Vapor Deposition-grown Graphene Films Research Articles

Transfer-Medium-Free Nanofiber-Reinforced Graphene Film and Applications in Wearable Transparent Pressure Sensors.

Graphene exhibits properties of atomic thickness, high transparency, and high carrier mobility, which is highly desirable for a flexible transparent conductive material. However, the electronic properties of large-area chemical vapor deposition grown graphene film suffer from insulated polymer contaminations introduced by the transfer process and the easily cracked nature. Here, we report a preparation method of a transfer-medium-free large-area nanofiber-reinforced graphene (a-PAN/G) film simply by annealing the electrostatically spun polyacrylonitrile (PAN) nanofibers on the graphene film. The film could be free-standing on water and suspended in air with high transparency and enhanced electrical and mechanical properties compared to that of a monolayer graphene film. The flexible transparent a-PAN/G films were demonstrated as active materials for sensitive pressure sensors. The obtained pressure sensors demonstrate high sensitivity (44.5 kPa-1 within 1.2 kPa), low operating voltage (0.01-0.5 V), and excellent stability for 5500 loading-unloading cycles, revealing promising potential applications in wearable electronics.

Thickness Control of Chemical Vapor Deposition-Grown Graphene Film by Oxygen Plasma Etching with Recycled Use of Ni Catalyst

Ni has been widely used as one of the most important metal catalysts for graphene growth with the chemical vapor deposition (CVD) method. Despite the many advantages, it is difficult to obtain high quality graphene from Ni due to the complexity in controlling the uniformity and thickness of multilayer graphene films. In this study, the thickness of multilayer graphene films grown on Ni was controlled by single-step oxygen plasma etching. The results show that the thickness of the graphene films proportionally decreased with an increase in the plasma etching time where the thickness was controlled from thick graphite films to thin graphene films with a transparency over 80%. Surface topology after oxygen plasma etching showed that uniform etching was achieved, for which the topmost surface of the resulting thin graphene is hydrophilic because of oxygen plasma irradiation, which is advantageous for coating organic layers in device fabrication. Moreover, because of the absence of a metal etching process, the recycled use of Ni catalysts is available, increasing the cost efficiency.

Patterning Graphene Film by Magnetic-assisted UV Ozonation

Developing an alternative method for fabricating microscale graphene patterns that overcomes the obstacles of organic contamination, linewidth resolution, and substrate damaging is paramount for applications in optoelectronics. Here we propose to pattern chemical vapor deposition grown graphene film through a stencil mask by magnetic-assisted ultraviolet (UV) ozonation under irradiation of a xenon excimer lamp. In this process, the paramagnetic oxygen molecules and photochemically generated oxygen radicals are magnetized and attracted in an inhomogenous external magnetic field. As a consequence, their random motions convert into directional, which can greatly modify or enhance the quality of graphene patterns. Using a ferromagnetic steel mask, an approximately vertical magnetic-field-assisted UV ozonation (BZ = 0.31 T, ∇BZ = 90 T · m−1) has a capability of patterning graphene microstructures with a line width of 29 μm and lateral under-oxidation less than 4 μm. Our approach is applicable to patterning graphene field-effect transistor arrays, and it can be a promising solution toward resist-free, substrate non-damaging, and cost effective microscale patterning of graphene film.

High sensitive formaldehyde graphene gas sensor modified by atomic layer deposition zinc oxide films

Zinc oxide (ZnO) thin films with various thicknesses were fabricated by Atomic Layer Deposition on Chemical Vapor Deposition grown graphene films and their response to formaldehyde has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors showed high response to formaldehyde with the resistance change up to 52% at the concentration of 9 parts-per-million (ppm) at room temperature. Meanwhile, the detection limit could reach 180 parts-per-billion (ppb) and fast response of 36 s was also obtained. The high sensitivity could be attributed to the combining effect from the highly reactive, top mounted ZnO thin films, and high conductive graphene base network. The dependence of ZnO films surface morphology and its sensitivity on the ZnO films thickness was also investigated.

Fabrication of sub-micrometer graphene ribbon using electrospun nanofiber

Here we demonstrate a simple and effective method to fabricate graphene ribbon with a sub-micrometer width down to 260 nm by using an electrospun polymer nanofiber as a physical etch mask. Our method involves electrospinning polystyrene nanofiber onto chemical vapor deposition-grown graphene film, followed the oxygen plasma etching to remove the exposed graphene without disturbing the underlying graphene. This work shows that the width of the resulting graphene ribbons can be engineered by controlling the nanofiber size and etch conditions. Based on this graphene ribbon, we fabricated a graphene-field effect transistor with a bottom-gated geometry, which shows an ambipolar characteristic with a hole and electron mobility of 1636 and 134 cm2/(V s), respectively. Our approach here may allow the fabrication of sub-micrometer graphene ribbon for graphene-based electronics.

Directly Drawing Self-Assembled, Porous, and Monolithic Graphene Fiber from Chemical Vapor Deposition Grown Graphene Film and Its Electrochemical Properties

Integration of graphene into macroscopic architectures represents the first step toward creating a new class of graphene-based nanodevices. We report a novel yet simple approach to fabricate graphene fibers, a porous and monolithic macrostructure, from chemical vapor deposition grown graphene films. Graphene is first self-assembled from a 2D film to a 1D fiberlike structure in an organic solvent (e.g., ethanol, acetone) and then dried to give the porous and crumpled structure. The method developed here is scalable and controllable, delivering tunable morphology and pore structure by controlling the evaporation of solvents with suitable surface tension. The fibers are 20-50 μm thick, with a typical electrical conductivity of ∼1000 S/m. The cyclic voltammetric studies show typical capacitive behavior for the porous graphene fibers with good rate stability and capacitance values ranging from 0.6 to 1.4 mF/cm(2). Decorated with only 1-3 wt % MnO(2), the graphene/MnO(2) composites exhibit remarkable enhancement of combined performance both with respect to discharge capacitance (up to 12.4 mF/cm(2)) and cycling stability. This special structure could facilitate chemical doping and electrochemical energy storage and find applications in catalyst supports, sensors, supercapacitors, Li ion batteries, etc.