AVS 60th International Symposium and Exhibition
    Helium Ion Microscopy Focus Topic Thursday Sessions
       Session HI-ThM

Paper HI-ThM9
Imaging of Graphene Films by Helium Ion Microscope

Thursday, October 31, 2013, 10:40 am, Room 203 A

Session: Basics of Helium Ion Microscopy
Presenter: S. Ogawa, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Authors: S. Ogawa, National Institute of Advanced Industrial Science and Technology (AIST), Japan
T. Iijima, National Institute of Advanced Industrial Science and Technology (AIST), Japan
S. Nakaharai, National Institute of Advanced Industrial Science and Technology (AIST), Japan
M. Hayashida, National Institute of Advanced Industrial Science and Technology (AIST), Japan
S. Sato, National Institute of Advanced Industrial Science and Technology (AIST), Japan
Correspondent: Click to Email
The helium ion microscopy is a unique technology for observation of soft materials such as low-k materials and photo resist patterns for LSI fabrication [1] and for nm order patterning. Graphene, a two-dimensional sheet of carbon atoms [2], is a promising channel material for next-generation transistors, and we have shown an on-off gating of current through a graphene nano-ribbon which was etched down by the helium ion nano beam using the helium ion microscope (HIM) [3] and by controlling electrical properties of the graphene films themselves by the helium ion dose [4]. On the other hand it is difficult to characterize whether the graphene films on the silicon oxide layer were single layers or not.

Graphene flakes were mechanically exfoliated from a crystal of HOPG using adhesive tape, and then deposited on a silicon wafer with a 300-nm-thick surface thermal oxide layer. The number of graphene layers was identified by sight with an optical microscope based on interference color and then characterized by HIM using brightness ratio of the graphene films and the silicon oxide surface. Brightness of the surface of the silicon oxide showed linear dependency to beam currents but with some offset for different HIM contrast conditions, and to normalize the brightness ratio at several imaging conditions, the brightness was compensated by the offset. HIM images show higher brightness ratio for single layer graphene films with darker brightness than multi-layer graphene films and much higher spatial resolution than the optical microscope, while it is not sufficient to determine layer numbers of the films so far. Helium ions dose higher than 1E16/cm2 decreased the brightness ratio. Detail of the brightness ratio and its dependency on the layers of the graphene films will be discussed.

This work was partly supported by JSPS through the “FIRST Program,” initiated by CSTP, Japan.

[1] S. Ogawa, et al., Jpn. J. Appl. Phys., 49 (2010) 04DB12, [2] K. Novoselov, et al., Science 306, 666 (2004), [3] S. Nakaharai, et al., Appl. Phys. Express 5 015101 (2012), [4] S. Nakaharai, et al., 2012 IEEE International Electron Devices Meeting (IEDM), Technical Digest p.72 (2012)