Growth and photoluminescence of ZnO thin films on Si(1 1 1) by PLD in oxygen adequate ambient

Polycrystalline ZnO thin films were synthesized on Si(1 1 1) substrates by pulsed laser deposition (PLD) under oxygen sufficient condition at temperatures ranging from 550 to . The results of in situ reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) show that the (0 0 2) orientation of ZnO thin films is deteriorated, but the full-width at half-maximum (FWHM) of (0 0 2) peak decreases as the substrate temperature (T_s) increases. In photoluminescence (PL) spectra at room temperature (RT), all the ZnO thin films show small ultraviolet (UV) peak FWHMs in the range of 83-95 meV. The thin film prepared at exhibits the narrowest UV peak FWHM of 83 meV and the biggest intensity ratio (122) of UV emission (UVE) to deep-level emission (DLE). When the T_s increases to , a low-energy peak in the UV region at around 381 nm (3.25 eV) appears, which maybe result from a donor-acceptor-pair (DAP) transition and be a signal of excess incorporation of oxygen in the thin film.     

Structural and optical properties of polycrystalline CdSexTe1−x (0 ≤ x ≤ 0.4) thin films

CdSe_xTe_1−x (0 ≤ x ≤ 0.4) ternary thin films have been deposited on quartz substrates at room temperature by a single source thermal evaporation. X-ray diffraction patterns and transmission electron microscope micrographs of these films showed that the films were of polycrystalline texture over the whole range studied and exhibit predominant cubic (zinc blende) structure with strong preferential orientation of the crystallites along (1 1 1) direction. Linear variation of the lattice constant with mole fraction x is observed obeying Vegard's law. The dependence of the optical constants, the refractive index n and extinction coefficient k, of the films on the mole fraction x was studied in the spectral range of 400-2500 nm. The normal dispersion of the refractive index of the films could be described using the Wemple-DiDomenco single-oscillator model. CdSe_xTe_1−x thin films of different composition have two direct and indirect transitions corresponding to energy gaps and . The variation in either or with x indicates that this system belongs to the amalgamation type. The variation follows a subquadratic dependence and the bowing parameters were found to be 0.36 and 0.48 eV for the direct, and indirect energy gaps, respectively. Direct linear variation of the ratio N/m^* with x is observed.     

Study of lithium behaviour in Si(Li) detectors

In this paper we describe the fabrication of a conventional lithium compensated silicon detector (Si(Li)) realized on Topsil silicon with bulk resistivity 0.9 to , using the process of ion drift introduced by Pell. Preliminary results of electrical and nuclear characterization are shown. A leakage current value of 4 pA is obtained under reverse bias voltage of , at pressure of and 113 K. An alpha test using triple source ²⁴¹Am, ²³⁹Pu, ²³³U was carried and a resolution on ²⁴¹Am peak around 42 keV was obtained with this type of detector. The fabricated detector present a good electrical and nuclear characteristics that can be used in X-ray spectrometry and widespread applications in research science, environment monitoring and natural radioactivity. The main contribution of this work is the demonstration of an easy-to-implement, low cost detector set that can be achieved with an inexpensive n⁺p diode.     

Contact angle of water droplet on apatite single crystals

Contact angles of water droplets on well-formed crystals of strontium and barium chlorapatites, Sr₅Cl(PO₄)₃ and Ba₅Cl(PO₄)₃, were observed. The contact angles of water on (1 0  0) and (1 0  1) faces of Sr₅Cl(PO₄)₃ were 74±8° and 53±5° and those on (1 0  0) and (1 0  1) faces of Ba₅Cl(PO₄)₃ were 52±5° and 33±1°, respectively. The surface tensions of the crystals were calculated using Neumann’s equation. They were 39.2±50 and 52.0±3.0 mJ m⁻² for (1 0  0) and (1 0  1) faces of Sr₅Cl(PO₄)₃, 52.5±2.9 and 63.0±0.5 mJ m⁻² for (1 0  0) and (1 0  1) faces of Ba₅Cl(PO₄)₃, respectively. The (1 0  1) face has larger surface tension than (1 0  0) face for both crystals. The chlorapatite crystals have tendency to elongate in 〈0 0 0 1〉 directions during the crystal growth process, indicating that (1 0  0) face is more stable than (1 0  1) face. This nature of crystal morphology is consistent with the surface tensions estimated from the water contact angles. The higher density of Ba₅Cl(PO₄)₃ than Sr₅Cl(PO₄)₃ is considered to cause the smaller contact angles of water droplet on Ba₅Cl(PO₄)₃ crystal than that on Sr₅Cl(PO₄)₃ crystal because the attractive force between the heavier atoms brings the larger surface tension of solid.     

Ion-molecule reactions in mixtures of methane with carbon tetrafluoride

Ion-molecule reactions have been measured for methane-carbon tetrafluoride mixtures of different composition using a quadrupole mass spectrometer with a high-pressure ion source. Concentration of methane in these mixtures ranged from 10% to 90% (at 10% increment). Primary ions , , F⁺, CF⁺ and were produced by electrons with energy of 300 eV. Secondary ions , , , , and were observed as the result of ion-molecule reactions. Relative current intensities for primary and secondary ions are presented as a function of both total mixture pressure and concentration of methane in the mixture. Potential of repeller electrode inside the ion source collision chamber was fixed at 5 V for all measurements. Total mixture pressure was changed from 0.7 to 33.3 Pa. Schemes of ion-molecule reactions were proposed.     

Synthesis and characterization of a new organic dihydrogenomonophosphate [3,5-(CH3O)2C6H3NH3]2(H2PO4)2

Chemical preparation, crystal structure, calorimetric studies and spectroscopic investigation are given for a new organic cation dihydrogenomonophosphate [3,5-(CH₃O)₂C₆H₃NH₃]₂(H₂PO₄)₂. This compound is triclinic with the following unit cell parameters: a=9.030(6) Å, b=16.124(5) Å, c=8.868(3) Å, α=75.04(3)°, β=110.71(4)°, γ=104.61(1)°, Z=4, V=1148.0(1) Å³, Z=2 and ρ_cal.=1.454 g cm⁻³. Crystal structure was solved and refined to R=0.04, 2752 independent reflections. The atomic arrangement can be described as inorganic layers of H₂PO₄⁻ anions parallel to planes, between which are located the organic groups. Solid-state and MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of the phosphorous and carbon signals to the independent crystallographic sites and to the various atoms of the organic groups.