A reliable method has been developed for making through-bond electrical contacts to molecules. Current-voltage curves are quantized as integer multiples of one fundamental curve, an observation used to identify single-molecule contacts. The resistance of a single octanedithiol molecule was 900 +/- 50 megohms, based on measurements on more than 1000 single molecules. In contrast, nonbonded contacts to octanethiol monolayers were at least four orders of magnitude more resistive, less reproducible, and had a different voltage dependence, demonstrating that the measurement of intrinsic molecular properties requires chemically bonded contacts.

Electrical contacts between a metal probe and molecular monolayers have been characterized using conducting atomic force microscopy in an inert environment and in a voltage range that yields reversible current-voltage data. The current through alkanethiol monolayers depends on the contact force in a way that is accounted for by the change of chain-to-chain tunnelling with film thickness. The electronic decay constant, βN, was obtained from measurements as a function of chain length at constant force and bias, yielding βN = 0.8±0.2 per methylene over a ±3 V range. Current-voltage curves are difficult to reconcile with this almost constant value. Very different results are obtained when a gold tip contacts a 1,8-octanedithiol film. Notably, the current-voltage curves are often independent of contact force. Thus the contact may play a critical role both in the nature of charge transport and the shape of the current-voltage curve.

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The deposition of a thin film in a rectangular groove has been simulated by a Monte Carlo method, taking into account collisions in the gas phase, desorption, and surface mobility. The model shows that conformal coating is best achieved by a low sticking coefficient.

Phase transitions that involve solid-state reactions between cobalt and thin films of germanium have been investigated. Germanides are formed by reacting Co (300 Å thick) with thin layers of Ge (∼2000 Å thick) deposited on silicon substrates. Germanium was deposited on Si by rapid thermal chemical-vapor deposition and cobalt was deposited onto Ge by evaporation. The Co/Ge/Si stacked structure samples were then rapid thermally annealed at atmospheric pressure in an inert ambient consisting of Ar. Using x-ray-diffraction spectroscopy, Co5Ge7 and CoGe2 are identified as the phases which form at 300 and 425 °C respectively. The sheet resistance was found to be a strong function of the annealing temperature and a minimum resistivity of approximately 35 μΩ cm is obtained after annealing at 425 °C. The minimum resistivity material corresponds to the CoGe2 phase with an orthorhombic crystal structure. Above 600 °C, the resistivity increases due to an instability of the solid-phase reaction between Co and thin Ge layers deposited on Si. This instability is attributed to rapid Co diffusion at the temperatures which are required to form CoGe2 along with structural defects in the Ge layer.