Characterization of gold contacts in GaAs-based molecular devices: Relating structure to electrical properties

Au/octadecanethiol/GaAs devices were prepared using different metallization conditions: direct deposition at 77 K and 300 K samples, and indirect deposition (Ar backfilling). Time-of-flight secondary ion mass spectrometry data indicate that ∼4x and ∼2x more gold penetrates through the SAM after direct deposition at 300 K and 77 K, respectively, than under Ar backfill conditions. However, these devices have significantly different conductances: Ar-backfill and 77 K samples have ∼200x and ∼70x, respectively, larger conductances than 300 K devices. An electrostatic model has been developed to explain the very large conductance changes due to small differences in device structure.