Xingguo Gao

Flexible and transparent graphene-based loudspeakers

Flexible and transparent graphene films have been fabricated via chemical vapor deposition method, and an extremely thin and lightweight loudspeaker was obtained by transferring the graphene films on both side of the polyvinylidene fluoride film. Once fed by sound frequency electric field, the graphene-based acoustic actuator could emit loud sounds in a wide frequency range. Such film loudspeakers are transparent, flexible, magnet-free and can be tailored into any shape and size, which have wide potential applications in fabricating new type of transparent and flexible devices.

Direct synthesis of graphene on SiO2 substrates by chemical vapor deposition

Continuous and uniform graphene films were directly grown on SiO2 substrates using a chemical vapor deposition system with two-temperature zones assembled. The carbon species from the high temperature zone nucleate in the low temperature zone, initiating the growing process of graphene. The films are predominantly single-layer graphene, with a small percentage of the area having a few layers, whose optical transmittance and electrical conductivity can be comparable with transferred metal-catalyzed graphene. This method avoids the need for either a metal catalyst or a complicated and skilled post growth transfer process and favors the application of graphene as a transparent electrode.

Facile synthesis of graphene on dielectric surfaces using a two-temperature reactor CVD system

Direct deposition of graphene on a dielectric substrate is demonstrated using a chemical vapor deposition system with a two-temperature reactor. The two-temperature reactor is utilized to offer sufficient, well-proportioned floating Cu atoms and to provide a temperature gradient for facile synthesis of graphene on dielectric surfaces. The evaporated Cu atoms catalyze the reaction in the presented method. C atoms and Cu atoms respectively act as the nuclei for forming graphene film in the low-temperature zone and the zones close to the high-temperature zones. A uniform and high-quality graphene film is formed in an atmosphere of sufficient and well-proportioned floating Cu atoms. Raman spectroscopy, scanning electron microscopy and atomic force microscopy confirm the presence of uniform and high-quality graphene.

Role of cobalt in room-temperature ferromagnetic Co-doped ZnO thin films

A series of Co-doped ZnOthin films were prepared under various deposition conditions using the pulsed laser deposition method. X-ray photoelectron spectroscopy(XPS) and XPS depth profiling were used to detect the elemental valence states of Zn, Co and O. It was found that the filmsdeposited under low temperature and high oxygen pressure exhibited intrinsic ferromagnetic properties due to oxidation of Co (Co2+) from the material. However, when the films were deposited under high temperature and low oxygen pressure, metallic cobalt (Co0) appeared and the ferromagnetism was greatly enhanced.