Mesoscopic and Condensed Matter Physics

Biography

Biography: Junji Haruyama

Abstract

Two-dimensional (2D) atom-thin layers have attracted significant attention after the discovery of primitive fabrication method of graphene, mechanical exfoliation of graphite using scotch tapes. As a van-der Waals engineering, various atom- thin layers and those hybridization have been recently realized. In the talk, first, I will present magnetism and spintronics arising from edges of 2D atom-thin layers, graphene, few-layer black phosphorus (BP) and hexagonal boron-nitride (hBN). I created nanomesh (NM) structures, consisting of honeycomb like array of hexagonal pores, with specified pore-edge atomic structure (i.e., zigzag type) on individual layers. Interestingly, hydrogen-terminated graphene NM (H-GNM) shows flat-band ferromagnetism, while it disappears in oxygen-terminated GNM. On the other hand, O-BPNM exhibits large ferromagnetism due to ferromagnetic spin coupling of edge O-P bonds, whereas it is eliminated in H-BPNM. O-hBNNM also shows large ferromagnetism due to edge O-B and O-N bonds, while it disappears in H-hBNNM. These are also highly sensitive to annealing temperatures to form zigzag pore edge. These open a considerable avenue for realizing 2D atom-thin flexible magnetic and spintronic devices, fabricated without using rare-earth magnetic atoms. Second, I will show creation of the world-thinnest Schottky junction on few-layer molybdenum disulfide (MoS2), one of the transition metal dichalcogenides. The 2H-phase of MoS2 has direct band gaps of 1.5−1.8 eV. It is demonstrated that electron-beam (EB) irradiation to the 2H-phase causes semiconductor- metal transition to 1T-phase and atomically-thin Schottky junction with barrier height of 0.13−0.18 eV is created at the interface of 2H/1T regions. These findings also indicate a possibility that the effective barrier height is highly sensitive to electrostatic charge doping and almost free from Fermi-level pinning when assuming predominance of the thermionic current contribution. This EB top-down patterning opens the possibility to fabricate in-plane lateral heterostructure FETs,which have shown promising scaling prospects in the nanometer range, and/or local interconnects directly with metallic phase (1T) between (2H)MoS2 transistors, resulting in ultimate flexible and wearable in-plane integration circuits without using 3D metal wirings. Finally, I will also briefly talk about introduction of spin-orbit interaction into graphene by light hydrogenation(<0.1%).