Characterization of chemically modified silicon (111), poly(methyl methacrylate), and poly(dimethylsiloxane) surfaces by chemical force microscopy and X-ray photoelectron spectroscopy

Silicon (111), poly(methyl methacrylate) (PMMA), and poly(dimethylsiloxane) (PDMS) substrates are modified with organic monolayers to control the acid/base or hydrophilic/hydrophobic behaviour of the surfaces. The controlled modification of the interface can lead to increased use of the semi-conductor or polymer materials in chemical and biochemical applications. X-ray photoelectron spectroscopy is used to determine the identity of atoms on the surface which can be used to confirm successful surface modification. Chemical force titrations probe intermolecular interactions between a chemically modified atomic force microscopy (AFM) tip and sample substrate as a function of pH. The modified AFM tips used for chemical force titration analyses are characterized using scanning electron microscopy, Auger electron spectroscopy, and scanning Auger mapping. A 16-thiohexadecanoic acid modified AFM tip is used to probe alkyl monolayer functionalized Si(111) surfaces terminated with methyl, carboxyl, and amine groups to determine the pK1/2 of the terminal functional groups. Native and hydrolyzed PMMA samples are also characterized using a 16-thiohexadecanoic acid modified AFM tip while a 1H,1H,2H,2H-perfluorodecanethiol modified AFM tip is used to analyze native, oxidized, and fluoroalkylsilane self-assembled monolayer modified PDMS substrates. The chemical force titration results on Si(111) surfaces modified by hydrosilylation and the data acquired using the 1H,1H,2H,2H-perfluorodecanethiol modified AFM tip are performed for the first time. Auger electron spectroscopy and scanning Auger mapping characterization of the modified AFM tips has also never been previously reported in the literature. Sample characterization by chemical force titrations and X-ray photoelectron spectroscopy is complemented by atomic force microscopy imaging, infrared spectroscopy, and water contact angle measurements.