High Resolution Electron Energy Loss Spectroscopy investigation of the copper/polyphenylquinoxaline interface formation

The interface formation between copper and polyphenylquinoxaline (PPQ) is investigated. High Resolution Electron Energy Loss Spectroscopy (HREELS) is used to determine the adsorption sites of the first incoming copper atoms onto the surface of the cured polymer. A broadening of the elastic peak during the first step of the metallization testifies to the interaction of Cu atoms on the polymeric surface. At low coverage, the aromatic groups of the PPQ are affected by the copper atoms as the intensity of the vibrational CH-ring stretching mode (at 3022 cm−1) slowly decreases together with the intensity of the loss feature near 804 cm−1 (out-of-plane deformation of the aromatic CH groups). A further metal deposition reduces the intensity of the loss feature located around 1100 cm−1 (in-plane bending mode of the aromatic CH groups). It is worth noting that none of the peaks observed in the virgin polymer disappears completely after metallization. Heating of the metallized polymer restores the intensity of these last two loss features at 800 and 1100 cm−1, supporting a diffusion of the Cu atoms into the bulk of the polymer, as previously observed by X-ray Photoelectron Spectroscopy.