DIFFERENT APPROACHES FOR SURFACE MODIFICATIONS: FORMATION OF INHIBITIVE FILM ON COPPER SURFACES AND SURFACES FUNCTIONALISED WITH Ag NANOPARTICLES

OF DOCTORAL DISSERTATION HELSINKI UNIVERSITY OF TECHNLOGY P.O. BOX 1000, FI-02015 TKK http://www.tkk.fi Author Kirsi Yliniemi Name of the dissertation Different Approaches for Surface Modifications: Formation of Inhibitive Film on Copper Surfaces and Surfaces Functionalised with Ag Nanoparticles Manuscript submitted 28 November 2007 Manuscript revised N/A Date of the defence 28 March 2008 Monograph Article dissertation (summary + original articles) Faculty Faculty of Chemistry and Materials Sciences Department Department of Chemistry Field of research Electrochemistry Opponent(s) Prof. Patrik Schmuki Supervisor Prof. Kyösti Kontturi (Instructor) Abstract The purpose of this study was to investigate different surface modifications and two different approaches have been studied in this Thesis. In the first part, the purpose was to study the mechanism for the formation of inhibitive copperbenzotriazole [Cu(I)-BTA] film and in the second part, the surface modifications were done with Ag nanoparticles to create for example antibacterial surfaces. The formation of an inhibitive [Cu(I)-BTA] film on copper and copper alloy surfaces has been investigated as a function of potential, alloying element and oxygen content in the surrounding environment. Measurements were performed using scanning electrochemical microscope (SECM) with which the change from a conductive to an insulating surface can be detected. The potential of copper substrate was observed to have a crucial effect on the formation of inhibitive [Cu(I)-BTA] film. At positive potentials (from -0.2 V to open circuit potential) the formation of the film can be detected as a function of exposure time for benzotriazole (BTAH). At negative potentials the copper surface stayed conductive even after four hours exposure leading to a conclusion that no inhibitive film can form on the surface. This leads to a final conclusion that adsorption is not enough for the inhibition of copper. Also, the effect of alloying elements (in this study silver and phosphorus) was observed. Both of these elements decreased the rate of film formation and in the case of silver enrichment on the surface, film formation was totally absent. Moreover, the role of oxygen in the film formation was studied in this thesis and it was observed that oxygen is needed for the formation of inhibitive film on copper surface. In addition, surface modifications with Ag nanoparticles – which possess interesting properties like antibacteriality and Surface-Enhanced Raman Scattering (SERS) – have been studied. When Ag nanoparticles are embedded into the sol-gel films it was observed that their presence increased the barrier properties of the film. Furthermore, the stability of the films was able to be improved by low temperature O2 and H2 plasma treatments. A novel route for the formation of ultra-thin films with attached Ag nanoparticles is outlined in this Thesis. Ultra-thin films do not show antibacterial properties, inducing that attached nanoparticles are not antibacterial in the tested system but sufficient amount of dissolution of silver is needed. This study also questions the currently widely used testing methods. SERS activity of the ultra-thin films is not observed but with a slight modification in synthesis to create thicker films containing more Ag on the surface produces good SERS enhancement. The enhancement factor is 1·10 which is a relatively high value when thinking of practical applications as a SERS probe.