2020 Fiscal Year Research-status Report
Novel terahertz NEMS bolometers by using two-dimensional nanomaterials
| Project/Area Number |
19K15023
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| Research Institution | Tokyo University of Agriculture and Technology |
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Principal Investigator |
張 亜 東京農工大学, 工学(系)研究科(研究院), 准教授 (80779637)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | terahertz / thermal sensor / NEMS resonator / 2D material |
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| Outline of Annual Research Achievements |
In the year of 2020, we have fabricated graphene NEMS devices, and measured the thermoelectric response.
(1). Fabrication of graphene NEMS devices The NEMS devices were fabricated by using monolayer and few-layer (6~8 layers) CVD-grown graphene. The graphene was transferred to SiO2/Si wafers by using a PMMA layer as a support. Then the graphene layer was etched into micro-scale dash shapes by using plasma etching, and metal electrodes were directly deposited on the graphene layer to form source and drain electrodes for the devices. Finally, the SiO2 layer below the graphene layer was selectively etched and the graphene doubly clamped films were released by using supercritical drying technique.
However, although clamped graphene films were successfully obtained, we have met a problem that there is some residual of photoresist on the graphene, and the metal electrodes do not strongly stick to the graphene layer. This makes the graphene layer loose and wrinkled after the supercritical drying, and the measurement of the mechanical resonances of the NEMS devices is very difficult.
(2). Measurement of thermoelectric response We have measured the photoelectric response of the graphene devices by using a 530 nm green laser diode. When graphene film was irradiated by the laser, a photovoltaic voltage was detected, indicating that the light has been absorbed and temperature rise was induced in the graphene layer.
These achievements and the knowhow obtained in the work form the basis of the realization of the research target, i.e., to develop graphene NEMS bolometers.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
The research has been delayed by the outbreak of the novel coronavirus disease (COVID-19). It greatly reduces the working time of the students who take part in the assistance of the experiments, and also reduce the usable time of the experimental facilities. As a result, the planned experiment cannot be fully finished, which will be continued in the year of 2021.
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| Strategy for Future Research Activity |
In the year of 2021, we will continue the fabrication of NEMS resonators, and perform the optical measurements by using the fabricated NEMS devices.
We have considered the following methods to solve the problem of photoresist residual. (1) We will optimize the cleaning process of the resist before the metal deposition, to increase the stiction of the metal-graphene junctions. (2) We will try new fabrication schemes to reduce the times of resist coating on the graphene layer. (3) In addition to the CVD-grown graphene, we will also try mechanically peeled-off graphene, which may have better mechanical properties than the CVD-grown graphene films.
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| Causes of Carryover |
Reasons Because of the outbreak of COVID-19, a part of the planned experiments was delayed. Therefore the planned budget for the experimental consumables was not fully used. Furthermore, since the international conferences we planned to attend were delayed also owing to the worldwide outbreak of the COVID-19, the planned travel expenses could not be used.
Usage plan The incurring amount will be mainly used for the following purposes; (1) to purchase consumers (graphene, chemicals, and etc) for the fabrication of the NEMS resonators, (2) to purchase electrical and optical components for the optimization of the NEMS measurement setup, (3) to pay the remunerations of the research assistant (graduated student), and (4)to pay the travel expenses and registration fees for attending conferences.
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