Microwave-excited Surface-wave Plasma Research Articles

Morphological changes of carbon thin films with nitrogen doping synthesized by microwave-excited surface wave plasma CVD

Nitrogen (N) doped graphene-based materials are of significant interest for various applications, such as, catalytic reactions, tribological energy generation, sensor devices and other electronic device applications. Most recently, the catalytic and noncatalytic growth of graphene structures at a low substrate temperature were explored by using the microwave-excited surface wave plasma (MW-SWP) chemical vapor deposition (CVD) technique. In this study, growth of carbon thin films is investigated by the MW-SWP CVD technique with nitrogen doping at various temperatures on the insulating substrates. It is obtained that partially graphitized carbon thin films can be obtained at a temperature as low as 150 °C on the quartz substrates. Interestingly, the morphological changes are observed with nitrogen doping and change in synthesis temperature for the carbon thin films grown by the MW-SWP CVD method. The partially graphitized carbon thin films form irregular morphologies at a lower temperature, while the morphology transforms with increase in temperature. At a certain growth temperature (500 and 700 °C), the carbon film shows granular morphology without addition of nitrogen, whereas the addition of nitrogen reduces the granular morphology and forming planar structures. Thus, these studies reveal the growth of carbon films with control morphology with respect to incorporation of nitrogen, which can be significant to develop carbon films and nanostructures for diverse fields of applications.

Effective reduction and doping of graphene oxide films at near-room temperature by microwave-excited surface-wave plasma process

The effective reduction of graphene oxide (GO) and incorporation of dopant elements on flexible soft substrates, such as plastics, polymers, papers etc. are of significant importance for energy-related devices and flexible wearable electronics. Here, we demonstrate a novel microwave-excited surface-wave plasma (MW-SWP) process to reduce insulating GO to highly conducting reduced graphene oxide (rGO) on the polyethylene terephthalate (PET) substrate as well as achieving reduction of free-standing GO paper at a near-room temperature. It is also observed that the GO coated on the both top and back surface of a PET substrate reduce simultaneously to obtain conducting rGO films. Most effective reduction was achieved using an argon-hydrogen gas mixture, whereas addition of nitrogen in the gas mixture enabled to incorporate nitrogen dopant in the rGO layers. The GO coated PET and freestanding GO films showed a sheet resistance in the range of MΩ/□, which reduced to an average value of 1.075 kΩ/□ and 134 Ω/□, respectively after the plasma treatment. Thus, the developed MW-SWP process can be significant to produce highly conducting rGO-based graphene films on a soft substrate as well as enabling fabrication of highly conducting freestanding rGO papers.

Synthesis of graphene by surface wave plasma chemical vapor deposition from camphor

AbstractWe demonstrate synthesis of graphene using the solid precursor camphor in a microwave excited surface wave plasma chemical vapor deposition technique. Highly sublimely camphor was introduced into the plasma chamber in the vapor phase along with Ar and uniform plasma formation was obtained. Rapid deposition of a graphene film on Cu foil was achieved at a relatively low temperature (<600 °C). Raman spectroscopy and transmission electron microscopy clearly showed that the deposited film on Cu foil consist of few‐layer graphene. Fully flexible transparent electrode was fabricated by transferring the graphene film with excellent properties for device application. magnified imageSynthesis of large‐area graphene film from solid botanical derivative camphor (C10H16O) in a surface wave microwave plasma CVD technique.

Double Probe Characteristics in High-Energy Electron Flux Presence

The effect of the high-energy electron flux on double probe characteristics is investigated theoretically and practically. Double probe characteristics are measured in a microwave-excited surface-wave plasma. One of the probes is directly exposed to the high-energy electron flux and the asymmetric double probe characteristics are measured. The ordinary double probe theory is modified in order to estimate the electron flux energy. Applied modifications of the theory consist of additional high-energy electron flux current flowing to one of the probe and the assumption of the probe potential dependence on bias voltage. The results obtained from the measured double probe characteristics correspond well to results obtained using a single Langmuir probe and retarding field analyzer.

Functionalization of Polymers Surfaces Using Microwave Plasma Chemical Modification

This paper reports the two topics of the low temperature chemical modification of polymer surfaces using microwave excited surface-wave plasma(SWP). First, for the improvement of hydrophilicity of polymer surfaces, we examined the surface treatment of polymethyl methacrylate(PMMA), polycarbonate(PC), and acrylonitrile-butadiene-styrene(ABS) resin surface using ion-assisted Ar plasma pretreatment followed by the SWP in Ar/CH3COOH gas mixture. Contact angle measurement and X-ray electron spectroscopy have been carried out to investigate the effect of the plasma treatment on the surface properties. Second, we have also studied the surface amination of polymers for medical use using SWP treatment with N,sub>2/H,sub>2 mixture gas or NH3 gas. We obtained about 100 % amino-group selectivity, denoted as NH2/N ratio, by using ammonia SWP.

Three‐dimensional numerical analysis on discharge properties of microwave excited ring dielectric line surface wave processing plasma device

AbstractA three‐dimensional simulation code with the finite difference time domain (FDTD) method combined with the electron fluid model has been developed for the microwave excited surface wave plasma in the RDL‐SWP device. This code permits the three‐dimensional numerical analysis of the spatial distributions of electric field, power absorption, electron density, and electron temperature. At a low gas pressure (about 10 mTorr), the numerical results were compared with the experimental measurements that show the validity of this 3D simulation code. A simplified analysis assuming that the electron density is spatially uniform has also been studied and its applicability is evaluated by the comparison of the 3D simulation and the analytical solutions. The surface wave eigenmodes are determined by the electron density, and it is found that the structure of the device strongly influences the spatial distribution of the electric fields of surface waves in a low‐density area (ne < 3.0 × 1011 cm−3). A method to irradiate by microwave the whole surface area of the plasma is proposed. The method is found to be effective in obtaining a high uniformity distribution of electron density. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 1–12, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10333

Three Dimensional Numerical Analysis on Discharge Properties of Microwave Excited Ring-Dielectric-Line Surface Wave Processing Plasma Device

A three dimensional simulation code with the finite difference time domain (FDTD) method combined with the fluid model for electron has been developed for the microwave excited surface wave plasma in the RDL-SWP device. This code permits the numerical analysis of the spatial distributions of electric field, power absorption, electron density and electron temperature. At low gas pressure of about 10 mTorr, the numerical results were compared with the experimental measurements that show the validity of this 3-D simulation code. A simplified analysis assuming that an electron density is spatially uniform has been studied and its applicability is evaluated by the 3-D simulation. The surface wave eigenmodes are determined by the electron density, and it is found that the structure of the device strongly influences to the spatial distribution of the electric fields of surface waves in a low density area (ne<3.0×1011cm-3). A method to irradiate a microwave to the whole surface area of the plasma is proposed which is found to be effective to obtain a high uniformity distribution of electron density.