Yanfei Xu

Porphyrin and Fullerene Covalently Functionalized Graphene Hybrid Materials with Large Nonlinear Optical Properties

The nonlinear optical properties of two novel graphene nanohybrid materials covalently functionalized with porphyrin and fullerene were investigated by using the Z-scan technique at 532 nm in the nanosecond and picosecond time scale. Results show that covalently functionalizing graphene with the reverse saturable absorption chromospheres porphyrin and fullerene can enhance the nonlinear optical performance in the nanosecond regime. The covalently linked graphene nanohybrids offer performance superior to that of the individual graphene, porphyrin, and fullerene by combination of a nonlinear mechanism and the photoinduced electron or energy transfer between porphyrin or fullerene moiety and graphene.

Nonlinear optical properties of graphene oxide in nanosecond and picosecond regimes

The nonlinear optical properties of graphene oxide (GO) were investigated at 532 nm in nanosecond and picosecond regimes. Results show that two-photon absorption dominates nonlinear absorption process of GO in the case of picosecond pulses, while excited state nonlinearities play an important role in the case of nanosecond pulses. Additionally, we compared nonlinear optical properties of three different dimensional carbon-based materials (two-dimensional graphene, one-dimensional carbon nanotube, and zero-dimensional fullerene) in nanosecond and picosecond regimes, respectively. The nonlinear mechanism of GO is distinctly different from nonlinear scattering of carbon nanotube and excited state nonlinearity of fullerene.

Transient thermal effect, nonlinear refraction and nonlinear absorption properties of graphene oxide sheets in dispersion.

The nonlinear refraction (NLR) properties of graphene oxide (GO) in N, N-Dimethylformamide (DMF) was studied in nanosecond, picosecond and femtosecond time regimes by Z-scan technique. Results show that the dispersion of GO in DMF exhibits negative NLR properties in nanosecond time regime, which is mainly attributed to transient thermal effect in the dispersion. The dispersion also exhibits negative NLR in picosecond and femtosecond time regimes, which are arising from sp(2)- hybridized carbon domains and sp(3)- hybridized matrix in GO sheets. To illustrate the relations between NLR and nonlinear absorption (NLA), NLA properties of the dispersion were also studied in nanosecond, picosecond and femtosecond time regimes.

Nonlinear optical and optical limiting properties of graphene oxide–Fe3O4 hybrid material

The nonlinear optical (NLO) and optical limiting properties of a graphene oxide hybrid material coordinated with Fe3O4 nanoparticles (GO–Fe3O4) were studied by using the Z-scan technique at 532 nm in the nanosecond and picosecond regimes. Results show that GO–Fe3O4 exhibits enhanced NLO and optical limiting properties in comparison with the pristine GO in the nanosecond regime. Compared with fullerene (C60) in toluene at different concentrations, GO–Fe3O4 exhibits a weaker optical limiting effect than C60 at high concentration, but shows a stronger optical limiting effect than C60 at low concentration in the high input fluence region.

Toward All-Carbon Electronics: Fabrication of Graphene-Based Flexible Electronic Circuits and Memory Cards Using Maskless Laser Direct Writing

Owing to its extraordinary electronic property, chemical stability, and unique two-dimensional nanostructure, graphene is being considered as an ideal material for the highly expected all-carbon-based micro/nanoscale electronics. Herein, we present a simple yet versatile approach to constructing all-carbon micro/nanoelectronics using solution-processing graphene films directly. From these graphene films, various graphene-based microcosmic patterns and structures have been fabricated using maskless computer-controlled laser cutting. Furthermore, a complete system involving a prototype of a flexible write-once-read-many-times memory card and a fast data-reading system has been demonstrated, with infinite data retention time and high reliability. These results indicate that graphene could be the ideal material for fabricating the highly demanded all-carbon and flexible devices and electronics using the simple and efficient roll-to-roll printing process when combined with maskless direct data writing.

Direct patterning on reduced graphene oxide nanosheets using femtosecond laser pulses

Micro- and nanostructures were fabricated directly on graphene nanosheets by controlling the conditions of femtosecond laser pulse etching. High quality graphene micro- and nanostructures with a minimum width of 492 nm were obtained as the graphene nanosheets used in our experiments were large-scale, uniform and highly conductive. Various complex patterns were successfully created through femtosecond laser etching. Furthermore, by managing the laser energy, the graphene under the Au electrodes could be completely or partly removed. This technology of direct patterning of micro- and nanostructures on graphene through femtosecond laser technology might pave the way for the integration of graphene-based electronic microdevices.

Periodic microstructures fabricated by multiplex interfering femtosecond laser beams on graphene sheet

We fabricated successfully microstructures on graphene sheet by using multiplex interfering femtosecond laser beams. The symmetry, period and the fabrication depth are all influenced by the amount of interfering femtosecond beams. Using this method we fabricated grating-like microstructures and square lattice. In addition, we developed double-exposure technique with 2-beam interference and achieved square and rhombus lattice on graphene sheet.