A Cross-Platform Investigation of Hg-Au Response Profiles Griffin M.J. 1 , Ippolito S.J.* 1 , Sabri Y.M. 1 , Kalantar-zadeh K. 2 , Matthews G.I. 2 , Bhargava S.K.* 1 1 Advanced Materials & Industrial Chemistry, School of Applied Sciences, RMIT University, Australia samuel.ippolito@rmit.edu.au, suresh.bhargava@rmit.edu.au, 2 Microelectronics and Materials Technology Centre, RMIT University, Australia Abstract: The amalgamation of elemental mercury (Hg) with gold (Au) thin-films is a commonly utilized mechanism for sensing Hg vapor in air. In this work, we investigate and compare the sensing mechanisms of a resistive based sensor and a quartz crystal microbalance (QCM) which both employ an Au thin-film sensitive layer which was deposited under identical conditions. Both sensors were tested concurrently at several operating temperatures ranging between 30 and 130°C. Contrary to models described in the literature, which suggests that the response profile should be independent of sensing platforms, this work clearly shows that the mechanisms are different for the two tested platforms. The QCM is shown to primarily respond to the surface bound Hg, including Hg-Hg bonds, whereas the resistive wheatstone-bridge device primarily responds to Hg diffused into the Au sensitive layer, resulting in different transient responses for the same Hg concentration under identical conditions for each sensor platform. Key words: mercury, gold, thin-film, sensor, QCM, conductometric. Background It is well known that the interaction between elemental mercury (Hg) and gold (Au) thin-films is a simple and accurate method for sensing Hg vapor concentrations in gaseous systems [1]. This can be achieved via the use of various transducer platforms which interrogate an Au sensitive layer for changes in either its mass or electrical conductivity. In the case of a resistive device, Raffa et al. [2] describe a detailed model for calculating the expected resistivity change caused by the Hg diffusing into the Au layer. The model was validated by using experimental sensor data to show that the sensor response magnitudes towards Hg concentrations below 100–200 ng·m −3 were linearly correlated. Whereas in the case of sensors which employ mass sensing mechanisms, Sabri et al. [3] develop a model for finding the sticking- probability as a function of equivalent Hg mono- layers on QCMs based Hg sensors which utilized either Au and Ag thin-film sensitive layers. As a part of experimental verification both groups developed transient-response models, through differing methods, for their sensors. Most notably they come to the same resulting root equation which employs an exponential decay, shown in Eq. 1. (1) However, the respective limitations of each model are different, suggesting a strong platform dependency of the formula derived. To further investigate this effect and to confirm that the transient-response of a Hg vapor sensor is platform dependent, experimental work has been undertaken to test both a quartz crystal microbalance (QCM) based sensor and resistive sensor under the same operating conditions. To achieve this, both sensors have been tested in the same gas sensing chamber at the same time to ensure that they would be exposed to the same concentration of Hg and interfering gas species under identical environmental conditions. With this in mind a direct comparison of the individual sensor responses between each platform is undertaken. Methodology Both sensors are based on quartz substrates with 150nm of Au deposited on the surface using electron-beam evaporation. A shadow mask is utilized during the fabrication process to form the QCM electrodes, after which electrical connections were bonded. Conversely DOI 10.5162/IMCS2012/P2.9.12 IMCS 2012 – The 14th International Meeting on Chemical Sensors 1731