Molecularly Mediated Thin Film Assembly of Nanoparticles on Flexible Devices: Electrical Conductivity versus Device Strains in Different Gas/Vapor Environment

The ability to precisely control nanoparticle-enabled electrical devices for applications involving conformal wrapping/bending adaptability in various complex sensing environments requires an understanding of the electrical correlation with the device strain and exposure to the molecular environment. This report describes novel findings of an investigation of molecularly mediated thin film assembly of gold nanoparticles on flexible chemiresistor devices under different device strains and exposure molecules. Both theoretical and experimental data have revealed that the electrical conductivity of the nanoparticle assembly depends on a combination of the device strain and the exposure molecules. Under no device strain, the electrical conductivity is sensitive to the molecular nature in the exposure environment, revealing a clear increase in electrical conductivity with the dielectric constant of vapor molecules. Under small device strains, the electrical conductivity is shown to respond sensitively to the strain directions (tensile vs compressive strain) and also to the dielectric constant of the vapor molecules in a way resembling the characteristic under no device strain. Under large device strains, the electrical conductivity is shown to respond to the difference in dielectric constant of the vapor molecules but, more significantly, to the device tensile and compressive strains than those under small device strains. This combination of device strain and dielectric characteristic is also dependent on the orientation of the microelectrode patterns with respect to the device strain direction, a finding that has important implications to the design of flexible arrays for a complex sensing environment.