Preparation and phase studies of the ternary semiconducting compounds ZnSnP2, ZnGeP2, ZnSiP2, CdGeP2, and CdSiP2

ZnSnP₂, ZnGeP₂, ZnSiP₂, CdGeP₂ and CdSiP₂ have been prepared in single or polycrystalline form by direct synthesis from the elements, combination of the group IV element with the II-V₂ phosphide, vapour transport or solution growth. Differential thermal analysis and X-ray powder diffraction studies have been used to determine the temperatures of phase transitions in each of these compounds. Of particular interest is the observation of a phase transition in CdSiP₂ at 1098° C some 22° C below the melting point. The thermal analysis studies of ZnSnP₂ indicate a peak, the cause of which is uncertain, at 720° C which is well separated from the melting temperature of 930° C; further ZnSnP₂ does not appear to be congruently melting and has a freezing point at 970° C. c/a ratios have been determined for all five compounds to 1 part in 2000.     

Strain engineering in single-, bi- and tri-layer MoS2, MoSe2, WS2 and WSe2

Nano Research - Strain is a powerful tool to modify the optical properties of semiconducting transition metal dichalcogenides like MoS2, MoSe2, WS2 and WSe2. In this work we provide a thorough...     

Growth of IrO2, SnO2, and SnO2:IrO2 crystals

Crystals of IrO₂, SnO₂, and SnO₂:IrO₂ have been grown by chemical vapor transport. The IrO₂ crystals are larger than any previously reported. The SnO₂ and SnO₂:IrO₂ crystals are optically clear and are suitable for optical properties studies. This is the first report on the growth of SnO₂:IrO₂ crystals.     

High-Frequency Point-Contact Spectroscopy of TiSi2, TaSi2, and VSi2

High-frequency point-contact spectroscopy as well as conventional low-frequency PC spectroscopy has been used for determining the spectral functions of the electron-phonon interaction (EPI) for three disilicides TiSi₂, TaSi₂, and VSi₂. The temperature dependences of resistivity have been calculated from obtained EPI functions. Comparison of calculated dependences with known experimental data allowed correction of the electron-phonon interaction constants for the studied disilicides.     

Mass Spectrometric Study of NF2, NF3, N2F2, and N2F4

Appearance potentia’s have been measured for selected ions from NF₂, NF₃, N₂F₂, and N₂F₄. Ionization-dissociation processes are identified and bond dissociation energies are calculated. In addition, the bond dissociation energy, D(F₂N–NF₂), has been directly measured to be 5.14±0.38 kj/mole (21.5± 1.6 kcal/mole). A summary is made of available thermochemical and mass spectrometric data for N–F compounds and some evidence is presented to support the designation of cis and trans structures for the N₂F₂ isomers.     

VLE data for CO2-CF2Cl2, N2-CO2, N2-CF2Cl2 and N2-CO2-CF2Cl

Knowledge about vapour-liquid (VLE) is required as a basis of reliable calculations for separation processes. Correlations available for the prediction of T, p, x, y data are less accurate for mixtures at high pressures and mixtures containing supercritical components. The results of VLE experiments are reported and compared with data calculated with equations of state.     

Electrical and tensile properties of Cu-ThO2, Au-ThO2, Pt-ThO2 and Au-Al2O3, Pt-Al2O3 alloys

Dispersion-strengthened alloys of Pt, Au and Cu containing ThO₂ and Al₂O₃ were prepared by precipitating the elements from a solution containing a suspension of the oxide phase. The precipitate deposited on the oxide particles of 0.05μm average diameter and produced dispersions of good homogeneity on compaction. Alloys containing less than 2 vol% oxide phase had sufficient ductility to permit fabrication of wire. Tensile strength and elongation, hardness, and electrical resistivity were measured as a function of temperature up to 1000°C. The dispersion-strengthening caused a relatively small increase in the resistivity of the alloys compared to the resistivity of the metals. The alloys are useful where high electrical or thermal conductivity combined with superior tensile strength, hardness and oxidation resistance at elevated temperatures, are desirable.     

Solid Ar, N2, CO, and O2 in Nanopores

Molecular solids enclosed in pores with diameters in the nm-range are a research field which attracts growing interest. The major questions asked in this context are: what is the structure and the dynamics? How are phase and glass transitions modified by the geometrical constraint? In this contribution we present structural information, by x-ray diffraction measurements, as well as thermodynamic characterization, by vapor pressure and heat capacity measurements, on Ar, which is usually considered the simplest of all condensates, and on the small diatomic molecules N₂, C0, O₂ in porous glasses with average pore diameters from 50 to 130Å.     

Acoustophotovoltaic effect in TlInSe2, TlInTe2, and TlGaTe2 single crystals

Procedures have been developed for growing TlInSe₂, TlInTe₂, and TlGaTe₂ single crystals. Float zoning has been shown to be the most effective process for the crystal growth of these compounds. The grown single crystals exhibit a sizeable acoustophotovoltaic effect.     

Low temperature specific heat of VSi2, NbSi2, and TaSi2

We present low temperature specific heat measurements of VSi₂, NbSi₂ and TaSi₂. The three disilicides crystallize in the same hexagonal structure (C40, space group P6₂22). The measured values of the electronic Density of States at the Fermi Energy,D(E_F), are in good agreement with theoretical band structure calculations. The obtained Debye temperatures vary asM ^–1/2 (M is the molar mass of the compound), showing that the interatomic forces are similar in the three disilicides. NbSi₂ and TaSi₂ are found to be superconductors at 0.130K and 0.353K respectively. The variation of the transition temperatures is discussed.Also affiliated with Laboratoire des Matériaux et du Génie Physique, ENSPG, INPG.     

The vapor pressure of 1, 1-dichloro-2, 2, 2-trifluoroethane (R123)

The vapor pressure of 1, 1-dichloro-2, 2, 2-trifluoroethane (R123) has been measured at temperatures between 256.4 and 453.8 K by ebulliometric and static techniques. These results have been combined to obtain a correlation for the vapor pressure from 256.4 K to the critical temperature.     

Comparison of the Electronic Structures of La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2

First-principles cluster calculations are reported of the local electronic structure of the three compounds: La₂CuO₄, Sr₂CuO₂Cl₂, and Sr₂CuO₂F₂. The copper ${\text{3d}}_{x^2 - y^2 } $ and the planar oxygen 2p _σ atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the ${\text{3}}d_{3z^2 - r^2 } $ atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.     

1,4-二叠氮-2,3-二叠氮甲基-2,3-二硝基丁烷的合成

以硝基甲烷为原料合成了1,4-二叠氮-2,3-二叠氮甲基-2,3-二硝基丁烷,总收率为37.8%。采用1HNMR﹑IR和MS对目标产物及中间体的结构进行了表征。在三羟甲基硝基甲烷的合成中,结合反应机理确定了氢氧化钙的用量为:n(CH3NO2)n(Ca(OH)2)=1001;通过对催化剂浓硫酸﹑三氟化硼—乙醚络合物和对甲苯磺酸的比较,得出对甲苯磺酸为中间体2,2-二甲基-5-羟甲基-5-硝基-1,3-二氧杂环己烷合成的较优催化剂;分别采用2,3-二羟甲基-2,3-二硝基-1,4-丁二醇四硝酸酯和2,3-二羟甲基-2,3-二硝基-1,4-丁二醇四对甲苯磺酸酯与NaN3反应,发现磺酸酯基易离去,叠氮化反应更易进行,收率较高;叠氮化反应的较优溶剂为DMSO。DSC分析表明,1,4-二叠氮-2,3-二叠氮甲基-2,3-二硝基丁烷的分解峰温为223.46℃。     

Degradation of 4-chlorophenol in TiO2, WO3, SnO2, TiO2/WO3 and TiO2/SnO2 systems

The present study was undertaken to evaluate the degradation performance of 4-chlorophenol (4-CP) using TiO2/WO3 and TiO2/SnO2 systems. A BET surface area analyzer, UV-vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were employed to characterize the photocatalyst. The band edge wavelength increased to 475 nm and gap energy decreased to 2.61 eV in the TiO2/WO3 system as compare to the single TiO2. Although the specific surfaces area of TiO2/WO3 decreases due to its larger size as compared to either TiO2 or WO3, the 4-CP degradation efficiency significantly increased as compared to single TiO2 or WO3 system at 435 nm wavelength. The TiO2/WO3 degradation of 4-CP at 369 nm was in fact inhibited. For TiO2/SnO2, the degradation efficiency also suffered at 369 nm, and only slightly increased compared to otherwise hardly 4-CP degraded in single TiO2 or SnO2 system. Since there is a significant accumulation of byproducts, the buildup of these intermediates on the catalyst surface may be responsible for their poor performance.     

Low toxicity of HfO2, SiO2, Al2O3 and CeO2 nanoparticles to the yeast, Saccharomyces cerevisiae

Increasing use of nanomaterials necessitates an improved understanding of their potential impact on environment health. This study evaluated the cytotoxicity of nanosized HfO₂, SiO₂, Al₂O₃ and CeO₂ towards the eukaryotic model organism Saccharomyces cerevisiae, and characterized their state of dispersion in bioassay medium. Nanotoxicity was assessed by monitoring oxygen consumption in batch cultures and by analysis of cell membrane integrity.CeO₂, Al₂O₃, and HfO₂ nanoparticles were highly unstable in yeast medium and formed micron-sized, settleable agglomerates. A non-toxic polyacrylate dispersant (Dispex A40) was used to improve nanoparticle stability and determine the impact of enhanced dispersion on toxicity. None of the NPs tested without dispersant inhibited O₂ uptake by yeast at concentrations as high as 1000 mg/L. Dispersant supplementation only enhanced the toxicity of CeO₂ (47% at 1000 mg/L). Dispersed SiO₂ and Al₂O₃ (1000 mg/L) caused cell membrane damage, whereas dispersed HfO₂ and CeO₂ did not cause significant disruption of membrane integrity at the same concentration. These results suggest that the O₂ uptake inhibition observed with dispersed CeO₂ NPs was not due to reduced cell viability. This is the first study evaluating toxicity of nanoscale HfO₂, SiO₂, Al₂O₃ and CeO₂ to S. cerevisiae. Overall the results obtained demonstrate that these nanomaterials display low or no toxicity to yeast.     

Low-temperature specific heat of YBa2Cu3O7, YBa2Cu3O6, Y2BaCuO5, YBa3Cu2O7, BaCuO2, and CuO

We have measured the low-temperature specific heat (1.3T20 K) and the dc magnetic susceptibility (100T250 K) of eight samples of the high-T _c superconductor Y _x Ba_3–x Cu₃O_7– (x=0.9, 1.0, 1.1) and of two samples of nonsuperconducting YBa₂Cu₃O₆₊. We have also performed specific heat measurements on the possible impurity phases: YBa₃Cu₂O₇, Y₂BaCuO₅, CuO, and BaCuO_2+x . The superconducting samples all have a nonzero, sample-dependent linear term * and an upturn inC/T at very low temperature. We show that this anomalous behavior is at least partly due to the presence of a small amount (1%) of BaCuO_2+x impurity phase in the measured samples. This is evidenced by the correlation between * and the Curie component of the susceptibility, which is proportional to the amount of paramagnetic impurities.     

Precision refractive index measurements of air, N2, O2, Ar, and CO2 with a frequency comb

We report precision measurements of the refractive indices of dry air, N(2), O(2), Ar, and CO(2), performed by using a frequency comb as the light source in a Mach-Zehnder interferometer setup. Improved dispersion formulas for all gases are derived with a sensitivity level of 10(-9). These results are valid for a wavelength range from 740 to 860 nm and are in good agreement with measurements from other groups.