The application of coherent anti-Stokes Raman scattering to temperature measurements in a pulsed high enthalpy supersonic flow

Broadband single pulse coherent anti-Stokes Raman scattering (CARS) experiments employing a folded box phase matching geometry in a shock tunnel flow are presented. Rovibrational spectra of molecular nitrogen, produced at the exit of a pulsed supersonic nozzle for a range of flow enthalpies, are examined. Difficulties peculiar to the application of the optical technique to a high enthalpy pulsed flow facility are discussed and measurements of flow temperatures are presented. Theoretically calculated values for temperatures based upon algorithms used to determine shock tunnel flow conditions agree well with experimental measurements using the CARS technique.     

Common stabilizations of Heegaard splittings of link exteriors

We give a condition for a pair of unknotting tunnels of a non-trivial tunnel number one link to give a genus three Heegaard splitting of the link complement and show that every 2-bridge link has such a pair of unknotting tunnels.     

Non-classical radiation emission by a coherent conductor

We report experimental evidence that the microwave electromagnetic field generated by a normal conductor, here a tunnel junction placed at ultra-low temperature, can be non-classical. By measuring the quadratures of the electromagnetic field at one or two frequencies in the GHz range, we demonstrate the existence of squeezing as well as entanglement in such radiation. In one experiment, we observe that the variance of one quadrature of the photo-assisted noise generated by the junction goes below its vacuum level. In the second experiment, we demonstrate the existence of correlations between the quadratures taken at two frequencies, which can be stronger than allowed by classical mechanics, proving that the radiation at those two frequencies are entangled.¹     

Syntheses, crystal and electronic structures of two new lead indium phosphates: Pb2In4P6O23 and Pb2InP3O11

Two compounds Pb₂In₄P₆O₂₃ and Pb₂InP₃O₁₁ in the new family of lead indium phosphates were synthesized by high temperature solution growth (HTSG) method and structurally characterized by X-ray single crystal diffraction, powder diffraction and electron microscopy. Two title compounds display different types of 3D architectures with interesting tunnel structure are built up of the InO₆ octahedra and PO₄ tetrahedra, sharing the corners or edges, and the Pb²⁺ cations are sitting in the tunnel. The structure of Pb₂In₄P₆O₂₃ features a novel 3D open framework which can be considered as built from the layer of {In₄(P₂O₇)(PO₄)₂}²⁻ parallel to the ac plane interconnected by bridging the single PO₄. The structure of Pb₂InP₃O₁₁ can be described by the assemblage of [InP₂O₁₁] units with monophosphate groups. The stereochemical activity of the Pb^II lone pair has also been discussed. The electronic band structure calculations for the two compounds have also been performed with the density functional theory method. The study of calculations and optical diffuse reflectance absorption spectrum measurement show both compounds are indirect band-gap insulators.     

Nb/A1-AlO_X/Nb隧道结的制备研究

通过改进RIE的刻蚀工艺和绝缘层的生长工艺,在SiO2/Si衬底上制备出了性能良好的超导Nb/A1-AlOX/Nb隧道结。采用CF4作为刻蚀气体,降低了RIE对结势垒层和衬底SiO2层的刻蚀。使用PECVD生长绝缘层SiO2,改善了绝缘性能,从而降低了隧道结的漏电流。     

某区放射性环境地质评价研究

在某区拟建隧洞沿线的条带状区域进行了放射性环境地质调查。共采集和分析岩土(芯)放射性核素镭、钍、钾样品111组,地下水和地表水样品5组;现场测定岩土放射性样品392组。结果表明,在该区域内,某煤矿巷道中煤层和砂岩接触带煤、砂岩中镭-226比活度出现高值异常,相应的内照射指数和外照射指数也超过相关标准中规定的放射性核素限量,该异常带环境γ辐射剂量率也较高。镭-226的富集可能源于煤中有机质对放射性核素的吸附和解吸过程。建议在隧道选线过程中尽力避让这一地段。     

Effect of deuterium on passivation of Si surfaces

A properly passivated silicon surface is chemically stable, and all interface properties are constant. The freshly etched Si surface is full of dangling bonds resulting in high surface activity and instability. Hydrogen treatment is a proper procedure to decrease the number of dangling bonds. We demonstrated that deuterium adsorbs on Si surface at room temperature much stronger than hydrogen. Moreover, in case of deuterium-passivated wafers the vacuum storage can be omitted without risking the non-controlled native oxidation of silicon for up to 5 h or more. It could be a suitable and more robust surface cleaning and passivation process for the industry, but heavy water is expensive. As a cheaper procedure, we showed that 1 min vapor phase treatment at 65 °C of heavy water (D₂O) + 50% HF (e.g. 20:1) mixture was enough to remove the native oxide and to passivate the Si surface without any degradation of the atomic surface flatness. The surface evolution of the D-passivated surface was followed by contact angle measurements, spectroscopic ellipsometry (SE), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), infrared absorption spectroscopy (IR), surface potential and surface photovoltage (SPV) mapping and light induced potential transient method. Qualification and the results were compared to the H-passivated, bare and native oxide covered Si surface. Our passivation test results confirmed that using D-passivation on Si surface is a promising method in the MOS technology and the interface engineering processes.     

Tunnel spin injection into graphene using Al2O3 barrier grown by atomic layer deposition on functionalized graphene surface

We demonstrate electrical tunnel spin injection from a ferromagnet to graphene through a high-quality Al₂O₃ grown by atomic layer deposition (ALD). The graphene surface is functionalized with a self-assembled monolayer of 3,4,9,10-perylene tetracarboxylic acid (PTCA) to promote adhesion and growth of Al₂O₃ with a smooth surface. Using this composite tunnel barrier of ALD-Al₂O₃ and PTCA, a spin injection signal of ∼30 Ω has been observed from non-local magnetoresistance measurements at 45 K, revealing potentially high performance of ALD-Al₂O₃/PTCA tunnel barrier for spin injection into graphene.     

Transient localized electron dynamics simulation during femtosecond laser tunnel ionization of diamond

A real-time and real-space time-dependent density-functional theory (TDDFT) is applied to simulate the nonlinear electron–photon interactions during femtosecond laser processing of diamond when tunnel ionization dominates. The transient localized electron dynamics including the electron excitation, energy absorption and electron density evolution are described in this Letter. In addition, the relationships among average absorbed energy, Keldysh parameter and laser intensity are revealed when the laser frequency is fixed.     

Low-alkali metal content in β-vanadium mixed bronzes: The crystal structures of β-Kx(V,Mo)6O15 (x=0.23 and 0.32) by single-crystal X-ray diffraction

The vanadium-molybdenum mixed oxide bronzes of composition K_0.23(V_5.35Mo_0.65)O₁₅ and K_0.32(V_5.48Mo_0.52)O₁₅ have a monoclinic structure with s.g. C2/m, Z=2, and unit-cell dimensions a=15.436(2), b=3.6527(5), c=10.150(1) Å, β=108.604(3)° and a=15.452(2), b=3.6502(5), c=10.142(1) Å, β=109.168(3)°, respectively, as determined by single-crystal X-ray diffraction. These compounds show the β-Na_xV₆O₁₅ tunnel structure, which is isostructural with bannermanite, natural sodium-potassium vanadate. Structure refinements from diffracted intensities collected in the 2-38°θ range converged to final R=5.58% and 7.48% for the two crystals, respectively. The V atoms are distributed on three different crystallographic sites. Partial substitution of V with Mo occurs in only one of these positions. Oxygen atoms involved in vanadyl groups point toward the tunnels. The K ions in the tunnels are coordinated by seven oxygen atoms. The alkali metal content in these crystals is much lower than the solubility limit found for the analogous Na containing compound.