Controllable chemical vapor deposition growth of few layer graphene for electronic devices.

Because of its atomic thickness, excellent properties, and widespread applications, graphene is regarded as one of the most promising candidate materials for nanoelectronics. The wider use of graphene will require processes that produce this material in a controllable manner. In this Account, we focus on our recent studies of the controllable chemical vapor deposition (CVD) growth of graphene, especially few-layer graphene (FLG), and the applications of this material in electronic devices. CVD provides various means of control over the morphologies of the produced graph ene. We studied several variables that can affect the CVD growth of graphene, including the catalyst, gas flow rate, growth time, and growth temperature and successfully achieved the controlled growth of hexagonal graphene crystals. Moreover, we developed several modified CVD methods for the controlled growth of FLGs. Patterned CVD produced FLGs with desired shapes in required areas. By introducing dopant precursor in the CVD process, we produced substitutionally doped FLGs, avoiding the typically complicated post-treatment processes for graphene doping. We developed a template CVD method to produce FLG ribbons with controllable morphologies on a large scale. An oxidation-activated surface facilitated the CVD growth of polycrystalline graphene without the use of a metal catalyst or a complicated postgrowth transfer process. In devices, CVD offers a controllable means to modulate the electronic properties of the graphene samples and to improve device performance. Using CVD-grown hexagonal graphene crystals as the channel materials in field-effect transistors (FETs), we improved carrier mobility. Substitutional doping of graphene in CVD opened a band gap for efficient FET operation and modulated the Fermi energy level for n-type or p-type features. The similarity between the chemical structure of graphene and organic semiconductors suggests potential applications of graphene in organic devices. We used patterned CVD FLGs as the bottom electrodes in pentacene FETs. The strong π-π interactions between graphene and pentacene produced an excellent interface with low contact resistance and a reduced injection barrier, which dramatically enhances the device performance. We also fabricated reversible nanoelectromechanical (NEM) switches and a logic gate using the FLG ribbons produced using our template CVD method. In summary, CVD provides a controllable means to produce graphene samples with both large area and high quality. We developed several modified CVD methods to produce FLG samples with controlled shape, location, edge, layer, dopant, and growth substrate. As a result, we can modulate the properties of FLGs, which provides materials that could be used in FETs, OFETs, and NEM devices. Despite remarkable advances in this field, further exploration is required to produce consistent, homogeneous graphene samples with single layer, single crystal, and large area for graphene-based electronics.