Raman and QCM Studies of PPG and PEG Adsorption on Cu Electrode Surfaces

Abstract

We investigate the behavior of Cu plating bath suppressor additives poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) using normal Raman spectroscopy, surface-enhanced Raman spectroscopy (SERS), and electrochemical quartz crystal microbalance (QCM) measurements. Raman and SERS show a clear spectroscopic trend of increased intensity in higher wavenumber modes in the CH stretching region as the environment is changed from pure material to solution to surface for both PEG and PPG. The spectral changes associated with PEG are larger than those associated with PPG, suggesting that the relatively more hydrophilic PEG undergoes more conformational changes upon surface association relative to the more hydrophobic PPG. Calculations show that the observed spectroscopic trend is associated with increased gauche character in the polymer backbone. QCM measurements show PEG adsorbs to the surface only in the presence of Cl − , while PPG adsorbs to the surface both with and without Cl − present. In the presence of Cl − , PPG forms a denser surface layer (0.598 μg/cm 2 ) compared to PEG (0.336 μg/cm 2 ) on a Cu underpotential deposition (UPD) layer on Au. These differences are consistent with the increased hydrophobicity of PPG relative to PEG.

Binder-Focused Approaches to Improve the Stability of Cathodes for CO2 Electroreduction

“…A custom spectroscopic Raman flow cell was used for in situ SERS measurements . SERS measurements were performed as previously reported , with a 531.9 nm laser (B&W Tek) providing sample excitation at approximately 45° relative to an 85 mm f/1.2 collection lens (Canon). The scattered radiation was then focused using an f/3.3 lens to the 50 μm slit of a SpectraPro 2300i monochromator (Princeton Instruments) with grating of 1200 grooves mm –1 .…”

Probing the Evolution of Surface Chemistry at the Silicon–Electrolyte Interphase via In Situ Surface-Enhanced Raman Spectroscopy

“…It is noted that a Cu mesh, instead of a Cu foil, was used as a current collector to enable Raman measurements through the sapphire window from the top, while allowing electrolyte to surround the electrode. A previously described electrochemical roughening procedure was performed on the Cu mesh to create nanostructures that induce surface plasmons. The SEM image of Cu mesh (Figure b) shows nanostructures of 100–150 nm sizes, which will exhibit the surface plasmon resonance with a 633 nm laser excitation source. , The roughened Cu mesh was dried under dynamic vacuum overnight and transferred into an Ar-filled glovebox, where approximately 30 nm of a-Si was deposited on both sides of the mesh using a physical vapor deposition method. , The Si/Cu electrode was kept under an inert atmosphere throughout the entire experimental process to minimize the formation of silicon oxides (SiO x ).…”

“…It is noted that a Cu mesh, instead of a Cu foil, was used as a current collector to enable Raman measurements through the sapphire window from the top, while allowing electrolyte to surround the electrode. A previously described electrochemical roughening procedure 14 was performed on the Cu mesh to create nanostructures that induce surface plasmons. The SEM image of Cu mesh (Figure 1b) shows nanostructures of 100− 150 nm sizes, which will exhibit the surface plasmon resonance with a 633 nm laser excitation source.…”

The Adsorption Structure of Polyethylene Imine on Copper Surfaces for Electrodeposition

“…Peaks a and b are assigned to symmetric and asymmetric CH 2 stretching modes. [28] Increasing intensity of the peak at higher wave numbers is ascribed to increasing gauche character along the C-O-C-C and O-C-C-O dihedral angles. [28] In comparison with the PEG studies, peak b exhibits significantly higher relative intensity, indicating increased gauche conformations along the polymer chain for adsorbed PEI.…”

“…Increasing ratio of gauche conformers upon adsorption was consistent with experimental and theoretical studies of PEG adsorption, which indicated a reorientation from predominantly trans conformations in solution to gauche. [25,28,29] Similar to the previous studies, we used surface-enhanced Raman spectroscopy (SERS) for conformational analysis of PEI on the chloridecovered Cu surface (Figure 6). Peaks a and b are assigned to symmetric and asymmetric CH 2 stretching modes.…”