Published Papers - OZAKI Nobuhiko

Observation of silicon surface nanoholes by scanning tunneling microscopy

N Ozaki, Y Ohno, M Tanbara, D Hamada, J Yamasaki, S Takeda （Part： Lead author )

SURFACE SCIENCE ( ELSEVIER SCIENCE BV )  493 ( 1-3 ) 547 - 554   2001.11  [Refereed]

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We have studied electron-irradiation-induced defects created on an electron exit surface of a Si thin film by means of scanning tunneling microscopy (STM). Several electron-irradiated areas with different electron doses are provided for STM observation. Transmission electron microscopy (TEM) observation reveals a number of silicon-surface-nanoholes of 2-3 nm in diameter and about 5 nm apart in an irradiated area whenever it receives the dose larger than 1.5 x 10(24) e/cm(2), while no distinctive TEM contrast of defects is observed in an area with lower dose. STM observation has shown that electron-irradiated surfaces are rougher than a nonirradiated surface. Examining the depth distribution of the areas with different doses, we have found that each irradiated surface exhibits two depth levels which are attributed to a rough surface and a bottom of surface nanoholes, respectively. Even in an area with the lowest dose (1.5 x 10(22) e/cm(2)) in this experiment we have observed distinctive STM contrasts, the arrangement and sizes of which are similar to those of the well-developed surface nanoholes observable by TEM. This STM observation shows that the arrangement of nanoholes on an electron exit surface is set up at the very early stage, followed by the excavating of nanoholes under prolonged electron irradiation. We suggest that nanoholes exist in the early stage when only a few atomic layers are removed from the initial surface. (C) 2001 Elsevier Science B.V. All rights reserved.

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Optical properties of Si nanowires on a Si{111} surface

N Ozaki, Y Ohno, S Takeda （Part： Lead author )

OPTICAL MICROSTRUCTURAL CHARACTERIZATION OF SEMICONDUCTORS ( MATERIALS RESEARCH SOCIETY )  588   99 - 103   2000  [Refereed]

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We have investigated optical properties of straight silicon nanowires by means of in-situ cathodoluminescence spectroscopy in a transmission electron microscope. The nanowires, grown on a Si{111} surface via vapor-liquid-solid growth mechanism, have no structural defects such as kink, and the diameter and growth direction are controlled by varying the growth conditions. We have found that the nanowires emit intense light. These lines have not been observed in other kinds of Si nanostructures such as porous Si.

VLS growth of Si nanowhiskers on a H-terminated Si{111} surface

N Ozaki, Y Ohno, S Takeda, M Hirata （Part： Lead author )

MICROCRYSTALLINE AND NANOCRYSTALLINE SEMICONDUCTORS-1998 ( MATERIALS RESEARCH SOCIETY )  536   305 - 310   1999  [Refereed]

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We have grown Si nanowhiskers on a Si{111} surface via the vapor-liquid-solid (VLS) mechanism. The minimum diameter of the crystalline is 3nm and is close to the critical value for the effect of quantum confinement. We have found that many whiskers grow epitaxially or non-epitaxially on the substrate along the < 112 > direction as well as the < 111 > direction.
In our growth procedure, we first deposited gold on a H-terminated Si{111} surface and prepared the molten catalysts of Au and Si at 500 degrees C. Under the flow of high pressure silane gas, we have succeeded in producing the nanowhiskers without any extended defects. We present the details of the growth condition and discuss the growth mechanism of the nanowhiskers extending along the < 112 > direction.

Silicon nanowhiskers grown on a hydrogen-terminated silicon {111} surface

N Ozaki, Y Ohno, S Takeda （Part： Lead author )

APPLIED PHYSICS LETTERS ( AMER INST PHYSICS )  73 ( 25 ) 3700 - 3702   1998.12  [Refereed]

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Using a hydrogen-terminated Si{111} surface as a substrate, we have grown Si nanowhiskers along the [112] direction by the vapor-liquid-solid mechanism. The minimum silicon core diameter was 3 nm and the maximum length was about 2 mu m. The minimum silicon core diameter is close to the critical value for visible light emission due to the quantum confinement effect. In contrast to an oxidized Si surface, the hydrogen-terminated surface facilitates the formation of small molten Au-Si catalysts at a lower temperature (500 degrees C) which is slightly above the eutectic temperature. The formation of catalysts and the subsequent growth at the low temperature yield thin Si nanowhiskers on a Si substrate. (C) 1998 American Institute of Physics. [S0003-6951(98)01051-1].

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