title: Effect of gold oxide in measurements of colloidal force.
abstract: Atomic force microscopy, contact-angle, and spectroscopic ellipsometry measurements were employed to investigate the presence and properties of gold oxide on the surface of gold metal. It was found that, in agreement with available literature, unoxidized gold surfaces were hydrophobic, whereas oxidation rendered the surface highly hydrophilic. The oxide could be removed with ethanol or base but appeared to be stable over long periods in water or salt solutions between pH 3 and 7. After oxidation, the oxide layer thickness, determined using ellipsometry, was consistent with an approximate monolayer of Au-O bonds at the gold surface. The presence of gold oxide was found to alter significantly the electrical double-layer characteristics of the gold surface below pH 6 and may explain the apparent inconsistencies in observed force behavior where gold is employed as well as aiding in design of future microfluidic systems which incorporate gold as a coating.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville 3010, Australia.
authors.forename: Rico F
authors.initials: RF
authors.lastname: Tabor
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Morfa
authors.forename: Franz
authors.initials: F
authors.lastname: Grieser
authors.forename: Derek Y C
authors.initials: DY
authors.lastname: Chan
authors.forename: Raymond R
authors.initials: RR
authors.lastname: Dagastine
mesh_terms: D003102:Colloids; D006046:Gold / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D017155:Wettability
chemical_list: D003102:Colloids; D010087:Oxides; D014867:Water; D006046:Gold