Krešimir Furić

Chemical and micro structural properties of TiO2 synthesized by sol-gel procedure

Abstract Nanosized TiO 2 powders were prepared using the sol-gel procedure. The selected colloidal suspensions were stabilized with polyethylene glycol (PEG). This polymer prevented sintering of TiO 2 particles during the calcination of the starting material. X-ray powder diffraction (XRD) phase analysis showed that the samples, obtained up to 500°C, were a mixture of anatase and brookite. In the samples, obtained at 850°C and higher temperatures, rutile as a single phase was detected. The TGA/DTA curves were dependent on the preparation of TiO 2 samples. The samples were also characterized by Fourier transform infrared spectroscopy and laser Raman spectroscopy. A new method, based on low-frequency Raman scattering, was proposed for the size determination of nanosized TiO 2 . The size determination of nanosized TiO 2 by low-frequency Raman scattering was in a good agreement with crystallite size values obtained by XRD.

DFT study of molecular structure and vibrations of 3-glycidoxypropyltrimethoxysilane.

Molecular structure and vibrational frequencies of 3-glycidoxypropyltrimethoxysilane (GPTMS) have been investigated by density functional theory (DFT) calculations using Beckes three-parameter exchange functional combined with Lee-Young-Parr correlation functional (B3-LYP) and standard basis set 6-311++G(d,p). In order to reveal some possible conformations of GPTMS, potential energy scan has been performed in three dihedral angles SiCCC, CCCO and OCCO. The calculations predict the existence of seven different conformations. Raman and IR spectra of liquid samples were recorded and complete assignment of the observed vibrational bands of GPTMS molecule has been proposed. Temperature dependence of Raman spectra between 203K and 293K was examined and vibrational modes characteristic for different conformers were detached.

Structural Modifications in Amorphous Ge Produced by Ion Implantation

Abstract Raman spectroscopy was used to analyze structural modifications of monocrystalline Ge implanted with 3×10 12 to 3×10 16 cm −2 74 Ge ions, at either room temperature (RT) or liquid nitrogen (LN) temperature. In all implanted samples, beyond the amorphization threshold dose (≃10 14 cm −2 ), a dose-dependent evolution of the amorphous matrix could be followed. However, changes induced in samples implanted at −196°C (LN) differed from those implanted at 21°C. Characteristic Raman parameters relevant for disorder assessment suggest relaxation of the amorphous network with ion dose in samples implanted at RT in contrast to the LN temperature samples, in which additional implantation produces further disordering. These findings are consistent with the results obtained by extended X-ray absorption fine structure spectroscopy (EXAFS) wherein again both a dose- and temperature-dependent evolution of the inter-atomic distance distribution was observed.

Raman study of phase transitions in pure and alloyed zirconia induced by ball-milling and a laser beam

Abstract High-temperature phases of ZrO 2 were obtained at room temperature by incorporating a few mole fractions of other oxides (MgO, Y 2 O 3 or CoO) in a zirconia crystal lattice using high-energy ball-milling. Raman spectra obtained after an adequate period of ball-milling show the formation of ZrO 2 MgO and ZrO 2 Y 2 O 3 cubic solid solutions and a ZrO 2 CoO tetragonal solid solution. However, in the case of pure monoclinic zirconia, the transformation from a monoclinic to a tetragonal structure could not be completed by the use of ball-milling only. The spectra of fully stabilized solid solutions did not change essentially with laser power, while insufficiently milled samples underwent phase changes when the laser power increased. In pure milled zirconia, annealing effects were observed.

Raman study of light-induced changes in silicon-hydrogen bond stretching vibration in aSi:H

Abstract Amorphous hydrogenated silicon films prepared by a dc magnetron sputtering method was soaked by light of an argon ion laser and studied “in situ” by Raman spectroscopy in order to resolve the apparent inconsistency in the assignments of the silicon—hydrogen bond stretching vibrations. The bond-stretching frequency region between 1850 and 2250 cm −1 was decomposed in two Gaussian-shaped bands. The laser—induced changes at the power density from 20 to 500 W/cm 2 show: a) the continious increase of the integrated intensity of the band at about 2100 cm −1 compared to the band at about 2000 cm −1 ; b) the frequency shift of both bands to the lower values; c) the linewidth decrease of the band at about 2000 cm −1 , and d) linewidth increase of the band at about 2100 cm −1 . Contrary to the previous proposals that in the stretching region of the Raman spectra only two bands exist, our data show the existence of four vibrational bands.

Vibrational spectroscopic and DFT calculation studies of cobalt(II) complexes with 3-hydroxypicolinic acid.

Two cobalt(II) complexes with 3-hydroxypicolinic acid (3-hydroxypyridine-2-carboxylic acid, 3-OHpicH), trans-[Co(3-OHpic)2(py)2] (2) and cis-[Co(3-OHpic)2(4-pic)2] (3) (py=pyridine; 4-pic=4-picoline or 4-methylpyridine), previously synthesized and characterized by X-ray diffraction, are here studied by Raman and mid-infrared spectroscopy with the help from the corresponding DFT vibrational calculations using B3LYP/6-311G(d,p) computational model. Intramolecular O-H⋯O hydrogen bond appears in both complexes 2 and 3, while weak C-H⋯O hydrogen bonds assemble molecules of 2 or 3 into 3D architecture. A complete presentation of all Raman, infrared and theoretical results is given for complex 3. The measured spectra are shown, relative intensities and bandwidths are discussed and the assignment of vibrational bands is given on the basis of the DFT calculations. The calculated spectra agree very well with the presented experimental findings, thanks to the suitable grouping of modes. The same vibrational calculations also reveal insignificant influence of H→CH3 substitution for the spectroscopic characterization of the complex. A careful study of differences between calculated and observed wavenumbers suggests that modified single-factor scaling is actually better than the classic multi-factor scaling approach.

“Boson” peak in Raman spectra of hydrogenated amorphous silicon

Hydrogenated amorphous silicon films were prepared by a dc magnetron sputtering method. Broad background signal observed in Raman spectra near the excitation line which is recently attributed to the recombination of nonthermal electron with nonthermal holes was decomposed from the phonon bands. The Stokes/ anti-Stokes ratio, depolarization ratio and the shape of the background signal have the characteristics typical for the “boson” peak in glasses. The appearance of the “boson” peak in a-Si:H is discussed in a model of the non-continuous structure of amorphous silicon, composed of the blobs of strongly connected silicon atoms placed around hydrogen clusters.

Implantation-induced disorder in amorphous Ge: Production and relaxation

Abstract Extended X-ray absorption fine structure and Raman spectroscopy have been utilised to measure implantation-induced micro-structural modifications in amorphous Ge including increases in bond length, broadening of the bond-angle distribution, and non-Gaussian static disorder as functions of ion dose. The resulting evolution of the inter-atomic distance distribution, over an ion dose range extending two orders of magnitude beyond that required for amorphisation, demonstrates the influence of implant conditions on amorphous phase structure. Results are attributed to increased fractions of three- and fivefold coordinated atoms as a means of accommodating implantation-induced point defects in the amorphous phase. In contrast, a common, ion-dose-independent structure is apparent following low-temperature, thermally-induced relaxation as consistent with the annealing of point defects in the amorphous phase. Structural relaxation is manifested by reductions in both bond-length and bond-angle distortion and the relaxation enthalpy for each component has been calculated separately.

Ir and raman study of Si1−xCx:H amorphous thin films

Abstract Amorphous hydrogenated a-Si1−xCx:H thin films have been obtained by means of DC magnetron sputtering in the benzene vapor. Comparative IR and Raman spectroscopy study of carbon incorporation in the silicon matrix have been performed. It was found that carbon incorporates in the form of the CH3groups, individual C-atoms and the C6H6 molecules.

Raman study of vibrational dynamics of aminopropylsilanetriol in gas phase

Raman spectrum of aminopropylsilanetriol (APST) in gas phase has been recorded at room temperature in macro chamber utilizing two-mirror technique over the sample tube. Unlike predominantly trans molecular conformation in condensed phase, the spectra of vapor show that the molecules are solely in gauche conformation with intramolecular hydrogen bond N···HO which reduces the molecular energy in respect to trans conformation by 0.152 eV. The assignment of the molecular spectra based on the DFT calculation is presented. The strong vibrational bands at 354 cm(-1), 588 cm(-1) and 3022 cm(-1) are proposed for verifying the existence of the ring like, hydrogen bonded structure. Special attention was devoted to the high frequency region, where hydrogen bond vibrations are coupled to stretchings of amino and silanol groups.