High-Sensitivity H₂ and CH₄ SAW Sensors with Carbon Nanowalls and Improvement in Their Performance after Plasma Treatment

We have developed surface acoustic wave (SAW) sensors with high sensitivity and a reversible response at room temperature (RT). The sensitive area of the sensor was prepared from vertically aligned graphene sheets, like carbon nanowalls (CNWs), which were deposited onto the quartz SAW sensor substrate. The CNWs were obtained by RF plasma-enhanced chemical vapor deposition (PECVD) at 600 °C, and their sensitivity was subsequently enhanced through hydrogen plasma treatment. The SAW sensors were tested at H2 and CH4 at RT, and they exhibited a reversible response for both gases at concentrations between 0.02% and 0.1%, with a detection limit of a few ppm. The additional hydrogen plasma treatment preserved the lamellar structure, with slight modifications to the morphology of CNW edges, as observed by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) investigations revealed the presence of new functional groups, a significant number of defects and electron transitions after the treatment. Changes in the chemical state on the CNW surface are most probably responsible for the improved gas adsorption after plasma treatment. These results identify CNWs as a promising material for designing new SAW sensors, with the possibility of using plasma treatments to enhance the detection limit below the ppm level

Laser-induced forward transfer of carbon nanowalls for soft electrodes fabrication

Symposium CC on Laser and Plasma Processing for Advanced Applications in Material Science held during the Annual Spring Meeting of the European-Materials-Research-Society (E-MRS), Lille, FRANCE, MAY 11-15, 2015International audienceCarbon nanowalls (CNW) are two-dimensional interconnected graphitic nanostructures that have a few mu m in length and height, reaching typical thicknesses of a few tens of nm. We present results on such layers synthesized in a low pressure argon plasma jet, injected with acetylene and hydrogen, on transparent substrates (quartz) heated at 600 degrees C, without catalyst. Thermogravimetric analysis reveals that the CNW are stable up to 420 degrees C in air, and Raman spectroscopy investigations highlight their graphene-like structure. Finally, using a pulsed Nd:YAG laser device (355 nm, 50 ps), we show that 2D-arrays of CNW (pixels and lines) can be printed by laser-induced forward transfer (LIFT), preserving their architecture and structure. Electrical measurements on 1 mu m thick CNW demonstrate typical values in the range of 357.5-358.4 Omega for the samples grown on Au/Cr electrodes, and in the range of 450.1-474.7 Omega for the LIFT printed lines (under positive, negative, and neutral polarization; 1 kHz-5 MHz frequency range; 500 mV and 1 V, respectively). Their morphology is highlighted by means of optical and electronic microscopy. Such structures have potential applications as soft conductive lines, in sensor development and/or embedding purposes. (C) 2015 Elsevier B.V. All rights reserved