| Project/Area Number |
05402014
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
物性一般(含基礎論)
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
SAKAI Akira KYOTO UNIVERSITY,DEP.OF ENGINEERING,PROFESSOR, 工学部, 教授 (80143543)
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| Co-Investigator(Kenkyū-buntansha) |
SAKURAI Toshio TOHOKU UNIVERSITY,INST.MAT.RES., PROFESSOR, 金属材料研究所, 教授 (20143539)
OSAMURA Kozo KYOTO UNIVERSITY,DEP.OF ENGINEERING,PROFESSOR, 工学研究科, 教授 (50026209)
HASEGAWA Yukio TOHOKU UNIVERSITY,INST.MAT.RES., ASSOC.PROFESSOR, 金属材料研究所, 助教授 (80252493)
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| Project Period (FY) |
1993 – 1994
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| Project Status |
Completed (Fiscal Year 1994)
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| Budget Amount *help |
¥35,100,000 (Direct Cost: ¥35,100,000)
Fiscal Year 1994: ¥10,100,000 (Direct Cost: ¥10,100,000)
Fiscal Year 1993: ¥25,000,000 (Direct Cost: ¥25,000,000)
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| Keywords | TIP / JUNCTION CAPACITANCE / SCANNING TUNNELING MICROSCOPY / 走査トンネル顕微鏡(STM) |
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| Research Abstract |
Tip-sample junction in STM is archetypical of the ultrasmall junctions. In this study, we have experimentally investigated the tip-sample capacitance and its dependence on the gap distance s. The results obtained are the following.
1. On silicon clean surfaces, the capacitance varies as In s for>500 nm. Such a gap dependence is what one expects for a sphere-plane capacitor. At s <100nm, however, the capacitance shows weaker gap dependence and no 1/s divergence.
2. Such a gap dependence was commonly observed on all silicon surfaces regardless of their orientation or doping. Also the capacitance shows flat C-V characteristics. These findings indicate that the space charge layr of semiconductor surfaces makes little contribution to the capacitance change. Strong Fermi level pinning by the surface states can explain the absence of the space-charge-layr effects.
3. Experiments on the clean gold surface with tips of different sharpness revealed a strong dependence of the capacitance on the tip geometry. With a sharp tip, the capacitance changes little with s. The effective tip radius R_<eff> obtained from the capacitance data excellently agrees with the real tip radius. On the other hand, the capacitance with a dull tip shows a large change with s but has R_<eff> much smaller than the real radius.
4. The effects of tip geometry can be understood by considering the field concentration to the tip apex which dominates the capacitance at small distances and hence R_<eff>. On a sharp tip with a spherical tip apex, R_<eff> agrees with the real tip radius. On a dull tip, a small protrusion determines the capacitance and R_<eff> becomes much smaller than the real tip radius. Calculation of the tip-sample capacitance using the image charge method also gives theoretical support to this interpretation.
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