An in situ XRD study of electroless copper deposition on a nylon film substrate using Rochelle salt as a complexing agent and formalin as reducing agent have been carried out using a purpose-designed cell to clarify the effect of additives and aeration on the initial stage of the deposition. The additives used were 2, 2'-dipyridyl (dpy), 4, 4'-dpy, polyethylene glycol (PEG) 300, PEG 600 and PEG 1000, which are usual additives for obtaining uniform distribution of crystal size in the Cu deposits. There has been little discussion of average crystal size, inclusion of Cu2O and other additive effects, or of bath aeration effect. The present study characterized the average crystal size of the Cu deposits as a function of additive concentration and plating time. It is suggested that 2, 2'-dpy promotes the codeposition of Cu2O with Cu. The addition of 4, 4'-dpy appeared to limit the diameter of the deposited Cu crystals, while the average particle size increased with plating time depending on the additives used. Acration of the plating bath greatly retarded the undesired codeposition of Cu2O in the presence of 2, 2'-dpy. XRD measurement showed no clear additive effect for PEG.
In order to acquire spectra of organic materials adsorbed on electrode surfaces by in situ infrared reflection absorption spectroscopy, several new techniques have been developed. The spectra of 2, 5-dihydroxythiophenol (DHT) and p-mercaptophenol (MP) adsorbed on polycrystalline gold electrodes were measured as a function of potential using these new in situ IRRAS techniques. The techniques developed in this work made it possible, in the fingerprint region, to monitor the changes in the vibrational properties of monolayer-adsorbed DHT and MP as a function of the applied potential. The overall spectral characteristics of both DHT and MP and their quinone derivatives in the adsorbed state closely resemble those of their solution-phase counterparts. The relatively high intensity of the signals observed for the adsorbed species provides strong evidence that both DHT and MP are adsorbed on gold with the molecular plane nearly perpendicular to the electrode surface and that their oxidation states change with potential change.
A study was carried out using photothermal deflection spectroscopy (PDS)-also known as the Mirage method-to detect underpotential deposition (UPD) of lead on silver. A laser beam for activation was first passed through a liquid electrolyte to be absorbed at the solid/liquid interface. The laser probe grazed the surface of the solid and was deflected by the gradient in the liquid, so that absorbed light heated the electrode surface causing a gradient in the refractive index of the liquid. Beam deflection was detected by a position sensitive detector as a photothermal deflection (PD) signal. The silver electrodes used were polycrystal, single crystal (111) and single crystal (100). For the (111) surface a very sharp UPD peak appeared in the current-potential curve and the corresponding PD signal also showed relatively abrupt changes. For the (100) surface, on the other hand the PD signal showed a two-step change and decay was relatively gentle. UPD was also investigated by electrochemical scanning tunneling microscopy, yielding in situ STM images of the electrode surface in the solution. After UPD, the surface stepline of the STM images changed slightly and the height of the steps decreased. In addition corrugations appeared on the surface.
A distinct electrical resistance change between a substrate and a torch has been found, that signals the nucleation and growth of diamond under the conditions of reverse bias in which the substrate is held at a negative potential to the torch. It appears that even the quality of diamond films and their deposition rates can be diagnosed using the profile of this resistance change. The results have been confirmed for a variety of substrate materials (Mo, Si, and Cu) over a wide range of synthesis conditions. A tentative model is proposed to explain the observed resistance change and interpret the above-mentioned phenomena. No such electrical resistance change has been observed under forward bias.
The Adsorbed structure of mercaptobenzothiazole (MBT) at silver and copper electrode surfaces was investigated in situ by surface-enhanced Raman scattering (SERS). The molecule has a thione-type structure in acidic solutions of pH<3 and an ionized-thiol-type structure in basic solutions of pH>9. Both types of MBT strongly adsorb on the electrodes through the sulfur atom. When thione-type MBT is adsorbed, the proton at the nitrogen atom is dissociated. In very strongly acidic solutions of pH<1, however, the adsorbed molecule is partly protonated. The protonation is enhanced by co-adsorbed halogen ions. The adsorbed MBT lies nearly flat at low coverages and stands nearly normal to the surface at high coverages.
A solution of silver methane sulfate and potassium iodide with HBPSA added was employed for the test solution and the electroplating bath. Differential capacity was found to decrease with increases in the concentration of HBPSA as did the grain size of the electrodeposits.