J. Trajić

Optical properties of PbTe:Mn

Abstract In this paper, we investigate Mn concentration and crystal growth rate influence on optical properties of PbTe:Mn single crystals. We measured far-infrared reflectivity spectra at room temperature in the 10–250 cm −1 spectral range. The analysis of the far-infrared spectra was made by a fitting procedure based on the model of coupled oscillators. In spite of the strong plasmon-LO phonon interaction, we found that the plasma frequency decreases as Mn concentration increases, while the crystal growth rate has the opposite effect. Also, we obtained the Mn impurity in-band mode at about 50 cm −1 .

Influence of Preparation Method on SOP Modes in ZnO Doped with CoO Nanoparticles

The aim of the present work is to study influence of preparation method on samples characteristics, creation and behavior of surface optical phonons (SOP) modes with change of concentration of doping elements by micro Raman spectroscopy. Nanocrystalline samples of ZnO(Co) were prepared by use of traditional wet chemistry method followed by calcinations and the microwave assisted hydrothermal synthesis. The phase composition of the samples (ZnO, Co3O4, ZnCo2O4) and the mean crystalline size (14–300 nm) were determined using X-ray diffraction measurements. In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm−1) for both type of samples. Main characteristic of experimental Raman spectrum are: sharp peak at 436 cm−1 and broad multi phonon structure at ~1150 cm−1, typical for ZnO; sharp peaks at 194, 482, 521, 618 and 691 cm−1 typical for Co3O4 and sharp peaks at 185, 475, 520, 610 and 690 cm−1 typical for ZnCo2O4 nanoparticles. The phonon of registered phase’s exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

Far-infrared investigations of the surface modes in CdS thin films

The properties of Cadmium sulphide (CdS) thin films were investigated by applying atomic force microscopy (AFM) and far–infrared spectroscopy. CdS thin films were prepared using thermal evaporation technique under a base pressure of 2 × 10−5 torr. The quality of these films was investigated by AFM spectroscopy. We apply far–infrared spectroscopy to investigate the optical properties of CdS thin films, and reveal the existence of a surface optical phonon (SOP) mode at 297 cm−1. For the first time, the dielectric function of CdS thin film is modeled as a mixture of homogenous spherical inclusions in air by the Maxwell–Garnet formula. In the analysis of the far–infrared reflection spectra, a numerical model for calculating the reflectivity coefficient for a system which includes films and substrates has been applied.

Structural Properties of Pb1-xMnxTe Alloys

Pb1-xMnxTe crystals were grown by Bridgman method and by molecular beam epitaxy (MBE). Structural properties of bulk crystals were studied both by optical microscopy after chemical polishing and etching, and by X-ray powder diffraction. For chemical polishing the solution of 5 vol.% Br2 in HBr at the room temperature after exposure for 2 minutes was determined A solution of 20g KOH in 1 ml H2O2, 2ml glycerol (C3H8O3), and 20 ml H2O at the room temperature after exposure for 6 minutes was found to be a suitable etching solution. The lattice parameters of samples obtained on different way (Bridgman and MBE) were determined.

Off-Resonant Raman Spectroscopy of ZnS Quantum Dots

ZnS nanoparticles were synthesized mechanochemically by high-energy milling. Samples were produced in three different milling times. The morphology of samples has been investigated by scanning electron microscopy (SEM). X-ray diffraction (XRD) investigation of synthesized nanocrystals identified cubic structure, and crystallite size was estimated to 1.9 nm (5 min milling), 2.3 nm (10 min) and 2.4 nm (20 min). These dimensions ensure strong confinement regime. Raman spectroscopy studies (100–500 cm−1) have been performed. Excitation source was 514.5 nm (EL = 2.41 eV), implying that we are in off-resonance regime. Dominant spectral structures are registered in spectral region 130–180 cm−1, around 265 cm−1 and around 345 cm−1. First two are assigned as combination modes and mode at 345 cm−1 as confined ZnS LO type phonon. Absence of TO mode with visible excitation is consequence of poor scattering efficiency and anti-resonant behavior. We report relatively strong, compared to confined ZnS LO type phonon, Raman activities of combination modes away from the resonance in the strong confinement regime in ZnS quantum dots (QD). We find that off-resonance Raman spectroscopy can be used for quick estimation of the dimension of produced ZnS QDs. Sum of second-order Raman active modes centered at 265 cm−1 dominates over LO-like mode at 345 cm−1 in strong confinement regime.

Structural Properties of Cu-Se-CuSe 2 Thin Films

This paper describes the structural and optical properties of Cu-Se-CuSe2 thin films. The surface morphology of thin films was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Formation of thin films is concluded to proceed unevenly, in the form of islands which later grew into agglomerates. The structural characterization of Cu-Se-CuSe2 thin film was investigated using X-ray diffraction pattern (XRD). The presence of two-phase system is observed. One is the solid solution of Cu in Se and the other is low-pressure modification of CuSe2. The Raman spectroscopy was used to identify and quantify the individual phases present in the films. Red shift and asymmetry of Raman mode characteristic for CuSe2 enable us to estimate nanocrystal dimension. In the analysis of the far-infrared reflection spectra, numerical model for calculating the reflectivity coefficient of layered system, which includes film with nanocrystallite inclusions (modeled by Maxwell–Garnet approximation) and substrate, has been applied. UV–VIS spectroscopy and photoluminescence spectroscopy are employed to estimate direct and indirect band gap of CuSe2.

Optical Properties and Electron–Phonon Interactions of CdTe1-XSex(In) Single Crystal

The far-infrared reflectivity spectra of CdTe0.97Se0.03 and CdTe0.97Se0.03(In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spacious distribution of free carrier as well as their influence on the plasmon–phonon interaction. We found that the long wavelength optical phonon modes of CdTe1-xSex mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm−1 is observed. In both samples, a surface layer with a low concentration of free carriers is formed.

Vibrational Spectroscopy of SOP Modes in ZnO Doped with CoO, MnO and Fe2O3

Nanocrystalline samples of ZnO doped with CoO, MnO and Fe2O3 were synthesized by traditional wet chemical method followed by calcinations. Samples where characterized by X-ray diffraction to determine composition of the samples (ZnO, Co3O4, Mn3O4, ZnMn2O4, ZnMnO3, ZnFe2O4 and Fe2O3) and the mean crystalline size (from 8 to 156 nm, depending on the sample). In this paper we report the experimental Raman scattering spectra (from 100 to 1600 cm−1 and from 200 to 1600 cm−1) with surface optical phonons (SOP) in range of 496−575 cm−1. This shows the change of position of SOP modes with crystalline size and change of intensity of SOP modes with change of concentration of doping elements. The phonon of registered phase’s exhibits effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.

Optical Properties of Plastically Deformed Copper: Ellipsometry and Raman Study

In this paper, we used Raman spectroscopy and spectroscopic ellipsometry to investigate optical properties of plastically deformed copper. Chemically pure copper prepared in a sample of square cross section (10 × 10 mm2) and about 50 mm long was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing. Information about microstructure with ultrafine grains is obtained by atomic force microscopy. The structure of the sample surface—the copper oxide and surface roughness over-layer—was registered by spectroscopic ellipsometry. By Raman spectroscopy, two types of lines are registered: narrow, with the width ∼7 cm−1; and wide, ∼40 cm−1, which implies that nano-sized crystal structures related to three-dimensional amorphous boundary spaces exist in the specimen.

INFRARED AND RAMAN SPECTROSCOPY STUDY OF ANTIMONY DOPED BARIUM TITANATE PREPARED FROM ORGANOMETALLIC COMPLEX

Pure and antimony doped barium titanate powders were prepared by polymeric precursors method through Pechini process, which was carried out as a three-stage process from organometallic complex. Obtained powder was pressed into pellets and sintering was performed at 1300 °C for 8 h with heating rate of 10 °C min-1. The formation of phase and crystal structure of pure and Sb-doped barium titanate was approved by XRD analysis, Raman and IR spectroscopy. The influence of Sb doping on microstructure of barium titanate ceramics was investigated by scanning electron microscopy. Therefore, the relation between grain size, structure and properties of the obtained ceramics was analyzed. Influence of Sb doping on barium titanate properties was discussed.