Minimum metallic conductivity in a thin crystal

Electrical conductivities of thin crystals of Bi₂(Te,S)₃ measured from 4.2°K to 300°K fall into four regions: 1) σ < 1.3×10^?5 S with positive temperature coefficient of conductivity; 2) 1.3×10^?5 S < σ < 1.4×10^?5 S with temperature independent conductivity; 3) 1.4×10^?5 S σ < 4×10^?5 S with negative temperature coefficient of conductivity, and 4) σ > 4×10^?5 S with hardly any temperature dependence. A disproportionately high fraction of samples falls into the second range; 1.3×10^?5 S < σ < 1.4×10^?5 S.     

硅的低温电学性质

本文在20°—300°K研究了室温载流子浓度2×10¹²—1×10²⁰cm^-3含硼或磷(砷)Si的电学性质。对一些p-Si样品用弱场横向磁阻法及杂质激活能法进行了补偿度的测定,并进行了比较。从霍尔系数与温度关系的分析指出,对于较纯样品,硼受主能级的电离能为0.045eV,磷施主能级为0.045eV,在载流子浓度为10¹⁸—10¹⁹cm^-3时发现了费米简并,对载流子浓度为2×10¹⁷—1×10¹⁸cm^-3的p-Si及5×10¹⁷—4×10¹⁸cm^-3的n-Si观察到了杂质电导行为。从霍尔系数与电导率计算了非本征的霍尔迁移率。在100°—300°K间,晶格散射迁移率μ满足关系式AT^-a,其中A=2.1×10⁹,α=2.7(对空穴);或A=1.2×10⁸,α=2.0(对电子)。另外,根据我们的材料(载流子浓度在5×10¹¹—5×10²⁰cm^-3间),分别建立了一条电阻率与载流子浓度及电阻率与迁移率的关系曲线,以提供制备材料时参考之用。     

The chemical diffusion coefficient in (low temperature)α-Ag2S determined by an electrochemical relaxation method

An electrochemically probed relaxation method has been used to determine the chemical diffusion coefficient, D?, of α-Ag₂+δS. The experiments were performed at 168°C and span the homogeneity range of this phase, which at this temperature is of the order of 10^-5 in δ. D? is found to have values between 0.02 and 0.15 cm² s^-1 and, as a function of nonstoichiometry, to reflect correctly the composition dependence of the thermodynamic factor, d ln a_Ag/d ln c_Ag. Using previously determined data for the thermodynamic factor, the component diffusion coefficient of Ag⁺ at 168°C is found to be D_Ag⁺=(5.4 ± 0.4) × 10^-8cm²s^-1.     

Thermal expansion measurements for estimating vacancy concentration in X-ray irradiated KCl single crystals

A sensitive capacitance technique is used for measuring changes in length (Δl) of KCl single crystals with temperature in the region 30–300°C. These measurements have been taken on KCl in (i) as-cleaved (ii) X-ray irradiated (iii) quenched and X-ray irradiated conditions (X-ray irradiation was always done at room temperature (≈ 30°C). The linear coefficient of thermal expansion (α) of the as-cleaved sample is 40.8 × 10^-6°C^-1. Variation of Δl with temperature in X-ray irradiated crystal shows two regions: (a) 30–180°C where α is 48.1 × 10^-6°C^-1, (b) 180–300°C where α is 40.4 × 10^-6°C^-1. Similar behaviour is exhibited by quenched and later X-ray irradiated KCl the first region is up to 140°C, beyond which the second region takes over. From these data, concentration of vacancies in X-ray irradiated KCl at room temperature is calculated to be 3.4 × 10¹⁷ cm^-3 which is in fairly good agreement with the value obtained from F-band absorption measurements on the sample. An attempt has been made to understand these results.     

The Mechanism of the Reactions Mg24 (d,p.) Mg23 and Mg26 (d,p.) Mg27 in the Deuteron Energy Range 1.3-2.5 MeV

The differential excitation functions of the low lying levels for the reactions Mg²⁴ (d, p) Mg²⁵ and Mg²⁶ (d, p.) Mg²⁷ have been measured in steps of 10 KeV in a deuteron energy range 1.3-2.5 MeV and at angles 20°–160y in steps of 20°. Thin isotopic targets (0.45 μ gm/cm²) on Ni backing (0.5 micron) were used. Auto-correlations, angular and group crosscorrelations, and probability distributions were calculated in terms of ERIOSON's theory of statistical fluctuations. The mean coherence width Γ for both reactions was found to be equal to 32 KeV which corresponds to a life time τ = 2.1 × 10^?20 sec. of the compound nucleus formation.     

BF+2注入多晶硅栅F迁移特性的分析与模拟

在深入分析BF⁺₂注入多晶硅栅F在多晶硅栅中迁移特性的基础上，建立了F在多晶硅栅中的迁移方程.采用有限差分法，模拟了BF⁺₂注入多晶硅栅F在多晶硅栅中的分布.模拟结果与二次离子质谱(SIMS)分析结果相符.给出了80keV，2×10¹⁵cm^-2 BF⁺₂注入多晶硅栅900℃，30min退火条件下F在多晶硅中的发射系数e=6×10关键词：     

α-Al2O3单晶中Fe3+离子的电子顺磁共振

本文对α-Al₂O₃单晶体中Fe³⁺离子在室温下,X波段进行了电子顺磁共振研究,发现Fe³⁺离子实际上占据四种磁性不等价晶位。在同一氧离子层间的两种晶位上的Fe³⁺离子具有相同的自旋哈密顿参量,而不同氧离子层间的晶位上的Fe³⁺离子具有不同的自旋哈密顿参量,两种自旋哈密顿参量为:(1)g_‖=2.001,g_⊥=2.003,D=1679 关键词：     

ESR of V3+ in zinc oxide single crystals

Electron spin resonance has been investigated in zinc oxide single crystals containing vanadium. Several groups of ordinary and forbidden transitions can be observed. The experimental results are interpreted with the aid of the spin Hamiltonian, for which the following parameters were determined:g∥=1.945; ⊥=1.937; ¦D¦=750×10^?4 cm^?1, ¦A¦=68 × 10^?4 cm^?1; ¦B ¦=93×10^?4 cm^?1; ¦A?P¦=65×10^?4cm^?1.     

80—500°K间InSb的电导率、霍尔效应及磁阻效应

文中报导了80—500°K间n型及p型InSb的电导率、霍尔系数及磁阻效应的测量,所用样品的杂质含量(补偿后)为4×10¹³—7×10¹⁷cm^-3。由结果的分析得出InSb的本征载流子浓度、禁带宽度及电子迁移率等数值,讨论了电子的散射机构以及强磁场下磁阻与磁场强度成一次方正比关系的可能原因。     

The GaP(001) surface and the adsorption of Cs

GaP(001) cleaned by argon-ion bombardment and annealed at 500°C showed the Ga-stabilized GaP(001)(4 × 2) structure. Only treatment in 10^?5 Torr PH₃ at 500°C gave the P-stabilized GaP(001)(1 × 2) structure. The AES peak ratio $\text{P}\text{Ga}$ is 2 for the (4 × 2) and 3.5 for the (1 × 2) structure. Cs adsorbs with a sticking probability of unity up to 5 × 10¹⁴ Cs atoms cm^?2 and a lower one at higher coverages. The photoemission measured with uv light of 3660 Å showed a maximum at the coverage of 5 × 10¹⁴ atoms cm^?2. Cs adsorbs amorphously at room temperature, but heat treatment gives ordered structures, which are thought to be reconstructed GaP(001) structures induced by Cs. The LEED patterns showed the GaP(001)(1 × 2) Cs structure formed at 180°C for 10 h with a Cs coverage of 5 × 10¹⁴ atoms cm^?2, the GaP(001)(1 × 4) Cs formed at 210°C for 10 hours with a Cs coverage of 2.7 × 10¹⁴ atoms cm^?2, the GaP(001)(7 × 1) and the high temperature GaP(001)(1 × 4), the latter two with very low Cs content. Desorption measurements show three stability regions: (a) between 25–150°C for coverages greater than 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.2 eV; (b) between 180–200°C with a coverage of 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.8 eV; (c) between 210–400°C with a coverage of 2.7 × 10¹⁴ atoms cm^?2, and an activation energy of 2.5 eV.     

A quantum cascade laser-based optical feedback cavity-enhanced absorption spectrometer for the simultaneous measurement of CH4 and N2O in air

Optical feedback cavity-enhanced absorption spectroscopy (OF CEAS) has been demonstrated with a thermoelectrically cooled continuous wave distributed feedback quantum cascade laser (QCL) operating at wavelengths around 7.84 μm. The QCL is coupled to an optical cavity which creates an absorption pathlength greater than 1000 m. The experimental design allows optical feedback of infra-red light, resonant within the cavity, to the QCL, which initiates self-locking at each TEM₀₀ cavity mode frequency excited. The QCL linewidth is narrowed to below the mode linewidth, greatly increasing the efficiency of injection of light into the cavity. At the frequency of each longitudinal cavity mode, the absorption coefficient of an intracavity sample is obtained from the transmission at the mode maximum, measured with a thermoelectrically cooled detector: spectral line profiles of CH₄ and N₂O in ambient air were recorded simultaneously and with a resolution of 0.01386 cm^?1. A minimum detectable absorption coefficient of 5.5×10^?8 cm^?1 was demonstrated after an averaging time of 1 s for this completely thermoelectrically cooled system. The bandwidth-normalised limit for a single cavity mode is 5.6×10^?9 cm^?1?Hz^?1/2 (1σ).     

Radiation enhanced diffusion in UO2 and (U,Pu)O2

Abstract

The radiation enhanced diffusion (coefficient D*) of U-233 and Pu-238 in UO₂ and (U, Pu)O₂ with 2.5 and 15% Pu was measured during fission in a nuclear reactor. Normal diffusion sandwiches with a thin tracer layer were used. A radio-frequency furnace allowed the temperatures to be varied between 130 and 1400°. Neutron fluxes (7 × 10¹² to 1.2 × 10¹⁴ n cm^?2 s^?1) and irradiation times (56 to 334 h) were also varied to cover ranges of fission rates [Fdot] between 7× 10¹¹ and 6.4 × 10¹³ f cm^?3 s^?1 and of doses F between 4.2 × 10¹⁷ and 3.1 × 10¹⁹ f cm³. Below ～1000°, D* was completely athermal and increased linearly with [Fdot]. It was described by D* = A[Fdot] with A = 1.2× 10^?29cm⁵. A possible temperature dependence was indicated between ～1000and 1200°. The results are explained in terms of thermal and pressure effects of fission spikes and are related with other studies of radiation damage as well as with technologically interesting processes occurring in UO₂ during irradiation.     

Photo-acoustic and photo-refractive detection of small absorptions in liquids

The sensitivities of pulsed photo-acoustic and photo-refractive (e.g., thermal lensing) techniques for the measurement of small absorptions in liquids have been evaluated both theoretically and experimentally. Electrostriction limits the sensitivity of both techniques, this limitation is less severe for the photo-refractive technique. The minimum absorption constants observed experimentally, for a 200-μm laser spot size in liquid N₂, are 4 × 10^-5 cm^-1 for the photo-acoustic measurement and 6 × 10^-7 cm^-1 for the photo-refractive measurement. The calculated electrostrictive limits are 2 × 10^-5 cm^-1 and 7 × 10^-11 cm^-1, respectively.     

Determination of the 5d6p 3F4-5d2 3F transition probabilities of Ba I

Whether the transitions between 6s5d ³D and 5d6p ³F can be used for laser cooling of barium heavily depends upon the transition probabilities of 5d6p ³F-5d^{2 3}F. Taking the transition 6s5d ³D₃-5d6p ³F⁴ as a scale, the leakage rate of 5d6p ³F₄-5d^{2 3}F was used to evaluate the transition probabilities. 706 nm laser pulses with different durations were applied to a barium atomic beam for 6s5d ³D₃-5d^{2 3}F₄ optical pumping, and the remaining percentages in 6s5d ³D₃ were measured. After exponential fitting, the transition probability of 5d6p ³F₄-5d^{2 3}F_3,4 was determined to be 2.1(4)×10⁴ s^?1, which is in agreement with theoretical calculations using the scaled Thomas-Fermi-Dirac method.     

Pressure broadening and shift of the first diffuse series doublet of indium due to the presence of helium and argon

The shift and half-width of In λ 3039 and In λ3256 was measured in Ar and He under pressures up to one thousand p.s.i. The temperature of the absorption tube was 850°C for In λ 3039 and 930°C for In λ 3256. The van der Waals interaction constant for In/Ar was found to be 1·5 x 10^-30 and 8·6 x 10^-31 cm⁶/sec for In λ 3039/Ar and In λ 3256/Ar respectively. In λ 3256 exhibited a small red shift in He for the range of r.d. (from 1 to 16) of He employed.     

Continuous wave optical parametric oscillator for quartz-enhanced photoacoustic trace gas sensing

A continuous wave optical parametric oscillator, generating up to 300 mW idler output in the 3–4 μm wavelength region, and pumped by a fiber-amplified DBR diode laser is used for trace gas detection by means of quartz-enhanced photoacoustic spectroscopy (QEPAS). Mode-hop-free tuning of the OPO output over 5.2 cm^-1 and continuous spectral coverage exceeding 16.5 cm^-1 were achieved via electronic pump source tuning alone. Online monitoring of the idler wavelength, with feedback to the DBR diode laser, provided an automated closed-loop control allowing arbitrary idler wavelength selection within the pump tuning range and locking of the idler wavelength with a stability of 1.7×10^-3 cm^-1 over at least 30 min. Using this approach, we locked the idler wavelength at an ethane absorption peak and obtained QEPAS data to verify the linear response of the QEPAS signal at different ethane concentrations (100 ppbv-20 ppmv) and different power levels. The detection limit for ethane was determined to be 13 ppbv (20 s averaging), corresponding to a normalized noise equivalent absorption coefficient of 4.4×10^-7 cm^-1  W/Hz^1/2. PACS 42.55.Wd; 42.65.Yj; 42.62.Fi     

Leed,aes and photoemission measurements of epitaxially grown GaAs(001), (111)A and (1̄1̄1̄)B surfaces and their behaviour upon cs adsorption

Epitaxially grown GaAs(001), (111) and (1?1?1?) surfaces and their behaviour on Cs adsorption are studied by LEED, AES and photoemission. Upon heat treatment the clean GaAs(001) surface shows all the structures of the As-stabilized to the Ga-stabilized surface. By careful annealing it is also possible to obtain the As-stabilized surface from the Ga-stabilized surface, which must be due to the diffusion of As from the bulk to the surface. The As-stabilized surface can be recovered from the Ga-stabilized surface by treating the surface at 400°C in an AsH₃ atmosphere. The Cs coverage of all these surfaces is linear with the dosage and shows a sharp breakpoint at 5.3 × 10¹⁴ atoms cm^?2. The photoemission reaches a maximum precisely at the dosage of this break point for the GaAs(001) and GaAs(1?1?1?) surface, whereas for the GaAs(111) surface the maximum in the photoemission is reached at a higher dosage of 6.5 × 10¹⁴ atoms cm^?2. The maximum photoemission from all surfaces is in the order of 50μA Im^?1 for white light (T = 2850 K). LEED measurements show that Cs adsorbs as an amorphous layer on these surfaces at room temperature. Heat treatment of the Cs-activated GaAs (001) surface shows a stability region of 4.7 × 10¹⁴ atoms cm^?2 at 260dgC and one of 2.7 × 10¹⁴ atoms cm^?2 at 340°C without any ordering of the Cs atoms. Heat treatment of the Cs-activated GaAs(111) crystal shows a gradual desorption of Cs up to a coverage of 1 × 10¹⁴ atoms cm^?2, which is stable at 360°C and where LEED shows the formation of the GaAs(111) (√7 × √7)Cs structure. Heat treatment of the Cs-activated GaAs(1?1?1?) crystal shows a stability region at 260°C with a coverage of 3.8 × 10¹⁴ atoms cm^?2 with ordering of the Cs atoms in a GaAs(1?1?1?) (4 × 4)Cs structure and at 340°C a further stability region with a coverage of 1 × 10¹⁴ at cm^?2 with the formation of a GaAs(1?1?1?) (√21 × √21)Cs structure. Possible models of the GaAs(1?1?1?) (4 × 4)Cs, GaAs(1?1?1?)(√21 × √21)Cs and GaAs(111) (√7 × √7)Cs structures are given.     

Mg+注入对GaN晶体辐射损伤的研究

在蓝宝石衬底上通过金属有机物化学气相沉积(metal-organic chemical vapor deposition，MOCVD)方法外延生长的GaN薄膜具有良好的结晶品质，χ_min达到2.00%. 结合卢瑟福背散射/沟道(Rutherford backscattering/channeling，RBS/C)和高分辨X射线衍射(high-resolution X-ray diffraction，HXRD)的实验测量，研究了不同剂量和不同角度Mg⁺注入GaN所造成的辐射损伤. 实验结果表明，随注入剂量的增大，晶体的辐射损伤也增大，注入剂量在1×10¹⁵atom/cm²以下，χ_min小于4.78%，1×10¹⁶atom/cm²是Mg⁺注入GaN的剂量阈值，超过这个阈值，结晶品质急剧变差，χ_min达到29.5%；随机注入比沟道注入的辐射损伤大，且在一定范围内随注入角度的增大，损伤也增大，在4×10¹⁵atom/cm²剂量下偏离〈0001〉沟道0°，4°，6°，9°时的χ_min(%)分别为6.28，8.46，10.06，10.85；经过700℃/10min+1050℃/20s两步退火和1000℃/30s高温快速退火后，晶体的辐射损伤都有一定程度的恢复，而且1000℃/30s高温快速退火的效果更好，晶体的辐射损伤可以得到更好的恢复. 关键词： GaN 卢瑟福被散射/沟道 高分辨X射线衍射 辐射损伤     

Ag离子注入非晶SiO2的光学吸收、拉曼谱和透射电镜研究

能量为200keV的Ag离子，以1×10¹⁶，5×10¹⁶，1×10¹⁷ cm^-2的剂量分别注入到非晶SiO₂玻璃，光学吸收谱显示：注入剂量为1×10¹⁶ cm^-2的样品的光吸收谱为洛伦兹曲线，与Mie理论模拟的曲线形状一致；注入剂量较大的5×10¹⁶，1×10¹⁷ cm^-2的谱线共振吸收增强，峰位红移并出现伴峰. 透射电镜观察分析表明，注入剂量不同的样品中形成的纳米颗粒的大小、形状、分布都不同，注入剂量较大的还会产生明显的表面溅射效应，这些因素都会影响共振吸收的峰形、峰位和峰强. 当注入剂量达到1×10¹⁷ cm^-2时，Ag纳米颗粒内部可能还形成了杂质团簇. 关键词： 离子注入 纳米颗粒 共振吸收 红移     

Modified Spectrophotometric Method for the Determination of Some Important Antibiotics Through Charge - Transfere Complexation Reaction with Chloranil

Abstract

A new modified Spectrophotometric procedures are presented for the determination of three pharmaceutical antibiotic compounds through charge-transfere complexation reaction with chloranil. The complex shows an absorption mAxima at 550 nm, having a molar absorptivity coefficient of 5.55×10³,7.81×10³ and 1.38×10⁴ 1. mol^?1cm^?1 for ampicillin, amoxycillin and neomycin, respectively. Optimization of the reaction conditions has been investigated Obediance to Beer's law (40μg/ml) permitted the assay of thes drugs in its dosage forms A variety of pharmaceutical dosage forms containing ampicillin, amoxycillin and neomycin are successfully analysed by the proposed procedure.