Hindawi Publishing Corporation Journal of Sensors Volume 2013, Article ID 823041, 6 pages http://dx.doi.org/10.1155/2013/823041 Research Article Vapor Phase Sensing Using Metal Nanorod Thin Films Grown by Cryogenic Oblique Angle Deposition Piyush Shah, 1 Dongquan Ju, 2 Xiaoxu Niu, 3 and Andrew M. Sarangan 1 1 Electro-Optics Graduate Program, University of Dayton, 300 College Park, Dayton, OH 45469-2951, USA 2 Department of Physics, Harbin Institute of Technology, Harbin 150001, China 3 Graduate Materials Engineering Program, University of Dayton, 300 College Park, Dayton, OH 45469-2951, USA Correspondence should be addressed to Andrew M. Sarangan; sarangan@udayton.edu Received 3 September 2013; Accepted 29 October 2013 Academic Editor: Matteo Tonezzer Copyright © 2013 Piyush Shah et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We demonstrate the chemical sensing capability of silver nanostructured ilms grown by cryogenic oblique angle deposition (OAD). For comparison, the ilms are grown side by side at cryogenic (∼100 K) and at room temperature (∼300 K) by e-beam evaporation. Based on the observed structural diferences, it was hypothesized that the cryogenic OAD silver ilms 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 ilms. 1. Introduction he detection and identiication of hazardous chemical and biological agents is important for several areas of defense and security as well as in other industries that deal with haz- ardous 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 tech- nique for chemical sensing; however the level of information that can be extracted is not comparable to most vibrational spectroscopy techniques [3]. Surface enhanced Raman scat- tering (SERS) has shown the ability to detect the presence of very low concentrations of chemical agents quickly [1, 4–6]. 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 nanos- tructured SERS substrates have the lexibility 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 ilm 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 ofer a signiicantly 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 ilms with very large efective surface areas. he technique is based on atomistic level self-shadowing. Whereas in typical thin ilm deposition setups the substrate is held normal to the vapor source, in the OAD setup the substrate is held at a very large oblique angle with respect to the incoming vapor lux. his angle creates shadows behind each condensing atom preventing subse- quent atoms from condensing in the shadowed areas. Instead, they land on the previously nucleated sites resulting in the evolution of columnar morphology. A detailed overview and potential applications of these thin ilms are given in the review paper by Hawkeye and Brett [10]. Even though OAD has been demonstrated to work well with metals like titanium (Ti), chromium (Cr), nickel (Ni), and so forth, it has shown limited success with sot metals like silver (Ag), gold (Au), and copper (Cu) [11, 12]. Most of the results with the latter