%0 Journal Article
%T Vapor Phase Sensing Using Metal Nanorod Thin Films Grown by Cryogenic Oblique Angle Deposition
%A Piyush Shah
%A Dongquan Ju
%A Xiaoxu Niu
%A Andrew M. Sarangan
%J Journal of Sensors
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/823041
%X We demonstrate the chemical sensing capability of silver nanostructured films grown by cryogenic oblique angle deposition (OAD). For comparison, the films are grown side by side at cryogenic (~100 K) and at room temperature (~300 K) by e-beam evaporation. Based on the observed structural differences, it was hypothesized that the cryogenic OAD silver films should show an increased surface enhanced Raman scattering (SERS) sensitivity. COMSOL simulation results are presented to validate this hypothesis. Experimental SERS results of 4-aminobenzenethiol (4-ABT) Raman test probe molecules in vapor phase show good agreement with the simulation and indicate promising SERS applications for these nanostructured thin films. 1. Introduction The detection and identification of hazardous chemical and biological agents is important for several areas of defense and security as well as in other industries that deal with hazardous chemicals [1]. Gas chromatography has the advantage of providing quick and accurate detection capability; however cost, size, and lack of portability have limited its widespread use [2]. Ion-mobility spectrometer is another popular technique for chemical sensing; however the level of information that can be extracted is not comparable to most vibrational spectroscopy techniques [3]. Surface enhanced Raman scattering (SERS) has shown the ability to detect the presence of very low concentrations of chemical agents quickly [1, 4¨C6]. Several groups have also demonstrated a portable Raman setup for chemical and biosensing applications [7, 8]. In many of these applications, colloidal silver nanoparticles are used as the SERS substrates, which limits these to only liquid phase applications [9]. On the other hand, silver nanostructured SERS substrates have the flexibility to work with liquids or vapors. Some of the earlier literature on SERS-based vapor sensing includes simulants for highly toxic chemicals such as nerve and mustard agents [7]. Most of these used electrochemically roughened silver substrates or silver film over nanosphere substrates. All of these techniques are limited by the available surface area for the vapor molecules to bind and adsorb onto. On the other hand, nanorod-based substrates can offer a significantly greater surface area for the same foot print area. Oblique angle physical vapor deposition technique has led to the evolution of a new class of thin films with very large effective surface areas. The technique is based on atomistic level self-shadowing. Whereas in typical thin film deposition setups the substrate is held
%U http://www.hindawi.com/journals/js/2013/823041/