surface is the formation of a dioxymethylene intermediate in which the carbonyl O atom of CH₂O is bound to a Ti atom at the five-fold-coordinated Ti⁴⁺ (Ti_5c) site and its carbonyl C atom bound to a nearby bridge-bonded oxygen (O_b) atom, respectively. During 355 nm irradiation, the dioxymethylene intermediate can transfer an H atom to the O_b atom, thus forming HCOO^- directly, which is considered as the main reaction channel. In addition, the dioxymethylene intermediate can also transfer methylene to the O_b row and break the C-O bond, thus leaving the original carbonyl O atom at the Ti_5c site. After the transfer of methylene, several pathways to products are available. Thus, we have found that O_b atoms are intimately involved in the photoinduced decomposition of CH₂O on the rutile TiO₂(100)-(1×1) surface.     

Experimental detection of relaxation phenomena in Rb2HfF6 by perturbed angular correlations

The differential perturbed angular correlation spectrum of ¹⁸¹Ta in Rb₂HfF₆ was studied as a function of temperature. The results indicate the existence of a temperature dependent mixture of pure static quadrupole interactions and pure multipole relaxation due to fluctuating electric quadrupole interactions.     

锐钛矿型TiO2(101)面原子几何及弛豫结构的第一性原理计算

采用平面波超软赝势方法计算了锐钛矿型TiO2(101)面的表面能和表面原子弛豫结构.首先对TiO2(101)面的6种不同的表面原子终止结构的体系总能量进行了计算,结果表明终止原子为两配位的O原子、次层为五配位的Ti原子的表面结构最为稳定.针对该表面研究了表面能和原子弛豫与模型中原子层数和真空厚度的关系,当原子层数为12层,真空厚度为0.4 nm时,表面能收敛度小于0.01 J/m2.研究发现:表面上两配位的O原子向里移动约0.0012 nm,五配位的Ti原子向里移动约0.0155 nm,弛豫后的Ti-O键长发生了较大变化,核外电荷发生了转移,结构趋于稳定.     

电场中(MgO)_2吸附H_2的理论研究

电场诱导MgO材料吸附H_2是一种有效的储氢方法,而较高的场强制约其广泛应用.本文在B3LYP/CC-PVTZ水平上对电场中(MgO)_2团簇的储氢性质进行了研究,结果表明仅需外加强度为0.005a.u.的电场,就能使其对单个H_2在Mg/O上的吸附能由无电场时的-0.143/-0.091 eV提高到-0.202/-0.134 eV.该场强远小于其他大尺寸MgO材料达到相同吸附强度所需的电场,表明降低材料尺寸是减少储氢所需电场强度的一种可能方法 .计算还表明电场中(MgO)_2最多能吸附8个H_2,相应的质量密度达到16.7 wt%.     

电场中(MgO)2吸附H2的理论研究

电场诱导MgO材料吸附H2是一种有效的储氢方法,而较高的场强制约其广泛应用。本文在B3LYP/CC-PVTZ水平上对电场中 (MgO)2团簇的储氢性质进行了研究,结果表明仅需外加强度为0.005 a. u. 的电场,就能使其对单个H2在Mg/O上的吸附能由无电场时的-0.143/-0.091 eV提高到-0.202/-0.134 eV. 该场强远小于其他大尺寸MgO材料达到相同吸附强度所需的电场,表明降低材料尺寸是减少储氢所需电场强度的一种可能方法。计算还表明电场中(MgO)2最多能吸附8个H2,相应的质量密度达到16.7 wt%。     

电场中(MgO)2吸附H2的理论研究

电场诱导MgO材料吸附H2是一种有效的储氢方法,而较高的场强制约其广泛应用。本文在B3LYP/CC-PVTZ水平上对电场中 (MgO)2团簇的储氢性质进行了研究,结果表明仅需外加强度为0.005 a. u. 的电场,就能使其对单个H2在Mg/O上的吸附能由无电场时的-0.143/-0.091 eV提高到-0.202/-0.134 eV. 该场强远小于其他大尺寸MgO材料达到相同吸附强度所需的电场,表明降低材料尺寸是减少储氢所需电场强度的一种可能方法。计算还表明电场中(MgO)2最多能吸附8个H2,相应的质量密度达到16.7 wt%。     

An investigation of the Electric Quadrupole Interaction (EQI) in (lead-barium) zirconate compounds by perturbed angular correlations

This letter reports the results of the hyperfine interactions in (lead-barium) zirconate compounds measured by angular correlations. The measured values are compared with the results of a lattice sum calculation.