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Tunable-sensitivity and flexibility are considered as two crucial characteristics for future pressure sensors or electronic skins. By the theoretical calculation model, we simulated the relationship curve between the sensitivity and PDMS pyramids with different spacings, and found that the spacing of pyramids is a main factor to affect the sensitivity of the capacitance pressure sensor. Furthermore, we fabricated the capacitance pressure sensors using graphene electrodes and the PDMS pyramid dielectric layers with different spacings. The measurement data were consistent with the simulation results that the sensitivity increases with the spacing of pyramids. In addition, graphene electrode exhibits prefect flexibility and reliability, while the ITO electrode would be destroyed rapidly after bending. These graphene pressure sensors exhibit the potential in the application in the wearable products for monitoring breath, pulse, and other physiological signals.

Recently, graphene-like nanofilm materials have attracted extensive attention as the fundamental building blocks for potential applications in optoelectronic devices. Here, we developed a simple and versatile technique to directly produce high-quality graphene nanowalls on silica substrate without any catalyst and post-transfer. It shows that the entire surface of silica substrate is fully covered with continuous graphene nanowalls with well-connected network. Moreover, the prepared optical films exhibit excellent optical absorption with a high absorbance of 95% at a wide range of waveband from visible to near infrared. Such a three dimensional film material with super-large surfaces and outstanding optical properties is further decorated with CdTe nanofilm and used as a photo-electrochemical working electrode. The prepared electrode exhibits a fast photo-responsive behavior with high photo-current density up to 3 mA/cm2. Our study identifies that graphene nanowalls served as an excellent transfer black body can enhance the photo-electrochemical performance of electrode when it is sensitized with semiconductor nanofilms.

A photo-electrochemical photo-anode of CdS-modified graphene foam (GF) was prepared by chemical vapor deposition method. The interconnected 3D scaffold network of the as-prepared CdS-modified GF composite not only facilitates the separation of photo-generated charge carrier, but also provides a direct pathway for charge transport in the conductive network, resulting in the enhanced photo-current response. Experimental results confirm that the deposition of the CdS nanowires (NWs) makes a major contribution to improving the photo-current density of as-prepared CdS NWs/GF photo-anode, which reaches a high value of 55 μA/cm2 with clear light-on and -off. Meanwhile, the PEC reaction leads to the photo-corrosion of CdS NWs/GF photo-anode, resulting in the prominent decrease of photo-current density during the photo-electrochemical reactions. Such a CdS-modified 3D GF photo-anode with impressive photovoltaic properties provides a promising platform for photo-electrochemical applications.

Due to their outstanding optical properties and superior charge carrier mobilities, organometal halide perovskites have been widely investigated in photodetection and solar cell areas. In perovskites photodetection devices, their high optical absorption and excellent quantum efficiency contribute to the responsivity, even the specific detectivity. In this work, we developed a lateral phototransistor based on mesoscopic graphene/perovskite heterojunctions. Graphene nanowall shows a porous structure, and the spaces between graphene nanowall are much appropriated for perovskite crystalline to mount in. Hot carriers are excited in perovskite, which is followed by the holes’ transfer to the graphene layer through the interfacial efficiently. Therefore, graphene plays the role of holes’ collecting material and carriers’ transporting channel. This charge transfer process is also verified by the luminescence spectra. We used the hybrid film to build phototransistor, which performed a high responsivity and specific detectivity of 2.0 × 103 A/W and 7.2*1010 Jones, respectively. To understand the photoconductive mechanism, the perovskite’s passivation and the graphene photogating effect are proposed to contribute to the device’s performance. This study provides new routes for the application of perovskite film in photodetection.

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 of2000 Ω·sq(-1) and a transmittance of80% (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.

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.

An all-optical modulator with high modulation efficiency based on a graphene-plasmonic slot waveguide structure is proposed. The modulation efficiency is enhanced by the strong interaction between the light and the graphene–plasmonic structure. A modulation efficiency of 0.21 dB μm−1 is obtained with the signal light at a wavelength of 1550 nm. A graphene–plasmonic slot waveguide device of length of 10 μm is fabricated in the experiment. Benefiting from the strong modulation, it is a promising candidate as an on-chip optical modulator with high modulation efficiency and micrometer-scale footprint.

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 sensor's 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.

Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetectors 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 method for the synthesis of large-size (>400 μm) single-crystal MoS2 film on a silicon dioxide (SiO2) substrate. The influence of Au foil in enlarging the size of single-crystal MoS2 is 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 indicate that Au foil can increase the temperature of the SiO2 substrate rapidly and decrease the temperature difference between the oven and substrate. Finally, the properties of the monolayer MoS2 film are further confirmed using back-gated field-effect transistors: a high photoresponse of 15.6 A W−1 and a fast photoresponse time of 100 ms. The growth techniques described in this study could be beneficial for the development of other atomically thin two-dimensional transition metal dichalcogenide materials.

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.

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.