Free-standing graphene on microstructured silicon vertices for enhanced field emission properties

Controlled deposition of graphene in different orientations relative to the substrate is challenging and majority of existing deposition methods lead to sheets that lay flat on the substrate surface, limiting the potential applications in which the exposed sheet surface area and the atomically thin edges of graphene are exploited. Here we describe a simple and general solution-based methodology for the fabrication of random arrays of free-standing few-layer graphene (FLG) flakes on micro-spikes engraved on Si substrates. This should greatly benefit applications using freestanding graphene, such as in energy storage/conversion devices and bright electron sources. As a proof of concept, it is shown that the FLG sheets protruding on the top of micro-spikes are good electron emitters with turn-on fields as low as 2.3 V mu m(-1) and field enhancement of few thousands. The emission performance and long-term stability achieved by this hierarchical deposition process are superior to that of planar graphene sheets and demonstrate promise for applications. Mechanisms leading to formation of free-standing FLG flakes are discussed.