AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP9
Surface Stress Induced during the Formation of Alkanethiol Self-Assembled Monolayers on Gold-Coated Cantilevers

Wednesday, November 6, 2002, 11:00 am, Room Exhibit Hall B2

Session: Surface Science Poster Session
Presenter: M. Godin, McGill University, Canada
Authors: M. Godin, McGill University, Canada
O. Laroche, McGill University, Canada
V. Tabard-Cossa, McGill University, Canada
B. Seivewright, McGill University, Canada
P Williams, Acadia University, Canada
B. Lennox, McGill University, Canada
P. Grütter, McGill University, Canada
Correspondent: Click to Email
Functionalized alkanethiol self-assembled monolayers (SAM) have proven to be quite versatile in producing sensing layers that are both selective and reactive to specific target molecules during chemical or biochemical sensing. By self-assembling these sensing layers onto the surface of standard atomic force microscope (AFM) cantilevers, we can design micromechanical sensors that are tailor-made to respond to very specific chemical signals. The surface stress induced at the sensing layer during chemical sensing is directly measured as a deflection of the cantilever.@footnote 1@ We have developed a new method@footnote 2@ of obtaining quantitative surface stress measurements from cantilever deflection signals that does not require the knowledge of the cantilever's Young's modulus, which is often difficult to estimate when different sensing layers are used or for commonly used SiN@sub x@. We systematically investigated the self-assembly process of alkanethiol monolayers on gold in order to model the surface stress buildup during chemical sensing, ultimately aiming to optimize the sensor's response. In particular, we studied the kinetics of alkanethiol SAM formation by combining real-time, in-situ, surface stress and thickness measurements. A differential micromechanical sensor was used to measure the surface stress evolution during SAM formation on gold-coated cantilevers from the vapor phase, while thickness measurements were performed by ellipsometry with sub-monolayer sensitivity. Results clearly demonstrate that analyte introduction and cell geometry play a determinant role in the structural development of the SAM, which not only affects the final stress values achieved, but also the kinetics during SAM buildup. Such considerations are crucial when optimizing sensor response through modeling or when comparing results achieved with different sensor systems. @FootnoteText@ @footnote 1@R. Berger et al. Science 276, 2021 (2000)@footnote 2@M. Godin et al. APL 79, 551 (2001).