Graphene Coatings for the Mitigation of Electron Stimulated Desorption and Fullerene Cap Formation

Graphene already has numerous applications in transmission electron microscopy. Here, we extend its application in electron microscopy by demonstrating its potential to stop electron induced desorption in nonconducting samples, where in essence charge build-up leads to surface atom desorption. Graphene films provide a conduction pathway to prevent charge build-up and do not interfere with the imaging process allowing the direct imaging of specimens sensitive to electron induced desorption. We also show that small graphene flakes on the surface of MgO transform to fullerenes or hemispherical fullerenes. The hemispherical fullerenes anchor to the MgO surface and are of particular interest as they suggest it should be possible to nucleate single walled carbon nanotubes on the surface of oxide supports without the need of a catalyst particle. T isolation of graphene by Novoselov and Geim in 2004 triggered mass interest in this material because of its amazing properties. It is believed that this material will eventually lead to remarkable applications in areas, such as biological engineering, optical electronics, ultrafiltration, composite materials, energy storage, and electronic devices. However, despite its great promise, real applications to date are somewhat limited, mostly because of technical difficulties, which, for the most part, one can anticipate will eventually be overcome. A key area where graphene applications are already making an impact and continue to develop is its use as an aid material in transmission electron microscopy (TEM). For example, the implementation of graphene membranes as a microscope slide to suspend atoms and molecules for their observation provides significant advantages over traditional amorphous carbon membranes. In addition, graphene membranes are excellent as cell windows for liquid cells, for in situ investigations of graphene at high bias and even as a template for the in situ catalyst-free growth of graphene and potentially of other 2D materials. In this work, we extend the application of graphene as an aid for TEM by demonstrating its potential to significantly reduce the effects of electron induced desorption, thus reducing specimen damage from exposure to an electron beam in a TEM. In practice, the technique will also be useful to prevent specimen damage because of electron stimulated desorption in low energy electron diffraction (LEED) and reflection high energy diffraction (RHEED). Several types of electron radiation damage can occur and they are discussed in greater detail by Egerton et al. These interactions can be elastic or inelastic events. Elastic scattering events in which the incoming electrons are electro-statically deflected by the Coulomb field from each atomic nucleus can lead to atom displacement or sputtering (atom removal). Elastic scattering processes are also responsible for electrondiffraction patterns, and, diffraction and phase contrast in the observed images. Inelastic interactions also occur and take place through incoming electrons having Coulomb interactions with the atomic electrons that surround each nucleus. These interactions are better known for their analytical potential for electron energy loss spectroscopy (EELS) and the emission of Received: June 4, 2014 Revised: August 10, 2014 Published: August 12, 2014 Article