On the Acceleration of Cu Electrodeposition by TBPS (3,3-thiobis-1-propanesulfonic acid): A Combined Electrochemical, STM, NMR, ESI-MS and DFT Study

Galvanostatic potential/time transient measurements confirm TBPS (3,3-thiobis-1-propanesulfonic acid, as received) as accelerant for copper electrodeposition.In-situ STM data reveal, however, identical structure motifs on single crystalline Cu(100) model substrates when exposed to TBPS containing electrolytes as previously reported for MPS (3-mercapto-1-propanesulfonic acid) and SPS (bis(3-sulfopropyl)disulfide). In all three cases MPS is found as chemisorbed species on the copper.In the present paper we discuss two hypotheses rationalizing both the accelerating effect of the TBPS (as received) on the copper electrodeposition and the appearance of MPS on the copper surface. The first possibility proposes that low levels of MPS and SPS are present in raw TBPS as origin for the observed acceleration. A second scenario suggests the formation of MPS as a result of the asymmetric TBPS decomposition. The latter hypothesis will be discussed on the basis of DFT calculations.