Nanoscale Raman Spectroscopy of graphene nanodevice structures

Abstract

Graphene is an atomically-thin 2-dimentional layer of carbon atoms. Since 2004, it has been attracting significant attention for various type of device applications due to its unique properties. In particular, applications of graphene for micro- and nanoscale devices is one of the most demanded and promising research fields. For further advancement of technological flexibility in designing graphene nanodevices, introducing defects to graphene could be a useful method to modify its material properties. Therefore, how to control defects in graphene and how to observe the effects of defects are one of the most important issues. For instance, the defect formed on graphene has been observed to make influence on the charge carrier concentration. Moreover, the defect introduction to graphene will change the phase of the graphene from crystalline to amorphous.

Tip-enhanced Raman Spectroscopy (TERS) is a combination of Scanning Probe Microscopy (SPM) and micro-Raman spectroscopy. While micro Raman has played a crucial role to characterise graphene material properties at a microscale level, TERS is considered to be a powerful tool to investigate and characterise nanostructure devices, defect density, and doping with high spatial resolution down to sub 100 nm.

In this work my aim is to establish TERS measurement techniques for various types of graphene. Then the TERS is applied for evaluating defect density, edge properties and strain induced in the graphene nanoelectronic and nanoelectromechanical devices to investigate the physics of graphene nanodevices. I have started to optimise the TERS tools on graphene to achieve high spatial resolution. Then I have applied TERS for studying the stress and strain and defect formation on suspended graphene on SiNWs. The result shows that the peak position is shifted in the TERS spectra and additionally the local defects at the edge of SiNW have been observed
with a spatial resolution of ~ 100 nm. Then I have introduced defects using helium ion irradiation on graphene nanoribbon (GNR). TERS is used to study the graphene edges and irradiation boundary of in the graphene channels. I have succeeded in taking TERS spectra across the edge of the He-ion-irradiated region on graphene for the first time and confirmed that higher spatial resolution is achievable with TERS.

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