Direct synthesis of tin oxide nanotubes on microhotplates using carbon nanotubes as templates
- PDF / 463,159 Bytes
- 7 Pages / 584.957 x 782.986 pts Page_size
- 114 Downloads / 244 Views
Richard E. Cavicchi,a) Douglas C. Meier, and Andrew Herzing Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Michael R. Zachariah Departments of Mechanical Engineering and Chemistry, University of Maryland, College Park, Maryland 20742; and Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 17 May 2010; accepted 4 October 2010)
Tin oxide (SnO2) nanotubes have been synthesized using carbon nanotubes (CNTs) as removable templates. The entire synthesis takes place on the microscale on a micromachined hotplate, without the use of photolithography, taking advantage of the device’s built-in heater. Well-aligned multiwalled CNT forests were grown directly on microhotplates at 600 °C using a bimetallic iron/alumina composite catalyst and acetylene as precursor. Thin films of anhydrous SnO2 were then deposited onto the CNT forests through chemical vapor deposition of tin nitrate at 375 °C. The CNTs were then removed through a simple anneal process in air at temperatures above 450 °C, resulting in SnO2 nanotubes. Gas sensing measurements indicated a substantial improvement in sensitivity to trace concentrations of methanol from the SnO2 nanotubes in comparison with a SnO2 thin film. The synthesis technique is generic and may be used to create any metal oxide nanotube structure directly on microscale substrates.
I. INTRODUCTION
Advances in microfabrication have made possible the miniaturization of the solid-state gas sensors based on a microhotplate platform. Reliable microhotplates, consisting of a micromachined membrane with integral heaters, thermometry, and electrical contacts are readily produced using complementary metal-oxide semiconductor (CMOS)compatible processing.1 The technical challenge for this class of devices is to develop solid-state sensing materials with improved sensitivity, chemical selectivity, response speed, and stability. Semiconducting metal oxides such as tin oxide (SnO2), zinc oxide (ZnO), titanium oxide (TiO2), and tungsten oxide (WO3) have been traditionally used as active materials in solid-state chemical gas sensing devices.2–4 Nanophase forms of these materials should be advantageous for gas sensing since a greater fraction of the material is surface exposed.5 Studies involving synthesis and characterization of nanoparticles and one-dimensional (1D) nanostructures including nanowires and nanobelts of metal oxides have a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.27 430
J. Mater. Res., Vol. 26, No. 3, Feb 14, 2011
http://journals.cambridge.org
Downloaded: 12 Mar 2015
been reported. Ogawa et al.6 measured the sensor responses from a dense SnO2 thin film and a porous nanoparticle film with a mean grain size of 7–12 nm, and found that the latter exhibited significantly higher sensitivity. Nanowire and nanotube (NT) structures are interesting because, like nanoparticles, a significant fraction of
Data Loading...
