R.P. Wijesundera

Tunable optoelectronic properties of CBD-CdS thin films via bath temperature alterations

The tunability of the band-gap value and electron affinity of the n-CdS by adjusting the growth parameters is very important as it paves the way to improve the efficiency of CdS-based solar cells by adjusting the band lineup with other p-type semiconductors. In this respect, polycrystalline n-CdS thin films were grown on FTO glass substrates at different bath temperatures (40–80 °C) by the chemical bath deposition technique. The structural, morphological and optoelectronic properties of CdS thin films were studied using x-ray diffraction, scanning electron microscopy, UV-Vis spectrometry, profilometry, atomic force microscopy, photoelectrochemical and Mott–Schottky measurements. Absorption measurements reveal that an energy-gap value of n-CdS can be adjusted from 2.27 to 2.57 eV and Mott–Schottky measurements indicate that the flat-band potential is increased from −699 to −835 V with respect to a Ag/AgCl electrode by decreasing the deposition bath temperature from 60 to 40 °C. This tunability of optoelectronic properties of n-CdS is very useful for applications in thin film solar cells and other devices.

Structural properties of the red-color overglazes on the Kakiemon-style porcelains produced in the later 17th century by means of X-ray diffraction (I)

As porcelanas do estilo Kakiemon produzidas nas areas de Arita (SAGA) na ilha Kyushu sao porcelanas japonesas famosas. As tecnicas de produzir porcelanas com os elegantes e brilhantes vidrados de cores vermelho brilhante foram encontradas e desenvolvidas nos anos 1650 (inicio do periodo Edo) primeiramente em fornos Kakiemon. Vidrados vermelhos e vidrados transparentes de porcelanas do estilo Kakiemon foram investigadas por meio de difracao de raios X com radiacao sincrotron. Os resultados sugerem que o brilho de cor vermelha e principalmente induzido pela correlacao microestrutural entre finas particulas de α-Fe2O3, como elementos emissores de cor vermelha, alem de outros oxidos como SiO2, Al2O3, CaO, KNaO, e PbO. A estabilidade dos vidrados na superficie da porcelana com vidrado vermelho esta relacionada com a fusao interfacial dos vidros existentes no vidrado vermelho calcinado e o vidrado transparente do corpo da porcelana. As antigas tencias de porcelana do estilo Kakiemon sao claramente baseadas nas propriedades microestruturais do material dos vidrados sobrepostos, os sub-postos e os transparentes, embora as tecnicas tenham sido encontradas e desenvolvidas experimental e acidentalmente no periodo Edo.

Correlation between glaze-colors and structural properties of the HIZEN celadons produced in the Edo period of Japan, by means of X-ray diffraction (І)

HIZEN celadons produced at Arita and Imari areas in Japan from 1630s to 1790s (Edo period) have been investigated by means of X-ray fluorescence analysis, and X-ray diffraction and X-ray absorption spectra using synchrotron radiation. It is found that, in the HIZEN celadons, the color brightness of the celadon glazes depends on the structural property of the raw basic ceramics taken at Imaizumi (Arita) and Ohkwachi (Imari), where the former is mainly Quartz-SiO2, and the later is Sanidine ((K,Na)Si3O8). It is confirmed that CaCO3 of natural wood ash added artificially into the raw celadon ceramics makes a glassy glaze on the surface of the basic body of the HIZEN celadons. Transition-metal ions (Cr, Cu, Zn) of very small amount are detected in the celadon glazes, in addition to Fe and Mn of small amount. It is considered that Cu and Cr are related to the color brightness of green-brown and blue-green in the HIZEN celadon glazes, respectively.

Local structures and electronic band states of α−Fe2O3 polycrystalline particles in the glazes of the HIZEN celadons produced in the Edo period of Japan, by means of X-ray absorption spectra (II)

HIZEN celadon glazes produced in 1630s to 1790s (Edo period, Japan) have been investigated by means of X-ray absorption spectra (XAS) near a Fe-K edge by using synchrotron radiation and a Mossbauer spectrum. The XAS suggest that the local structure around Fe2O3 fine powders is slightly different between the Izumiyama ceramics of mainly the Quartz-SiO2 and Ohkawachi ceramics of mainly the feldspar of (K,Na)Si3O8 (Sanidine), and that the glazes of the HIZEN celadons include the Fe2O3 fine powders in the glassy state, though the X-ray diffraction patterns of the glassy celadon glazes do not show any peaks of the Fe2O3 structure. The Mossbauer spectrum suggests that the celadon glaze of Seiji (m) includes only Fe3+ ions, but not Fe2+ ions. This indicates the existence of Fe2O3 in the celadon glaze. It is interpreted that the colored brightness of the HIZEN celadons is induced by the structural properties of the used raw celadon ceramics and the other transition-metal ions of Cr, Cu, Zn in the celadon glazes, but not by the chemical reaction from Fe2O3 to FeO under the deoxidizing thermal treatment at higher temperature in a kiln.

Methods for improving n-type photoconductivity of electrodeposited Cu2O thin films

Electrodeposition technique is very useful for depositing n-type Cu2O thin films on various substrates. However, most of the reported n-type Cu2O thin film electrodes exhibit not only n-type photoactivity but also p-type photoactivity in photoelectrochemical cells. In this study, current–voltage characteristics and zero bias spectral response measurements were employed to investigate the possibilities to remove/minimize this unwanted p-type behaviour of n-type Cu2O thin films electrodeposited on Ti substrate. For this, prior deposition of Cu thin films on Ti substrate, low temperature annealing of Cu2O films in air and optimization of deposition bath pH were investigated. Growth of a very thin Cu film improved the n-type photosignal significantly and reduced the p-type photoresponse of the films. Films electrodeposited using an acetate bath of pH 6.1 produced only the n-type photoresponse. Low temperature annealing of Cu2O films in air improved the n-type photoresponse and it was found that annealing at 100 °C for 24 h produces the best result. These methods will be very useful to obtain electrodeposited Cu2O thin film with improved n-type photoactivity suitable for applications in thin film solar cells and other devices.

Correlation between the green-like coloration and the structural and electronic properties of celadon glazes (I)

Celadon glazes have been investigated by means of ordinary X-ray fluorescence analysis, and X-ray diffraction and X-ray absorption spectra using synchrotron radiation. The tentative glazes are prepared by mixing raw celadon materials of Masuda feldspar, limestone, quartz, and extra-added Fe2O3 of about 1wt% at thermal treatment till about 1300 °C. It is found that the glaze-colors strongly depend on the Fe2O3 amount and the high-temperature treatment under oxidizing and deoxidizing in the used kiln. Especially, the characteristic color of blue-green, white-green-brown, and white-blue-green result from complex hybridized 3d5L and 3d6L bands. The 3d6L hybridization is induced by an electronic exchange interaction between an empty 3d6 orbital of Fe ions and an occupied 2p orbital of surrounding O ions in the (SiO2 - Al2O3 - CaO) basic complex ceramics of glass-state under the deoxidizing thermal treatment.

Structural and electronic properties of iron oxides in the celadon glazes (II)

Celadon glazes have been investigated by means of an X-ray absorption spectrum (XAS) near a Fe-K edge by using synchrotron radiation and a Mossbauer spectrum. High-temperature treatments under CO-deoxidizing and oxidizing till about 1300 oC show the different glaze-color each other. The XAS analyses suggest that the deoxidized celadon glaze (Seiji A) and the oxidized one (Seiji C) have a modified α-Fe2O3 structure and an ideal one, respectively, but not FeO structure. The Mossbauer spectra also suggest that the celadon glaze-color depends on the hybridized 3d5L and 3d6L bands near an electronic Fermi level (EF), where the hybridization is induced by an electronic exchange interaction between 3d orbitals of Fe ions and 2p orbitals of surrounding O ions in the celadon glaze of glass-state.