We report a metal to insulator transition (MIT) in disordered films of molecularly linked gold nanoparticles (NPs). As the number of carbons (n) of alkanedithiol linker molecules (C(n)S2) is varied, resistance (R) at low temperature (T = 2 K) and at 200 K, as well as trends in R vs T data at intermediate temperatures, all point to an MIT occurring at n = 5. We describe these results in a context of a Mott-Hubbard MIT. We find that all insulating samples (n > or = 5) exhibit a universal scaling behavior R approximately exp[(T0/T)nu] with nu = 0.65, and all metallic samples (n < or = 5) exhibit weaker R-T dependencies than bulk gold. We discuss these observations in terms of competitive thermally activated processes and strong, T-independent elastic scattering, respectively.

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We investigate electrical characteristics of single-electron electrode/nanoisland/electrode devices formed by alkanedithiol assisted self-assembly. Contrary to predictions of the orthodox model for double tunnel junction devices, we find a significant ( approximately fivefold) discrepancy in single-electron charging energies determined by Coulomb blockade (CB) voltage thresholds in current-voltage measurements versus those determined by an Arrhenius analysis of conductance in the CB region. The energies do, however, scale with particle sizes, consistent with single-electron charging phenomena. We propose that the discrepancy is caused by a multibarrier junction potential that leads to a voltage divider effect. Temperature and voltage dependent conductance measurements performed outside the blockade region are consistent with this picture. We simulated our data using a suitably modified orthodox model.

Films of butanedithiol interconnected nanoparticles can exhibit a percolation-driven insulating to metal transition. To explore properties of materials with interpolating behavior, we have measured conductance of these films with systematically varying thickness. Films below a certain threshold coverage exhibit thermally assisted conductance and conductance suppression near zero bias indicative of single-electron-charging barriers. In analogy with semiconductors, we show that these films permit transistor-type gating of film conductivity.

Digital computers use binary states, typically represented by 0 and 5 V, to store and process information at all stages of a calculation. If more states (ideally a continuum) were available in between, density of information could be dramatically increased. Here we show that self-assembled nanoparticle films can feature such continuous state or analogue information storage. Information provided by an arbitrary gate voltage is ‘written’ by trapping charges in local, gate-modified potentials when films are cooled below 175 K. The information is ‘read’ using the film’s built-in ability to sense charge via Coulomb blockade. Application of a time-dependent, multi-step writing gate voltage generates conductance maps corresponding to multi-valued continuous information. As a proof of concept, we exploit this technique to store ‘UT’ in Morse code.