Fabrication of CNTs-based Gas Sensor Field Emission and Field-effect Transistor

Abstract

In this study the growth of high-density multi-wall nanotubes (MWNTs) on oxidized Si substrate was investigated The obtained average length and diameter of the CNTs were approximately 4 52 and 45 nm respectively The adsorption of metal nanoparticle on nanotube surfaces and the fabrication of MWNT-based gas sensors were also examined Ag adsorption to the MWNTs significantly increased device sensitivity and provided a 5 31% increase in RT sensitivity over that of MWNTs for an ambient isopropyl alcohol gas concentration of 800 ppm The response speed and stability of the fabricated sensor were favorable Moreover the direct transfer of high-density MWNTs from a SiO2/Si substrate to a flexible substrate was demonstrated The strong adhesion of the MWNTs with the flexible substrate was maintained although the substrate was bent into an extreme state with a radius of curvature of 993 μm The surface modification of the MWNT-networked films with size-controlled Au nanoclusters enhanced gas sensitivity The flexible MWNT sensor exhibited reproducibility fast response high stability and high sensitivity Results demonstrate the feasibility of manufacturing flexible MWNT gas sensors using the transfer process This finding represents a major step toward low-cost and large-scale production of this class of device The measurements of MWNT-based field emission show that a low turn-on electric field with the emission current density of 10 μA/cm2 could be achieved because of metal adsorption The measured values of Eto for Au- and Ag-coated MWNTs were 5 33 4 84 and 3 94 V/μm The comparative investigation indicates that Ag nanoparticle decoration on MWNT decreased work function from 5 eV to 3 94 eV The enhanced field emission properties of metal-coated MWNTs were caused mainly by low effective work function The flexible field emission with MWNT thin films was fabricated using a transfer method In the turn-on electric field with emission current density of 10 μA/cm2 the measured values of Eto with and without bending test were 3 60 and 3 72 V/μm The MWNT film showed good mechanical stability at a significantly small bending radius of 5 mm The good mechanical bendability is due to the cracking-resistant nanotube morphology A simple method for selectively separating semiconducting SWNTs (s-SWNTs) was developed The samples were examined by Raman spectroscopy with an excitation laser of 633 and 785 nm wavelengths The spectrum reveals that metallic SWNTs and regioregular poly(3-dodecylthiophene) were completely removed and s-SWNTs were remained SWNT-based field-effect transistors (FETs) were fabricated by dip-coating method The device with selective extraction had a high on/off ratio and low subthreshold swing The transistor with selective extraction had an on/off ratio of 107 and a subthreshold swing of 154 mV/dec The proposed convenient and effective s-SWNT sorting process can be used in the commercial manufacturing of SWNT-based FETs for low-cost and large-scale electronic devices

Date of Award	2016 Jul 7
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)