Growth, conductivity, and vapor response properties of metal ion-carboxylate linked nanoparticle films

Abstract

Nanoparticles of metals (Au, Ag, Pd, alloys) in the size range 1–3 nm diameter can be stabilized against aggregation of the metal particles by coating the metal surface with a dense monolayer of ligands (thiolates). The stabilization makes it possible to analytically define the nanoparticle composition (for example, Au₁₄₀(hexanethiolate)₅₃, I) and to elaborate the chemical functionality of the protecting monolayer (for example, Au₁₄₀(C6)₃₅(MUA)₁₈, II, where C6 = hexanethiolate and MUA = mercaptoundecanoic acid). Network polymer films (II_film) on interdigitated array electrodes can be prepared from II, based on cation coordination (i.e., Cu²⁺, Zn²⁺, Ag⁺, methyl viologen) by the carboxylates of MUA. The electronic conductivity of the II_film network polymer films occurs by electron hopping between the Au₁₄₀ nanoparticle cores, and offers an avenue for investigation of metal-to-metal nanoparticle electron transfer chemistry. The report begins with a brief summary of what is known about metal nanoparticle electron transfer chemistry. The investigation goes on to assess factors that influence the dynamics of film formation as well as film conductivity, in the interest of better understanding the parameters affecting electron hopping rates in II_film network polymer films. Finally, sorption of organic vapors into II_film causes a decreased electronic conductivity and increased mass that can be assessed using quartz crystal microbalance measurements. The change in electronic conductivity can be exploited for the sensing of organic vapors.