When Pd nanoparticles are fabricated on a solid surface with a nanometer-scale interparticle distance and exposed to hydrogen gas, the electrical conductivity between the nanoparticles changes due to hydrogen adsorption and absorption. This phenomenon has been applied for hydrogen-gas sensing. In the hydrogen-gas sensing utilizing nanoparticles, precise control of interparticle distance is important, as the above-mentioned conductivity changes are enhanced when the interparticle distance is less than a few nanometers. However, fabrication of such nanoparticles is not straightforward. We solved this problem by developing the piezoelectric resonance method, and a nanometer-scale interparticle distance was achieved. This method evaluates the interparticle distance without contact with the substrate or nanoparticles by analyzing the attenuation change in a piezoelectric resonator located beneath the substrate. In this study, we fabricated Pd nanoparticles covered with an Au submonolayer using this method, and it was observed that the conductivity changes are improved compared to pure Pd nanoparticles.
Nakamura et al. (Wed,) studied this question.