Hang, Shuojin

Mizuta, Hiroshi

Moktadir, Zakaria

English

Southampton (e-Prints Soton)

 Irradiation Induced Tunnel Barrier in Graphene  Shuojin Hang 1, Zakaria Moktadir 1, Hiroshi Mizuta 1,2  1Faculty of Physical Sciences and Engineering, University of Southampton, UK 2 Japan Advanced Institute of Science and Technology (JAIST), Japan   We have shown that helium ion milling on graphene could introduce wide range damage (fig.1) around the channel due to backscattered ions and recoiled atoms from substrate [1]. In order to fully utilize the ultra-fine resolution of the helium ion microscope (HIM) and its precise controllability on irradiation dose, we propose a tunnel barrier formation technique by modest ion irradiation. We observed a mobility reduction of more than five orders  of  magnitude  in  graphene  nanoribbons  (GNR)  upon  gradually  increased  He+ irradiation, indicating a metal-to-insulting transition (MIT) (fig.2). It has been shown that point defects formed by irradiation can cause strong localization [2]. As a result we deem it is possible to form a quantum dot (QD) by making narrow (<10nm) tunnel barriers via controlled irradiation, as demonstrated in the case of carbon nanotube [3]. Devices with structure shown in fig. 3 have been fabricated on exfoliated graphene using electron beam lithography. Ti/Au of 10nm/80nm were deposited to form contacts. Side gates  are  located  50nm  from  the  channel.  The  room-temperature  conductance modulation against side gate (SG), plunger gate (PG) and back gate (BG) are shown in fig.4. The local gates show comparable modulating ability to the back gate. In the next step, HIM irradiation will be applied to create barriers.    Fig.1.  (a)Raman  mapping  on  the  FWHM  of  G  peak  outlining  the  damage  extent  of ~350nm near a HIM-carved 30nm wide line (arrow). (b) Field effect electron (left) and hole (right) mobility measured for different irradiation dose for several values of back-gate voltage. (c) Schematic of a graphene QD device with irradiation-defined barriers. (d) The ID/VG graph for a pre-irradiation GNR device controlled by SG, PG and BG. References [1]  S. Hang, Z. Moktadir, and H. Mizuta, Carbon N. Y., vol. 72, 233–241, 2014. [2]  S. Nakaharai, T. Iijima, S. Ogawa, S. Suzuki, S. Li, and K. Tsukagoshi,  ACS Nano, vol. 7, no. 7, 5694–5700, 2013. [3]  M. Suzuki, K. Ishibashi, K. Toratani, D. Tsuya, and Y. Aoyagi, Appl. Phys. Lett., vol. 81, no. 12, 2273, 2002.  

Irradiation induced tunnel barrier in graphene

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