Manifestation of a size effect in the behavior of the intrinsic absorption edge of nanostructured polycrystalline zinc oxide thin films

We have studied the behavior of the intrinsic absorption edge in zinc oxide thin films in the temperature range 80–300 K. We have observed that the intrinsic absorption edge in films with crystal sizes of ≈45 nm or larger is described by the empirical Urbach’s rule, while in films with crystallite sizes of ≈15 nm, it is described by a modified Urbach’s rule. We have calculated the effective frequency of phonons taking part in formation of the absorption edge. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 275–277, March–April, 2007.     

Structure and optical properties of films of the ternary compound CuGa5Se8

We have used a laser deposition method to obtain films of the ternary compound CuGa₅Se₈. We have studied their composition and structure. We have established that both the crystals and the films of the indicated compound crystallize in a defect-containing chalcopyrite structure. We have determined the energy and nature of the optical transitions from the transmission spectra in the region of the intrinsic absorption edge. We have calculated the valence-band crystal-field (Δ_CF) and spin–orbit (Δ_SO) splitting energies according to Hopfield’s quasicubic model for the ternary compound CuGa5Se8.     

Optical properties of films of the ternary compound CuIn<Subscript>3</Subscript>Se<Subscript>5</Subscript>

We have used the laser vaporization method to obtain films of the ternary compound CuIn₃Se₅ and have studied the composition and structure of the films obtained. We have determined the energy and nature of the optical transitions for the indicated compound from the transmission spectra in the region of the intrinsic absorption edge. We have calculated the valence-band crystal-field (Δ_CF) and spin-orbit (Δ_SO) splitting energies according to Hopfield’s quasicubic model for the ternary compound CuIn₃Se₅. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 82–85, January–February, 2007.     

Absorption spectra of ZnO:Li thin films in the region of a phase transition

We have studied the temperature variation of the intrinsic absorption edge for ZnO:Li films obtained by high-frequency magnetron sputtering. We have observed anomalous behavior of the optical bandgap width in the vicinity of the temperature of a ferroelectric phase transition at T = 327 K. For the first time, we have observed the appearance of this phase transition on the thermally stimulated depolarization (TSD) current curves.     

Investigation of CuInSe2 films by the method of photoacoustic spectroscopy

We investigated the photoacoustic spectra of polycrystalline thin CuInSe₂ films obtained by the method of pulsed laser evaporation onto glass substrates at 100–450°C. The spectra were taken near the fundamental optical absorption edge using a high-resolution spectrometer and microphone-type sensor. We show the relation between the photoacoustic spectrum and the structural properties of films. The interference effect observed is discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 583–586, July–August, 1999.     

Exciton-phonon interaction in Y2O3 and Sc2O3 thin films

An investigation is made of the fundamental absorption edge of Y₂O₃ thin films. Based on its temperature dependence the exciton-phonon interaction is studied, which makes it possible to interpret the absorption edge as the absorption of self-localized excitons. A number of parameters of the energy spectrum of the investigated films are determined. I. Franko State University, 50, Dragomanov St., L'vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 132–134, January–February, 1999.     

Transmission spectra of films of Mn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se solid solutions

Films of Mn_1−x Fe _x Se (x = 0–0.45) solid solutions were flash-sputtered. We measured the transmission spectra of the films in the wavelength range 200–1000 nm at room temperature. From these spectra, we calculated the absorption coefficients and determined the fundamental absorption edge, the position of which is shifted from 2.65 eV in MnSe to 2.30 eV in solid solutions of compositions x = 0.20–0.45. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 136–138, January–February, 2007.     

Photoelectric properties ofp-CuInSe2 thin films obtained by pulsed laser vaporization

Using the method of phase-sensitive detection, we investigated the photoconductivity spectra of polycrystalline p-CuInSe₂ films obtained in vacuum by the method of pulsed laser vaporization of initial single crystals. We show that, in contrast to single crystals, films are characterized by monopolar photoconductivity in the extrinsic and intrinsic regions of optical absorption and by a linear mechanism of recombination of nonequilibrium charge carriers at the intensities of illumination 0–100 mW/cm² in the temperature range 80–300 K. Institute of the Solid-State and Semiconductor Physics, National Academy of Sciences of Belarus, 17, P. Brovka St., Minsk 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii. Vol. 66, No. 1, pp. 138–141, January–February, 1999.     

Dispersion of light and EDGE absorption of thin Y2O3 films

We measured the dispersion of light in thin Y₂O₃ films in the visible and near UV regions of the spectrum. The spectrum of edge absorption is investigated. We found the parameters of a single-oscillator approximation and determined the dispersion energy and the ionicity of bonding. I. Franko L’vov State University, 50, Dragomanov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 651–654, September–October, 1997.     

Temperature dependence of the bandgap width in FeIn2Se4 single crystals

We have used the Bridgman method to grow single crystals of the ternary compound FeIn₂Se₄ and we have determined their composition and structure. We measured the transmission spectra in the intrinsic absorption edge region in the temperature range 20–300 K. From the transmission spectra, we determined the bandgap width and plotted its temperature dependence. We show that the E_g(T) dependence has a shape typical for semiconductor compounds.     

Electrical and optical characterization of (PEO+PVAc) polyblend films

Solid polymer blend films based on polyethylene oxide and polyvinyl acetate (PVAc) were prepared in various concentrations by solution cast technique. The features of complexation of the blend films were studied by X-ray diffraction. The electrical conductivity of films was found to increase with increasing PVAc concentration. The conductivity–temperature plots were found to follow Arrhenius nature and showed a decrease in activation energy with increasing PVAc concentration. Optical properties like absorption edge and direct and indirect band gaps were estimated for pure and blend films from their optical absorption spectra. It was found that the energy gap and band edge values shifted to lower energies on blending with PVAc.     

Investigation of optical properties of thin CuGaTe2 films

Thin films of copper tellurogallate were obtained by the method of pulsed laser spraying. The structure of the films and the parameters of the unit cell were determined by the x-ray method. It is shown that the films possess p-type conduction and their resistivity decreases with an increase in the substrate temperature. From the transmission near the edge of the fundamental absorption band a determination was made of the energy of interband transitions, crystalline cleavage, and spin-orbital splitting. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 946–949, November–December, 1998.     

Effect of thermal annealing on r.f. sputtering-deposited nanocrystalline GaN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> thin films

GaNAs thin films were deposited on Corning glass substrates by radio frequency (r.f.) sputtering in molecular nitrogen ambient. The stoichiometry in the GaNAs alloy was controlled by changing the nitrogen incorporation in the film during the growth process, through the variation of the r.f. power in the range 30–80 watts which produced films with N concentrations in the range: x = 0.85–0.90. The structural and optical properties of the GaNAs thin films were studied by X-ray diffraction (XRD), photoacoustic (PA) and photoluminescence (PL) spectroscopies. XRD measurements show a broad diffraction band with a peak close to the (002) diffraction line of the GaN hexagonal phase, and a slight shoulder at the position corresponding to the (111) GaAs cubic phase. The PA absorption spectra showed a remarkable shift to higher energies of the absorption edge as the r.f. power decreases corresponding to the films with higher N concentrations. Thermal annealing of the GaNAs films at temperatures of 450 °C produced a GaAs nanocrystalline phase with grain sizes in the range 10–13 nm, as confirmed by the XRD measurements that showed a well-defined peak in the (111) GaAs direction, and also by the PA spectra which showed an absorption band at energies around 1.45 eV due to the quantum confinement effects. PL spectra of thermal-annealed GaNAs films showed a very intense emission at 1.5 eV which we have associated to transitions between the first electron excited level and acceptor states in the GaAs nanocrystallites.     

Fundamental absorption edge of thin films of Bi4Si3O12

The fundamental absorption edge of thin films of Bi₄Si₃O₁₂ is investigated. On the basis of its temperature dependence, exciton-phonon interaction is investigated, which made it possible to interpret the absorption edge as the absorption of autolocalized excitons. The temperature dependence of the forbidden band width is given. I. Franko Lvov State University, 50, Dragomanov St., Lvov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 232–235, March–April, 1997.     

Synthesis and characterization of electron beam evaporated LiCoO<Subscript>2</Subscript> thin films

LiCoO₂ thin films were prepared by electron beam evaporation technique using LiCoO₂ target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10⁻⁴ mbar. The films prepared at substrate temperature T _s < 573 K were amorphous in nature, and the films prepared at T _s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–e_g absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t_2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006     

Optical absorption and exciton-phonon interaction in solid solutions Cu<Subscript>6</Subscript>PS<Subscript>5</Subscript>I<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

We have studied the optical absorption edge of solid solutions Cu₆PS₅I_{1 − x} Cl _x at high absorption levels in the temperature range of 77–320 K. In a superionic state, we have revealed the Urbach behavior of the absorption edge, determined its parameters, and studied their temperature and concentration variations. We consider exciton-phonon interaction as a mechanism by which the Urbach bundle is formed and show that this bundle can be described in terms of the Dow-Redfield model.     

Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Characterization of organic thin films with resonant soft X-ray scattering and reflectivity near the carbon and fluorine absorption edges

The use of soft X-rays near the carbon absorption edge (∼270–300 eV) for small angle X-ray scattering and X-ray reflectivity experiments has significantly expanded the scientific capabilities to investigate thin films of soft matter that are primarily composed of carbon and low Z heteroatoms. In this perspective, we will delineate the basic operating principles and underlying physics of these methods and exemplify their impact by discussing a few recent applications. An extension of these methods to the fluorine edge is also included, demonstrating that the general concepts are also applicable to absorption edges of hetero atoms in soft matter. A short perspective of some future developments is provided.     

Effect of pyrene and acetophenone on photostability of poly(methylphenylsilane) films

We have used investigations of low-temperature photoluminescence and thermally stimulated luminescence to study the effect of acetophenone and pyrene dopants on the photochemical stability of poly(methylphenylsilane) (PMPS) films. We have established that pure PMPS films and acetophenone-doped PMPS films degrade on exposure to UV radiation due to breaking of Si-Si bonds followed by formation of crosslinks between the macromolecules. At the same time, pyrene inhibits degradation of PMPS to a significant extent. This proves that photoinduced breaking of the Si-Si bond can occur upon excitation of the macromolecule to the first triplet T₁(σσ*) state, since acetophenone sensitizes while pyrene quenches the intrinsic phosphorescence of PMPS. So the photochemical stability of PMPS can be improved by introducing a dopant which quenches triplet excitations of the macromolecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 315–320, May–June, 2007.     

Optical and IR studies on r.f. magnetron sputtered ultra-thin MoO3 films

Ultra-thin MoO₃ films were deposited onto glass and Si substrates by r.f. magnetron sputtering. The optical and IR properties of the films were studied in the range of 250 to 1000 nm and 400 to 1500 cm⁻¹, respectively. The optical transmission spectra show a significant shift in absorption edge. The energy gap of the films deposited at 373 K and 0.1 mbar was found to be 3.93 eV, and it decreases with increasing substrate temperature and decreasing sputtering pressure. The IR transmittance spectra shows strong modes of vibrations of Mo=O and Mo–O–Mo units of MoO₃ molecule. A significant change in energy gap and a shift in frequency of IR modes were observed in ultra-thin MoO₃ films.