Dr. Guangzhao Mao
AFM Characterization of Various Nano-Systems

Wayne State University

Abstract

Atomic force microscopy (AFM) is capable of providing three-dimensional topography of a solid/liquid interface with sub-nanometer spatial resolution and tip/surface interaction with piconewton force sensitivity. AFM is particularly useful for the understanding and control of self-assembly by providing images and force curves during real-time transformation from individual molecules to molecular nano-clusters and thin films. Self-assembly has been actively pursued as a bottom-up approach to nanotechnology. The capability of AFM in capturing nanostructure transformation is illustrated by two examples, one involving highly ordered crystalline nano-clusters on templates and the other concerning the temperature-responsive behavior of an amorphous copolymer. The first example describes our recent efforts in achieving site-specific deposition and nucleation of nanocrystals. Nanopatterns formed by self-assembly of alkyl amphiphiles are used as templates to control the nucleation of semiconductors as well as drug nanocrystals. The nano-confinement effect impacts device miniaturization and drug delivery. The second example describes the temperature-dependent phase transition and association behavior of a copolymer of N-isopropylacrylamide with 1-vinylimidazole and polyethylene glycol. AFM captures the coil-to-globule phase transition in the adsorbed polymer film, which is completely reversible with temperature but dependent on film thickness. Stimuli-responsive polymers are promising components of drug and gene delivery systems and as molecular switches of protein activity.