Jiarui Yang

Observation of microscale superlubricity in graphite.

Through experimental study, we reveal superlubricity as the mechanism of self-retracting motion of micrometer sized graphite flakes on graphite platforms by correlating respectively the lock-up or self-retraction states with the commensurate or incommensurate contacts. We show that the scale-dependent loss of self-retractability is caused by generation of contact interfacial defects. A HOPG structure is also proposed to understand our experimental observations, particularly in term of the polycrystal structure. The realisation of the superlubricity in micrometer scale in our experiments will have impact in the design and fabrication of micro/nanoelectromechanical systems based on graphitic materials.

Measurement of the cleavage energy of graphite

The basal plane cleavage energy (CE) of graphite is a key material parameter for understanding many of the unusual properties of graphite, graphene and carbon nanotubes. Nonetheless, a wide range of values for the CE has been reported and no consensus has yet emerged. Here we report the first direct, accurate experimental measurement of the CE of graphite using a novel method based on the self-retraction phenomenon in graphite. The measured value, 0.37±0.01 J m−2 for the incommensurate state of bicrystal graphite, is nearly invariant with respect to temperature (22 °C≤T≤198 °C) and bicrystal twist angle, and insensitive to impurities from the atmosphere. The CE for the ideal ABAB graphite stacking, 0.39±0.02 J m−2, is calculated based on a combination of the measured CE and a theoretical calculation. These experimental measurements are also ideal for use in evaluating the efficacy of competing theoretical approaches.

A graphite nanoeraser

We present here a method for cleaning intermediate-size (up to 50 nm) contamination from highly oriented pyrolytic graphite and graphene. Electron-beam-induced deposition of carbonaceous material on graphene and graphite surfaces inside a scanning electron microscope, which is difficult to remove by conventional techniques, can be removed by direct mechanical wiping using a graphite nanoeraser, thus drastically reducing the amount of contamination. We discuss potential applications of this cleaning procedure.

Optical methods for determining thicknesses of few-layer graphene flakes.

Optical microscopy (OM) methods have been commonly used as a convenient means for locating and identifying few-layer graphene (FLG) on SiO2/Si substrates. However, it is less clear how reliably optical images of FLG could be used to determine the sample thickness. In this work, various OM methods based on color differences and color contrasts are presented and their reliabilities are evaluated. Our analysis shows that these color-based OM methods depend sensitively on certain parameters of the measuring system, particularly the light source and the reference substrate. These parameters have usually been overlooked and less controlled in routine experiments. From evaluating the performance of these OM methods with both virtual and real FLG samples, we propose some practical guidelines for minimizing the impact of these less-controlled experimental parameters and provide a user-friendly MATLAB script for facilitating the implementation.

Mechanics and Multidisciplinary Study for Creating Graphene-Based van der Waals Nano/Microscale Devices

Elastic resonators are the core elements for various types of nano/micro scale instruments and devices (e.g. gyroscopes, mass and acceleration sensors, AFM, SNOM). However due to the inevitable thermal dissipation in the elastic deforming modes their quality factor dramatically reduces as size shrinks, which is the bottleneck challenge for the application in nano devices. Van der Waals (vdW) oscillators recently invented (Zheng QS, Jiang Q, Phys Rev Lett, 88:045503, 2002) have two orders of magnitude higher in both motion speed and quality factor, that are the two major factors determining the performance of various nano/microscale devices, for example nano/micromechanical gyroscopes. Based on the vdW oscillators a completely new class of nano/micro devices is proposed. Furthermore the recently discovered self-retraction motion between two large scale sheared graphite flakes (Zheng QS, et al, Phys Rev Lett, 100:067205, 2008) has greatly promoted the graphene based vdW devices. By combining with the mature microfabrication technology for mass production, the graphene-based vdW sliding devices offer a great candidate for a new type of nano/micro devices, as well as high-density/high-speed hard diskettes. In this paper we report new experimental and theoretical advances in these fields, including self-retraction motion and dissipation mechanisms, challenges in surface physics and chemistry, novel stripe/kink structures arising from instabilities, transferring, self-assembling, and ultrahigh-speed record technology.