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Raman scattering and photoluminescence (PL) emission of Cu[sub x]Ga[sub y]Se[sub 2] thin films, grown by metalorganic chemical vapor deposition (MOCVD) on GaAs (100) and by physical vapor deposition (PVD) on Glass/Mo substrates, were studied at room and low temperatures as a function of composition. Line width changes of Raman bands in the temperature range 20–300 K indicate the formation of a more disordered Cu[sub x]Ga[sub y]Se[sub 2] phase with increasing Ga content. It is most likely that Raman bands observed at 193 and 199 cm-1 in the Ga-rich samples at low temperatures are associated with defect-related interface modes. The intensity increase of these bands and the photoluminescence intensity enhancement may be correlated to an increase in defect concentration in the Ga-rich phase. The radiative recombination in defect-rich Ga-rich samples with a higher degree of disorder apparently supports the PL emission. The observed changes are more pronounced in MOCVD than in PVD grown films. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structural and optical properties of nitrogenated amorphous carbon films, grown by rf-magnetron sputtering on silicon substrates, were studied by Raman and photoluminescence (PL) spectroscopy as a function of the nitrogen concentration and the substrate bias voltage V[sub b]. For films deposited with V[sub b]=10 V, the photoluminescence emission was most intense at nitrogen concentrations in the carrier gas of 25% (75% Ar), while the intensity ratio I(D)/I(G) of the Raman bands of disordered graphite (D band) and graphite (G band) partially substituted by nitrogen exhibited a minimum simultaneously observed with a minimum of G-band frequency and a maximum of G-band width. Changes in spectral characteristics of Raman scattering at a concentration of 25% (≅30 at %) are indicative of an increase of sp³-bonded fraction and disorder. PL-enhancement coincides, in this case, with structural changes and is probably correlated to the substitution of nitrogen in the tetrahedraly bonded amorphous matrix. In the case of films deposited in a pure nitrogen atmosphere, N[sub 2] = 100%, no significant PL-intensity changes appeared to exist between films deposited at low positive (10 V) and highly negative (-200 V) substrate bias. After several months of sample storage in air, samples grown at negative V[sub b] were found to preserve their structural and optical properties, while films grown at positive bias (V[sub b]=10) and nitrogen concentrations in the carrier gas above 70% (≅40 at %) delaminated. [ABSTRACT FROM AUTHOR]

Presents a Raman and photoluminescence study, on silicon (Si) quantum wires fabricated on crystalline silicon (100). In-depth look at the splitting of the Raman phonon; Comparison of the Raman spectrum of silicon nanowires with the Raman spectrum of virgin crystalline silicon; Examination of the polarization dependence of the photoluminescence emission.

Abstract: The structural properties of Ge doped polycrystalline CuGaSe2 films with potential applications in solar cell device technology have been studied by Raman spectroscopy at 300 K and by Photoluminescence (PL) spectroscopy at 300 K and 2 K. The films were intentionally doped with max. 200 keV Ge ions using one- and three-stage ion implantation processes. The Raman spectra of as grown films are dominated by the A1-mode (breathing mode) of the CuGaSe2 absorber at 184 cm−1. It was found, that in doped films the Raman mode intensities are reduced and the B2-modes (TO at 249 cm−1 and LO at 273 cm−1) take over. This implies an increase in structural disorder induced, probably, by bond reorientation effects that favor excitation of asymmetric lattice vibrations (B2) instead of the symmetric ones (A1). Moreover, it was found, that the Raman bands of doped films exhibit asymmetric broadening representative of a Fano line-shape. Changes were more pronounced in films doped at one-stage. The PL-emission of films subjected to one-stage process was enhanced, which supports an increase in structural disorder particularly for these films. On the contrary, for films doped in three-stages, the PL bands are less intensive and the Raman bands are less broadened. [Copyright &y& Elsevier]

The structural and optical properties of technologically interesting pyrolytic carbons formed from cured novolac resin and cured novolac/biomass composites were studied by X-Ray Diffraction Analysis (XRD), and Fourier Transform Infrared (FTIR), Raman and Photoluminescence (PL) spectroscopy. Pyrolysis of the cured materials took place at temperatures in the range 400-1000 °C. The most important weight loss, shrinkage and structural changes of pyrolyzed composites are observed at temperatures up to 600 °C due to the olive stone component. In the same temperature range, the changes in pyrolyzed novolac are smaller. The spectroscopic analysis shows that novolac pyrolyzed up to 900°C has less defects and disorder than the composites. However, above 900°C, pyrolyzed novolac becomes more disordered compared to the pyrolyzed composites. It is concluded that partial replacement of novolac by olive stone in the composite materials leads to the formation of a low cost, good quality product. [ABSTRACT FROM AUTHOR]

The optical properties of carbon materials formed by pyrolysis of novolac-resin/biomass composites were studied by Raman, photoluminescence (PL) and (modulated) photoreflectance (PR) spectroscopy in dependence of the pyrolysis temperature and the heating rate. In the Raman spectra, the frequency, width and intensity ratio of the disordered graphitic D-band to the graphitic G-band, ID/IG, indicate an increase in ordered sp2-bonds in composites pyrolyzed at 1000 °C in comparison with those at lower pyrolysis temperatures. Moreover, the intense PL, observed at 2.2 eV for pyrolysis temperatures in the range 400–600 °C, is significantly decreased at temperatures ≥800 °C, which implies that the materials pyrolyzed at higher temperatures have less defects. According to the results of Raman-studies and complementary FTIR-studies, the material pyrolyzed at 1000 °C exhibits spectral characteristics similar to those of activated charcoal. A weak PR-band observed at 2 eV in the spectra of activated charcoal gives an indication of the (optical) band gap of charcoal and related composite materials. Materials pyrolyzed at high temperatures (≥1000 °C) are expected to be suitable for electrochemical applications. [Copyright &y& Elsevier]

The structural and optical properties of amorphous carbon films, grown by r.f.-magnetron sputtering on silicon substrates, were studied by Raman and photoluminescence spectroscopy in dependence of the substrate bias voltage Vb. The intensity ratio I(D)/I(G) of the Raman bands of disordered graphite (D-band) and graphite (G-band) decreased significantly (a) by reversing bias from positive (+10 V) to negative (−20 V) and (b) by reducing the negative bias from −200 to −120 V. The intensity ratio I(D)/I(G) exhibited an almost flat minimum in the bias-region from −120 to −20 V which is indicative of an increase of the fraction of sp3-bonded material. In the same bias-range, photoluminescence emission at 2.2–2.5 eV appeared blue-shifted and more efficient. Changes in photoluminescence energy are attributed to increase of sp3 content of the films becoming more transparent when deposited at substrate-bias between −20 and −120 V. Increase of photoluminescence intensity is probably related to increased number of defects due to increasing structural disorder. [Copyright &y& Elsevier]