Electron transport in self-assembled organic thin films

We examine the transport properties of unique supermolecule/nanoparticle assemblies and take a different approach to the transport analysis, though based on familiar fundamental principles. We experimentally investigate the electronic properties of random arrays of two-dimensional gold nanoparticles (AuNPs) consisting of metal junctions linked by optically active dithiol-PZnn supermolecules. The conductance of the assemblies was determined as a function of bias voltage, particle size, particle distribution, and the dithiol-PZnn supermolecule. Using normalized differential conduction analysis, we find that the mechanism is thermally assisted tunneling (TAT), where the response is independent of the particle size and distribution.


Fig. a shows a general device configuration, in which Au NPs disordered bimodal array is deposited on the substrate, interconnected with dithiol-PZnn linkers. The temperature dependence of conductance of different samples were shown in Fig. b and fit well to an Arrhenius model or a variable-range hopping model. Fig. c compares the apparent activation energies obtained from Arrhenius analysis.


Differential analysis of transport of functionalized AuNPs shows temperature dependence of d ln(I)/dV for a variety of AuNP arrays and supermolecule linkers and led us to propose that thermally assisted tunneling is the mechanism controlling transport. This transport process is illustrated in Figure d-g, which shows an idealized band diagram as a function of molecular length. The energy at which the majority of tunneling occurs is above the Fermi energy (at temperatures above 0 K) but below the LUMO and, therefore, likely associated with an energetic metal or molecular state, as expected for a thermally assisted tunneling mechanism.