Microcantilevers, adsorption-induced

FIGURE 7.4 (a) Deflection, Az, and change in surface stress, Ac, of a gold-coated AFM microcantilever are plotted as a function of time after exposure to vapors of alkanethiols with different chain lengths, (b) Adsorption-induced surface stress at saturation coverage (AOjai) is plotted as a function of alkyl chain length for = 4, 6, 8, 12, and 14. (From Berger, R., et al. 1997. Science 276 2021. Reprinted with permission from AAAS.)... 

S. Kim, K.D. Kihm, Effect of adsorption-induced surface stress change on the stiffness of a microcantilever used as a salinity detection sensor. Appl. Phys. Lett. 93(8), 081911 (2008)... 

Advantage has been taken of the nanomechanical effects of molecular adsorption, confined to one surface of a microcantilever, to utilize these devices for sensors. Surfiice adsorption can be characterized as either physisorption or chemisorption. Physisorption is a result of among other effects, London-type dispersion forces resulting from an induced d le and induction forces caused by surface electric fields. On the other hand, chemisorption is accompanied by charge transfer between adsorbed molecules and the surfree or the presence of covalent bonds between the adsorbate and the surface atoms. The mechanical... 

However, adsorbate could induce various kinds of stresses accompanied with versatile patterns of relaxation and reconstruction [59, 81, 82]. The spacing between the first and the second atomic layers expands if an adsorbate such as C, N, and O buckles into space between the atomic layers even if there is contraction of bonds between the adsorbates and the host atoms [81]. For example, H, C, N, O, S, and CO adsorbates on a metal surface could change the surface stress and cause surface reconstmction because of bond making and breaking. Surface adsorption of sodium ions also increases the stiffness of a microcantilever [83]. 

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