AVS 51st International Symposium
    Applied Surface Science Wednesday Sessions
       Session AS+BI-WeA

Paper AS+BI-WeA5
Surface Analysis by Friction Force Microscopy

Wednesday, November 17, 2004, 3:20 pm, Room 210A

Session: Biological Applications of Surface Analysis
Presenter: G.J. Leggett, University of Sheffield, UK
Authors: G.J. Leggett, University of Sheffield, UK
N.J. Brewer, Dundee University, UK
K.S.L. Chong, University of Sheffield, UK
Correspondent: Click to Email
The characterisation of surface chemical structure on the nanometre scale still presewnts significant challenges. Friction force microscopy (FFM) is a widely accessible technique typically provided as standard on commercial atomic force microscoopes. It is capable of providing significant insights into variations in surface chemical composition and molecular organisation. The sensitivity of FFM to changes in molecular organisation will be illustrated with data from studies of self-assembled monolayers (SAMs) on Au and Ag. It will be shown that unexpected packing density differences, revealed by FFM, correctly predict the variation in the photo-oxidation kinetics of these materials. FFM suggests that while SAMs of methyl temrinated adsorbates on Ag are more closely packed on than they are on Au, the reverse is the case for monolayers of carboxylic acid terminated thiols. Methyl terminated SAMs on Ag oxidise more slowly than similar monolayers on Au, while the reverse is true for carboxylic acid terminated SAMs, reflecting the strong influence of molecular packing on photo-oxidation kinetics. The kinetics of SAM photo-oxidation have also been studied and quantified by FFM. Samples of carboxylic acid terminated thiols were exposed to UV light for varying periods of time and then immersed in solutions of methyl terminated thiols. Oxidised adsorbates were replaced by solution-phase thiols. For macroscopic samples, the variation in the coefficient of friction determined by FFM as a function of SAM photo-oxidation correlates closely with the variation in the contact angle (ie, as oxidation proceeds the SAMs become increasingly hydrophobic, and exhibit an increasingly small coefficient of friction). Similar types of analysis may be used to quantify rates of reactions in photopatterned materials SAMs. For materials with structures as small as a few tens of nm, fabricated by scanning near-field optical lithography, FFM enables the monitoring of chemical reactivity.