Ugo Bertocci

Compositional Control in Electrodeposited Pt100 − x Cu x Alloys

The electrodeposition of Pt 100-x Cu x alloys is demonstrated using an electrolyte comprised of 1 mol/L H 2 SO 4 , 0.001 mol/L K 2 ptCl 4 , and 0.1 mol/L CuSO 4 . Film growth proceeds by facile Cu underpotential deposition occurring in parallel with Pt overpotential deposition, with the latter controlling the overall rate of alloy deposition. Pt and depositions are monitored in real time using an electrochemical quartz crystal microbalance. Pt deposition from 1 mol/L H 2 SO 4 + 0.001 mol/L K 2 PtCl 4 is diffusion limited at potentials below -0.150 V saturated sulfate electrode and occurs with close to 100% current efficiency. In the added presence of CuSO 4 , alloy deposition occurs, supported by the exothermic enthalpy of mixing. Monitoring the steady-state mass/charge ratio enables the composition of the growing film to be evaluated with submonolayer precision. For a given potential, the film composition so determined is in excellent agreement with the alloy composition determined for 1 μm thick films using a combination of ex situ methods. The potential dependence of the alloy composition is described by an asymmetric regular solution model with an extremum for alloying enthalpy of -18.9 ± 0.2 kJ/mol.

An integrated electrochromic nanoplasmonic optical switch.

We demonstrate active switching of light through a nanoslit based plasmonic devices using electrochromic Prussian blue nanocrystals, and achieve large (∼95%) transmission modulation by switching the nanocrystals between oxidized and reduced states.

Superconformal Ni Electrodeposition Using 2-Mercaptobenzimidazole

Ni superconformal filling of sub-micrometer trenches is demonstrated using a Watts bath containing an inhibitor 2-mercaptobenzimidazole (MBI). Hysteretic voltammetry marks the breakdown of the MBI-induced passive-state coincident with the onset of Ni deposition. Chronoamperometry reveals that disruption of MBI inhibition is a strong function of the immersion conditions and potential conditioning. The passive to active transition involves a competition between potential-dependent MBI adsorption and its subsequent deactivation and/or consumption during Ni deposition. Breakdown of the MBI-passivating layer results in sulfide formation and its incorporation into the Ni film. The current efficiency of Ni deposition on the activated surface is close to that for the additive-free electrolyte. For recessed surface features, such as trenches, inhibition-breakdown initiates preferentially at the bottom corners. Scanning and transmission electron microscopy (SEM/TEM) studies show the growth front within the trenches initially develops as a v-notch shape while negligible deposition occurs on the free surface. This is followed by the onset of Ni deposition over the entire surface profile that results in trench filling by geometrical leveling. Depending on the specimen immersion process a distinct microstructural transition marks the change in growth mode from a superconformal deposition mode to geometrical leveling during trench filling.

Effect of Large Voltage Modulations on Electrodes Under Charge-Transfer Control

The experimental test of the validity of a mathematical treatment of the effect of large a-c voltage modulations on the behavior of electrodes under charge-transfer control was carried out for the case of the hydrogen evolution reaction. A frequency analysis of the resulting current showed that both d-c and a-c components of the faradaic current were in quantitative agreement with the predictions of the mathematical model. Deviations from the calculated values, which were observed in certain conditions (particularly at higher frequencies), were explained as the effect of the ohmic-drop error. 7 refs.