| Project/Area Number |
03452075
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied materials
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MAEDA Koji The Univ.of Tokyo, Applied Physics, Professor, 大学院・工学系研究科, 教授 (10107443)
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| Co-Investigator(Kenkyū-buntansha) |
MERA Yutaka The Univ.of Tokyo, Applied Physics, Res.Associate, 大学院・工学系研究科, 助手 (40219960)
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| Project Period (FY) |
1991 – 1993
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| Project Status |
Completed (Fiscal Year 1993)
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| Budget Amount *help |
¥6,900,000 (Direct Cost: ¥6,900,000)
Fiscal Year 1993: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1992: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1991: ¥5,200,000 (Direct Cost: ¥5,200,000)
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| Keywords | Scanning Tunneling Microscopy / 1 / f Noise / Fluctuations / Tunneling / Surface / Nano Contact / Ultra High Vacuum / Probe Tip / STM / 電界放射 / 仕事関数 |
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| Research Abstract |
The generation mechanism of conspicuous low frequency noise (including 1/f fluctuations) observed in the tunneling current of scanning tunneling microscopes was studied experimentally by investigating combinations of Pt-Ir tips and Au films or crystalline graphite and of W tips and graphite samples in ultra high vaccum. For 1/f noise, the noise intensity at a fixed current increases with increasing bias voltage. The noise power varies from place to place in a sample surface of Au film. The spatial variation of the noise has a positive correlation with the magnitude of the tunneling barrier height phi measured by the z-modulation method. The demodulated signal in the z-modulation experiments also exhibits fluctuations with a 1/f spectrum of the relative magnitude nearly equal to that in the current noise. Tips capable of imaging graphite surface in atomic resolution sometimes yield random telegraphic noise with a Lorentzing spectrum, which is well understood by considering that the shar
… More
p tips select a single relaxation process that happens to be located in the narrow current path.
The temperature dependence of 1/f fluctuations in the tunneling current of scanning tunneling microscopes was measured for graphite smaples in ultra high vacuum. The noise spectra in the temperature range between 65K and room temperature show the frequency dependence of 1/f^a type with alpha ranging around unity. The noise intensity at 100 Hz varies with temperature exhibiting two discernible peaks. The latter fact contradicts with the theoretical expectation from the phonon number fluctuation model which predicts monotonic increase of noise intensity with temperature. The experimental results are best explained by the model assuming thermally activated multiple relaxation processes. The frequency factor of the order of 1014 Hz which yields a good fit with the experimental data suggests that the origin of the 1/f noise is some mobile "defects" dispersed over the sample surfce at positions remote from the probe tip. Less
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