Jinhao Zhou

Synthesis of nitrogen-doped graphene by chemical vapour deposition using melamine as the sole solid source of carbon and nitrogen

Nitrogen doping is a promising method to modulate the electrical properties of graphene. However, the reported nitrogen-doped graphene (NG) films usually show low electron concentration and low carrier mobility. In this study, we have demonstrated the chemical vapour deposition of NG films, where melamine was used as the sole source of both carbon and nitrogen. The studies show that the nitrogen content and configurations are strongly dependent on the growth temperature. At a growth temperature of 990 °C, the total N content and graphitic-N/total N simultaneously reached the maximum values of ∼5.6 at% and ∼40%, respectively. Further, the electrical studies reveal that the NG film displays typical n-type behaviour in air. The Dirac point and mobility were determined to be ∼−25 V and ∼74 cm2 V−1 s−1, respectively, which indicate that the as-synthesized NG film has high electron concentration and high carrier mobility. This can be attributed to the significant increase in the ratio of graphitic-N to total N, because graphitic-N has a higher electron donor ability and shows lower carrier scattering than do pyridinic-N and pyrrolic-N. This study is beneficial for not only the carrier transport mechanism, but also potential applications of NG film.

Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers

Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and wide-wavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses.

Observation of tunable electrical bandgap in large-area twisted bilayer graphene synthesized by chemical vapor deposition.

Although there are already many efforts to investigate the electronic structures of twisted bilayer graphene, a definitive conclusion has not yet been reached. In particular, it is still a controversial issue whether a tunable electrical (or transport) bandgap exists in twisted bilayer graphene film until now. Herein, for the first time, it has been demonstrated that a tunable electrical bandgap can be opened in the twisted bilayer graphene by the combination effect of twist and vertical electrical fields. In addition, we have also developed a facile chemical vapor deposition method to synthesize large-area twisted bilayer graphene by introducing decaborane as the cocatalyst for decomposing methane molecules. The growth mechanism is demonstrated to be a defined-seeding and self-limiting process. This work is expected to be beneficial to the fundamental understanding of both the growth mechanism for bilayer graphene on Cu foil and more significantly, the electronic structures of twisted bilayer graphene.

Graphene-Based D-Shaped Polymer FBG for Highly Sensitive Erythrocyte Detection

Graphene-based silica fiber-optic sensors, with high sensitivity, fast response, and low cost, have shown great promise for gas sensing applications. In this letter, by covering a monolayer of p-doped graphene on a D-shaped microstructured polymer fiber Bragg grating (FBG), we propose and demonstrate a novel biochemical probe sensor, the graphene-based D-shaped polymer FBG (GDPFBG). Due to the graphene-based surface evanescent field enhancement, this sensor shows high sensitivity to detect surrounding biochemical parameters. By monitoring the Bragg peak locations of the GDPFBG online, human erythrocyte (red blood cell) solutions with different cellular concentrations ranging from 0 to 104 ppm were detected precisely, with the maximum resolution of sub-ppm. Such a sensor is structurally compact, is clinically acceptable, and provides good recoverability, offering a state-of-the-art polymer-fiber-based sensing platform for highly sensitive in situ and in vivo cell detection applications.

Highly sensitive and selective fiber-optic Fabry-Perot volatile organic compounds sensor based on a PMMA film

A compact fiber-optic Fabry-Perot interferometric (FFPI) volatile organic compounds (VOCs) sensor is fabricated based on a single mode fiber (SMF) and a polymethyl methacrylate (PMMA) film. The VOCs induce the swelling effect and refractive index changes of PMMA film. The swelling of PMMA film affects the cavity length of Fabry-Perot interferometer resulting in shift of resonant dip, while the change in refractive index influences reflection resulting in change of extinction ratio (ER). The sensitivities of 2.7 pm/ppm for ethanol and 2.17 pm/ppm for acetone are achieved. Moreover, this sensor is insensitive to the inorganic gases. In addition, it has the advantages of ease of fabrication and high sensitivity to VOCs.

Growth and properties of large-area sulfur-doped graphene films

Heteroatom doping can effectively tune the structure and properties of graphene. Theoretical calculations indicate that sulfur doping can effectively modify the band structure and further modulate the carrier transport properties of graphene. However, it is still a big challenge to synthesize large-area sulfur-doped graphene (SG) films with a high sulfur doping concentration and reasonable electrical properties since sulfur has a much larger atomic radius than carbon. In this study, the solid organic source thianthrene (C12H8S2) is employed as both a carbon source and sulfur dopant to grow large-area, few-layered SG films via chemical vapor deposition (CVD). The results show that the doping concentration, doping configuration and electrical properties can be effectively tuned via the hydrogen flux. The sulfur doping concentration is as high as 4.01 at% and the maximal mobility of SG can reach up to 270 cm2 V−1 s−1, which are the highest ever reported for sulfur-doped graphene.

Flexible, transparent and high-power triboelectric generator with asymmetric graphene/ITO electrodes

The reported flexible and transparent triboelectric generator (FTTG) can only output ultralow power density (∼2 μW cm(-2)), which has seriously hindered its further development and application. The low power density of FTTG is mainly limited by the transparent material and the electrode structure. Herein, for the first time, a FTTG with a superior power density of 60.7 μW cm(-2) has been fabricated by designing asymmetric electrodes where graphene and indium tin oxide (ITO) act as top and bottom electrodes respectively. Moreover, the performance of FTTG with graphene/ITO (G/I) asymmetric electrodes (GI-FTTG) almost remains unchanged even after 700 cycles, indicating excellent mechanical stability. The excellent performance of GI-FTTG can be attributed to the suitable materials and unique asymmetric electrode structure: the extraordinary flexibility of the graphene top electrode ensures the GI-FTTG excellent mechanical robustness and stability even after longer cycles, and the bottom electrode with very low sheet resistance guarantees lower internal resistance and higher production rate of induction charges to obtain higher output power density. It shows that light-emitting diodes (LED) can be easily powered by GI-FTTG, which demonstrates that the GI-FTTG is very promising for harvesting electrical energy from human activities by using flexible and transparent devices.

A Highly Sensitive Fiber-Optic Microphone Based on Graphene Oxide Membrane

We present a fiber-optic microphone (FOM) based on graphene oxide (GO) membrane in this study. A Fabry–Perot cavity consisting of a single-mode fiber and a piece of GO membrane works as the acoustic sensing structure. Using the GO as the core acoustic sensing component, the fabricating process of the FOM is demonstrated to be simple and efficient. Acoustic tests show that this FOM achieves an average minimum detectable pressure of 10.2 μPa/Hz 1/2, while maintaining a linear acoustic pressure response and a flat frequency response in the range of 100 Hz to 20 kHz. These results indicate the excellent suitability of this FOM for acoustic detection in the audible range with high sensitivity and high fidelity.

Highly sensitive fiber-optic Fabry-Perot geophone with graphene-coated PMMA membrane

A highly sensitive fiber-optic Fabry-Perot interferometric geophone (FFPG) with graphene coated PMMA membrane is proposed and demonstrated, where the graphene coating is used for enhancement of the mechanical strength of the membrane. It is found that the sensitivity of the FFPG is much higher than that of the conventional electrical geophone. Such a novel all-optical geophone with low cost, high sensitivity, electromagnetic interference immunity, easy fabrication and robust structure would have great potential for use in oil/gas exploration and seismic wave detection.

Broadly-tunable pulse generation in cavity-free graphene random fiber lasers

Broadly-tunable pulse generation in cavity-free graphene random lasers is reported, with tunable pulsewidths across two orders-of-magnitude to less-than 900 ps, tunable repetition over three orders-of-magnitude up to 3 MHz, and 41-dB singly-polarized extinction ratio.