Study of Copper Underpotential Deposition on Gold using Optical Second Harmonic Generation and the Quartz Crystal Microbalance

Abstract

The second harmonic (SH) signal was generated using 1.064 μm radiation from a Nd:YAG laser operating at a 5 Hz repetition rate. The beam diameter was 3 mm at the electrode surface with an operating energy per pulse of about 8 mJ. The collected SH light was focused onto the entrance slit of an f/3 monochromator that was tuned to 532 nanometers. A photomultiplier was used for detection of the SH signal and the output averaged by a gated integrator/boxcar averager. A filter removed the 1.064 micron fundamental from the collected SH radiation. A reference SH signal was generated using a similar detection line from a quartz crystal, tuned to the peak of a Maker fringe, in order to normalize out fluctuations in the laser output. A modified, three electrode, spectroelectrochemical cell with a VIS/NIR transparent window was used. The reference electrode used was a Ag/AgCl microreference tip, and was placed approximately 1 mm from the edge of the gold mirror electrode. A platinum auxiliary electrode provided a current source for the cell.