Abstract
Carbon nanowalls (CNWs), two-dimensional "graphitic" platelets that are typically oriented vertically on a substrate, can exhibit similar properties as graphene. Growth of CNWs reported to date was exclusively carried out at a low pressure. Here, we report on the synthesis of CNWs at atmosphere pressure using "direct current plasma-enhanced chemical vapor deposition" by taking advantage of the high electric field generated in a pin-plate dc glow discharge. CNWs were grown on silicon, stainless steel, and copper substrates without deliberate introduction of catalysts. The as-grown CNW material was mainly mono- and few-layer graphene having patches of O-containing functional groups. However, Raman and X-ray photoelectron spectroscopies confirmed that most of the oxygen groups could be removed by thermal annealing. A gas-sensing device based on such CNWs was fabricated on metal electrodes through direct growth. The sensor responded to relatively low concentrations of NO2 (g) and NH3 (g), thus suggesting high-quality CNWs that are useful for room temperature gas sensors.PACS: Graphene (81.05.ue), Chemical vapor deposition (81.15.Gh), Gas sensors (07.07.Df), Atmospheric pressure (92.60.hv)
Highlights
Graphene possesses many extraordinary properties and has been the subject of intense scientific interest [1,2,3,4,5,6,7,8,9,10,11,12]
We report on the synthesis of Carbon nanowalls (CNWs) using dc PECVD at atmospheric pressure by taking advantage of the high electric field generated in a pin-plate dc glow discharge
The dimensions of individual CNWs ranged from about 200 × 200 nm2 (Figure 2e) to 1 × 1 μm2 (Figure 2c), which can be controlled by the growth time
Summary
Graphene possesses many extraordinary properties and has been the subject of intense scientific interest [1,2,3,4,5,6,7,8,9,10,11,12]. Most of the product CNWs are nonaggregated with large surface area, which makes the product readily useful for various applications such as sensing and catalysis This is in contrast to stacked CNWs that require additional dispersion, such as through ultrasonication, to obtain individual CNWs. To illustrate the advantage of our growth method, CNWs deliberately grown between metal electrodes were used for detection of low-concentration gases including NO2 and NH3, thereby demonstrating a one-step gas sensor fabrication process. The reactor temperature was measured as close to 700°C (the preset furnace temperature) using a thermocouple This suggests that the energy dissipated in the dc glow discharge was non-thermal (electrons were preferentially heated by the plasma) and heavy species (e.g., gas molecules, atoms, radicals, and ions) were not substantially heated by the plasma. Sensor current was measured using a Keithley 2602 source meter
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