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4 Acta Physica Polonica A

4 2009

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Optical Characterization of Laser-Synthesized Anatase TiO_{2} Nanopowders by Spectroscopic Ellipsometry and Photoluminescence Measurements

100%

Šćepanović M. , Grujić-Brojčin M. , Mirić M. , Dohčević-Mitrović Z. , Popović Z.

Acta Physica Polonica A

2009

tom 116

nr 4

603-606

Nanosized titania (TiO_{2}) is synthesized by laser-induced pyrolysis using TiCl_{4} as a liquid precursor. X-ray diffraction and Raman scattering confirmed anatase structure of TiO_{2} nanocrystals. The dielectric function ε(ω) of TiO_{2} nanopowders has been determined by spectroscopic ellipsometry in the energy range from 1.5 to 6 eV at room temperature. The features observed in ε(ω) have been fitted to analytical line shapes by using the second derivatives of experimental spectra. The energies corresponding to different interband electronic transitions have been determined. Photoluminescence measurements have been carried out in vacuum for T = 20 K and T = 300 K. Under laser irradiation with sub-band gap photon energy, anatase nanocrystals have displayed strong visible photoluminescence emission. In this broad photoluminescence band different variations of line shape and position with excitation energy and temperature are observed for nanopowders with different crystallite size, pointing out to the various electronic transitions mediated by defect levels within the band gap.

Optical Characterization of Graphene and Highly Oriented Pyrolytic Graphite

86%

Kostić R. , Mirić M. , Radić T. , Radović M. , Gajić R. , Popović Z.

Acta Physica Polonica A

2009

tom 116

nr 4

718-721

We present a symmetry analysis of allowed infrared and Raman modes in graphene and highly oriented pyrolytic graphite. Surface structure for highly oriented pyrolytic graphite is examined using atomic force microscopy. As experimental tools, we used infrared spectroscopic ellipsometry in order to investigate the pseudodielectric function of highly oriented pyrolytic graphite in the mid-infrared range (500-7000 cm^{-1}) and Raman spectroscopy to investigate the influence of layers number decrease. As a result, we propose a method for an experimental verification of graphene.

Modelling the Variable Angle Reflection and Transmission from Metamaterial Slabs

86%

Isić G. , Vasić B. , Mirić M. , Jokanović B. , Bergmair I. , Gajić R. , Hingerl K.

Acta Physica Polonica A

2009

tom 116

nr 4

631-634

We consider metamaterial slabs composed of perfectly conducting split-ring resonators. Assuming bianisotropic constitutive relations, we describe an S-parameter retrieval method that allows us to obtain the full material parameter tensors from numerically calculated S parameters. The retrieval has been done for various angles of incidence, ranging from 0° to 75°. It has been found that the parameters depend on the angle of incidence, but that this dependence is relatively small.

Ellipsometric Measurements of Plastically Deformed Copper

86%

Mirić M. , Rudolf R. , Anžel I. , Hadžić B. , Romčević M. , Trajić J. , Romčević N.

Acta Physica Polonica A

2009

tom 116

nr 4

715-717

Chemically pure copper (99.99) prepared in the sample of square cross-section (10×10 mm^{2}) and length about 50 mm was extremely plastically deformed with the repeated application of equal channel angular pressing. Equal channel angular pressing was applied as an effective technique for producing bulk nanoscaled structures. It is well known that severe plastic deformation of metallic materials often leads to microstructure with ultrafine grains and cross-sections which remain about equal before and after deformation. Optical properties of the sample were studied using spectroscopic ellipsometry in UV-VIS range. The parameters of the sample like copper oxide and surface roughness overlayer were calculated using two-film model together with the Bruggeman effective medium approximation.