First-principles investigation on diffusion behaviours of H isotopes: From W(110) surface into bulk and in bulk W

The diffusion behaviours of hydrogen (H), deuterium (D), and tritium (T) from W(110) surface into bulk and in bulk W are investigated using a first-principles calculations combined with simplified models. The diffusion energy barrier is shown to be 1.87 eV from W(110) surface to the subsurface, along with a much reduced barrier of 0.06 eV for the reverse diffusion process. After H enters into the bulk, its diffusion energy barrier with quantum correction is 0.19 eV. In terms of the diffusion theory presented by Wert and Zener, the diffusion pre-exponential factor of H is calculated to be 1.57×10^-7 m²·s^-1, and it is quantitatively in agreement with experimental value of 4.1×10^-7 m²·s^-1. Subsequently, according to mass dependence (√1/m ) of H isotope effect, the diffusion pre-exponential factors of D and T are estimated to be 1.11×10^-7 m²·s^-1 and 0.91×10^-7 m²·s^-1, respectively.     

镧掺杂BaSnO3薄膜的电学和光学特性

利用射频磁控溅射法在(LaAlO₃)_0.3(SrAl_0.5Ta_0.5O₃)_0.7 (001)单晶基底上生长了镧掺杂BaSnO₃外延薄膜. 通过Hall效应和热电势测量证实了镧掺杂BaSnO₃薄膜具有n型简并半导体特征, 并且基于载流子浓度和Seebeck系数计算出电子的有效质量为0.31m₀ (m₀为自由电子质量). 镧掺杂BaSnO₃薄膜在可见波段具有良好的透明性(透过率大于73%). 基于介电模型对薄膜的透过率曲线进行拟合, 从拟合结果中不仅得到了薄膜的厚度为781.2 nm, 能带宽度为3.43 eV、 带尾宽度为0.27 eV和复光学介电常数随波长的变化规律, 而且也强力地支持了基于电学参数计算电子有效质量的正确性.     

kHz激光与固体靶相互作用产生的X射线源

利用kHz激光与固体靶相互作用产生了平均流强为1.3×10⁷ photons·sr^-1·s^-1的X射线源, 研究了激光的对比度和能量对激光与固体靶相互作用产生的X射线能谱及K_α 产额的影响, 使用刀边成像技术测量了X射线源的源尺寸, 并进行了初步的成像实验. 实验中观察到对于非相对论级别的激光脉冲, 降低激光的对比度有利于提高K_α 产额, 而使用高对比度高强度激光, 更有利于获得高通量高信噪比X射线源. 关键词： kHz激光 固体靶 X射线     

Diffusion of W on A W(211) plane

The diffusion of W on a (211) plane of a W field emitter has been re-examined by means of the fluctuation autocorrelation method. Diffusion along channels yielded E = 16.8 ± 0.5 kcal, D₀ = (3 ± 1) × 10⁻⁵ cm² s⁻¹. For diffusion across channels E =6.6 kcal, D₀ = 4 × 10⁻⁹cm² s⁻¹ at T < 752 K, and E = 24 kcal, D₀ = 5 × 10⁻⁴ cm² s⁻¹ at T > 752 K. The results for diffusion along channels yield E and D₀ values intermediate between recent results by Wang and Ehrlich [Surf. Sci. 206 (1988) 451] using field ion microscopy (E = 19 kcal, D₀ = 7.7 × 10⁻³ cm² s⁻¹) and Tringides and Gomer [J. Chem. Phys. 84 (1986) 4049], using the same method as the present work but a larger slit (E = 13.3 kcal, D₀ = 7 × 10⁻⁷ cm² s⁻¹). The results for cross channel diffus good agreement with those of Tringides and Gomer below 752 K, where these authors stopped. The new high temperature results suggest that the channel wall exchange mechanism postulated by Tringides and Gomer for cross channel diffusion at low T gives way to diffusion by climbing over the channel walls with higher E but also higher D₀ above 752 K. Possible reasons for the discrepancies between these three sets of results and the absence of cross channel diffusion in the work of Wang and Ehrlich are briefly discussed.     

Fabrication and characterization of the normally-off N-channel lateral 4H–SiC metal–oxide–semiconductor field-effect transistors

In this paper, the normally-off N-channel lateral 4H–Si C metal–oxide–semiconductor field-effect transistors(MOSFFETs) have been fabricated and characterized. A sandwich-(nitridation–oxidation–nitridation) type process was used to grow the gate dielectric film to obtain high channel mobility. The interface properties of 4H–Si C/SiO_2 were examined by the measurement of HF I–V, G–V, and C–V over a range of frequencies. The ideal C–V curve with little hysteresis and the frequency dispersion were observed. As a result, the interface state density near the conduction band edge of 4H–Si C was reduced to 2 × 10~(11) e V~(-1)·cm~(-2), the breakdown field of the grown oxides was about 9.8 MV/cm, the median peak fieldeffect mobility is about 32.5 cm~2·V~(-1)·s~(-1), and the maximum peak field-effect mobility of 38 cm~2·V~(-1)·s~(-1) was achieved in fabricated lateral 4H–Si C MOSFFETs.     

溶胶凝胶法制备以HfO2为绝缘层和ZITO为有源层的高迁移率薄膜晶体管

采用溶胶凝胶法制备了h-k氧化铪HfO₂薄膜, 经500℃退火后, 获得了高透过率、表面光滑、低漏电流和相对高介电常数的HfO₂薄膜. 并采用氧化铪作为绝缘层和锌铟锡氧化物作为有源层成功地制备了底栅顶接触结构薄膜晶体管器件. 获得的薄膜晶体管器件的饱和迁移率大于100 cm²·V^-1·s^-1, 阈值电压为-0.5 V, 开关比为5×10⁶, 亚阈值摆幅为105 mV/decade. 表明采用溶胶凝胶制备的薄膜晶体管具备高的迁移率, 其迁移率接近低温多晶硅薄膜晶体管的迁移率.     

Photoresponse and trap characteristics of transparent AZO-gated AlGaN/GaN HEMT

AZO-gated and Ni/Au-gated AlGaN/GaN HEMTs are fabricated successfully,and an excellent transparency of AZOgated electrode is achieved.After a negative gate bias stress acts on two kinds of the devices,their photoresponse characteristics are investigated by using laser sources with different wavelengths.The effect of photoresponse on AZO-gated electrode device is more obvious than on Ni/Au-gated electrodes device.The electrons are trapped in the AlGaN barrier of AZO-gated HEMT after it has experienced negative gate bias stress,and then the electrons can be excited effectively after it has been illuminated by the light with certain wavelengths.Furthermore,the trap state density D_T and the time constantτ_T of the AZO-gated Schottky contact are extracted by fitting the measured parallel conductance in a frequency range from10 kHz to 10 MHz.The constants of the trap range from about 0.35 μs to 20.35 μs,and the trap state density increased from1.93×l0~(13)eV 1·cm~2 at an energy of 0.33 eV to 3.07×10~(11) eV~1·cm~2 at an energy of 0.40 eV.Moreover,the capacitance and conductance measurements are used to characterize the trapping effects under different illumination conditions in AZO-gated HEMTs.Reduced deep trap states' density is confirmed under the illumination of short wavelength light.     

铜-钼源漏电极对非晶氧化铟镓锌薄膜晶体管性能的改善

在铜(Cu)和非晶铟镓锌氧化物(a-IGZO)之间插入30 nm厚的钼(Mo)接触层, 制备了具有Cu-Mo源漏电极的a-IGZO薄膜晶体管(TFT). Mo接触层不仅能够抑制Cu与a-IGZO有源层之间的扩散, 而且提高了Cu电极与玻璃基底以及栅极绝缘层的结合强度. 制备的Cu-Mo结构TFT与纯Cu 结构TFT相比, 具有较高的迁移率(～9.26 cm²·V^-1·s^-1)、更短的电流传输长度(～0.2 μm)、更低的接触电阻(～1072 Ω)和有效接触电阻率(～1×10^-4Ω·cm²), 能够满足TFT 阵列高导互联的要求.     

Crystal growth,spectral properties and Judd–Ofelt analysis of Pr: CaF_2-YF_3

The 0.6 at.% Pr~(3+)-doped CaF_2-YF_3 crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure. The absorption spectrum, emission spectrum, Judd–Ofelt analysis and fluorescence decay curve at room temperature were discussed. The fluorescence lifetime of Pr: CaF_2-YF_3 crystal was 45.46 μs, and the σem ·τ of ~3P_0→~3H_6 and ~3P_0→~3F_2 transitions were calculated to be 80.92 × 10~(-20) cm~2·μs and 388.7 × 10~(-20) cm~2·μs, respectively. The FWHMs are 20.1 nm and 6.8 nm, which are higher than those of Pr: LiYF_4, Pr:LiLuF_4, Pr: LiGdF_4 and Pr: BaY_2F_8 crystals. The results show that the Pr: CaF_2-YF_3 crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.     

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.     

Dynamic behaviors of water contained in calcium-silicate-hydrate gel at different temperatures studied by quasi-elastic neutron scattering spectroscopy

The dynamic behaviors of water contained in calcium-silicate-hydrate(C-S-H) gel with different water content values from 10%to 30%(by weight),are studied by using an empirical diffusion model(EDM) to analyze the experimental data of quasi-elastic neutron scattering(QENS) spectra at measured temperatures ranging from 230 K to 280 K.In the study,the experimental QENS spectra with the whole Q-range are considered.Several important parameters including the bound/immobile water elastic coefficient A,the bound water index BWI,the Lorentzian with a half-width at half-maximum(HWHM) Γ_1(Q) and Γ_2(Q),the self-diffusion coefficients D_(t1) and D_(t2) of water molecules,the average residence times τ_(01)and τ_(02),and the proton mean squared displacement(MSD)(u~2) are obtained.The results show that the QENS spectra can be fitted very well not only for small Q(≤1 A~1) but also for large Q.The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI.The distinction between bound/immobile and mobile water,which includes confined water and ultra-confined water,can be seen by the fitted MSD.All the MSD tend to be the smallest value below 0.25 A~2(the MSD of bound/immobile water) as the Q increases to 1.9 A~1 no matter what the temperature and water content are.Furthermore,by the abrupt changes of the fitted values of D_(t1),τ_(01),and Γ_1(Q),a crossover temperature at 250 K,namely the liquid-to-crystal-like transition temperature,can be identified for confined water in large gel pores(LGPs) and/or small gel pores(SGPs) contained in the C-S-H gel sample with 30% water content.     

电离辐射对部分耗尽绝缘体上硅器件低频噪声特性的影响

本文针对辐射前后部分耗尽结构绝缘体上硅(SOI)器件的电学特性与低频噪声特性开展试验研究. 受辐射诱生埋氧化层固定电荷与界面态的影响, 当辐射总剂量达到1 M rad(Si) (1 rad = 10^-2 Gy)条件下, SOI器件背栅阈值电压从44.72 V 减小至12.88 V、表面电子有效迁移率从473.7 cm²/V·s降低至419.8 cm²/V· s、亚阈斜率从2.47 V/dec增加至3.93 V/dec; 基于辐射前后亚阈斜率及阈值电压的变化, 可提取得到辐射诱生界面态与氧化层固定电荷密度分别为5.33×10¹¹ cm^{- 2}与2.36×10¹² cm^-2. 受辐射在埋氧化层-硅界面处诱生边界陷阱、氧化层固定电荷与界面态的影响, 辐射后埋氧化层-硅界面处电子被陷阱俘获/释放的行为加剧, 造成SOI 器件背栅平带电压噪声功率谱密度由7×10^{- 10} V²·Hz^-1增加至1.8×10^-9 V² ·Hz^-1; 基于载流子数随机涨落模型可提取得到辐射前后SOI器件埋氧化层界面附近缺陷态密度之和约为1.42×10¹⁷ cm^-3·eV^-1和3.66×10¹⁷ cm^-3·eV^-1. 考虑隧穿削弱因子、隧穿距离与时间常数之间关系, 本文计算得到辐射前后埋氧化层内陷阱电荷密度随空间分布的变化.     

Etching mask optimization of InAs/GaSb superlattice mid-wavelength infared 640×512 focal plane array

In this paper we focused on the mask technology of inductively coupled plasma(ICP) etching for the mesa fabrication of infrared focal plane arrays(FPA).By using the SiO_2 mask,the mesa has higher graphics transfer accuracy and creates less micro-ripples in sidewalls.Comparing the IV characterization of detectors by using two different masks,the detector using the SiO_2 hard mask has the R_0A of 9.7×10~6 Ω·cm~2,while the detector using the photoresist mask has the R_0A of3.2 × 10~2 Ω·cm~2 in 77 K.After that we focused on the method of removing the remaining SiO_2 after mesa etching.The dry ICP etching and chemical buffer oxide etcher(BOE) based on HF and NH4 F are used in this part.Detectors using BOE only have closer R_0A to that using the combining method,but it leads to gaps on mesas because of the corrosion on AlSb layer by BOE.We finally choose the combining method and fabricated the 640×512 FPA.The FPA with cutoff wavelength of 4.8 μm has the average R_0A of 6.13 × 10~9 Ω·cm~2 and the average detectivity of 4.51 × 10~9 cm·Hz~(1/2).W~(-1)at 77 K.The FPA has good uniformity with the bad dots rate of 1.21%and the noise equivalent temperature difference(NEDT) of 22.9 mK operating at 77 K.     

First-principles hybrid functional study of the electronic structure and charge carrier mobility in perovskite CH_3NH_3SnI_3

We calculate the electronic properties and carrier mobility of perovskite CH_3NH_3SnI_3 as a solar cell absorber by using the hybrid functional method. The calculated result shows that the electron and hole mobilities have anisotropies with a large magnitude of 1.4 × 10~4cm~2·V~(-1)·s~(-1) along the y direction. In view of the huge difference between hole and electron mobilities, the perovskite CH3NH3 Sn I3can be considered as a p-type semiconductor. We also discover a relationship between the effective mass anisotropy and electronic occupation anisotropy. The above results can provide reliable guidance for its experimental applications in electronics and optoelectronics.     

Mo-SiO2-C3H6催化反应体系的ESR动态表征

文章考察了Mo-SiO₂催化剂体系在丙烯歧化反应过程中的动态ESR波谱,发现在催化歧化反应过程中有两种Mo⁵⁺顺磁中心,一种为扰动八面体配位,g_||=1.89,g_⊥=1.94;另一种为扰动四棱锥配位,g_||=1.86,g_⊥=1.95。测得同位素^95,97Mo⁵⁺的各向异性超精细耦合常数A_||=90.3×10^-4cm^-1,A_⊥=44.8×10^-4cm^-1;观测到反应产生的积炭信号,g≈2.0O₂;氧阴离子自由基信号g₁=2.018,g₂=2.011,g₃=2.005。用LCAO-MO理论对上述Mo⁵⁺的ESR波谱进行计算,求得分子轨道系数,发现并总结出△g_||/△g_⊥与△g成直线关系,并建议用△g_||/△g_⊥=4(△E(B₂→E))/(△E(B₂→B₁)(β₁/ε)²之比值作为衡量C_4v扰动程度的尺度。     

An ingenious approach of determining hydrogen isotope solubilities, diffusivities and permeabilities in GWHER-1 stainless steel

In this paper, by using an ingenious method, the hydrogen isotope solubilities and diffusivities in GWHER-1 stainless steel have been determined by a vacuum heating degassing approach at the temperature range of 597-1022 K on a set of specimens with different sizes previously charged for 24 h under a hydrogen isotope pressure of 105 Pa in the temperature range of 800-1000 K. The permeabilities are then derived from the relation Φ = DKs. It is found D = 1.52 ×10^-6exp（-54100/RT）, Ks = 2.2×10^-exp（-5400/RT） and Φ = 3.3 ×10^-12exp（-59500/RT） for hydrogen, where Ks （Sieverts＇ constant） is given in Pa^-1/2, D in m2.s^-1.Pa^-1/2, T in K and R=8.31 J.mol^-1.K^-1. By taking isotope effects into account, the corresponding Arrhenius relations for deuterium and tritium are also deduced.     

流延法制备高锂离子电导Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3固态电解质及其环氧树脂改性

以溶胶凝胶法合成的高纯Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3(LATP)纳米晶体粉末为原料,通过流延法成膜,在950℃下煅烧5 h合成LATP固态电解质片;对其进行环氧树脂改性后,能量色散X射线光谱元素图像表明环氧树脂完全浸入LATP内部,可以有效防止水渗透.研究发现流延法合成的LATP固态电解质在25℃?C时电导率高达8.70×10~(-4)S·cm~(-1)、活化能为0.36 eV、相对密度为89.5%.经过环氧树脂改性后电导率仍高达3.35×10-4S·cm-1、活化能为0.34 e V、相对密度为93.0%.高电导隔水的环氧树脂改性LATP固态电解质可作为锂金属保护薄膜用于新型高比容量电池.     

单根In掺杂ZnO纳米带场效应管的电学性质

采用化学气相沉积法合成了In掺杂ZnO纳米带,并对其进行了X射线衍射、光致发光及透射电镜表征.基于单根纳米带,采用廉价微栅模板法制备了背栅场效应管,利用半导体参数测试仪测量了场效应管的输出(Ids-Vds)和转移(Ids-Vgs)特性,得出相关电学参数,其中迁移率值为622 cm2·V-1·s-1,该值明显优于包括ZnO在内的大多数材料;讨论了迁移率提高的可能原因.     

三角对称晶场下d8电子组态的EPR参量的普遍公式及其应用

本文考虑到d⁸电子组态中所有自旋三重态和自旋单态对基态的影响,用高阶微扰法导出了d⁸电子组态在三角对称晶场下光谱和基态EPR普遍公式。发现在三角对称晶场下,d⁸电子组态离子的g_⊥ > g_‖或g_⊥ < g_‖和D > 0或D < 0是以立方对称晶场为界,晶体中顺磁离子的配体沿C₃轴伸长或压缩所致。利用所得公式计算了NiCl₂和NiSiF₆·6H₂O晶体的EPR参量,其结果与实验吻合较好。     

Nonlinear parametric interactions in ion-implanted semiconductor plasmas having strain-dependent dielectric constants

We report nonlinear parametric interactions using a hydrodynamic model of ion-implanted semiconductor plasmas having strain-dependent dielectric constants(SDDC). High-dielectric-constant materials are technologically important because of their nonlinear properties. We find that the third-order susceptibility varies in the range 10~(-14)~(–10)~(-12)m~2·V~(-2) for ion-implanted semiconductor plasmas, which is in good agreement with previous results. It is found that the presence of SDDC in ion-implanted semiconductor plasma modifies the characteristic properties of the material.