15:30-16:00

Photocontrol of Single-Electron Tunneling via Molecular Dots in a Metal-Insulator-Semiconductor Structure

We have proposed multi-functional single-electron memory devices utilizing organic molecules as quantum dots. So far, single-electron tunneling through molecular dots, including C₆₀ and phthalocyanine molecules, has been demonstrated in a metal-insulator-semiconductor (MIS) structure which is basic component in single-electron memory.

In this seminar, I will present photo-control of single-electron tunneling via molecular dots in the MIS structure. Here, diarylethene molecules, which are kinds of photoisomerization molecules, were used as quantum dots. This is because energy level of this molecule involves considerable change due to open- and closed-ring photoisomerization. Very recently, I have demonstrated single-electron tunneling in the devices at 20 K. Furthermore, the threshold voltages were reversibly changed by UV and VIS light irradiations. The value was kept even after turning off the light, indicating that diarylethene molecules worked as optical memory in a practical structure. This result is one of inimitable features of organic molecules and strong point against inorganic quantum dots. Our proposed device configuration has high potential for a breakthrough in Si-based technology.

Speaker

Dr. Ryoma Hayakawa, ICYS-MANA Researcher, NIMS

Chair

Dr. Yutaka Wakayama, MANA Scientist, NIMS

16:00-16:30

Fabrication of Graphene and Boron Nitride Layers on Metal Surfaces by Surface Segregation

The typical sp2?bonded two dimensional materials such as graphene and hexagonal boron nitride (h-BN) with honeycomb crystal structure, are attractive in fundamental research because of their remarkable properties and chemical stability. High quality graphene and h-BN layers over large scale can provide new opportunities in potential applications, especially h-BN is considered as an appealing substrate dielectric for use in improving graphene based electronic devices. Therefore, synthesis of high quality graphene and h-BN layers is highly desirable. Here we report the fabrication of single-layer graphene on carbon-doped single-crystal Pt(111) (0.05 %) and Pd(111) (0.5 %) substrate. It is found that uniform single-layer graphene islands about 50μm formed on Pt(111) surfaces. Continuous, wafer-scale, single-layer graphene can be achieved on Pd(111) surfaces by adjusting the experimental parameters. The atomic structure of graphene islands has been investigated by scanning tunneling microscopy (STM), which exhibit hexagonal atomic lattice and morie pattern for Pt(111) and Pd(111) substrates, respectively. Recently, few-layer h-BN on Fe-Cr-Ni alloy has been successfully fabricated of by surface segregation. The present synthesis can provides a novel technique for large scale graphene fabrication used for fundamental research as well as device integration.

Speaker

Dr. Jin-Hua Gao, ICYS-Sengen Researcher, NIMS

Chair

Dr. Yasushi Yamauchi, Nano Characterization Unit, NIMS