Gold nanoparticle/PPI-dendrimer based chemiresistors: Vapor-sensing properties as a function of the dendrimer size

Gold nanoparticle/poly(propyleneimine) (PPI) composite films comprising dendrimers of generation one to five are prepared via layer-by-layer self-assembly. The thickness of the films is determined by atomic force microscopy and ranges between 19 and 32 nm. Field-emission scanning electron microscopy (FE-SEM) images show that the bulk of the films consist of nanoparticles with a diameter of about 4 nm. Current–voltage measurements are used to characterize the electrical properties of the films. The resistivity of the films depends strongly on the size of the dendrimers and increases exponentially with increasing dendrimer generation. This result is discussed in terms of an activated tunneling model for charge transport. The chemical sensitivity of the films is probed by dosing them with vapors of toluene, 1-propanol, and water in a concentration range between 100 and 5000 ppm. All vapors cause an increase of the films’ resistances. While the sensitivity to toluene and 1-propanol increases significantly with increasing dendrimer generation, the sensitivity to water is rather independent of the dendrimer size. This behavior is qualitatively explained by different sorption sites for the different classes of analytes used.