Chapters authored
Pulse-Current Electrodeposition of Gold
Pulse-current electrodeposition and a sulfite-based electrolyte were used in fabrication of pure gold films. Surface of the pulse-electrodeposited gold film possessed less defect, lower roughness, smaller grain size, and denser texture when compared with the gold film prepared by constant-current electrodeposition. Microstructures and compressive yield strength of the electrodeposited gold could be controlled by regulating the pulse on-time and off-time intervals in pulse-current electrodeposition. The gold film prepared under the optimum conditions showed an average grain size at 10.4 nm, and the compressive yield strength reached 800 MPa for a pillar-type micro-specimen having dimensions of 10 μm × 10 μm × 20 μm fabricated from the pulse-electrodeposited gold film. Average grain size of the pulse-electrodeposited gold film was much smaller, and the compressive yield strength was much higher than the values reported in other studies. The high strength is due to the grain boundary strengthening mechanism known as the Hall-Petch relationship. In general, the pulse-electrodeposited gold films showed yield strength ranging from 400 to 673 MPa when the average grain size varied by adjusting the pulse-electrodeposition parameters.
Part of the book: Novel Metal Electrodeposition and the Recent Application
Electrodeposition of Gold Alloys and the Mechanical Properties
Strengthening of electrodeposited gold-based materials is achieved by alloying with copper according to the solid solution strengthening mechanism. Composition of the Au–Cu alloys is affected by the applied current density. The mechanical properties are evaluated by micro-compression tests to evaluate the mechanical properties in microscale to take consideration of the sample size effect for applications as microcomponents in MEMS devices. The yield strength reaches 1.15 GPa for the micropillar fabricated from constant current electrodeposited Au–Cu film, and the film is composed of 30.3 at% Cu with an average grain size of 5.3 nm. The yield strength further increases to 1.50 GPa when pulse current electrodeposition method is applied, and the Cu concentration is 36.9 at% with the average grain size at 4.4 nm.
Part of the book: Novel Metal Electrodeposition and the Recent Application
Electrodeposition of High-Functional Metal Oxide on Noble Metal for MEMS Devices
MEMS gas sensors could exert a significant impact on the automotive sector since future legislation is expected to stipulate the monitoring of NOx and unburned fuel gases in vehicle exhausts. Among the materials, zinc oxide and TiO2 are the most promising and extensively used materials for monitoring of NOx gas since zinc oxide and TiO2 show the high sensitivity, good stability, and fast response. Electrochemistry is a potential method to fabricate zinc oxide and TiO2 for the applications since it is carried out at relatively low temperature and can cooperate with photolithography, which is an important process in MEMS. This study integrated zinc oxide/gold-layered structure and TiO2/NiP hybrid structure on elastic fabrics, respectively, to realize an elastic gas sensor. Electroless plating (EP) and cathodic deposition were used to metallize and deposit metal oxides on elastic fabrics. Supercritical carbon dioxide (scCO2) was further introduced into the electrochemical process to enhance the composite reliability.
Part of the book: Novel Metal Electrodeposition and the Recent Application