Helium ion microscopy of graphene: beam damage, image quality and edge contrast

Abstract

A study to analyse beam damage, image quality and edge contrast in the helium ion microscope (HIM) has been undertaken. The sample investigated was graphene. Raman spectroscopy was used to quantify the disorder that can be introduced into the graphene as a function of helium ion dose. The effects of the dose on both freestanding and supported graphene were compared. These doses were then correlated directly to image quality by imaging graphene flakes at high magnification. It was found that a high magnification image with a good signal to noise ratio will introduce very significant sample damage. A safe imaging dose of the order of 10 13 He + cm −2 was established, with both graphene samples becoming highly defective at doses over 5 × 10 14 He + cm −2 . The edge contrast of a freestanding graphene flake imaged in the HIM was then compared with the contrast of the same flake observed in a scanning electron microscope and a transmission electron microscope. Very strong edge sensitivity was observed in the HIM. This enhanced edge sensitivity over the other techniques investigated makes the HIM a powerful nanoscale dimensional metrology tool, with the capability of both fabricating and imaging features with sub-nanometre resolution.

Raman study of damage extent in graphene nanostructures carved by high energy helium ion beam

“…No significant shifts of all the peaks were observed. A Zeiss ORION scanning helium ion microscope (HIM) was used for precision patterning [16][17][18][41][42][43][44]. We consistently accelerated He + ions at 30kV to obtain good image brightness and contrast.…”

Diamond-Like Carbon Nanofoam from Low-Temperature Hydrothermal Carbonization of a Sucrose/Naphthalene Precursor Solution

“…The HIM provides a stronger surface sensitivity compared to the electron microscope. The HIM also yields images with a better signal-to-noise ratio [115]. Detailed modeling of the HIM image formation with secondary electron analysis has been provided [116].…”

The effect of residual gas scattering on Ga ion beam patterning of graphene

“…This behaviour follows the typical amorphization trajectory of graphene, where pristine graphene is first transformed into nanocrystalline graphene with defects (stage 1 disorder), and then further into amorphous carbon (stage 2 disorder). It is also commonly observed for exposures to Ar þ ions, 24,25 He þ ions, [26][27][28] or even electrons. 29 However, the small mass of the He þ ions and electrons results in less efficient momentum transfer and lower sputtering yield, therefore the dose at which the transition from stage 1 to stage 2 occurs is consequently much higher.…”