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Item Computational Study of I-V characteristics of ITO/Cu2 O/Metal junctions, Technical Session of Institute of Physics(Processing of the Technical Session of Institute of Physics, 1999) Wijesinghe, W.M.P.L.; Siripala, W.; Jayasuriya, K.D.; Kalingamudali, S.R.D.A theoretical model for current-voltage (I-V) characteristics of back-to-back diode systems was developed using the ideal diode equation. A computer model was developed using the language C++ to fit the experimental data to the theoretical equation and to determine the ideality factors and reverse saturation currents of each diode. This model was tested with commercial back-to-back diode systems. The values obtained for the above parameters from the theoretical fits were in very good agreement with the standard values. The experimental I-V characteristics data obtained for fabricated ITO/Cu2O/Metal (Au, Ag and Hg) structures were fitted to the model and values for the relevent parameters were obtained. These values indicate that the fabricated systems are back to back diodes except the ITO//Cu2O/Hg structure. Using this model, a good understanding of I-V characteristics of metal-semiconductor-metal diodes can be gained and thereby the quality of junction devices can be tested.Item A Home Made Double Slab Pyranometer for Irradiance Measurements(Proceedings of the 44th Technical Session of the Sri Lanka Association for the Advancement of Science (SLAAS), 1988) Punyasena, M.A.; Jayasuriya, K.D.Item ITO/ u-Cu2O/ p-Cu2S thin film solar cell(Srilanka association for the advancement od science proceedings of 53rd Anuual Session., 1997) Perera, L.D.R.D.; Wijesundara, R.; Jayasuriya, K.D.; de Silva, K.T.L.; Jayanetti, J.K.D.S.Item An experimental determination of the effect of pressure on the Fe3+/?Fe ratio of an anhydrous silicate melt to 3.0 GPa(American Mineralogist, 2006) Jayasuriya, K.D.; O-Neill, H.S.C.; Berry, A.J.; McCammon, C.C.; Campbell, S.J.; Foran, G.The effect of pressure on the Fe3+/?Fe ratio of an anhydrous andesitic melt was determined from 0.4 to 3.0 GPa at 1400 �C with oxygen fugacity controlled internally by the Ru + RuO2 buffer. Values of Fe3+/?Fe were determined by M�ssbauer spectroscopy on quenched glasses with a precision of �0.01, one standard deviation. This precision was verified independently by XANES spectroscopy of the same samples. The XANES spectra show a systematic increase in energy and decrease in intensity of the 1s ? 3d transition with increasing pressure. The results to 2.0 GPa are in good agreement with predictions from density and compressibility measurements fitted to a Murnaghan equation of state, but the datum at 3.0 GPa has higher Fe3+/?Fe than predicted from the trend established by the lower-pressure data. This might be due to a coordination change in Fe3+ at high pressure; although there is no evidence for this in the M�ssbauer spectra, such a change could account for the change in intensity of the 1s ? 3d transition in the XANES spectra with pressure.Item A Mössbauer study of the oxidation state of Fe in silicate melts(American Mineralogist, 2004) Jayasuriya, K.D.; O-Neill, H.S.C.; Berry, A.J.; Campbell, S.J.Fe3+/?Fe ratios were determined from M�ssbauer spectra recorded for a series of 17 anorthite-diopside eutectic glasses containing 1 wt% 57Fe2O3 quenched from melts equilibrated over a range of oxygen fugacities from fO2~ 105 bars (Fe3+/?Fe = 1) to 10?13 bars (Fe3+/?Fe = 0) at 1682 K. Fe3+/Fe2+ was found to be proportional to fO2 to the power of 0.245 � 0.004, in excellent agreement with the theoretical value of 0.25 expected from the stoichiometry of the reaction Fe2+O + 0.25 O2 = Fe3+O1.5. The uncertainty in the Fe3+/?Fe ratios determined by M�ssbauer spectroscopy was estimated as � 0.01 (1?) from the fit of the data to the theoretical expression, which is significantly less than that quoted for previous measurements on silicate glasses; this results from fitting the spectra of a large number of systematically varying samples, which allows many of the ambiguities associated with the fitting procedure to be minimized. Fe3+/?Fe ratios were then determined for samples of the anorthite-diopside eutectic composition equilibrated at selected values of fO2, to which up to 30 wt% Fe2O3 had been added. Fe3+/?Fe was found to vary with ?Fe (or FeOT), but both the 1 wt% and high FeOT data could be satisfactorily fit assuming the ideal stoichiometry (i.e., Fe3+/Fe2+ ?fO2 1/4) by the inclusion of a Margules term describing Fe2+-Fe3+ interactions. The large negative value of this term indicates a tendency toward the formation of Fe2+-Fe3+ complexes in the melt. The resulting expression, using the ideal exponent of 0.25, gave a fit to 289 Fe3+/?Fe values, compiled from various literature sources, of similar quality as previous empirical models which found an exponent of ~0.20. Although the empirical models reproduce Fe3+/?Fe values of glasses with high FeOT reasonably well, they describe the data for 1 wt% FeOT poorly. The non-ideal values of the exponent describing the dependence of Fe3+/?Fe on fO2 at high FeOT are an artifact of models that did not include a term explicitly to describe the Fe2+-Fe3+ interactions. An alternative model in which Fe in the silicate melt is described in terms of three species, Fe2+O, Fe3+O1.5, and the non-integral valence species Fe2.6+O1.3, was also tested with promising results. However, at present there is no model that fits the data within the assessed accuracy of the experimental measurements.Item XANES calibrations for the oxidation state of iron in a silicate glass(American Mineralogist, 2003) Jayasuriya, K.D.; Berry, A.J.; O?Neill, H.S.C.; Campbell, S.J.; Foran, G.J.Fe K-edge X-ray absorption near edge structure (XANES) spectra were recorded for a series of anorthite-diopside eutectic glasses containing 1 wt% 57Fe2O3 quenched from melts equilibrated over a range of oxygen fugacities at 1409 �C. The Fe3+/?Fe ratios were determined previously by 57Fe M�ssbauer spectroscopy and vary between 0 (fully reduced) and 1 (fully oxidized). Using the M�ssbauer results as a reference, various methods for extracting Fe3+/?Fe ratios from XANES spectra were investigated. The energy of the 1s ? 3d pre-edge transition centroid was found to correlate linearly with the oxidation state. Correlations also exist with the energy of the K absorption edge and the area of peaks in the derivative spectrum associated with the 1s ? 4s and crest (1s ? 4p) transitions. The Fe3+/? Fe ratios determined from linear combinations of end-member spectra (Fe3+/? Fe ~0 and ~1) were found to deviate significantly from the M�ssbauer values. This may indicate the susceptibility of this method either to errors arising from the treatment of the background or to changes in Fe2+ or Fe3+ coordination with the Fe3+/? Fe ratio. The general applicability of any XANES calibration for determining oxidation states is limited by variations in the Fe coordination environment, which affects both the intensity and energy of spectral features. Thus previous calibrations based on mineral spectra are not applicable to silicate glasses. Nevertheless, systematic trends in spectral features suggest that Fe3+/? Fe values may be obtained from XANES spectra, with an accuracy comparable to M�ssbauer spectroscopy, by reference to empirical calibration curves derived from compositionally similar standards.Item Surfactant assisted ball-milling of barium ferrite(IEEE Transactions on Magnetics, 1994) Jayasuriya, K.D.; Wu, E.; Kaczmarek, W.A.; Campbell, S.J.The effects of wet-milling barium ferrite in the presence of cationic or anionic surface active substances have been investigated by X-ray diffraction and Mossbauer spectroscopy measurements. Evidence for superparamagnetic relaxation of fine particles, both in the surfactant assisted ball-milled samples and in samples dry-milled in air is obtained from the room temperature and 4.2 K Mossbauer spectra. The similarity between samples milled at pH 3 with the cationic or anionic surfactants is due to electrostatic interactions of the surfactants' hydrocarbon groups with the positively charged barium ferrite surfaceItem A Mössbauer effect study of barium ferrite ball-milled in air(Hyperfine Interactions, 1994) Jayasuriya, K.D.; Kaczmarek, W.A.; Wu, E.; Campbell, S.J.The effects of dry-milling BaFe12O19 in air for periods of 190, 360, 590, 690 and 1000 h have been investigated by X-ray diffraction and M�ssbauer effect measurements. The sizes of the BaFe12O19 particles decrease on milling, as expected, although a partial decomposition of BaFe12O19 to ?-Fe2O3 is found to take place on extended milling (1000 h). The room temperature M�ssbauer spectra are consistent with superparamagnetic relaxation associated with the fine BaFe12O19 and ?-Fe2O3 particles. The X-ray diffraction patterns of all the milled samples exhibit features indicative of a disordered structural state, consistent with the nanoscale particles and a nanostructured state.Item A Mössbauer study of ball-milled Co?Fe?Si?B: II: with surfactants(Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993) Jayasuriya, K.D.; Campbell, S.J.; Calka, A.; Jing, J.The use of a range of organic surface active substances in the ball milling of Co?Fe?Si?B has been studied by X-ray diffraction and M�ssbauer effect measurements. Effects characteristic of superparamagnetic relaxation of the magnetic moments are observed in the M�ssbauer spectra of samples milled with either an anionic or a cationic surfactant. This behaviour is linked with the decreased particle size and high shape homogeneity of surfactant-aided milled samples compared with the amorphous powders resulting from standard dry milling. Impurity iron-oxide phases are also found to occur in samples milled in the presence of surfactants.Item A Mössbauer study of ball-milled Co?Fe?Si?B: I: dry milling(Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993) Jayasuriya, K.D.; Campbell, S.J.; Calka, A.; Jing, J.X-ray diffraction and M�ssbauer effect measurements of ball-milled Co?Fe?Si?B material which had first been re-crystallized from amorphous melt-spun ribbon are presented. Fully amorphous powders have been obtained after only 50 h milling with a ball-to-powder ratio of BPR ? 84. The amorphous powders exhibit chemical and structural inhomogeneities compared with the starting melt-spun amorphous ribbons.