Cindra A. Widrig

The investigation of redox reactions with a scanning tunneling microscope: Experimental and theoretical aspects

Abstract The tunneling current between the tip and a sample in a scanning tunneling microscope (STM) can be enhanced by the presence of an electroactive adsorbate on the sample. We have used the transfer Hamiltonian mechanism to determine the dependence of this current on various system parameters like the bias voltage, the energy of reorganization, and electronic coupling of the redox centre to the tip and the substrate. We estimate that a fast redox couple would rise give to currents in the pA to nA range; furthermore, the adsorbate density of states will be reflected in d j /d V . We also discuss experimental considerations in examining electron transfer via a redox adsorbate using an STM.

Search for cold fusion using Pd-D2O cells and Ti-D mixtures

We have searched for cold fusion produced in an electrolytic cell with Pd cathode and Pt anode. The electrolyte was 0.1 molar LiOD in 99.8% D2O. A 2-mm rod of polycrystalline Pd and a 4-mm rod of single crystal Pd were used. No radiation was detected above background by a BF3 neutron and Ge γ-X detector. The D2 loading of the Pd was 0.8 D per Pd atom reaching saturation after 4 hours. We also attempted to duplicate the work of Scaramuzzi and co-workers on the Ti-D2 system. Both powder and pieces of Ti were used. The material was cycled several times between 1100 K and 77 K. No neutron, γ- or x-ray emission above background was observed. The results of a barrier penetration calculation for H-like atoms are presented. The high fusion rates reported for PdDx. are much larger than those expected from theoretical calculations on these systems.

Scanning tunneling microscopy and atomic-force microscopy of n-alkanethiolate monolayers spontaneously adsorbed at gold surfaces

Monolayer films of alkanethiolates CH3(CH2)nSH at Au(111) films on mica were examined by scanning tunneling microscopy (STM) (n equals 1,9,17) and AFM (n equals 1 - 17). The resulting atomically resolved images reveal the packing arrangement of the overlayer. Observed images correspond to a hexagonally packed array of adsorbates with respective nearest- and next-nearest-neighbor spacings of 0.50 +/- 0.02 nm and 0.87 +/- 0.04 nm with STM and 0.52 +/- 0.03 nm and 0.90 +/- 0.04 nm with the AFM. This packing agrees with the expected ((root)3 X (root)3)R30 degree(s) adlayer structure of the adsorbate. We believe the STM images reflect the arrangement near the gold-bound sulfur interface, whereas the AFM images reveal the arrangement of the alkyl chains.