Gregory S. Ferguson

The rate of decomposition of a thin anodic film of gold oxide (Au2O3) was monitored as a function of time under ultrahigh vacuum with either continuous or short-intermittent irradiation by a typical photon flux in an x-ray photoelectron spectrometer. Continuous exposure of a specimen to x rays greatly accelerated its rate of decomposition, leading to a loss of more than half of the film during 8 h of irradiation. For comparison, exposure of a specimen to only the occasional irradiation necessary to collect data led to an order-of-magnitude slower rate of decomposition over the same period. These results distinguish between the effects of beam-time and ultrahigh vacuum for the decomposition of gold oxide and provide useful guidelines for minimizing their influence on x-ray photoelectron spectroscopy measurements.

The hydrolysis of alkyl and aryl thiosulfates (Bunte salts), to produce the corresponding thiol and bisulfate ion, is autocatalytic in the absence of added acid and proceeds at greatly accelerated rates in organic solvents at room temperature relative to the same reaction in aqueous solution. Kinetics studies of the hydrolysis of n ‐hexadecyl thiosulfate and p ‐nitrophenyl thiosulfate allowed the determination of the associated rate constants. Control experiments indicate that the enhancement of the rate was not due to the preconcentration of the reactant and the bisulfate catalyst within reverse micelles. Rather, it appears to be related to the properties of the solvent and differences in solvation of the reactant, product, and/or transition state. High‐throughput measurements of the induction periods across a reaction population were fit well by a Gaussian function.

Sliding angles of polar and nonpolar droplets on well-defined surfaces, formed by adsorption of self-assembled monolayers from solutions containing binary mixtures of alkanethiols, depend on the contact-angle hysteresis but not the work of adhesion.

The roll-off angle of hexadecane droplets was measured on a family of nearly ideal surfaces having similar structures but different interfacial free energies. The variation in interfacial energy was reflected in the contact angles of hexadecane, which provide a measure of the work of adhesion. The hysteresis in the contact angle on these surfaces was low and approximately constant, thereby approximately removing it as a variable and allowing for an assessment of any dependence of the roll-off angle on work of adhesion directly. The results revealed no such dependence, consistent with the descriptions of early researchers in this area.

An impedance-based Point Defect Model (PDM) was developed for the potentiostatic, anodic formation of gold oxide at potentials of 1.40–1.70 V vs SHE in H₂SO₄ (0.1 M and 0.5 M). Film thickness and refractive indices were determined at each oxide formation potential using spectroscopic ellipsometry. The thickness of the oxide increases linearly with increasing potential. Mott-Schottky analysis shows that the oxide exhibits both n-type and p-type character and the dominant defect density is calculated to be in the order of 10²¹−10²² (1 cm⁻³). The PDM was optimized upon experimental EIS data to extract values for model parameters and accounts well for the experimental observations in both the steady-state time and frequency domains.

The facile self‐assembly of monolayers films derived from N ‐(2‐aminoethyl)‐2, 2, 4‐trimethyl‐1‐aza‐2‐silacyclopentane on silicon/silicon dioxide substrates from the solution phase is reported. This adsorbate reacts with silanols at the surface to produce a covalent siloxane linkage to the substrate via ring‐opening and produces no byproduct(s). The resulting diamine surface reacts with maleic anhydride or succinic anhydride to produce the corresponding carboxylic‐acid terminated surfaces. The kinetics of these reactions and their products were characterized by contact‐angle goniometry, optical ellipsometry, and X‐ray photoelectron spectroscopy.

Although gold does not form a native oxide under ordinary conditions, its surface can be oxidized electrochemically and the resulting oxide film studied. We have used this approach to examine the effects of anodization potential, anodization time, pH, and presence or absence of dissolved oxygen on the open-circuit decomposition of anodic gold oxide using a combination of in situ ellipsometric, potentiometric, coulometric, and microgravimetric measurements. As expected, increasing the anodization time or potential resulted in more inert films that persisted for longer times in the absence of an applied potential. We also found that this decomposition was faster at low and high pH, but slow at neutral pH. Decomposition of the oxide film was also inhibited by the presence of dissolved oxygen in the contacting electrolyte solution.