[18p-E308-1~18] 17.2 グラフェン

▲ [18p-E308-6] In-situ Electrical Conductance Measurement of Suspended Graphene Nanoribbon by Transmission Electron Microscopy

〇(D)Chunmeng LIU¹、Ryo Okubo¹、Xiaobin Zhang²、Muruganathan Manoharan¹、Hiroshi Mizuta^1,3、Yoshifumi Oshima¹ (1.JAIST、2.Shibaura Inst. of Technology、3.Hitachi Cambridge Lab.)

キーワード：suspended graphene nanoribbon, structure-depended properties, in situ TEM observation

The peculiar aspect of a finite-size graphene nanoribbon (GNR) is that its electrical conductance strongly depends on the edge structure. First principle calculation showed that the band gap appeared for both armchair and zigzag GNRs. Recently, this prediction has been verified. However, structure-dependence of GNRs on their electrical conductance property has rarely been investigated, especially for a suspended GNR which does not have interaction with any substrate.In this study, we will focus on the fabrication and electrical conductance measurement of suspended GNRs with controllable width and edge structure by in-situ transmission electron microscope (TEM) observation.In this experiment, we used a commercial silicon chip with a slot window for in-situ TEM observation. Firstly, electrodes and pads were deposited on the chip. Nano-gaps were then fabricated by cutting the electrodes at the center using FIB. Then, chemical vapor deposition-grown monolayer graphene was transferred onto the prepared chip. Finally, the GNRs were patterned using EBL, and followed with the O2 plasma etching step to remove the exposed graphene.Fig.1a shows the TEM image of the suspended GNR fabricated across the nano-gap, which is about 250 nm in width. The measured linear relation between current and voltage provides resistance of the GNR is about 2.4 kΩ. After that, the suspended GNR was cleaned by Joule heating, and then sculpted by a convergent electron beam in TEM mode, until its width was reduced down to several nanometers. During the narrowing process, the resistance of the GNR increased followed with reduction in its width. Finally, we successfully fabricated an ultranarrow GNR with width of 1.8 nm. The relationship between current and bias voltage indicate that an energy band gap was opened in this narrow GNR. Since the one-half of the nonlinear gap is measured to be 600 meV, the band gap of this 1.8 nm wide GNR can be approximately calculated to be 300 meV.