Lorraine C. Nagle

Ammonia Borane Oxidation at Gold Microelectrodes in Alkaline Solutions

Borane-based electroless plating baths are of interest in many microelectronics applications such as barrier and capping layers for copper integrated circuit interconnect. To optimize the plating baths a thorough understanding of the role of the bath constituents is required. To this end we have employed microelectrodes to investigate the oxidation mechanism of boranes in alkaline solutions. In this paper we present data for the simpler ammonia borane (AB) oxidation and compare it with the previous analysis of dimethylamine borane (DMAB) oxidation. Both AB and DMAB are shown to oxidize in two steady-state mass transport-controlled oxidation waves for specific concentration ranges. Particular emphasis is placed on the analysis of the second oxidation wave observed at less negative potentials and the differences observed in the analysis of AB and DMAB in this potential region. The potential range for oxidation, the optimum concentration, and a suggested mechanism for oxidation are shown.

Anomalous electrochemical behaviour of palladium in aqueous solution

Palladium electrode surfaces in aqueous sulphuric acid solution were activated or disrupted by repeated growth and reduction of multilayer hydrous oxide films. A very low percentage (<1.0%) of the metal deposited on reduction of such films existed initially in an unusually active state. This active palladium exhibited a reversible redox transition at ca. 0.24 V (RHE) at 25°C and the charge involved in the latter process was directly proportional to the much larger charge value associated with the reduction of the HO2 component in the multilayer hydrous oxide deposit. The charge associated with the active state of the metal decreased gradually, in a first-order manner, subsequent to the generation of the active state. The nature of the active state of metal surfaces, which is assumed to be of considerable importance in heterogeneous catalysis and electrocatalysis, is discussed briefly.

Nanoporous Gold Catalyst for Direct Ammonia Borane Fuel Cells

Nanoporous gold (NPG) electrodes were fabricated in film and wire array formats by selectively dealloying Ag from Au0.18Ag0.82. The ammonia borane (AB) oxidation reaction was studied by cyclic voltammetry at the NPG electrodes. The onset potential for the oxidation at NPG in a wire array format shifted to more negative potentials than that observed at a Au disc and higher currents were realised. An onset potential of -1.30 V vs. SCE was recorded which is 0.28 V lower than that at a Au disc. The oxidation current for 20 mM AB in 1 M NaOH increased from 2.65 mA cm -2 at a Au disc to 13.1 mA cm -2 at a NPG wire array. NPG is a viable candidate as an anode catalyst for a direct ammonia borane fuel cell.

Active Site and Electrocatalytic Behavior at Palladium Electrode Surfaces

The electrocatalytic properties of palladium are of interest in connection with direct formic acid fuel cell development. Cyclic voltammograms recorded for activated palladium electrodes in sulphuric acid solution exhibit a quasi-reversible surface redox transition at ca. 0.25 V (RHE) and, in the presence of formic acid, the oxidation of the latter undergoes a dramatic change in rate at the same potential. Catalysis in this case evidently involves surface active site behaviour, low coverage protruding palladium species undergoing oxidation in a repetitive manner, the resulting surface cations coordinating bisulphate anions and acting as mediators for the formic acid oxidation reaction.

Direct Oxidation of Ammonia Borane as an Alternative Fuel at Nanoporous Au

Environmental Protection Agency (EPA STRIVE research fellowship entitled “Zero Carbon Emission Micro Fuel Cell Design”; Contract No. 2007-FS-ET-6-M5)

3D interconnection by FIB assisted Pt deposition and electroless nickel deposition on the sides and edges of an I-Seed

This paper reports on the development of a 3D interconnection process leading to the successful assembly of a five-layer 3-D 1 mm cube module. This proof of concept module demonstrates the capability for successful integration and interconnection of commercial off the shelf components to fabricate functional modules in 1 mm cube dimensions. It also demonstrates that use of established volume scale technologies like flip-chip dicing and patterning techniques are viable for fabricating these 1 mm modules. The demonstrator consists of LEDs bonded to the six sides of the 1 mm cube, interconnected and powered up. The work particularly report on two different processes to fabricate the interconnection pattern using direct focused ion beam (FIB) assisted Pt deposition and electroless metal deposition, which again patterned by FIB. Uniform thickness of the deposit and excellent coverage on all six sides is achieved by electroless nickel deposition. Voltage current characterisation of the deposited Pt shows a resistivity value of 1864 plusmn 100 muOmega cm, whereas electroless Ni film shows a resistivity of 25 muOmega cm due to boron inclusion. 100 nm Au layer is deposited by chemical displacement reaction to enhance the conductivity and solderability of the film

DMAB Oxidation for Electroless Deposition from Alkaline Solutions

Dimethylamine borane (DMAB) is a versatile reducing agent which may be catalytically oxidised at a wide range of materials. Metals of interest to the ICT industry that may be deposited from DMAB based solutions include gold, nickel, cobalt, platinum and copper. It also facilitates a wide range of magnetic alloy materials with low codeposition of boron. This work has focused on analysing the mechanism for DMAB oxidation in the first case at gold to assist in the plating bath formulations for optimised deposition and plating bath operation.