S.C. Xu

Graphene/Cu nanoparticle hybrids fabricated by chemical vapor deposition as surface-enhanced Raman scattering substrate for label-free detection of adenosine.

We present a graphene/Cu nanoparticle hybrids (G/CuNPs) system as a surface-enhanced Raman scattering (SERS) substrate for adenosine detection. The Cu nanoparticles wrapped by a monolayer graphene shell were directly synthesized on flat quartz by chemical vapor deposition in a mixture of methane and hydrogen. The G/CuNPs showed an excellent SERS enhancement activity for adenosine. The minimum detected concentration of the adenosine in serum was demonstrated as low as 5 nM, and the calibration curve showed a good linear response from 5 to 500 nM. The capability of SERS detection of adenosine in real normal human urine samples based on G/CuNPs was also investigated and the characteristic peaks of adenosine were still recognizable. The reproducible and the ultrasensitive enhanced Raman signals could be due to the presence of an ultrathin graphene layer. The graphene shell was able to enrich and fix the adenosine molecules, which could also efficiently maintain chemical and optical stability of G/CuNPs. Based on the G/CuNPs system, the ultrasensitive SERS detection of adenosine in varied matrices was expected for the practical applications in medicine and biotechnology.

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.

SERS detection of R6G based on a novel graphene oxide/silver nanoparticles/silicon pyramid arrays structure

We present a novel surface-enhanced Raman scattering (SERS) substrate based on graphene oxide/silver nanoparticles/silicon pyramid arrays structure (GO/Ag/PSi). The SERS behaviors are discussed and compared by the detection of R6G. Based on the contrast experiments with PSi, GO/PSi, Ag/PSi and GO/AgA/PSi as SERS substrate, the perfect bio-compatibility, good homogeneity and chemical stability were confirmed. We also calculated the electric field distributions using Finite-difference time-domain (FDTD) analysis to further understand the GO/Ag/PSi structure as a perfect SERS platform. These experimental and theoretical results imply that the GO/Ag/PSi with regular pyramids array is expected to be an effective substrate for label-free sensitive SERS detections in areas of medicine, food safety and biotechnology.

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.

Direct synthesis of graphene on any nonmetallic substrate based on KrF laser ablation of ordered pyrolytic graphite

We present a method for few-layer graphene growth on nonmetallic substrates using excimer KrF laser ablation of ordered pyrolytic graphite. The graphene is scalable and its thickness is controllable. It can be deposited on virtually any nonmetallic substrates at a relative low temperature of 750??C. This laser-based method is highly efficient and the whole growing process takes less than 100?s. Raman spectroscopy confirms the formation of sp2-bonded carbon with a grain size of about 40?nm. The optical transmittance and conductivity of the graphene films are comparable with exfoliated or metal-catalyzed graphene. This work demonstrates a promising laser-based, transfer-free technique for synthesis of 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.

Sapphire-based graphene saturable absorber for long-time working femtosecond lasers

We report a long-time working femtosecond laser using metal-free sapphire-based graphene as a saturable absorber (SA). The sapphire-based graphene yielded excellent nonlinear saturable absorption properties and was demonstrated to be suitable as an SA for an ultrafast solid-state laser. Stable mode-locked pulses of 325 fs were obtained at a central wavelength of 1032 nm with a repetition rate of 66.3 MHz. At pump power of 8.23 W the average output power was 1.78 W and the highest pulse energy reached 26.8 nJ with a peak power of 72.6 kW. Our work opens up a facile route for making reliable graphene SA in the mode-locking technique and also displays an exciting prospect in making low-cost and ultrafast lasers.

Direct growth of graphene on quartz substrate as saturable absorber for femtosecond solid-state laser

We present a novel method for the direct metal-free growth of graphene on quartz substrate. The direct-grown graphene yields excellent nonlinear saturable absorption properties and is demonstrated to be suitable as a saturable absorber (SA) for an ultrafast solid-state laser. Nearly Fourier-limited 367 fs was obtained at a central wavelength of 1048 nm with a repetition rate of 105.7 MHz. At a pump power of 7.95 W, the average output power was 1.93 W and the highest pulse energy reached 18.3 nJ, with a peak power of 49.8 kW. Our work opens an easy route for making a reliable graphene SA with a mode-locking technique and also displays an exciting prospect in making low-cost and ultrafast lasers.