A study of the optical absorption induced in vacuum thermolysis of aluminum trihydroxide

The diffuse reflection spectroscopy technique was used to investigate the color centers (CC) in the products of thermolysis and photolysis of disperse Al(OH)₃ in a vacuum. The spectra were recorded in situ in the region of 2.5–6.0 eV and 4000–12,000 cm⁻¹. It was found that in thermolysis of Al(OH₃) production of Al is accompanied, by transformation of the IR spectra of the compound and overtone vibrations of OH groups and by the appearance of an absorption band (AB) at 4.0 eV with a shoulder at 4.4 eV. A similar AB is induced by UV irradiation of Al(OH)₃ in a vacuum. In the position of the maximum and shape, the AB at 4.0 eV in aluminum oxide produced by thermolysis of Al(OH)₃ coincides with the AB of CC responsible for light- and temperature-stimulated degradation of white anode oxide coatings on Al(Al-AOC). This suggests that in Al-AOC, CC are formed in decay of structural O_mH_n groups. In Al oxide and in Al-AOC, their nature is discussed with the use of data on optical absorption of radiation-induced defects in Al₂O₃. Research Institute of Physics at St. Petersburg State University, St. Petersburg 1, Ul’yanovskaya St., Petrodvorets St. Petersburg, 198904, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 400–404, May–June, 1998.     

Spectroscopic parameters of CHFCl2, CHClF2, C2F6, and C3F8 molecules

We investigate the IR spectra of solutions of R-21,-22,-116, and R-218 in liquid argon at 90K. The frequencies, half-widths, and absolute integral intensities of all of the absorption bands recorded are obtained and interpreted. Scientific-Research Institute of Physics, 1, Ul'yanovskaya Str., Petrodvorets, St. Petersburg, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 297–301, May–June, 1997.     

Spectroscopic studies of uranyl-acetonitrate complex formation in solutions

In the present work uranyl-acetonitrile complex formation is studied on the basis of analysis of vibrational (IR absorption and Raman) spectra of UO₂(NO₃)₂·6H₂O and UO₂(ClO₄)₂·7H₂O. From the present results and coordination critera for nitrate groups and acetonitrile, it is concluded that in the UO₂ (NO₃)₂·6H₂O-acetonitrile system, acetonitrile molecules are in the second coordination sphere of the uranyl ion. In a benzene solution of uranylperchlorate with added acetonitrile, acetonitryl is substituted for a water molecule in the first coordination sphere of the uranyl ion. In the coordination the vibration frequency of C≡H of acetonitrile (2240 cm⁻¹) is shifted by 21 cm⁻¹ to the shortwave region. Possible reasons for the relatively small change in this frequency are discussed. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 179–183, March–April, 1997.     

Molecular mechanism of gelation upon the addition of water to a solution of poly(acrylonitrile) in dimethylsulfoxide

The solidification of a solution of poly(acrylonitrile) (PAN) in dimethylsulfoxide (DMSO) upon introduction of water into the solution is studied by Raman spectroscopy. In the absence of water, DMSO molecules are found to produce dipole-dipole bonds with PAN molecules. Upon the introduction of water, DMSO molecules produce hydrogen bonds with it and bands at 1005 and 1015 cm⁻¹ appear in the Raman spectrum, which are assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. Simultaneously, water molecules produce hydrogen bonds with PAN molecules: R-C≡N...H-O-H...N≡C-R, where R is the carbon skeleton of a PAN molecule. Accordingly, a band at 2250 cm⁻¹ arises in the Raman spectrum, which is assigned to the valence vibrations of C≡N bonds producing hydrogen bonds with a water molecule. When the water content is low and the DMSO concentration is high, the length of the hydrogen bonds varies in wide limits and the band at 2250 cm⁻¹ is wide. As the water content rises, DMSO molecules come out of PAN, the variation of the hydrogen bond length in it decreases (the band at 2250 cm⁻¹ narrows), and a high-viscosity system (gel) arises that consists of PAN molecules bonded to water molecules via “equally strong” hydrogen bonds.     

Photoluminescence of thin amorphous-nanocrystalline silicon films

Photoluminescence spectra of thin hydrogenated-silicon films having mixed amorphous-nanocrystalline phase composition have been studied. Fabry-Perot interference was found to affect strongly the shape of the spectra. An analysis of the spectra made with inclusion of interference corrections shows that only one emission band forms in the 0.6–1.0 μm region due to carrier recombination at centers of the same type. Fiz. Tverd. Tela (St. Petersburg) 41, 153–158 (January 1999)     

Infrared spectra of brassinolide and castasterone steroid phytohormones and their 24-epi derivatives

Absorption bands in IR spectra of brassinolide, castasterone, and their 24-epi derivatives in the frequency range 3800–1000 cm^–1 have been interpreted. A number of spectral features distinguishing brassinolide from castasterone have been found. The conducted analysis shows that the structural differences manifest themselves in IR spectra of the investigated brassinosteroids in the region of stretching vibrations of CO–H, C=O, C–OH, C–O–C, CH₃, CH₂, and CH groups. The main distinctions in IR spectra of brassinolides and castasterones are due to the B ring structure.     

A series of free exciton lines in zinc diarsenide

A structure corresponding to the n=1, 2, and 3 free-exciton states is observed in the optical transmission spectra of zinc diarsenide at 5 K. The band gap for E⊥C at temperatures of 5–300 K and the exciton binding energy (17.5 eV) are determined. Fiz. Tverd. Tela (St. Petersburg) 40, 877–878 (May 1998)     

Raman scattering in a near-surface n-GaAs layer implanted with boron ions

Structure in the Raman scattering spectra of near-surface n-GaAs layers (n=2×10¹⁸ cm⁻³) implanted with 100 keV B⁺ ions in the dose range 3.1×10¹¹–1.2×10¹⁴ cm⁻² is investigated. The qualitative and quantitative data on the carrier density and mobility and on the degree of amorphization of the crystal lattice and the parameters of the nanocrystalline phase as a result of ion implantation are obtained using a method proposed for analyzing room-temperature Raman spectra. Fiz. Tverd. Tela (St. Petersburg) 41, 1495–1498 (August 1999)     

Calculation of the binding energy of electrons and positrons in a dielectric cluster

An analysis is made of analytic expressions for the binding energy of electrons and positrons in dielectric clusters. Calculations are made of the sizes of critical argon and xenon clusters for which the binding energy is near-zero. Fiz. Tverd. Tela (St. Petersburg) 40, 1376–1378 (July 1998)     

On the nature of the spectral shift caused by photoluminescence fatigue in porous silicon

Luminescence spectra of porous silicon with a regular columnar-layered structure have been studied. A substantial narrowing of the luminescence band in samples of this type and a considerable shift of the band induced by fatigue have been established. An explanation for the spectral shift of the luminescence band resulting from fatigue relaxation is proposed for the first time. Fiz. Tverd. Tela (St. Petersburg) 39, 2137–2140 (December 1997)     

Investigation of Saha-Boltzmann equilibrium in the analyte zone of a two-jet plasma generator

Relative populations of the excited levels for Cr(I), Cr(II), Fe(I) and Fe(II) in the argon plasma flow of an arc two-jet plasma generator used in spectrochemical analysis were measured. The range of the total energy E of excitation and ionization was 4.5–8.0 and 12.5–16.0 eV, respectively. It is shown that the populations of atom and ion levels are linear with respect to energy lower than E∼15 eV. For ionic lines with energy close to 15.5–16.0 eV the line intensities behave anomalously against equilibrium values. This can be associated with charge transfer between the analyte and argon ions. Deviation of I from LTE values increases in the plasma zones below and above the site of jet confluence, where the plasma temperature decreases. A. P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1a Favorskii St., Irkutsk, 664033, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 575–581, September–October, 1997.     

Structure of the free exciton luminescence band of heteroepitaxial ZnSe/GaAs layers

The exciton reflectance and photoluminescence spectra of epitaxial ZnSe/GaAs layers with a thickness of 2–4 μm are investigated in the temperature range 10–120 K. It is shown that one of the causes of the formation of the doublet structure of the A _n=1 photoluminescence band is interference of the exciton radiation at the boundaries of the near-surface dead layer. Fiz. Tverd. Tela (St. Petersburg) 40, 881–883 (May 1998)     

IR Spectroscopic signs of malignant neoplasms in the thyroid gland

We use Fourier transform IR spectroscopy to study thyroid tumor tissues which were removed during surgery. The IR spectra of the tissues with pathological foci are compared with data from histologic examination. In the region of N–H, C–H, and C = O stretching vibrations, the IR spectra of the tissues for thyroid cancer are different from the IR spectra of tissues without malignant formations. We identify the spectral signs of thyroid cancer. We show that IR analysis is promising for identification of thyroid pathology at the molecular level.     

Fine structure of the permittivity spectrum of a fluorite crystal

The experimental curve of the permittivity of fluorite is decomposed, for the first time, into 11 components in the range 10.5–18 eV (90 K) and 18 components in the range 10–35 eV (300 K) by the Argand diagram method. Three parameters are determined for each component: the energy at band maximum, the half-width of the band, and the oscillator strength. A scheme is proposed for the nature of the components of the permittivity of fluorite. Fiz. Tverd. Tela (St. Petersburg) 41, 1614–1615 (September 1999)     

Interfacial magnetism in stressed semiconductors with antiferromagnetic ordering

Stressed heterojunctions with antiferromagnetic ordering, in which the primary semiconductors have mutually inverted band spectra, are investigated. It is shown that the interface-bound states formed in these heterojunctions are split with respect to spin. As a result, if the Fermi level falls within one of the bands of the interface states, magnetic ordering is induced in the plane of the interface, i.e., the interfacial magnetism phenomenon can be observed. Fiz. Tverd. Tela (St. Petersburg) 39, 1295–1298 (July 1997)     

Interface optical anisotropy in a heterostructure with different cations and anions

A theory of optical anisotropy and quantum-confined Pockels effect in CA/C′A′(001) quantum-well structures with different cations and anions, i.e. for C≠C′ and A≠A′, has been developed. The theory is based on a generalized effective-mass method, in which the boundary conditions for the envelope functions were constructed taking into account the mixing of heavy-and light-hole states under normal incidence of the hole on the interface. It is shown that an absorption anisotropy in interband transitions occurs for different mixing coefficients t _l−h in the boundary conditions for the right-hand (A-C′) and left-hand (A′-C) interfaces. An analysis is made of the interface contribution to the anisotropy induced by an external electric field for coinciding and different band offsets at the interfaces. The microscopic sp ³ s* tight-binding model is used to estimate the difference between the t _l−h(A-C′) and t _l−h(A′-C) coefficients. Fiz. Tverd. Tela (St. Petersburg) 40, 1925–1931 (October 1998)     

Wide-band approximation in the problem of charge transfer of a desorbed particle at a metal surface

Electron transfer processes between a desorbed particle and a metal surface (charge transfer) are studied in the approximation of a wide but finite band. The effect of a change in the width of the surface band produced by adsorbed atoms on the emission probability of neutrals and ions is investigated. Fiz. Tverd. Tela (St. Petersburg) 40, 161–163 (January 1998)     

Electronic and electronic-vibrational phenomena in the new organic conductor ϰ-(ET)2[Hg(SCN)2Cl] with a metal-insulator transition

The reflection spectra and optical conductivity spectra of the new organic conductor ϰ-(ET)₂[Hg(SCN)₂Cl] with a metal-insulator transition in the spectral regions 700–5500 and 9000–40 000 cm⁻¹ have been studied in polarized light at 300 K. A comparisonis made between the spectra obtained and the corresponding spectra of related isostructural conductors based on the ET molecule, and also the properties of the crystal structure of the investigated compounds. An electronic transition between the ET molecules of the dimer (ET) ₂ ⁺ in the spectral region 700–5500 cm⁻¹ has been identified, as have the features of the electronic-vibrational structure arising as a consequence of the interaction of this transition with the completely symmetric intramolecular vibrations of the ET molecule. It is found that the conductor with the stronger dimer interaction between the ET molecules has the higher the transition temperature. Fiz. Tverd. Tela (St. Petersburg) 39, 1313–1319 (August 1997)     

Study of optical properties and molecular structure of plasma polymerized diethylene glycol dimethyl ether

This paper deals with plasma polymerization processes of diethylene glycol dimethyl ether. Plasmas were produced at 150 mtorr in the range of 10 W to 40 W of RF power. Films were grown on silicon and quartz substrates. Molecular structure of plasma polymerized films and their optical properties were analyzed by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy. The IR spectra show C–H stretching at 3000–2900 cm^-1, C=O stretching at 1730–1650 cm^-1, C–H bending at 1440–1380 cm^-1, C–O and C–O–C stretching at 1200–1000 cm^-1. The concentrations of C–H, C–O and C–O–C were investigated for different values of RF power. It can be seen that the C–H concentration increases from 0.55 to 1.0 au (arbitrary unit) with the increase of RF power from 10 to 40 W. The concentration of C–O and C–O–C decreases from 1.0 to 0.5 au in the same range of RF power. The refraction index increased from 1.47 to 1.61 with the increase of RF power. The optical gap calculated from absorption coefficient decreased from 5.15 to 3.35 eV with the increase of power. Due to its optical and hydrophilic characteristics these films can be applied, for instance, as glass lens coatings for ophthalmic applications.     

Light-Induced shifts in the frequency of a multiphoton radiooptical SHF resonance in alkali atoms

A computation is carried out for light-induced shifts in the frequency of a multiphoton radiooptical SHF resonance in alkali atoms on the basis of the quantum formalism of spherical tensors. The components of a light-induced shift in frequency at magneto-independent 0–0– and 1,–1-transitions in⁸⁷Rb atoms under the conditions of isotopic filtration of the resonance light of pumping are calculated. The difference between the temperatures of a filter cell is discovered at which the point of zero shift in the frequency of radiooptical resonance is attained. The components of the light-induced shift of frequency in optically oriented⁸⁷Rb and¹³³Cs atoms are compared in the absence of collisional reorientation in excited state. The prevailing role of the tensor component of light-induced shift in pumping by the D₁-line of a head doublet and the effect of the orientational dependence of the frequency of a multiphoton resonance on change in the sign of the pumping source radiation polarization are noted. St. Petersburg State Polytechnical University, 29 Politekhnicheskaya Str., St. Petersburg, 195251, Russia. Translated from Zburnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 832–838, November–December, 1998.