Graphene flakes obtained by local electro-exfoliation of graphite with a STM tip

Abstract

Graphite surfaces can be manipulated by several methods to create graphene structures of different shapes and sizes. Scanning tunneling microscopy (STM) can be used to create these structures either through mechanical contact between the tip and the surface or through electro-exfoliation. In the latter, the mechanisms involved in the process of exfoliation at an applied voltage are not fully understood. Here, we show how a graphite surface can be locally exfoliated in a systematic manner by applying an electrostatic force with a STM tip at the edge of a terrace, forming triangular flakes several nanometers in length. We demonstrate, through experiments and simulations, how these flakes are created by a two-step process: first a voltage ramp must be applied at the edge of the terrace, and then the tip must be scanned perpendicular to the edge. Ab initio electrostatic calculations reveal that the presence of charges on the graphite surface weakens the interaction between layers allowing for exfoliation at voltages in the same range as those used experimentally. Molecular dynamics simulations show that a force applied locally on the edge of a step produces triangular flakes such as those observed under STM. Our results provide new insights into surface modification that can be extended to other layered materials.

Nanocrystalline graphene at high temperatures: insight into nanoscale processes

“…This observed migration is different and slower than the previously reported high mobility of carbon nanostructures and graphene nanoakes on top of a graphitic substrate with weak interactions between nanostructures and substrate. 31,42,43 Previous experimental observations have shown a super uidic behavior of graphene nanoakes (GNF) even at temperatures as low as 5 K. 44 Similarly, theoretical calculations show a high diffusion coefficient of (6.7 AE 0.6) Â 10 À6 cm 2 s À1 for GNF on top of defect-free graphene substrates at 300 K. 43 This is consistent with our molecular dynamics studies (MD) at 1500 K, which also show fast diffusion of GNF on top of graphene (ESI Video S2 †). Considering this high mobility of GNF on top of graphene, it would not be possible to image this migration at high temperatures with our current exposure time of 1 s. However, in case of nanocrystalline graphene, the graphene substrate is highly defective and the defects limit diffusion by locally pinning GNFs.…”

Reactivity on and of Graphene Layers: Scanning Probe Microscopy Reveals

“…by 7 V voltage ramp with sequential scanning, Fig. 19c, [102]) or to lithographically burn-out arbitrary shapes with nm precision (by continuous scanning in air with bias ! +2 V, Fig.…”

“…b The use of corrals in HOPG for the confinement of tip-induced polymerization of diacetylene assemblies [96]. Direct exfoliation (c, [102]) and oxidative etching (d, [103]) of graphene layers with STM tip. a adapted with permission from [94] • AFM to determine film thickness (via mechanical scratching of grafted film), morphology and roughness; • STM to prove nanoscale arrangement of grafted species, to distinguish them from physisorbed impurities and for spatially controlled degrafting (see below); • XPS to prove chemical nature/integrity of functional groups (after grafting or any subsequent treatment of the grafts).…”

Engineering carbon materials with electricity

“…Rubio-Verdú and colleagues showed that a scanning tunneling microscopy (STM) tip could be used to locally exfoliate HOPG by applying an electrostatic force at the edge of a terrace, forming triangular flakes [48]. Macroscopic exfoliation of graphite was demonstrated by Gao et al [49].…”