Towards controlled graphene properties: Direct synthesis on dielectrics and Tuning via stress

Interest in graphene since its isolation in 2004 has rapidly escalated. It has been described as nature's thinnest elastic material and its exceptional mechanical and electronic properties make it an extremely exciting material. Within the realm of electronics , it is its one atoms thickness, planar geometry, high current-carrying capacity and thermal conductivity and potential to open a gap when existing as a narrow ribbon that hold particular promise. These features make it ideally suited for further miniaturizing electronics to form ultra-small devices and components for future semiconductor technology. In order for graphene to realize its potential in electronics various obstacles need to be overcome. One of the more important aspects is its actual synthesis. Various routes exis t to synthesize graphene; however, most are not best suited for integration into current silicon technology. The primary routes are through graphite exfoliation, epitaxial graphene, graphene oxide and chemical vapor deposition. Most of these routes require the graphene to be transferred onto a dielectric or, as in the case of SiC, require high temperatures. To use graphene as the basis of field-effect transistors at room temperature one needs to modify graphene's semi-metallic nature so as to open a band gap. When existing as narrow strips (nanoribbons) quantum confinement effects lead to band gap formation. Most band gap engineering routes use multiple lithographic steps to fabricate a graphene device. This leads to contamination and disorder to the flake. Dry lithograp hy-free techniques can help, nonetheless technical difficulties still remain. Anoth er approach is chemical modification, for example, graphene oxide in which hy-droxyl and other chemical groups attach to graphene. Although the technique is able to lift the degeneracy of the π band at the Fermi level of graphene, it is difficult to control its electronic properties and avoid defect formation. A more attractive route to control graphene's properties is through mechanical strain engineeri ng which modifies graphene's geometrical structures. For example, substrate-induced sublattice symmetry breaking in expitaxially grown graphene can give rise to ener gy gaps; scanning tunneling microscopic studies show evidence for strain-induced spatial modulations in the local conductance of graphene on SiO 2 ; strain with triangular symmetry induces strong gauge field that effectively act as a uniform magnetic field exceeding 10 T. However most of these experiments are based on graphene layers with fixed static strain. Thus, new techniques allowing for strain on demand are quite important in order to …