Abstract
Two-dimensional (2D) materials usually have a layer-dependent work function, which require fast and accurate detection for the evaluation of their device performance. A detection technique with high throughput and high spatial resolution has not yet been explored. Using a scanning electron microscope, we have developed and implemented a quantitative analytical technique which allows effective extraction of the work function of graphene. This technique uses the secondary electron contrast and has nanometre-resolved layer information. The measurement of few-layer graphene flakes shows the variation of work function between graphene layers with a precision of less than 10 meV. It is expected that this technique will prove extremely useful for researchers in a broad range of fields due to its revolutionary throughput and accuracy.
Highlights
Two-dimensional (2D) materials usually have a layer-dependent work function, which require fast and accurate detection for the evaluation of their device performance
It needs to be tailored to particular device applications for optimised performance, work function engineering is an important step in the transition from lab-scale devices to industrial applications[5]
Several techniques have already been demonstrated for the characterisation of the work function of graphene[6,7]. The application of these techniques appears to be limited by various environmental factors and specimen interactions in scanning probe techniques[9], such as low throughput/low spatial resolution for photoelectron emission spectroscopy (PEEM)[14]
Summary
Secondary electron images of few-layer graphene were obtained from both scanning electron microscopes (Carl Zeiss Supra and FEI Strata DB235) and a helium ion microscope (Carl Zeiss Orion Plus). The base chamber vacuum was approximately 2 × 10−5 mBar. In the HIM imaging process, SE images were obtained from a Carl Zeiss Orion Plus scanning helium ion microscope. The beam current was kept at 1 pA which resulted in an irradiation dose of approximately 5 × 1011 ions/cm[2] for each scan. When imaging graphene on the SiO2/Si substrate, the charge neutralization system (electron flood gun) was always turned on to compensate positive charges introduced by He+ irradiation (Flood gun energy: 500 eV; Flood time: 10 μ s). By differentiating the measured grid voltage – intensity curve we can obtain the SE spectrum
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