Leyong Yu

Direct Growth of Graphene Films on 3D Grating Structural Quartz Substrates for High-Performance Pressure-Sensitive Sensors.

Conformal graphene films have directly been synthesized on the surface of grating microstructured quartz substrates by a simple chemical vapor deposition process. The wonderful conformality and relatively high quality of the as-prepared graphene on the three-dimensional substrate have been verified by scanning electron microscopy and Raman spectra. This conformal graphene film possesses excellent electrical and optical properties with a sheet resistance of <2000 Ω·sq(-1) and a transmittance of >80% (at 550 nm), which can be attached with a flat graphene film on a poly(dimethylsiloxane) substrate, and then could work as a pressure-sensitive sensor. This device possesses a high-pressure sensitivity of -6.524 kPa(-1) in a low-pressure range of 0-200 Pa. Meanwhile, this pressure-sensitive sensor exhibits super-reliability (≥5000 cycles) and an ultrafast response time (≤4 ms). Owing to these features, this pressure-sensitive sensor based on 3D conformal graphene is adequately introduced to test wind pressure, expressing higher accuracy and a lower background noise level than a market anemometer.

High-efficiency, stable and non-chemically doped graphene–Si solar cells through interface engineering and PMMA antireflection

In graphene–Si (Gr–Si) solar cells, chemical doping could remarkably enhance the performance of the cells, but weakens their stability, which limits their further application. However, in terms of the efficiency of pristine cells, the interfacial defect states and the increased thickness of the oxide layer in air also make high-efficiency and stable cells more difficult to achieve. Here we directly grew carbon nanowalls (CNWs) as a passivation layer onto the Si surface, which could obviously increase the efficiency. On the other hand, a poly(methyl-methacrylate) (PMMA) film was retained after transferring graphene, which could not only keep the graphene intact, but could also serve as an efficient antireflection layer for greater light absorption of the Si. A maximum PCE of 8.9% was achieved for a PMMA-bilayer Gr-CNWs-Si solar cell. Our cell’s efficiency showed a slight degradation after being stored in air for 4 months. This result is far superior to other previously reported stability data for chemically doped Gr–Si solar cells. The PMMA-Gr-CNWs-Si solar cell, with high efficiency and stability, possesses important potential for practical photovoltaic applications.

Three-dimensional conformal graphene microstructure for flexible and highly sensitive electronic skin

We demonstrate a highly stretchable electronic skin (E-skin) based on the facile combination of microstructured graphene nanowalls (GNWs) and a polydimethylsiloxane (PDMS) substrate. The microstructure of the GNWs was endowed by conformally growing them on the unpolished silicon wafer without the aid of nanofabrication technology. Then a stamping transfer method was used to replicate the micropattern of the unpolished silicon wafer. Due to the large contact interface between the 3D graphene network and the PDMS, this type of E-skin worked under a stretching ratio of nearly 100%, and showed excellent mechanical strength and high sensitivity, with a change in relative resistance of up to 6500% and a gauge factor of 65.9 at 99.64% strain. Furthermore, the E-skin exhibited an obvious highly sensitive response to joint movement, eye movement and sound vibration, demonstrating broad potential applications in healthcare, body monitoring and wearable devices.

Ultrafast growth of large-area monolayer MoS2 film via gold foil assistant CVD for a highly sensitive photodetector

Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetector owing to its tunable band gap and high absorption coefficient. However, controlled synthesis of high quality, large area monolayer molybdenum disulfide (MoS2) is still a challenge in practical application. In this work, we report a gold foil assistant chemical vapor deposition (CVD) method of large size (>400 μm) single crystal MoS2 film on silicon dioxide (SiO2) substrate. The influence of Au foil in enlarging the size of single crystal MoS2 were investigated systemically using thermal simulation in Ansys workbench 16.0, including thermal conductivity, temperature difference and thermal relaxation time of the interface of SiO2 substrate and Au foil, which indicated that Au foil could increase the temperature of the SiO2 substrate rapidly and decrease the temperature difference between the oven and substrate. At last, the property of the monolayer MoS2 film was further confirmed by the back-gated field effect transistors (FETs), a high photo-response of 15.6 A/W and a fast photo-response time of 100 ms was obtained. The growth techniques described in this study could be benefit for the development of other atomically thin two-dimensional transition metal dichalcogenides (TMD) materials.

Flexible electrochemical biosensors based on graphene nanowalls for the real-time measurement of lactate

We demonstrate a flexible biosensor for lactate detection based on l-lactate oxidase immobilized by chitosan film cross-linked with glutaraldehyde on the surface of a graphene nanowall (GNW) electrode. The oxygen-plasma technique was developed to enhance the wettability of the GNWs, and the strength of the sensors oxidation response depended on the concentration of lactate. First, in order to eliminate interference from other substances, biosensors were primarily tested in deionized water and displayed good electrochemical reversibility at different scan rates (20-100 mV s-1), a large index range (1.0 μM to 10.0 mM) and a low detection limit (1.0 μM) for lactate. Next, these sensors were further examined in phosphate buffer solution (to mimick human body fluids), and still exhibited high sensitivity, stability and flexibility. These results show that the GNW-based lactate biosensors possess important potential for application in clinical analysis, sports medicine and the food industry.

Interband and intraband photocurrent of self-assembled InAs/InAlAs/InP nanostructures

The interband and intraband photocurrent properties of InAs/InAlAs/InP nanostructures have been studied. The doping effect on the photoluminescence properties of the quantum dots and the anisotropy of the quantum wire interband photocurrent properties are presented and discussed. With the help of interband excitation, an intraband photocurrent signal of the InAs nanostructures is observed. With the increase of the interband excitation power, the intraband photocurrent signal first increases and then decreases, which can be explained by the variance of the ground state occupation of the InAs nanostructures and the change of the mobility and lifetime of the electrons. The temperature dependence of the intraband photocurrent signal of the InAs nanostructures is also investigated.

A stably enhanced transparent conductive graphene film obtained using an air-annealing method

A simple and effective air-annealing technique was developed to stably improve both the electrical conductivity and light transmission of pristine graphene. After the graphene film was annealed in air at 250 °C for 80 min, the mobility and carrier concentration were both significantly enhanced, and the sheet resistance was greatly reduced with a decrease rate of ~33%. Meanwhile, the transparency was also improved by more than 3%. The mechanism is carefully discussed. The reason might be that air-annealing conditions provide a suitable atmosphere to etch and remove amorphous carbons. More importantly, the enhanced transparent conductive properties of the air-annealed graphene films were extraordinarily stable, and remained almost unchanged for 100 days.

In situ fabrication of graphene nanowalls as active surface-enhanced Raman scattering substrate

Graphene-wall (G-wall) nanostructure was directly grown on the surface of copper foil by plasma enhanced chemical vapor deposition (PECVD) method, and then was employed as active G-wall surface-enhanced Raman scattering (GW-SERS) substrate. To investigate the SERS activity of this G-wall substrate, rhodamine 6G was used as a target molecule. And better Raman enhancement ability was observed, compared with the graphene film on the copper foil. Meanwhile, this novel G-wall based GW-SERS substrate not only maintained the high SERS activity, but also could be easily obtained in large scale. Moreover, the substrate could avoid the use of noble metals, self-assembled steps, complicated photolithograph treatments, as well as the graphene transferring processes. And the GW-SERS substrate could provide the high SERS activity and eliminate fluorescence background noise. Hence, this GW-SERS substrate could be potentially applied for detecting trace amount of analytes in future analytical detection fields.