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Growth of carbon nanowalls at atmospheric pressure for one-step gas sensor fabrication.

Yu K, Bo Z, Lu G, Mao S, Cui S, Zhu Y, Chen X, Ruoff RS, Chen J - Nanoscale Res Lett (2011)

Bottom Line: 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).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA. jhchen@uwm.edu.

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).

No MeSH data available.


Morphology of the as-grown CNWs displayed in the SEM images. (a) An SEM image of CNWs on a silicon substrate; primary beam incident kinetic energy was 30 keV. (b) CNWs uniformly distributed on the substrate over approximately 1 cm2. (c-e) The CNWs were quasi-transparent to the SEM electron beam. (f) The cluster of CNWs is "flower-like".
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Figure 2: Morphology of the as-grown CNWs displayed in the SEM images. (a) An SEM image of CNWs on a silicon substrate; primary beam incident kinetic energy was 30 keV. (b) CNWs uniformly distributed on the substrate over approximately 1 cm2. (c-e) The CNWs were quasi-transparent to the SEM electron beam. (f) The cluster of CNWs is "flower-like".

Mentions: Figure 1 shows a schematic of the atmospheric dc PECVD system for the CNW synthesis without any catalysts. The morphology of the as-grown CNWs is displayed in the SEM images shown in Figure 2. The CNWs were uniformly distributed on the Si substrate (Figure 2a,2b). The total area on the substrate that was covered with CNWs depended on the discharge power and the distance between the electrodes. In our experiments, the area covered with CNWs could be up to approximately 1 cm2. 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. The thickness of the CNWs was typically below 10 nm, (top-view of CNWs, Figure 2c,2e; side-view of CNWs, Figure 2d). Small pinholes were observed in the CNWs (Figure 2e). Wu et al. used a dc bias of -185 V to promote growth and vertical alignment [26]. Hiramatsu et al. stated that the reactant type influences the CNW morphology [30], in the case of C2F6/H2, they synthesized vertically aligned CNWs using a radio-frequency plasma. In our experiments, most of the CNWs were randomly oriented but pointing away from the substrate surface, although a dc bias of 2.2 kV was applied between the electrodes throughout the growth process. In some areas, CNW clusters were found (Figure 2f) sparsely distributed on the substrate. Each CNW cluster had a "flower-like" shape with CNWs projecting in all directions, which is similar to the observations made by Chuang et al [35]. Similar structures were also found for CNWs grown on a Cu substrate (see Figure S-1 in Additional file 1).


Growth of carbon nanowalls at atmospheric pressure for one-step gas sensor fabrication.

Yu K, Bo Z, Lu G, Mao S, Cui S, Zhu Y, Chen X, Ruoff RS, Chen J - Nanoscale Res Lett (2011)

Morphology of the as-grown CNWs displayed in the SEM images. (a) An SEM image of CNWs on a silicon substrate; primary beam incident kinetic energy was 30 keV. (b) CNWs uniformly distributed on the substrate over approximately 1 cm2. (c-e) The CNWs were quasi-transparent to the SEM electron beam. (f) The cluster of CNWs is "flower-like".
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211258&req=5

Figure 2: Morphology of the as-grown CNWs displayed in the SEM images. (a) An SEM image of CNWs on a silicon substrate; primary beam incident kinetic energy was 30 keV. (b) CNWs uniformly distributed on the substrate over approximately 1 cm2. (c-e) The CNWs were quasi-transparent to the SEM electron beam. (f) The cluster of CNWs is "flower-like".
Mentions: Figure 1 shows a schematic of the atmospheric dc PECVD system for the CNW synthesis without any catalysts. The morphology of the as-grown CNWs is displayed in the SEM images shown in Figure 2. The CNWs were uniformly distributed on the Si substrate (Figure 2a,2b). The total area on the substrate that was covered with CNWs depended on the discharge power and the distance between the electrodes. In our experiments, the area covered with CNWs could be up to approximately 1 cm2. 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. The thickness of the CNWs was typically below 10 nm, (top-view of CNWs, Figure 2c,2e; side-view of CNWs, Figure 2d). Small pinholes were observed in the CNWs (Figure 2e). Wu et al. used a dc bias of -185 V to promote growth and vertical alignment [26]. Hiramatsu et al. stated that the reactant type influences the CNW morphology [30], in the case of C2F6/H2, they synthesized vertically aligned CNWs using a radio-frequency plasma. In our experiments, most of the CNWs were randomly oriented but pointing away from the substrate surface, although a dc bias of 2.2 kV was applied between the electrodes throughout the growth process. In some areas, CNW clusters were found (Figure 2f) sparsely distributed on the substrate. Each CNW cluster had a "flower-like" shape with CNWs projecting in all directions, which is similar to the observations made by Chuang et al [35]. Similar structures were also found for CNWs grown on a Cu substrate (see Figure S-1 in Additional file 1).

Bottom Line: 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).

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA. jhchen@uwm.edu.

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).

No MeSH data available.