The Application of Raman Spectroscopy to the Study of the Uranyl Mineral Coconinoite Fe2Al2(UO2)2(PO4)4(SO4)(OH)2 · 20H2O

ABSTRACT

Raman spectra of the uranyl-containing mineral coconinoite, Fe₂Al₂(UO₂)₂(PO₄)₄(SO₄)(OH)₂ · 20H₂O, are presented and compared with the mineral's infrared spectra. Bands connected with (UO₂)²⁺, (PO₄)^3?, (SO₄)^2?, (OH)^?, and H₂O stretching and bending vibrations are assigned. Approximate U?O bond lengths in uranyl, (UO₂)²⁺, and O?H…O hydrogen bond lengths are calculated from the wavenumbers of the U?O stretching vibrations and (OH)^? and H₂O stretching vibrations, respectively, and compared with published data for similar natural and synthetic compounds.     

Thermal Dehydration and Vibrational Studies of ZnK4(P3O9)2 · 6H2O

The thermal dehydration of ZnK₄(P₃O₉)₂ · 6H₂O was studied in the range 25–500°C by thermogravimetric analysis (TGA and DSC) and X‐ray diffraction. We found, based on the TGA and DSC scans, the dehydration of this salt takes place in three stages with a loss of the six water molecules. The infrared and Raman spectra of ZnK₄(P₃O₉)₂ · 6H₂O have been recorded and interpreted using a factor group analysis. The internal modes are assigned in terms of POP and PO₂ structural units using experimental and theoretical IR and Raman frequencies.     

Diode-pumped Tm:KY(WO4)2 laser passively Q-switched with PbS-doped glass

Glass doped with PbS quantum dots is presented as a saturable absorber (SA) for a passive Q-switching of a diode-pumped 1.9 μm Tm:KYW laser. Output pulses with energy of 44 μJ at a repetition rate of 2.5 kHz with an average output power of 110 mW were obtained. The Q-switching conversion efficiency was 33%. The absorption saturation intensity of the glass doped with PbS quantum dots with a mean radius of 5.2 nm at a wavelength of 2 μm was measured to be 1.5 MW/cm².     

The modification effect in magnetization behaviors for CoFe2O4–p-NiFe2O4 binary ferrofluids

The magnetization curves of CoFe₂O₄ ferrofluids, p-NiFe₂O₄ paramagnetic fluids and CoFe₂O₄–p-NiFe₂O₄ binary ferrofluids, in which the volume fraction of CoFe₂O₄ particles φ _Co is 0.6% and one of p-NiFe₂O₄ particles φ _Ni is 0.2%, 0.4%, 0.6% and 0.8% respectively, prepared by the Massart method, have been measured at room temperature. Comparison of the experimental data from the CoFe₂O₄ ferrofluids with the Langevin theory curves demonstrates a considerable difference between them, but a curve fitted using a model of a gas-like compression (MGC) agrees with the experimental data very well. The experimental results show that the magnetization of the CoFe₂O₄–p-NiFe₂O₄ binary ferrofluid is not a simple summation of the ferrimagnetic CoFe₂O₄ part and the paramagnetic p-NiFe₂O₄ part. From the fitted results, it was found that the saturation magnetization of the CoFe₂O₄ part of the binary ferrofluid depends non-monotonically on the p-NiFe₂O₄ particle volume fraction, and the CoFe₂O₄ part is a stronger “hard” magnet than CoFe₂O₄ in simple ferrofluids. The magnetization behavior of the binary ferrofluids is explained by the modification of the microstructure of CoFe₂O₄ nanoparticle system by the p-NiFe₂O₄ nanoparticle system.     

Highly efficient continuous-wave intracavity frequency-doubled Nd:YVO4-LBO laser at 457 nm under diode pumping into the emitting level 4F3/2

The continuous-wave high efficiency laser emission of Nd:YVO₄ at the fundamental wavelength of 914 nm and its 457 nm second harmonic obtained by intracavity frequency doubling with an LBO nonlinear crystal is investigated under pumping by diode laser at 880 nm into emitting level ⁴F_3/2. 6.5 W at 457 nm with M ²=1.8 was obtained from a 5-mm-thick 0.4 at.% Nd:YVO₄ laser medium and a 15-mm-long LBO nonlinear crystal in a Z-type cavity for 18.6 W absorbed pump power. An optical-to-optical efficiency with respect to the absorbed pump power was 0.35. Comparative results obtained for the pump with diode laser at 808 nm, into the highly-absorbing level ⁴F_5/2, are given in order to prove the advantages of the 880 nm wavelength pumping.     

Efficient 1.06 μm laser operation in an unprocessed Nd3+:BaGd2(MoO4)4 cleavage microchip

A 1.2 mm thick microchip cleaved from a 1.2 at.% Nd³⁺: BaGd₂(MoO₄)₄ crystal was used as the laser gain medium directly. The laser cavity mirrors were coated on the microchip without cutting and polishing. In the 1.06 μm quasi-CW laser operation, the microchip was pumped by a Ti:sapphire laser with a duty cycle of 10%, the threshold is 10 mW, and the slope efficiency is 50%. In the CW laser operation pumped by a diode laser, the threshold and slope efficiency are 140 mW and 33%, respectively. The results demonstrate that the unprocessed surfaces of the cleaved microchip have good enough flatness and parallelism for laser operation.     

Ab initio investigation of tensile strengths of metal(1 1 1)/α-Al2O3(0 0 0 1) interfaces

Ab initio calculations using plane wave pseudopotential method within density funtional theory are applied to investigate mechanical and electronic properties of Al-terminated Me(1 1 1)/Al₂O₃(0 0 0 1) (Me = Al, Ag, Cu, Nb) interfaces. Stress–displacement relationships of separation perpendicular to the interface are calculated. It is shown that obtained results such as work of separation and tensile strength can be understood from electronic structure.     

Mid-infrared laser-induced grating experiments of C2H4 and NH3 from 0.1–2 MPa and 300–800 K

Laser-induced thermal gratings (LITG) were generated in mixtures of ethylene and ammonia in nitrogen using mid-infrared laser radiation from a grating-tuned, low-pressure, pulsed (5 ms pulse width) CO₂ laser, and read out with a continuous wave Nd:YLF laser. The LITG signal intensity was measured as a function of pressure (0.1–2 MPa) and temperature (300–800 K, at 0.1 and 1 MPa) by tuning the laser to the accidental coincidences of the 10P(14) and 10R(6) emission lines with molecular absorption transitions of C₂H₄ and NH₃, respectively. Comparisons are made with theoretical predictions for the grating efficiency from a simple thermalization model. A theoretical comparison of the temporal LITG signal response for three excitation pulse shapes – a delta function, a realistic pulse, and a square wave is presented. Furthermore, it is shown that for NH₃, most of the decrease of the LITG signal intensity with increasing temperature is due to the corresponding decrease in fractional molecular absorption of the pump beam radiation. The diagnostic capabilities of the mid-infrared LITG experiment is demonstrated for spatially resolved ethylene measurements with long laser pulses in a premixed stoichiometric CH₄–air flame at atmospheric pressure. Received: 17 March 2000 / Revised version: 23 March 2000 / Published online: 13 September 2000     

Heavy-quark mass dependence in global PDF analyses and 3- and 4-flavour parton distributions

We study the sensitivity of our recent MSTW 2008 NLO and NNLO PDF analyses to the values of the charm- and bottom-quark masses, and we provide additional public PDF sets for a wide range of these heavy-quark masses. We quantify the impact of varying m _c and m _b on the cross sections for W, Z and Higgs production at the Tevatron and the LHC. We generate 3- and 4-flavour versions of the (5-flavour) MSTW 2008 PDFs by evolving the input PDFs and α _S determined from fits in the 5-flavour scheme, including the eigenvector PDF sets necessary for calculation of PDF uncertainties. As an example of their use, we study the difference in the Z total cross sections at the Tevatron and LHC in the 4- and 5-flavour schemes. Significant differences are found, illustrating the need to resum large logarithms in $Q^{2}/m_{b}^{2}$ by using the 5-flavour scheme. The 4-flavour scheme is still necessary, however, if cuts are imposed on associated (massive) b-quarks, as is the case for the experimental measurement of $Zb\bar{b}$ production and similar processes.     

Li_2SO_4—Li_2B_2O_4,Li_2SO_4—(NH_4)_2SO_4赝二元系相图及离子导电性研究

本文用差热分析和X射线衍射方法对Li_2SO_4-Li_2B_2O_4和Li_2SO_4-[NH_4]_2SO_4两个赝二元系相图进行了研究。Li_2SO_4-Li_2B_2O_4是共晶体系,共晶温度为720℃,共晶点在含75mol％Li_2SO_4处。在Li_2SO_4-[NH_4]_2SO_4体系中只有一个包晶化合物LiNH_4SO_4,它在186℃附近有一个固态相变。 研究了Li_2BO_4晶态和非晶态及Li_2SO_4-(NH_4)_2SO_4体系中三种不同成分样品的离子导电性,发现在400℃以下非晶态Li_2B_2O_4的电导率比晶态至少高两个数量级,而且电导激活能大大降低。Li_2NH_4SO_4高温相电导激活能为0.12eV,而室温相为0.70eV.含Li_2SO_440mol％的样品(即LiNH_4SO_4和[NH_4]_2SO_4二相混合物)在高温相的电导率比纯LiNH_4SO_4高约两个数量级,这表明在一种离子晶体中加入适量的另一种离子晶体,可以使前者的电导率大幅度提高。     

Electronic excitation energies in TiO<Subscript>2</Subscript> in the fluorite phase

The ab initio pseudopotential method within the generalized gradient approximation (GGA) and quasiparticle approximation has been used to investigate the electronic properties of titanium dioxide in the rutile, anatase, and fluorite structures, respectively. Here we present the GW approximation for the electronic self-energy, which allows to calculate excited-state properties, especially electronic band structures. For this calculation, good agreement with the experimental results for the minimum band gaps in rutile and anatase phase is obtained. In the fluorite phase we predict that titanium dioxide will be an indirect (Γ to X) wide band-gap semiconductor (2.367 or 2.369 eV) and the properties remain to be confirmed by experiment.     

High-efficiency eye-safe intracavity Raman laser at 1531 nm with SrWO4 crystal

A high-efficiency diode-end-pumped Q-switched eye-safe linearly-polarized intracavity Raman laser at 1531 nm is demonstrated, with Nd:YVO₄ as the laser medium and SrWO₄ as the Raman crystal. The highest average power of 1.93 W is achieved, with an incident pump of 15.6 W and a repetition rate of 35 kHz. The narrowest pulse duration of 4.9 ns and the highest peak power of 32.2 kW are obtained at a repetition rate of 5 kHz.     

CaAs(100)的(NH_4)_2S_x和P_2S_5/(NH_4)_2S_x表面钝化

利用光致发光谱、X射线光电子谱和俄歇电子谱等技术研究了(NH_4)_2S_x和P_2S_5/(NH_4)_2S_5化学钝化GaAs(100)表面.结果表明,(NH_4)_2S_x中S钝化可以完全去除GaAs表面的氧化物.P_2S_5/(NH_4)_2S_x中P_2S_5对降低G_2A_5表面态密度,提高光致发光强度是有效的.钝化表面P氧化物存在对防止GaAs表面初期氧化起重要作用.     

[MnHg(SCN)4(H2O)2]·2C4H9NO(MMTWD)晶体的光谱分析

根据商群对称性分析法对MMTWD晶体的振动模作了理论计算.计算结果显示,通过实验可观察到的拉曼散射峰和红外反射带应分别不超过297和148个.运用实验的手段,分别测定晶体的拉曼光谱和红外光谱,给出了MMTWD晶体在50～3 000 cm-1范围内的拉曼光谱图和400～4 000 cm-1范围里的红外光谱图,并对光谱中的谱线作了指认.给出了MMTWD晶体的分子结构示意图,最终确定MMTWD晶体结构为三维网状结构,说明在众多新型光功能材料当中MMTWD晶体是一种更适合生长成较大尺寸且稳定性较好的非线性光学晶体,在光电子领域中具有良好的应用前景.     

Superionic phase transition in (NH4)2SeO4·2NH4HSeO4 single crystal at 378 K

Abstract

DTA, structural and electric conductivity investigations were made for (NH₄)₄H₂(SeO₄)₃ single crystals. A high-temperature phase transition at 378 K to a superionic phase was found. The phase is characterized by a high electrical conductivity (～4.10^?3 Ω^?1 cm^?1) and a low activation energy (0.11 eV).     

Thermally activated dewetting of organic thin films: the case of pentacene on SiO<Subscript>2</Subscript> and gold

The morphology of pentacene organic thin films deposited on SiO₂ and Au(111) surfaces using organic molecular beam deposition (OMBD) has been characterized by a multi-technique approach. Among the techniques applied were X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and thermal desorption spectroscopy (TDS). Our rather detailed studies reveal that on both substrates the growth is strongly influenced by dewetting and islanding phenomena, yielding very rough surfaces. Surprisingly, substantial changes in the morphology were observed also after deposition on room-temperature samples on a time scale of several hours. The rather extensive set of in situ XPS data was analyzed in the framework of a simple model, which allows us to derive rather detailed information on the roughness parameters.     

Lepton flavor violation decays τ −→μ − P 1 P 2 in the topcolor-assisted technicolor model and the littlest Higgs model with T-parity

The new particles predicted by the topcolor-assisted technicolor (TC2) model and the littlest Higgs model with T-parity (called LHT model) can induce the lepton flavor violation (LFV) couplings at tree level or one loop level, which might generate large contributions to some LFV processes. Taking into account the constraints of the experimental data on the relevant free parameters, we calculate the branching ratios of the LFV decay processes τ ^?→μ ^? P ₁ P ₂ with P ₁ P ₂=π ⁺ π ^?, K ⁺ K ^? and $K^{0}\bar{K}^{0}$ in the context of these two kinds of new physics models. We find that the TC2 model and the LHT model can indeed produce significant contributions to some of these LFV decay processes.