EEIS 東京大学大学院 工学系研究科 電気系工学専攻

TAKAHASHI Takuji Professor

Komaba Campus

Nano Physics & Device Technology
Nanostructural physics
Thin film/Surface and interfacial physical properties
Electron device/Electronic equipment

Nanometer world explored by nanoprobes - "Observe" what are invisible to our eyes -

Our laboratory aims to establish new methods for evaluating physical properties in the nanometer range by making full use of the nanoprobe technology that has high spatial resolution at nanometer scale and to contribute to the exploration of new devices through understanding of those physical properties.

Research field 1

Multi-angle evaluation of solar cell material

For solar cells, multi- or micro-crystalline materials are preferable from the view point of their fabrication cost, but there is concern about the degradation of solar cell performance due to grain boundaries included in those materials. In order to investigate very local photovoltaic property around the grain boundaries, we have developed photo-assisted Kelvin probe force microscopy (P-KFM) and applied it to observation of photovoltage distribution on the CIGS solar cells. If, in addion, the carriers (electrons and holes) excited by light are recombined non-radiatively in the solar cell, the performance will be degraded because electrical energy cannot be extracted outside. Since the heat is released by such non-radiative recombination, we have developed photo-thermal mode atomic force microscopy (PT-AFM) where very fine thermal expansion of the sample can be precisely observed by AFM. Then we have investigated microscopically how grain boundaries affect the non-radiative recombination of photo-generated carriers in the CIGS materials.
Research field 2

Development of new nanoprobing methods

In nanoprobes, we can detect an electrostatic force generated by external voltage application between a tip and sample. From the dependence of the electrostatic force on the d.c. bias voltage and on the frequency of the a.c. voltage, we also can investigate degree of surface depletion and influence of interface states. We have proposed dual bias modulation method, being effective for electrostatic force detection particularly at a high frequency, and have applied it for investigation of surface and interface states in CIGS solar cell materials.
Research field 3

Operation analysis of carbon nanotube FET channel

Since a carbon nano-tube (CNT) is a pure one-dimensional conductor ideally, very high performance will be expected in a field effect transistor (FET) with CNT channels. In the CNT-FET with multiple channels where high-speed operation will be possible, it is important to reveal uniformity of electrical property among many CNT channels. We have developed a new method of magnetic force microscopy (MFM) that acts as a magnetic field sensor with high spatial resolution. By means of this method, quantitative current evaluation is realized through a current-induced magnetic field detection, and we succeeded in analyzing the operation mode of a single CNT channel intentionally selected from many channels.
Research field 4

Investigation of physical properties in quantum nanostructure

Using the light-illuminated scanning tunneling microscopy (STM) we originally developed, we have investigated optical properties like photo-absorption property in a single InAs wire structure. As for electrostatic force detection in AFM and consequent surface potential determination by KFM, in addition, we have proposed both the sampling method which improves a sensitivity of electrostatic force detection and the intermittent bias application method which improves a spatial resolution for surface potential determination. By means of them, charge accumulation phenomena in the InAs quantum dots have been investigated.
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