Artifacts in a-SNOM Imaging of Soft Materials

Jia Ru Yu^1,2*, Wei Ssu Liao², Ing Shouh Hwang³, Chi Chen¹

¹Research Center of Applied Science, Academia Sinica, Taipei City, Taiwan
²Department of Chemistry, National Taiwan University, Taipei City, Taiwan
³Institute of Physics, Academia Sinica, Taipei City, Taiwan

* Presenter:Jia Ru Yu, email:puddingdes@gmail.com

Aperture-type scanning near-field optical microscope (a-SNOM) is a potential tool to obtain simultaneous information of topography and spectroscopy for biological samples or polymers. So far the application of a-SNOM imaging of soft materials is still very limited and frustrated. Usually scanning soft materials by soft tips causes serious sample destruction and topographic artifacts. The ambiguity and artifacts of topography will affect the physical or chemical interpretation of the experiment.
In this study, we obtain simultaneous topography and fluorescence mapping of dye-labeled lipids by our home-made SNOM system. For a soft a-SNOM tip (k = 0.6 N/m) operating in the contact mode, a reverse contrast between the AFM topography and a-SNOM fluorescence mapping is obtained. However, for a hard a-SNOM tip (k = 43 N/m) operating in the torsional resonance (TR) mode, no reverse contrast can be observed. The strong adhesion between the tip and the lipids in the contact mode operation is the source of the topographic artifact. We can conclude that the TR mode is more appropriate for a-SNOM imaging of soft materials to get the accurate and higher-resolution AFM topography.

Keywords: AFM artifact, a-SNOM, lipid