The 210th MANA & 92nd ICYS Joint Seminar
Dr. Xianlong Wei & Dr. Rudder Wu
| Date | June 17, Friday |
| Time | 15:30-16:30 |
| Place | Seminar Room #431, MANA Bldg., NAMIKI, NIMS |
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15:30-16:00
Phonon-assisted electron emission from one-atom-thick carbon nanotube shells
How electrons can escape from solid surfaces into vacuum is an important problem from both fundamental and technological viewpoints. However, how electrons can escape from the surfaces of one-atom-thick materials (e.g. graphenes, shells of carbon nanotubes (CNTs)) has seldom been studied and is still not properly answered. Along the direction normal to the surfaces of one-atom-thick materials, electrons are confined by a one-atom-thick quantum well. Such confinement will make electron behaviors normal to the surface of one-atom-thick materials, such as electron emission, much different from that normal to the surface of a three-dimensional solid.
Herein, a thorough study on lateral electron emission from one-atom-thick CNT shells is presented. Electron emission from side surface of individual electrically-biased CNTs is studied both experimentally and theoretically. A new electron emission mechanism named as phonon-assisted electron emission is proposed, and the corresponding theoretical model well describes experimentally-measured electron emission from CNTs. It is shown that, the electrons moving along an electrically-biased CNT can overflow from the one-atom-thick tube shell due to the absorption of hot forward-scattering optical phonons. Low working voltage, low working temperature, high emission density, abnormal spatial distribution of emission density, and side emission character make phonon-assisted electron emission primarily promising in electron source applications.
Speaker
Dr. Xianlong Wei, ICYS-MANA Researcher, NIMS
Chair
Dr. Dmitri Golberg, MANA PI, NIMS
16:00-16:30
Ubiquitous Element Strategies for Precious Metal Containing Protective Coatings
In this seminar, my research activities on reducing and replacing the use of platinum group metals (PGMs) in protective coatings will be presented. Particular focus of the talk will be placed on understanding the fundamental mechanisms underlying the apparent beneficial effects of platinum addition.
The current study was carried out to investigate both chemical and micromechanical influences of Pt in a systematic manner. Pt modified Ni-Al specimens were prepared with incremental addition of Pt (0, 5 10 to 15 wt%) while maintaining the aluminum content constant at 15 wt%. Results of the study demonstrated that higher Pt content produced a thinner and more continuous oxide scale. The addition of Pt was also found to lower the coefficient of thermal expansion (CTE) of coatings at 1100oC by approximately 5%, and thereby, reduce the CTE mismatch between the Al2O3 scale and the intermetallic bond coat. This could partly explain the reason behind the suppression of interfacial rumpling with increasing platinum addition. Examples of current experimental activities on reducing and replacing the use of platinum group metals (PGMs) for next-generation TBC systems will also be discussed.
Speaker
Dr. Rudder Wu, ICYS-Sengen Researcher, NIMS
Chair
Dr. Tadaharu Yokokawa, Principal Researcher, High-Performance Alloys Group, High Temperature Materials Unit, NIMS