Complete identification of the Ti-related levels in GaP

A complete understanding of the electrical and optical properties of all the Ti-related levels is deduced from a number of different characterization techniques performed on several types of Ti-doped GaP materials (n-type, p-type and semi-insulating) grown by LEC. The Ti³⁺ /Ti⁴⁺ donor level and the Ti²⁺ /Ti³⁺ acceptor level are found at E_v + 0.92 and about E_c - 0.56 eV, respectively. Likewise, a comprehensive scheme of the two internal transitions ³T₂→³A₂ of the Ti²⁺ charge state and ²T₂→²E of the Ti³⁺ charge state is given.     

Impurity levels of iron-group ions in TiO2(II)

Photocurrent measurements on oxidized, single-crystal TiO₂ undoped and doped with V, Cr, Mn or Fe were made both before and after exposure to white light from a tungsten lamp; they revealed a band of states centered at 2.0 eV below the conduction-band edge E_c that appears to be the band of surface states active in the photoelectrolysis of water. They also revealed a band of bulk states extending from near the valence-band edge E_v to about 1.9 eV below E_c. The ESR signals from V⁴⁺, Cr³⁺ and Fe³⁺ ions in oxidized samples and from Mn³⁺ ions in reduced samples were measured before and after exposure to white and monochromatic light; changes in the ESR signal intensities allow placement of the V⁴⁺: d¹ level about 2.1 eV below E_c, the Cr³⁺: d³ level about 2.7 eV belo E_c, the Fe³⁺ level at or just below the valence band edge E_v which is 3.0 eV below E_c, the Fe²⁺ level approximately at E_c, the Mn³⁺ level about 1.9 eV below E_c. Comparison of experiments on oxidized and reduced samples suggests that the bulk states are associated with cation vacancies, and measurements with polarized light gave anisotropies that are qualitatively interpretable with a cation-vacancy model for the oxidized samples.     

Electrical characterization of argon-ion sputtered n-GaAs

Epitaxially grown n-type GaAs was sputtered with 0.5 keV Ar ions at doses of 10¹² and 10¹⁵ ions/cm². The sputter-induced defects in the GaAs were characterized using deep-level transient spectroscopy (DLTS) and the effect of these defects on the characteristics of Au Schottky barrier diodes (SBD's) fabricated on the sputtered GaAs was evaluated by current-voltage measurements. It was found that the barrier height of the SBD's decreased with ion dose from 0.97 eV for unsputtered diodes to 0.48 eV after sputtering at a dose of 10¹⁵/cm². DLTS showed the presence of a multitude of sputter-induced defects at and near the GaAs surface. The defects formed during the initial stages of sputtering had the same properties as some of the primary defects introduced during electron and proton irradiation of GaAs. Isochronal annealing at temperatures of up to 350°C showed that although some defects were removed by annealing, others appeared.     

Ni/SnO_2复合薄膜的制备与光电性能

采用旋涂法将溶胶-凝胶法制备的Ni/Sn O2凝胶在玻璃基底上镀膜,得到了Ni/Sn O2复合薄膜,探讨了镍掺杂量、煅烧温度对薄膜结构和形貌的影响。通过X射线衍射、红外光谱、扫描电子显微镜等测试手段对Ni/Sn O2复合膜的结构和形貌进行表征。结果显示,500℃下煅烧的薄膜样品的结晶度较高,粒径小,颗粒分布均匀。用紫外-可见分光光度计和四探针电阻仪对其进行光学、电学性能测试,结果显示:适量的Ni掺杂可以提高Sn O2薄膜在近紫外光区的吸收,Ni/Sn O2薄膜在近紫外光区的吸收随着Ni2+掺杂摩尔分数从5%增加到10%而逐渐减小。当Ni2+掺杂摩尔分数为6%时,Ni/Sn O2复合薄膜的导电性能最好。     

A spectroscopic ellipsometric investigation of new critical points of Zn1−xMnxS epilayers

Zn_1−xMn_xS epilayers were grown on GaAs (1 0 0) substrates by hot-wall epitaxy. X-ray diffraction (XRD) patterns revealed that all the epilayers have a zincblende structure. The optical properties were investigated using spectroscopic ellipsometry at 300 K from 3.0 to 8.5 eV. The obtained data were analyzed for determining the critical points of pseudodielectric function spectra, (E) = ₁(E) + i₂(E), such as E₀, E₀ + Δ₀, and E₁, and three E₂ (Σ, Δ, Γ) structures at a lower Mn composition range. These critical points were determined by analytical line-shapes fitted to numerically calculated derivatives of their pseudodielectric functions. The observation of new peaks, as well as the shifting and broadening of the critical points of Zn_1−xMn_xS epilayers, were investigated as a function of Mn composition by ellipsometric measurements for the first time. The characteristics of the peaks changed with increasing Mn composition. In particular, four new peaks were observed between 4.0 and 8.0 eV for Zn_1−xMn_xS epilayers, and their characteristics were investigated in this study.     

晶体NiF2的吸收光谱和电子顺磁共振谱的一种完全对角化计算

采用半自洽场(semi-SCF)自由Ni²⁺的d轨道波函数、点电荷-偶极子模型和Ni²⁺-6X^-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立结构参数与光谱、电子顺磁共振(EPR)谱(零场分裂D,E和顺磁g因子)之间的定量关系.利用能量矩阵完全对角化方法(CDP)和高阶微扰方法,统一解释NiF₂晶体的局部结构、吸收光谱和电子顺磁共振谱(EPR).比较两种方法计算得到的零场分裂D,E和顺磁g因子.结果表明:①高阶微扰方法算出的D,E值误差大;②能量矩阵完全对角化方法(CDP)算出的D,E值、光谱、顺磁g因子的值都与实验符合很好.     

Secondary ion emission from clean and K-covered Ni surfaces near threshold impact energies

Clean and K-covered Ni surfaces are bombarded with low energy (10–500 eV) beams of He⁺, Ne⁺, Ar²⁺, and Kr⁺ ions, and the emitted ion yield is measured as a function of beam energy. The apparent threshold energies for K⁺ and Ni⁺ emission are proportional to the ionic binding energies of K⁺ and Ni⁺ to the Ni surface. From comparison of the ion and neutral yield curves, it is suggested that these ions are emitted via momentum transfer collisions similar to neutral sputtering.     

掺杂晶体材料Al2O3∶Ni2+中顺磁离子N2+局域结构及其电子顺磁共振参量的研究

按照叠加模型和微扰理论,建立了电子顺磁共振（EPR）参量（D, g_∥, g_⊥）与Al_2O3∶Ni²⁺晶体局域结构之间的定量关系. 利用EPR参量决定了Al₂O₃∶N i²⁺晶体的局域结构. 通过考虑适当的晶格畸变,成功地解释了Al₂O₃∶Ni²⁺晶体基态很大的零场分裂和各向异性的g因子. 获得了Ni²⁺ 离子上方最近邻的三个O^2-离子偏向111〕晶轴0.603°, 而Ni²⁺离子下方的三个O^2-离子偏向〔111〕晶轴0.598°.     

Phase transitions and electrical properties of CsH(SO4)0.76(SeO4)0.24 mixed crystals

The study by X-ray diffraction, calorimetry, vibrational and impedance spectroscopy of CsH(SO₄)_0.76(SeO₄)_0.24 new solid solution is presented. Crystals of this composition undergo two phase transitions at T = 333 and 408 K. The last one at 408 K is a superionic-protonic transition (SPT) related to a rapid [HS(Se)O₄⁻] reorientation and fast H⁺ diffusion. A sudden jump in the conductivity plot confirms the presence of this transition. Above 408 K, this high temperature phase is characterized by high electrical conductivity (7 × 10^t-3 Ω⁻ cm⁻¹) and low activation energy (E_a < 0.3 eV).     

Axial energy distributions of Li and F desorbed from LiF surfaces by fast ion impact

Initial axial kinetic energy (E_z) distributions of Li⁺ and F⁻ secondary ions desorbed from LiF surfaces, bombarded by low current (500 particles/s) N³⁺ beams in the 0.075–7.5 MeV primary ion energy (E_PI) range, were measured by using the time-of-flight technique. In this energy range, the electronic energy loss, S_e, increases from 25 to 160 eV/Å, while the nuclear stopping power, S_n, decreases from 8.0 to 0.25 eV/Å. The observed F⁻ initial axial kinetic energy distribution can be described by the linear collision cascade theory and no other contribution was found. The F⁻ total yield decreases proportionally to S_n. The Li⁺ distribution presents a remarkable deviation from the cascade prediction, indicating the existence of additional mechanisms related to the electronic energy-loss process. For the range of E_PI studied, these mechanisms produce a Li⁺ energy distribution with a Maxwell-Boltzman-like shape, which vanishes above E_z 10 eV and presents a maximum at E_z 1.2 eV. The Li⁺ yield is nonlinear with the electronic energy loss, S_e. A simple desorption model, based on the spatial distribution of the energy deposited by the projectile and on the effective energy-loss concept, is presented. This spatial distribution of the deposited energy is due to secondary electron cascades and is connected with a ESD-like mechanism on the surface.     

两种宽谱带蓝光发射材料的制备、表征及光学特性

合成了两种以钙为中心金属离子的有机电致发光材料2-(2-羟基苯基)苯并噻唑钙Ca(BTZ)₂和2-(2-羟基苯基苯并噻唑)-(1,10-邻菲罗啉)合钙Ca(BTZ)₂phen。通过红外光谱、紫外-可见光吸收光谱、循环伏安曲线、原子力显微镜以及光致发光光谱表征了材料的结构、光学带隙、能带结构、成膜性以及光学性能。实验结果表明,在DMSO溶液中,Ca(BTZ)₂的紫外吸收峰主要为290,330,422nm;Ca(BTZ)₂phen的紫外吸收峰主要为292,330,428nm。Ca(BTZ)₂的荧光发射峰为458nm和500nm,色坐标为x=0.2176,y=0.3223;Ca(BTZ)₂phen的荧光发射峰主要为465nm和514nm,色坐标为x=0.2418,y=0.3817。利用真空热蒸镀法可以得到均匀致密的Ca(BTZ)₂phen的薄膜,其粗糙度为1.56。Ca(BTZ)₂薄膜也有望通过旋涂制备。实验发现Ca(BTZ)₂与Ca(BTZ)₂phen的荧光光谱几乎覆盖整个可见光区域,为宽谱带发光材料,有望设计成合理的器件结构实现白光发射。     

Computational exploration and screening of novel Janus MA2Z4 (M = Sc−Zn,Y−Ag,Hf−Au; A=Si,Ge; Z=N,P) monolayers and potential application as a photocatalyst

By high-throughput calculations, 13 thermally and environmentally stable Janus MA₂Z₄ monolayers were screened from 104 types of candidates. The 13 stable monolayers have very high charge carrier concentrations (×10¹⁵ cm⁻²), which are better than those of the well-known graphene and TaS₂. Because of their excellent conductivity, the 6 monolayers with band gaps less than 0.5 eV are identified as potential electrode materials for hydrogen evolution reaction applications. For potential applications as photoelectric or photocatalytic materials, bandgaps (E_g-HSE) higher than 0.5 eV remained, which resulted in 7 potential candidates. Based on optical absorption analysis in the visible-light range, H-HfSiGeP₄ and H-MoSiGeP₄ have higher absorption ability and optical conductivity, which is quite impressive for optoelectronic, solar cell device, and photocatalysis applications. Additionally, the transmittance coefficient of Janus MA₂Z₄ monolayers is approximately 70%−80% in the visible-light range, which implies that these monolayers show good light transmittance. For potential applications as photocatalysts, the redox potential and charge effective mass analysis indicate that H-HfSiGeP₄, H-MoSiGeP₄, T-ScSiGeN₄, and T-ZrSiGeN₄ are suitable photocatalysts for CO₂ reduction reactions. Using high-throughput identification, 13 types of new and stable Janus MA₂Z₄ monolayers were explored, and the basic properties and potential applications were investigated, which can reduce the time for experiments and provide basic data for the material genome initiative.     

Ni与钇稳定的氧化锆(111)表面相互作用以及界面活性的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 系统研究了Ni原子在钇稳定的氧化锆(YSZ)(111)和富氧的YSZ(YSZ+O)(111)表面不同位置的吸附, 以及CO和O₂分子在Ni₁(单个镍原子)/YSZ和Ni₁/YSZ+O表面吸附的几何与电子结构特征. 结果表明: 1) 单个Ni原子倾向于吸附在O原子周围, 几乎不吸附在Y原子周围, 且Ni原子在氧空位上吸附最稳定; 2)和YSZ相比, 单个Ni原子在YSZ+O表面易发生氧化现象, Ni原子失去1.06 e电子, 被氧化成了Ni⁺, 吸附能力更强; 3)被氧化的Ni催化活性大幅下降, 大大减弱了表面对O₂和CO等燃料气体的吸附作用.     

Upper bound to the charge-transfer energy on a 2D Wigner lattice in high-Tc cuprates

Assuming that the energy of a 2D Wigner lattice, which has been frequently observed on the CuO₂ plane in layered high-T_c cuprates, is composed of Coulomb energy, kinetic energy, and charge-transfer energy which is necessary to transfer electrons or holes onto the CuO₂ plane (the magnitude of the energy is expected to be of the order of the work function of the compound constituting the plane from which the electrons are transferred, if the CuO₂ plane easily accepts the electrons or holes, as if the CuO₂ plane were crystal surface), we find in the mean-field approximation, that the total energy for a unit lattice, E₀, can be given by a function of the charge-transfer energy E_φ as E₀= (E_φ−E_φ⁰+O((E_φ−E_φ⁰)₂)(>0), where the value of E_φ⁰(1.5 in the ground state, for example) is independent of the lattice configuration. This relation implies that the upper bound to the charge-transfer energy is given by E_φ⁰. The smallness of E_φ⁰, compared with the work function of ordinary metals and alloys (with the work function around 4 eV), is necessary for the realization of the 2D Wigner lattice in many layered high-T_c cuprates.     

Transient behavior of the thermal ion emission from KCl(0 0 1) upon polarity reversal of the electric extraction field

The technique of polarity reversal of the external electric extraction field (strength: 10² V/cm) was applied to study the relaxation of the thermal ion emission from the KCl(0 0 1) single crystal surface. Transient currents of the K⁺ and K₂Cl⁺ ions upon switching from the emission suppression to the ion extraction mode were recorded as a function of the evaporation time, the temperature, and the time of field reversal. The temperature dependence of the time constants of the K⁺ ions obtained from the exponential decreases of the emission currents to their steady-state emission resulted as logτ_h(s)=−(13.39±0.56)+(12.42±0.49)10³/T in a high temperature interval of 826–930 K after a prolonged heating period and as logτ_l(s)=−(20.65±1.04)+(16.77±0.81)10³/T in a low temperature interval of 750–801 K at the initial stage of evaporation, with corresponding activation energies of E_h(K⁺)=2.47±0.14 eV and E_l(K⁺)=3.32±0.16 eV, respectively. The transient currents can be interpreted by a partial adsorption of the suppressed ion currents at the kinks of the surface steps. The differences in the high- and low-temperature runs may be attributed to a strong coarsening of the surface at higher temperatures, which occurs as a bunching of monosteps to macrosteps and/or to an enrichment and segregation of divalent impurities at the surface. The transient behavior of the molecular K₂Cl⁺ ions seems to be strongly correlated with that of the K⁺ ions. This correlation is possibly caused by changes of the strength or the sign of the local electrical field connected with the excess charge at the kinks.     

计算晶体CdCl2:Ni2+的电子顺磁共振谱的完全对角化和高阶微扰方法

采用半自洽场自由Ni²⁺的d轨道波函数和点电荷-偶极子模型,建立局部结构、光谱与电子顺磁共振(EPR)谱(零场分裂D和顺磁g因子)之间的定量关系.利用完全对角化方法(CDP)和高阶微扰方法,统一解释CdCl₂:Ni²⁺晶体的局部结构、光谱和电子顺磁共振谱(EPR),并比较两种计算方法得到的结果.     

Co,Zn共掺铌酸锂电子结构和吸收光谱的第一性原理研究

利用基于密度泛函的第一性原理的计算方法,研究了Co单掺及Co和Zn共掺LiNbO_3晶体的电子结构和吸收光谱.研究显示,各掺杂体系铌酸锂晶体的带隙均较纯铌酸锂晶体变窄. Co:LiNbO_3晶体禁带宽度为3.32 eV; Co:Zn:LiNbO_3晶体, Zn的浓度低于阈值或达到阈值时,禁带宽度分别为2.87或2.75 eV. Co:LiNbO_3晶体在可见-近红外光波段2.40, 1.58, 1.10 eV处形成吸收峰,这些峰归结于Co 3d分裂轨道的跃迁;加入抗光折变离子Zn~(2+),在1.58, 1.10 eV处的吸收峰增强,可以认为Zn~(2+)与Co~(2+)之间存在电荷转移,使e_g轨道电子减少,但并不影响t_(2g)轨道电子.结果表明,晶体中的Co离子在不同共掺离子下可充当深能级中心(2.40 eV),或可充当浅能级中心(1.58 eV),两种情况下,掺入近阈值的Zn离子均有助于实现优化存储.     

Hydrogen diffusion in crystalline semiconductors

The diffusion of hydrogen in semiconductors is complicated by the existence of several charge states (notably H⁺ in p-type material and H^- or H⁰ in n-type material, at least for Si) and also that hydrogen is present in a number of different forms, namely atomic, molecular or bound to a defect or impurity. Since the probability of formation of these different states is dependent on the defect or impurity type and concentration in the material and on the hydrogen concentration itself, then the apparent hydrogen diffusivity is a function of the sample conductivity and type and of the method of hydrogen insertion. Under conditions of low H⁺ concentration in p-type Si, for example, the diffusivity is of the order of 10^-10 cm² · s^-1 at 300 K and is consistent with the value expected from an extrapolation of the Van Wieringen and Warmoltz expression D_H = 9.4 × 10^-3 exp[-0.48 eV/kT] cm² · s^-1. The characteristics of hydrogen diffusion in n- and p-type Si and GaAs are reviewed in this paper, and the retardation of hydrogen permeation by molecular formation and impurity trapping is discussed. The measurement of several key parameters, including the energy levels for the hydrogen donor and acceptor in Si and the diffusivity of the H⁰ and H^- species, would allow a more quantitative treatment of hydrogen diffusion in semiconductors.     

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.     

Ge20Sb15Se65薄膜的热致光学特性变化研究

采用磁控溅射法制备了Ge₂₀Sb₁₅Se₆₅薄膜, 研究热处理温度(150—400 ℃)对薄膜光学特性的影响. 通过分光光度计、X射线衍射仪、显微拉曼光谱仪对热处理前后薄膜样品 的光学特性和微观结构进行了表征, 并根据Swanepoel方法以及Tauc公式分别计算了薄膜折射率色散曲线和光学带隙等参数. 结果表明当退火温度(T_a)小于薄膜的玻璃转化温度(T_g)时,薄膜的光学带隙(E_g^opt)随着退火温度的增加由1.845 eV上升至1.932 eV, 而折射率由2.61降至2.54; 当退火温度大于薄膜的玻璃转化温度时,薄膜的光学带隙随退火温度的增加由1.932 eV降至1.822 eV, 折射率则由2.54增至2.71. 最后利用Mott和Davis提出的非晶材料由非晶到晶态的结构转变模型对结果进行了解释, 并通过薄膜XRD和Raman光谱进一步验证了结构变化是薄膜热致变化的重要原因. 关键词： 20Sb₁₅Se₆₅薄膜')" href="#">Ge₂₀Sb₁₅Se₆₅薄膜 热处理 光学带隙 折射率