Chemically Cleaved Graphite Support Films for Electron Microscopy

Today, high resolution electron microscopy is seriously limited by the noise which results from the irregularity of the substrates used. For example, this limitation is of particular significance in recent attempts (1) to elucidate by electron microscopy the nucleotide sequence of D N A by chemical at tachment of base-specific, heavy metal markers. The following technique was originally developed in conjunction with efforts to improve the "visibili ty" of markers presently being employed in such studies. Fern~ndez-Mor~n (2) has pointed out that single crystal substrates have the advantage of being smooth and presumably regular. However, the preparation of appropriate films is difficult; previously adhesives have been used to cleave single graphite crystals (3,1), and thin crystals of graphite have been grown epitaxially on single crystals of nickel (4). Here we report a chemical method involving alkali splitting of graphite oxide. Graphite oxide is an unusual sandwich compound composed of alternate layers of carbon and oxygen with each carbon layer thought to be organized in the hexagonal lattice array characteristic of graphite (5). I t is cleaved into thin lamellae by immersion in dilute solutions of NaOH. These lamellae, some of which are thought to be only one carbon atom thick, apparently remain complexed with oxygen but can be reduced to pure graphite by appropriate treatment (6). The extremely thin graphite sheets thus formed are then suspended on perforated films to serve as specimen-supporting substrates.