Papers by A.R Kumarasinghe
Resonant Photoemission and STM Study of Anatase TiO_2(101) and (001)
STM, LEED and resonant UPS studies on single crystal anatase TiO2 (101) 1x1 and (001) 1x4 surface... more STM, LEED and resonant UPS studies on single crystal anatase TiO2 (101) 1x1 and (001) 1x4 surfaces are reported. The (101) surface exhibits a saw tooth like structure with triangular shaped large terraces with monatomic steps ˜ 4 Åhigh. Atomically resolved STM images show the (101) surface has a bulk (1x1) termination and is unreconstructed. A defect peak is observed near 1 eV BE in UPS and arises from the loss of surface oxygen. This state is clearly observed with STM and investigated using I/V measurements. Ti 3p-3d resonant photoemission of the surfaces are compared with rutile TiO2 (110) and features in the valence band at around 6 and 8 eV BE are assigned regions of weak and strong Ti-O hybridization respectively. Constant initial state spectroscopy reveals differences in cation-anion hybridization between the two surfaces, while repeated sputtering shows the (001) surface to be more resistant to the creation of O vacancies than the (101) face.
Surface Science, 2005
The adsorption of bi-isonicotinic acid (2,2 0 -bipyridyl-4,4 0 -dicarboxylic acid) on the surface... more The adsorption of bi-isonicotinic acid (2,2 0 -bipyridyl-4,4 0 -dicarboxylic acid) on the surface of anatase TiO 2 (1 0 1) and (0 0 1) single crystals has been investigated using XPS and NEXAFS. The searchlight effect of NEXAFS has been used to determine the adsorption geometry of BINA on these surfaces. The pyridyl rings in BINA are found to be oriented at 20°± 3°from the surface normal on the (1 0 1) surface and at 53°± 5°from the surface normal on the reconstructed (0 0 1) surface.
Resonant photoemission of anatase TiO2 (101) and (001) single crystals
Physical Review B, 2003
The resonant behavior of anatase TiO2 (101) and (001) surfaces has been investigated using synchr... more The resonant behavior of anatase TiO2 (101) and (001) surfaces has been investigated using synchrotron photoemission spectroscopy. The data are compared with earlier photoemission work from rutile TiO2(110) and calculations for bulk anatase in order to elucidate the degree of Ti-O hybridization in the valence band. The results for the (101) surface show good general agreement with bulk band-structure calculations.
Surface Science, 2007
The adsorption of the aromatic amino acid, phenylalanine on a TiO 2 rutile (1 1 0) single crystal... more The adsorption of the aromatic amino acid, phenylalanine on a TiO 2 rutile (1 1 0) single crystal surface has been investigated with photoemission and NEXAFS (near edge X-ray absorption fine structure) spectroscopy. The results indicate initial adsorption via the carboxylate group in a bidentate configuration with the phenyl ring oriented at approximately 25°to the surface normal. The amino group remains as NH 2 . Subsequent layers of phenylalanine appear to adsorb as neutral molecules with H-bonding between NH 2 and C@O groups.
Physical Chemistry Chemical Physics, 2013
The electronic structure and magnetism of nanocrystalline graphite prepared by ball milling of gr... more The electronic structure and magnetism of nanocrystalline graphite prepared by ball milling of graphite in an inert atmosphere have been investigated using valence band spectroscopy (VB), core level near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and magnetic measurements as a function of the milling time. The NEXAFS spectroscopy of graphite milled for 30 hours shows simultaneous evolution of new states at B284.0 eV and at B290.5 eV superimposed upon the characteristic transitions at 285.4 eV and 291.6 eV, respectively. The modulation of the density of states is explained by evolution of discontinuities within the sheets and along the fracture lines in the milled graphite. The magnetic measurements in the temperature interval 2-300-2 K at constant magnetic field strength show a correlation between magnetic properties and evolution of the new electronic states. With the reduction of the crystallite sizes of the graphite fragments, the milled material progressively changes its magnetic properties from diamagnetic to paramagnetic with contributions from both Pauli and Curie paramagnetism due to the evolution of new states at B284 and B290.5 eV, respectively. These results indicate that the magnetic behaviour of ball-milled graphite can be manipulated by changing the milling conditions.
Thin Solid Films, 1994
The photocurrent quantum efficiency of a polycrystalline cadmium sulphide anode in a KI + 12 solu... more The photocurrent quantum efficiency of a polycrystalline cadmium sulphide anode in a KI + 12 solution is found to increase on the deposition of a thin film of Prussian blue. It is suggested that the Prussian blue film traps holes generated in cadmium sulphide and efficiently transfers to the redox species in solution.
The Journal of Physical Chemistry C, 2013
Semiconductor Science and Technology, 1995
A photovoltaic cell was fabricated by sandwiching a monolayer of the pigment cyanidin adsorbed on... more A photovoltaic cell was fabricated by sandwiching a monolayer of the pigment cyanidin adsorbed on nano-porous n-TiO, film (deposited on conducting tin oxide glass) within a transparent polycrystalline film of p-CUI, filling the intercrystallite pores of the porous n-TiOn film. Photoexcited dye is found to inject electrons into n-TiO, and holes into p-CUI, generating photocurrents and Dhotovoltaaes that are imDressivelv hiah for a dve-sensitized solid-state photovoltak cell.
Semiconductor Science and Technology, 1993
When illuminated, dye-coated semiconductor electrodes inject electrons (holes) into the conductio... more When illuminated, dye-coated semiconductor electrodes inject electrons (holes) into the conduction (valence) band so that the photoresponse of highbandgap semiconductors is extended to the visible region. It is found that when low-bandgap semiconductor electrodes are coated with dyes, the photocurrent in the bandgap region wavelengths is also enhanced. The effect is explained as originating from suppression of the recombination of carriers generated by photons captured directly by the semiconductor surface.
Comparison of the electronic structure of anatase and rutile TiO2 single-crystal surfaces using resonant photoemission and x-ray absorption spectroscopy
Physical Review B, 2007
A comparison of the electronic structure of rutile (110), anatase (101), and anatase (001) single... more A comparison of the electronic structure of rutile (110), anatase (101), and anatase (001) single-crystal surfaces has been made using resonant photoemission and x-ray absorption spectroscopy. Under identical preparative conditions, the anatase (101) surface shows the lowest Ti3d and 4sp hybridization in the states close to the valence-band maximum of the three surfaces. It also shows the highest concentration of
Journal of Photochemistry and Photobiology A: Chemistry, 2002
We report UHV STM/STS studies on nanocrystalline TiO 2 films in the presence and absence of adsor... more We report UHV STM/STS studies on nanocrystalline TiO 2 films in the presence and absence of adsorbed dye sensitisers (chlorophyll b and a Ru-bipyridyl dye). Interconnected and aggregated TiO 2 nanocrystallites with mean diameters typically of 30-80 nm and different pore sizes are observed in STM images. The results obtained show that the surface apparent bandgap (SABG) depends strongly on tip height above the surface. However, under controlled tunnelling conditions, the SABG of as-prepared thin films is consistent with the bulk bandgap of 3.2 eV, but a quite different, lower SABG is observed when a sensitising dye is adsorbed. Moreover, the characteristic measured in this case is dependent on the choice of dye, showing that the STM I/V characteristic is sensitive to the adsorbed dye, rather than merely to the effect of surface adsorbed water. We discuss possible mechanisms for this effect, and the use of this effect in the optimisation of dye-sensitised photovoltaic cells (DSPECs).
Nanoporous TiO2 photoanode sensitized with the flower pigment cyanidin
Journal of Photochemistry and Photobiology A: Chemistry, 1997
The flower pigment cyanidin anchors into nanoporous films of TiO2 by surface complexation. A phot... more The flower pigment cyanidin anchors into nanoporous films of TiO2 by surface complexation. A photoelectrochemical cell made from cyanidin-sensitized nanoporous TiO2, as a film deposited on conducting glass and with the I− + I3− redox couple in acetonitrile, generates high photocurrents of good stability.
Electronic properties of the interface between p-CuI and anatase-phase n-TiO[sub 2] single crystal and nanoparticulate surfaces: A photoemission study
The Journal of Chemical Physics, 2007
We present a study of the growth of the p-type inorganic semiconductor CuI on n-type TiO2 anatase... more We present a study of the growth of the p-type inorganic semiconductor CuI on n-type TiO2 anatase single crystal (101) surfaces and on nanoparticulate anatase surfaces using synchrotron radiation photoemission spectroscopy. Core level photoemission data obtained using synchrotron radiation reveal that both the substrate (TiO2) and the overlayer (CuI) core levels shift to a lower binding energy to different degrees following the growth of CuI on TiO2. Valence band photoemission data show that the valence band maximum of the clean substrate differs from that of the dosed surface which may be interpreted qualitatively as due to the introduction of a new density of states within the band gap of TiO2 as a result of the growth of CuI. The valence band offset for the heterojunction n-TiO2p-CuI has been measured using photoemission for both nanoparticulate and single crystal TiO2 surfaces, and the band energy alignment for these heterojunction interfaces is presented. With the information obtained here, it is suggested that the interface between p-CuI and single crystal anatase-phase n-TiO2 is a type-II heterojunction interface, with significant band bending. The measured total band bending matches the work function change at the interface, i.e., there is no interface dipole. In the case of the nanoparticulate interface, an interface dipole is found, but band bending within the anatase nanoparticles remains quite significant. We show that the corresponding depletion layer may be accommodated within the dimension of the nanoparticles. The results are discussed in the context of the functional properties of dye-sensitized solid state solar cells.
Efficient Photosensitization of Nanocrystalline TiO2 Films by a New Class of Sensitizer: cis-Dithiocyanato bis(4,7-dicarboxy-1,10-phenanthroline)ruthenium(II)
Chemistry Letters, 1998
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Papers by A.R Kumarasinghe