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Your search keyword '"Lemmetyinen, H."' showing total 408 results
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408 results on '"Lemmetyinen, H."'

18. Annealing of the deep recombination center in GaInP/AlGaInP quantum wells grown by solid-source molecular beam epitaxy

Author

Dekker, J., Tukiainen, A., Xiang, N., Orsila, S., Saarinen, M., Toivonen, M., Pessa, M., Tkachenko, N., and Lemmetyinen, H.

Subjects
Annealing -- Research, Molecular beams -- Research, Photoluminescence -- Usage, Quantum wells -- Research, Semiconductors -- Optical properties, Physics
Abstract

The effect of rapid thermal annealing on bulk GaInp and GaInP/AlGaInP quantum wells grown by solid source molecular beam epitaxy is investigated using deep level transient spectroscopy and time resolved photoluminescence. After the rapid thermal annealing, decreases in the concentration of several deep level traps became apparent. Results also suggest that the defect labeled N3, 0.83 eV, below the conduction band, is the dominant recombination center.

Published
1999

19. Light-induced electron transfer in pyropheophytin-anthraquinone dyads: vectorial charge transfer in Langmuir-Blodgett films

Author

Tkachenko, N.V., Tauber, A.Y., Hynninen, P.H., Sharonov, A.Y., and Lemmetyinen, H.

Subjects
Thin films, Multilayered -- Research, Charge transfer -- Research, Electron donor-acceptor complexes -- Research, Anthraquinones -- Research, Molecular spectra -- Research, Chemicals, plastics and rubber industries
Abstract

The vectorial photoinduced electron transfer mechanism of solid Langmuir-Blodgett films has been optimized using four types of donor-acceptor compounds. Two measuring approaches, namely, the measurement of time-resolved and steady-state fluorescence and the transient photoelectric method, were employed to characterize the electron transfer function of the multilayered thin films. It was shown that the deposition direction of the donor-acceptor active layers can control the direction of the electron transfer.

Published
1999

34. Subthreshold carrier losses from GaInP quantum wells measured by time resolved photoluminescence.

Author

Dekker, J., Dumitrescu, M., Tukiainen, A., Orsila, S., Uusimaa, P., Pessa, M., Tkachenko, N. V., and Lemmetyinen, H.

Subjects
QUANTUM wells, TIME-resolved spectroscopy, PHOTOLUMINESCENCE
Abstract

We report here on measurements of carrier loss processes in GaInP quantum wells made using time resolved photoluminescence spectroscopy. Measurements were made as a function of temperature and excitation intensity on quantum wells with different confinement barrier heights. The measurements reveal three distinct lifetime components identifiable by their activation energy and excitation intensity dependence. The lifetime components are assigned to thermionic emission of holes from the quantum well, nonradiative recombination at deep level defects, and radiative band-to-band recombination. The valence band offsets between GaInP and AlGaInP have been determined from the activation energy for thermionic emission of holes and are found to increase from 0.096 to 0.147 eV as the Al content in the waveguide layer increased from 50% to 70%. The relative contributions of the different carrier loss mechanisms to the subthreshold current of GaInP quantum well lasers is also discussed. [ABSTRACT FROM AUTHOR]

Published
2002
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40. Pt-functionalized Fe2O3 photoanodes for solar water splitting: the role of hematite nano-organization and the platinum redox state

Author

Warwick, M. E. A., Barreca, D., Bontempi, E., Carraro, G., Gasparotto, A., Maccato, C., Kaunisto, K., Ruoko, T. -P., Lemmetyinen, H., Sada, C., Goenuellue, Y., Mathur, S., Warwick, M. E. A., Barreca, D., Bontempi, E., Carraro, G., Gasparotto, A., Maccato, C., Kaunisto, K., Ruoko, T. -P., Lemmetyinen, H., Sada, C., Goenuellue, Y., and Mathur, S.

Abstract

Pt/alpha-Fe2O3 nanocomposites were synthesized on fluorine-doped tin oxide (FTO) substrates by a sequential plasma enhanced-chemical vapor deposition (PE-CVD)/radio frequency (RF) sputtering approach, tailoring the overall Pt content as a function of sputtering time. The chemico-physical properties of the as-prepared systems were extensively investigated by means of complementary techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDXS), secondary ion mass spectrometry (SIMS), and optical absorption spectroscopy, and compared to those of the homologous Pt/alpha-Fe2O3 systems annealed in air prior and/or after sputtering. The obtained results evidenced that the material compositional, structural and morphological features, with particular regard to the Pt oxidation state and hematite nano-organization, could be finely tailored as a function of the adopted processing conditions. Pt/alpha-Fe2O3 systems were finally tested as photoanodes in photoelectrochemical (PEC) water splitting experiments, evidencing a remarkable interplay between functional performances and the above-mentioned material properties, as also testified by transient absorption spectroscopy (TAS) results.

Published
2015

41. Graphene-intercalated Fe2O3/TiO2 heterojunctions for efficient photoelectrolysis of water

Author

Kaouk, A., Ruoko, T. -P., Gonullu, Y., Kaunisto, K., Mettenborger, A., Gurevich, E., Lemmetyinen, H., Ostendorf, A., Mathur, S., Kaouk, A., Ruoko, T. -P., Gonullu, Y., Kaunisto, K., Mettenborger, A., Gurevich, E., Lemmetyinen, H., Ostendorf, A., and Mathur, S.

Abstract

Interfacial modification of alpha-Fe2O3/TiO2 multilayer photoanodes by intercalating few-layer graphene (FLG) was found to improve water splitting efficiency due to superior transport properties, when compared to individual iron and titanium oxides and heterojunctions thereof. Both metal oxides and graphene sheets were grown by plasma-enhanced chemical vapor deposition. Compared to the onset potential achieved for alpha-Fe2O3 films (1 V vs. RHE), the alpha-Fe2O3/TiO2 bilayer structure yielded a better onset potential (0.3 V vs. RHE). Heterojunctioned bilayers exhibited a higher photocurrent density (0.32 mA cm(-2) at 1.23 V vs. RHE) than the single alpha-Fe2O3 layer (0.22 mA cm(-2) at 1.23 V vs. RHE), indicating more efficient light harvesting and higher concentration of photogenerated charge carriers. For more efficient charge transport at the interface, a few layer graphene sheet was intercalated into the alpha-Fe2O3/TiO2 interface, which substantially increased the photocurrent density to 0.85 mA cm(-2) (1.23 V vs. RHE) and shifted the onset potential (0.25 V vs. RHE). Ultrafast transient absorption spectroscopy studies indicated that the incorporation of FLG between the alpha-Fe2O3 and TiO2 layers resulted in reduced recombination in the alpha-Fe2O3 layer. The results showed that graphene intercalation improved the charge separation and the photocurrent density of the FTO/alpha-Fe2O3/FLG/TiO2 system.

Published
2015

44. Pt-functionalized Fe2O3 photoanodes for solar water splitting: the role of hematite nano-organization and the platinum redox state

Author

Warwick, M. E. A., primary, Barreca, D., additional, Bontempi, E., additional, Carraro, G., additional, Gasparotto, A., additional, Maccato, C., additional, Kaunisto, K., additional, Ruoko, T.-P., additional, Lemmetyinen, H., additional, Sada, C., additional, Gönüllü, Y., additional, and Mathur, S., additional

Published
2015
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50. Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics

Author

90243261, 30378806, 00168288, Imahori, H, Fujimoto, A, Kang, S, Hotta, H, Yoshida, K, Umeyama, T, Matano, Y, Isoda, S, Isosomppi, M, Tkachenko, NV, Lemmetyinen, H, 90243261, 30378806, 00168288, Imahori, H, Fujimoto, A, Kang, S, Hotta, H, Yoshida, K, Umeyama, T, Matano, Y, Isoda, S, Isosomppi, M, Tkachenko, NV, and Lemmetyinen, H

Published
2005

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