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Open Physics
|
2010
|
vol. 8
|
issue 4
628-633
EN
The structural, electronic and elastic properties of the cubic boron nitride (BN) compound are investigated by a first-principle pseudopotential method. The calculations show that the structural phase transition from the zinc-blende(ZB) structure to the rocksalt (RS) structure occurs at a transition pressure of 1088 GPa and with a volume reduction of 3.1%. Both the ZB and RS structures of BN have indirect gaps, with energy gaps of 4.80 eV and 2.11 eV, respectively. The positive pressure derivative of the indirect band gap (Γ-X) energy for the the ZB phase and the predicted ultrahigh metallization pressure are attributed to the absence of d occupations in the valence bands. The increase of the shear modulus with increasing pressure implies that the lattice stability becomes higher when BN is compressed.
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Ultrathin Glass for the Photovoltaic Applications

84%
EN
Chemically strengthened ultrathin glass with a thickness of less than 1 mm has many advantages, such as flexibility, smooth surface, good transmittance, excellent gas and water barrier, much higher toughened in relations to thermally tempered glass, higher impact resistance, increased corrosion resistance and much higher abrasion rate. Chemical strengthening process is a process where an ion exchange occurs by diffusion between the glass panes and the brine solution bath. The deeper penetration of the glass surface by ions contained in the brine bath contributes to the hardness of the glass sheets, which reduces the occurrence of surface defects that cause reflections. From the point of view of photovoltaic applications ultrathin glass significantly reduces the weight of the whole photovoltaic panel structure with respect to known solutions. Furthermore, the reduction of the glass thickness increases the transmission of solar energy in the visible range directly through the glass. In addition, chemical tempered glass has a lower reflectance of light from the surface than the thermally tempered glass. What is more, ultrathin glass is perfect substrate for deposition of nanomaterials, i.e. conductive films or quantum dots. In this work we demonstrate that chemically strengthened ultrathin glass is a perfect material for the photovoltaic applications, i.e. as a substrate for deposition of thin layers and for the design of photovoltaic modules of reduced weight.
EN
The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.
Open Physics
|
2007
|
vol. 5
|
issue 1
103-109
EN
The electronic structures of doped Sb2O5 by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results showed that the substituted IV-family elements act as acceptors in Sb2O5. Partial DOSs indicates that by substituting Ge(GeSb) or Sn(SnSb), there may be a larger contribution to the total DOSs near EF than by substituting Si, which suggests that doping Ge or Sn in Sb2O5 produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely to exist in the substituted position rather than in the interstitial position in Sb2O5, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb2O5. Ionization energy results show that GeSb or SnSb, two among the three impurities considered, act as shallow acceptors in Sb2O5, thus producing a higher concentration of holes.
EN
Thin films of copper selenide (CuSe) were physically deposited layer-by-layer up to 5 layers using thermal evaporation technique onto a glass substrate. Various film properties, including the thickness, structure, morphology, surface roughness, average grain size and electrical conductivity are studied and discussed. These properties are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ellipsometer and 4 point probe at room temperature. The dependence of electrical conductivity, surface roughness, and average grain size on number of layers deposited is discussed.
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