Abstract
The remarkable mechanical and electronic properties of graphene make it an ideal candidate for next generation nanoelectronics. With the recent development of commercial-level single-crystal graphene layers, the potential for manufacturing household graphene-based devices has improved, but significant challenges still remain with regards to patterning the graphene into devices. In the case of graphene supported on a substrate, traditional nanofabrication techniques such as e-beam lithography (EBL) are often used in fabricating graphene nanoribbons but the multi-step processes they require can result in contamination of the graphene with resists and solvents. In this letter, we report the utility of scanning helium ion lithography for fabricating functional graphene nanoconductors that are supported directly on a silicon dioxide layer, and we measure the minimum feature size achievable due to limitations imposed by thermal fluctuations and ion scattering during the milling process. Further we demonstrate that ion beams, due to their positive charging nature, may be used to observe and test the conductivity of graphene-based nanoelectronic devices in situ.
Highlights
Scanning helium ion microscopy (SHIM) and ion milling has emerged as a tool capable of fabricating graphene devices[1,2] with feature sizes down to ~5 nm[3]
As the ion beam is raster-scanned over the device, the accumulation of positive charge on the surface precludes the ejection of secondary electrons energetic enough to be detected[7]
As the width of the strip is increased to 12 nm (Fig. 1b), more electrons are conducted into the device and are sufficient enough to overcome the loss of secondary electrons due to the impinging ion beam
Summary
Scanning helium ion microscopy (SHIM) and ion milling (performed with the same instrument) has emerged as a tool capable of fabricating graphene devices[1,2] with feature sizes down to ~5 nm[3]. Simple graphene structures consisting of a strip and a pad (Fig. 1) were fabricated using such direct-write lithography[1] in a SHIM (see Methods section), with the graphene grounded to the instrument for charge compensation due to loss of secondary electrons. If the pad in the center of the device is not grounded because the graphene strip is poorly conducting, compensating electrons may not flow into the pad This will cause a depression of the graphene work function and subsequent lower yield of secondary electrons, resulting in a darker image. This effect may be used to test conductivity of devices in situ, thereby allowing for the estimation of the quality of a graphene conductor. Electrical conductivity in the patterned graphene structures was explored in situ by varying the size and width of the connecting strip in each device
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