Resistive Sensors Based on Self-Assembled Core-Shell Nanoparticles

Abstract

A gas sensor allows the detection thanks to the specific reactivity of its sensitive material towards the target gas. The use of resistive sensors is based on measuring the variation of their electrical conductivity when the target gas is in contact with the sensitive material. In our study, we chose to work with self assembled core-shell nanoparticles as sensing materials. The idea consists on decorating spherical gold nanoparticles, insensitive to the target gases, with a shell based on a different material. The latter provides the specific sensitivity to the sensor. Previous works in our laboratory focused on Au@Pd and Au@Pt nanoparticles as H2 sensors. These works were extended to other shell materials to examine their sensitivity towards H2 as well as other target gases including NH3. Au@ZnO, Au@SnO2 and Au@Ag nanoparticles were synthetized and then assembled by Langmuir Blodgett technique. The assembly resulted in close-packed core-shell nanoparticle monolayers. These layers were transferred, by simple dip-coating, to a glass slide supporting interdigitated electrodes. Sensing performances of the as fabricated sensors were evaluated through the resistivity changes in the discontinuous particle assemble. The sensitivity of Au@ZnO and Au@SnO2 based sensors was tested towards H2 while Au@Ag based sensors were tested under NH3. All sensors showed responses towards the target gases. The effect of humidity and the sensing temperature on the sensing performances were studied. Besides, among the main sensor proprieties requested and studied we note : sensitivity, selectivity, response and recovery times. Assembles of core-shell nanoparticles organized with Langmuir-Blodgett technique demonstrated attractive sensing performances towards H2 and NH3 in extended concentration ranges. Another important contribution concerns the elucidation of the sensing mechanisms. Various analytical techniques including Temperature Programmed Desorption, Temperature Programmed Reduction and Microcalorimetry were used to allow the discussion of the sensing performances towards mechanisms. Figure 1