2003 Fiscal Year Final Research Report Summary
Generation and Relaxation Processes of Electronic Excited States Measured with Photon Counting and Molecular Image Observation
| Project/Area Number |
13440204
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
機能・物性・材料
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| Research Institution | Tohoku University |
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Principal Investigator |
FOKUMURA Hiroshi TOHOKU UNIVERSITY, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (50208980)
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| Co-Investigator(Kenkyū-buntansha) |
HATANAKA Koji TOHOKU UNIVERSITY, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助手 (90312545)
HOBLEY Jonathan TOHOKU UNIVERSITY, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助手 (40332499)
NISHIO Satoru TOHOKU UNIVERSITY, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (40252340)
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| Project Period (FY) |
2001 – 2003
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| Keywords | Scanning tunneling microscopy / Liquid solid interface / Self assembled monolayers / Weak luminescence measurement |
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| Research Abstract |
Tunneling-current-induced luminescence from tin-doped indium oxide (ITO) surfaces covered with a variety of molecules was measured using an inverted microscope combined with a scanning tunneling microscope (STM) at several applied bias voltages between 3.5 and -3.5 V. Visible luminescence was observed when negative bias voltages of less than -l.5 V were applied to the ITO surface. The luminescence intensity increased upon increasing the absolute value of the negative bias voltage. Furthermore, the amplification factor strongly depended on the type of molecule deposited on the ITO surface. Measurements of the luminescence spectra allowed us to conclude that the molecules covering ITO substrates never themselves emitted upon stimulation with the STM probe tip. A mechanism for the luminescence enhancement is proposed, which is based upon resonance between the LUMO of the molecules and the valence band of the ITO.
Self-assembled structures of a variety of molecules at a solution-graphite interface have been investigated with scanning tunneling microscopy. The electronic properties of these structures were studied with electron-tunneling spectra obtained from current-voltage curves. For instance, pyrenyl groups were found to form a pi-stacked assembly when it was co-adsorbed with 4,4'-dipyridyl although these remained isolated in the uni-component self-assembled structure. The electron-tunneling spectra of the pyrenyl groups for two different structures suggested that the band gap between HOMO and LUMO is smaller in the pi-stacked assembly than that in an isolated pyrene moiety, which can be explained with the Davidov splitting. The offset voltage in a tunneling spectrum was considered to be due to a resonant tunneling through the potential well formed in physisorbed molecules.
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Research Products
(14 results)
