Physics

Permanent URI for this collectionhttp://repository.kln.ac.lk/handle/123456789/3750

Browse

Now showing 1 - 20 of 248

Direct Observation of Surface States at the TiO2 Electrolyte Interface
(Journal of Electrochemical Society, 1981) Siripala W; Tomkiewicz M
Relaxation Spectrum Analysis was suggested as a general technique for mearsurements of charge accumulation modes and their corresponding relaxation times at the space charge layer of a semiconductor with strong emphasis on semiconductor liquid junction interfaces. Among all the reported results(2-4),none was, as yet, confirmed by an independent technique.
The Interrelation Between the Potential Distribution and the Dark Charge Transfer Across n-TiO2 - Aqueous Electrolyte Interface
(Symposia on Photoelectrochemical Process and Measurements Techniques for Photoelectrochemical Solar Cells, 1981) Tomkiewicz M; Siripala W
Interactions Between Photoinduced and Dark Charge Transfer across n-TiO[sub 2]Aqueous Electrolyte Interface
(Journal of Electrochemical Society, 1982) Siripala W; Tomkiewicz M
An intermediate of the dark reductive reaction of with an aqueous electrolyte was identified. This intermediate forms surface states on the semiconductor. The energy and surface concentration of these states were evaluated by impedance measurements. We report on sub?bandgap photoresponse due to excitation of electrons from the valence band to these states. The potential?photocurrent behavior of these states is unique and is being fully accounted for by the proposed mechanism of their dynamic formation and annihilation.
The specific heat capacity of GE varnish (200-400K)
(Journal of Physics E: Scientific Instruments, 1982) Jayasuriya, K.D.; Campbell, S.J.; Stewart, A.M.
The specific heat capacity of GE varnish, a commonly used adhesive and insulator, is found to vary linearly with temperature over the range 200-330K. The deviation of the heat capacity above this temperature is associated with the approach to the curing temperature of this resin.
The critical specific heat of terbium
(Journal of Physics F: Metal Physics, 1983) Jayasuriya, K.D.; Gopal, E.S.R.; Campbell, S.J.; Stewart, A.M.
Specific heat measurements have been carried out on a high-purity single crystal of terbium of mass 3.734 g between temperatures of 200 and 400K. The data around the Neel temperature TN, have been analysed in terms of the equation C+or-=(A+or-/ alpha +or-) mod t mod - alpha +or-(1+E+or- mod t mod x+or-)+B+or-+D+or-t where t=(T-TN+or-)/TN+or-. The parameters obtained from our best fit are alpha += alpha =-0.20+or-0.03, A+/A-=0.58+or-0.34, B+=B-=21.68+or-13.93 J mol-1 K-1, E+/E-=-2.06+or-4.12, D+=D-=4.99 J mol-1 K-1 and TN+=TN-=229.9503+or-0.0035K. This fit is valid in the critical regions -3.4
Electrolyte Electroreflectance Study of CdIn2Se4 Liquid Junction Solar cells
(American Physical Soc. Meeting, Los Angeles,USA, 1983) Tomkiewicz M; Siripala W
Observation of Intrinsic Surface States at the TiO2 Aqueous-Electrolyte Interface by Sub Band-Gap Electroreflectance Spectroscopy
(Physical Review Letters, 1983) Siripala W; Tomkiewicz M
Surface states were detected with sub?band-gap electroreflectance spectroscopy in the presence of electrolytes that can adsorb on the surface of TiO2. The energy of these states is located 1.3 eV below the conduction band and they can be detected only in the weak accumulation mode. The potential distribution at the interface as a function of the electrolyte was investigated by impedance spectroscopy. These results were interpreted in terms of "intrinsic" surface states of the unsolvated surface.
Surface Recombination at n-TiO2 Electrodes in Photoelectrolytic Solar Cells
(Journal of Electrochemical Society, 1983) Siripala W; Tomkiewicz M
The photocurrent?potential behavior of photoelectrodes in liquid junction configuration is investigated. The Gartner model is modified to include the surface recombination. Impedance and photocurrent?potential measurements reveal the presence of a high density of surface states at the interface, covering more than half a monolayer. A total of four parameters are used to characterize the surface states. Two of these parameters appear in the expression for both the quantum efficiency?potential dependence and the expression for the capacitance due to these states. The other two parameters appear separately in conjunction with each experiment. The model is tested by perturbating the steady state of the system by strong background illumination which induces higher injection rate of carriers. The effect of the background illumination is interpreted as the change in the equilibrium distribution of the surface states which will result in the increase in surface recombination of photocarriers.
Characterization of Surface States at a Semiconductor Electrolyte Interface by Electroreflectance Spectroscopy
(Journal De Physique, 1983) Tomkiewicz M; Siripala W
Supra bandgap and subband gap Electrolyte Electroreflectance is being used to characterize surface states at semiconductor liquid interfaces. The surface states can manifest themselves either through direct optical transitions as in the case of n - TiO2 - aqueous electrolyte interface or through their effect on the response of the Fermi level to small changes in the electrode potential as in the case of single crystal CdIn2Se4 in polysulfide solutions.
Electroreflectance and photoinduced charge seperation in eletrochemically doped trans-polyacetylene liquid junction device
(Chemical Physics Letters, 1983) Peramunage, D.; Tomkiewicz, M.; Ginley, D.S.
Liquid junction solar cells, made from electrochemically doped p-type trans-polyacetylene in contact with aqueous solution of methyl viologen, were constructed. The turn-on potential was found to be +1.0 V versus SCE. The spectral response showed low quantum efficiency (?10?4) for photoinduced charge separation with a threshold around 1.5 eV. The electroreflectance showed the presence of two transitions at 1.45 and at 1.6 eV. A tentative assignment of these transitions is proposed.
Specific heat study of the transition from ferromagnetism to antiferromagnetism in terbium
(Journal of Magnetism and Magnetic Materials, 1984) Jayasuriya, K.D.; Campbell, S.J.; Stewart, A.M.; Gopal, E.S.R.
The specificheat of single crystal terbium has been measured over the range 200?400 K. A value for the latent heat of (13.6 � 0.6) J mol?1 is obtained at the first order antiferromagnetic to ferromagnetic transition temperature Tc = (221.45 � 0.03) K. A temperature hysteresis of (0.24 � 0.03) K is observed in the transition.
Electrolyte Electroreflectance of Single-Crystal CdIn2Se4 in a Photoelectrochemical Solar Cell
(Journal of Electrochemical Society, 1984) Tomkiewicz M; Siripala W
Electroreflectance was used to evaluate the optical properties of in polysulfide solution, before and after photoetching. The variations of signal intensity with electrode potential were used to trace the band position as a function of potential. It was found that the optical transition fits a three?dimensional parabolic model of the density of states, with direct transition at 1.825 eV. When the crystal is photoetched, there is a shift of 98� in the phase factor and a decrease in the broadening parameter from 0.42 to 0.32 eV. By monitoring the signal intensity with potential, it was shown that, irrespective of photoetching, the Fermi level is pinned as reverse bias conditions are approached. The pinning is ascribed to surface states that most likely originate from the adsorption of the electrolyte. The variation of the flatband potential with electrode potentials was calculated and was determined to occur because of the changes in the potential of the Helmholtz layer; the energy distribution and the density of states, which are responsible for those changes in potential of the Helmholtz layer, were also calculated.
A specific heat study of natural haematite around the Morin transition and the effects of entrapped water
(Journal of Physics and Chemistry of Solids, 1985) Jayasuriya, K.D.; Stewart, A.M.; Campbell, S.J.
The Morintransition in samples of natural haemitite has been examined by specificheat and M�ssbauer measurements. Specificheat measurements on as-received samples reveal an anomaly at ? 273.2 K and irregular behaviour at higher temperatures. However, heat treatment of samples demonstrated that these effects were due to water trapped inside the natural specimens. No anomaly due to the Morintransition was observed in the specificheat although the expected changes in the M�ssbauer hyperfine parameters were observed for the different magnetic phases below and above the Morintransition. The results are consistent with a coexistence of the two phases and a spread of temperatures ? 40 K over which the transitions take place throughout the material of purity 99.6 wt%.
Magnetic transitions in dysprosium: A specific-heat study
(Physical Review B, 1985) Jayasuriya, K.D.; Campbell, S.J.; Stewart, A.M.
The magnetic transitions of the heavy rare-earth metal dysprosium have been examined by specific-heat measurements using a small single crystal (0.6782 g) and a large polycrystalline sample (43.25 g). A value for the latent heat of 39.1�1.5 J mol-1 is obtained at the discontinuous transition from ferromagnetism to helical antiferromagnetism, and a temperature hysteresis of 1.2�0.4 K is observed at this transition. The data around the continuous transition from helical antiferromagnetism to paramagnetism at the N�el temperature TN=179.90�0.18 K have been analyzed in terms of the equation & &)+B�+D�t, where t=(T-TN)/TN. Agreement to within two standard errors was obtained for the critical parameters of the single-crystal and polycrystalline data. The value of the critical exponent ? obtained from the data of the single crystal is 0.24�0.02, whereas that obtained from the data of the polycrystalline sample is 0.14�0.05. We find that the scaling law ?+=?- is valid for the dysprosium critical data. In order for the condition B+=B-, predicted by theory, to be satisfied we found it necessary to include the confluent singular term in E in our fit. The values of ? that we obtain are not close to the predictions of renormalization-group theory for magnetic systems with short-range exchange interactions.
Specific heat study of a holmium single crystal
(Journal of Physics F: Metal Physics, 1985) Jayasuriya, K.D.; Campbell, S.J.; Stewart, A.M.
The magnetic transition at the Neel temperature, TN, of the heavy rare-earth metal holmium has been examined by specific heat measurements. The transition at TN=(132.245+or-0.080)K is found to be continuous and the data around TN have been analysed in terms of the equation C+or-=(A+or-/ alpha +or-) mod t mod - alpha +or-(1+E+or- mod t mod x+or-)+B+or-+D+or-t where t=(T-TN)/TN. The value of the critical exponent alpha is 0.27+or-0.02 for the data in the critical regions -3.8
Electrolyte electroreflectance study of surface optimization of n-CuInSeâ in photoelectrochemical solar cells
(Journal of Electrochemical Society, 1986) Shen, Wu-Main; Siripala W; Tomkiewicz, M.; Cahen, D.
Electrolyte electroreflectance is used to show that the main effect of Br2/MeOH etching of CuInSe2 is to remove the pinning of the Fermi level, which is due to a monolayer of states located 0.17V positive to the potential of CuInSe2 the solution. The flatband potential of in polysulfide solution was found to be ?0.62V vs. the solution potential, while in polyiodide solution it is shifted to ?0.70V vs. the potential of that solution. This shift can explain some of the improvement in performance in polyiodide compared to polysulfide. The bandgap of CuInSe2 was found to be a direct transition at 1.01 eV with a three?dimensional critical point.
Optical Investigation of the Electrodeposited Cuprous Oxide Film Electrodes using Photocurrent Spectroscopy
(1986) Siripala W
Thermally grown Cuprous Oxide has known as a p-type semiconductor and the p-type conductivity is attributed to the Copperion vacancies created in the crystal lattice during the oxide formation. However, we have observed, for the first time, that the cathodically deposited Cu2O films on various metal substrates produce n-type photoconductivity. Photoelectrodes were used in a photoelectrochemical call containing an aqueous electrolyte. Photocurrent-potential behaviour demonstrate that the photoresponse is anodic and the analysis of the spectral response measurements reveal thet Cu2O has a direct bandgap of 2.0 eV. Tenactive assignment of Oxygen ion vacancies in the electrodposited cupprous Oxide films, which would result in n-Cu2O, is proposed.
The specific heat of samarium metal (80-400 K)
(Materials Chemistry and Physics, 1986) Jayasuriya, K.D.; Stewart, A.M.; Campbell, S.J.
We have measured the specific heat of several high purity polycrystalline specimens of samarium metal over the temperature range 80 K to 400 K. A broad peak is observed at TNh ~106K, the temperature at which antiferromagnetic ordering first sets in with ordering of the moments on hexagonal sites. This behaviour contrasts with the sharp peak observed by previous workers on samarium samples of lower purity.
Observation of n-type Photoconductivty in Electrodeposited Copper Oxide Film Electrodes in a Photoelectrochemical cell
(Solar Energy Materials, 1986) Siripala, W.; Jayakody, J.R.P.
Copper oxide films were cathodically deposited on various metal substrates (Cu, Ti and Pt) using a basic solution of CuSO4, and it is found that they produce n-type photoconductivity in a photoelectrochemical cell. The photoresponse of these films is more pronounced than the previously known thermally grown p-Cu2O films, and the n-type behaviour could be converted to p-type by heating the samples in air. It is tentatively proposed that oxygen ion vacancies in the electrodeposited copper oxide films would result in n-Cu2O.
Thermally Stimulated Current-Voltage Characteristics of Cu2O/CuxS Diode
(1988) Kalingamudali, S.R.D.; Siripala, W.
A simple method was developed to fabricate a p-n junction diode of CU20/CuxS and it Was observed that the stability as well as the current-voltage characteristics of the diode could be improved significantly by controlling the system parameters at the fabricating stage. The diode characteristics of the fabricated diode was compared with a commercial germanium diode. High temperature measurements under the reverse bias conditions revealed that there are two distinct current transport mechanisms that would lead to high leakage current across the junction. Namely, two distinct current peaks were observed at the reverse bias. This was interpreted as the thermally enhanced tunneling at the junction due to the existance of defect interface states. We beleive that proper surface treatment might reduce the density of interface state, and then lead to better diode characteristics. Comparing with the ideal diode equation, it was observed�that the current transport mechanisms are complicated in the CU20/CuxS diode. �