Noncontact Atomic Force Microscopy - Yale School of Engineering ...

P.II-07
Atomic Force Microscopy Study of Cross-Linked C32H66 Monolayer by
Low-Energy (10eV) Hyperthermal Bombardment
Y. Liu 1 , H.Y. Nie 2 , D.Q. Yang 2 , M.W. Lau 2 and J. Yang 1
1 Department of Mechanical and Materials Engineering, University of Western Ontario, Ontario, Canada
2 Surface Science Western, University of Western Ontario, Ontario, Canada
Email: yliu452@uwo.ca
Low-energy (10eV) hydrogen projectiles generated in a special production prototype
reactor are being developed in our study to only break the C-H bonds with other bonds
intact on C32H66 monolayer, as spin cast on a silicon wafer. The generation of free carbon
radicals leads to neighboring cross-link and form covalent C-C bonds [1]. The newly
formed surface is characterized by a combination of XPS, optical contact angle
measurement and dynamic atomic force microscopy (AFM). Especially, AFM study is
focused on to correlate with the results from other two techniques. Roughness AFM
results demonstrate a temporal behavior of C32H66 monolayer surface modification,
corresponding to bombardment time which is proportional to the influence during
bombardment process. The transiting roughness measurements can also interpret the
directional properties of the formed covalent C-C bonds.
The controllability of the surface modification is additionally demonstrated by the
evolution of hydrophibilicity of the monolayer as measured by the aid of AFM and
contact angle measurements. Phase image by tapping mode AFM provides necessary
contrast on other mechanical properties and/or adhesion energy to evaluate the untreated
and treated areas on an incompletely bombarded monolayer surface [2]. The results are
further associated with the measurements from force modulation and torsion resonance
modes to provide a critical bombardment time essential to carry on a complete
bombardment and guarantee the surface homogeneity. All of the results confirm crosslinking
C-C bonds as formed after bombardment and explain the enhanced surface and
mechanical properties through the developed hyperthermal bombardment.
[1] Z. Zheng, X.D. Xu, X.L. Fan, W.M. Lau, and R.W.M. Kwok, J. Am. Chem. Soc. 126, 12336 (2004)
[2] J. 1. Tamayo, J. and R. Garcia, Appl. Phys. Lett., 71, 2394 (1997).
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