Abstract
Contamination on two-dimensional (2D) crystal surfaces poses serious limitations on fundamental studies and applications of 2D crystals. Surface residues induce uncontrolled doping and charge carrier scattering in 2D crystals, and trapped residues in mechanically assembled 2D vertical heterostructures often hinder coupling between stacked layers. Developing a process that can reduce the surface residues on 2D crystals is important. In this study, we explored the use of atomic force microscopy (AFM) to remove surface residues from 2D crystals. Using various transmission electron microscopy (TEM) investigations, we confirmed that surface residues on graphene samples can be effectively removed via contact-mode AFM scanning. The mechanical cleaning process dramatically increases the residue-free areas, where high-resolution imaging of graphene layers can be obtained. We believe that our mechanical cleaning process can be utilized to prepare high-quality 2D crystal samples with minimum surface residues.
Highlights
Two-dimensional (2D) crystals have attracted widespread attention in recent years due to their emerging properties and potential applications in various fields (Butler et al 2013; Fiori et al 2014)
We explored the potential of using atomic force microscopy (AFM) to remove surface residues from 2D crystals (Goossens et al 2012; Jain et al 2018; Lindvall et al 2012; Rosenberger et al 2018; Schweizer et al 2020)
The surface of 2D crystals prepared by mechanical transfer can suffer from PDMS residues and requires special attention, especially for surface-sensitive studies
Summary
Two-dimensional (2D) crystals have attracted widespread attention in recent years due to their emerging properties and potential applications in various fields (Butler et al 2013; Fiori et al 2014). 2D heterostructures prepared by assembling various 2D crystals in the lateral or vertical directions serve as new platforms for various investigations and applications (Geim and Grigorieva 2013). In these systems, the surface quality of 2D crystals, including the degree of residual surface contamination, is important, and surface contamination on 2D crystals often poses serious limitations on fundamental studies and applications (Chen et al 2016; Dean et al 2010).
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