Laser-based processing of polymer nanocomposites for chemical sensing applications

Pulsed laser deposition (PLD) has been used to fabricate polymer/carbon nan ocomposite thin films for use in chemical sensors (chemiresistors). Ethylen e vinyl acetate copolymer (EVA) films (undoped and 20% carbon by weight) we re deposited using an ArF excimer laser (193 nm) at fluences between 150 an d 300 mJ/cm(2). The structure and morphology of the deposited films were ch aracterized using Fourier transform infrared spectroscopy (FTIR), Raman sca ttering, and transmission and scanning electron microscopy (TEM). An analys is of the FTIR spectra indicates that a film deposited using an undoped EVA target is primarily polyethylene, suggesting that the acetate group is pho tochemically or photothermally removed from the starting material. Gas phas e measurements of the laser-evaporated material using a quadrupole time of flight mass spectrometer confirm the production of the acetyl radical on th e target surface. Analysis of TEM of films deposited using C-doped targets shows that the carbon black particles (initially 50 nm particles in 1 mum a gglomerates) are broken down into particles that are less than or equal to 50 nm in the deposited film. Incorporation of carbon into the target reduce s the degree of photochemical damage of the starting material, as shown in the FTIR spectra of the deposited film. The sensitivity and response time o f chemiresistors fabricated from 6 mum thick composite films on top of gold electrodes were measured using toluene vapor (548 ppm). The chemiresistors exhibited a reversible and fast (<1.3 s) response to the vapor. In compari son to data reported in the literature, chemiresistors fabricated from PLD films are significantly better than devices fabricated using a more convent ional polymer film growth technique. (C) 2001 American Institute of Physics .