Title: Advances in Ambient and Liquid AFM: Nanoscale Structure, Dynamics, and Mechanics

Speaker: Roger Proksch
 
Date/Time: 10：00-12：00 AM， Dec. 12, 2017 (Tues.)
 
Location: Room 234， Chemistry Building

Abstract：

The Atomic Force Microscope was invented in 1986,[i] opening a window into the nanoscale world beyond the diffraction limit of traditional optics. From the beginning, researchers were captivated by the possibilities of “smallifying” existing laboratory techniques to the newly accessible nanometer length scale, perhaps most memorably captured by the phrase “lab on a tip”.[ii]

In this talk, we will explore some recent results in observation of structure and dynamics in a variety of systems ranging from polymer dynamics in ambient conditions, 3D atomic resolution mapping of the structure of the solid-liquid interface, defect dynamics in crystal lattice and biologically relevant materials, and molecules in fluid. In particular, dynamics can now be captured at frame rates ranging from >1,000 seconds/image to <100 milliseconds/image.

Beyond topography, one of the most natural extensions of AFM – given that the cantilever tip touches the sample surface – is stiffness and modulus measurements.  While there are numerous techniques for quantifying elastic and inelastic properties with the AFM, we will focus on Bimodal AFM theory[iii] and experiments[iv] where more than one resonant vibrational mode of the cantilever is used. In particular, bimodal AFM has allowed very high-resolution and high-speed modulus measurements on a wide variety of samples, ranging from soft gels and polymers to much stiffer metals and ceramics, with modulus values ranging from less than 10 MPa to >100 GPa. Notably, these measurements can cover greater than three orders of magnitude in modulus with the same cantilever, both in ambient and fluid conditions. These measurements are in part enabled by photothermal actuation[v] and a new interferometric detection scheme[vi] that allows calibration of the frequency-dependent cantilever sensitivity and stiffness.

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[i] Binnig, Quate, and Gerber, Physical review letters 56 930 (1986).
[ii] Meyer, Ernst, Hans J. Hug, and Roland Bennewitz. Scanning probe microscopy: the lab on a tip. Springer Science & Business Media, 2013.
[iii] T. R. Rodriguez and R. Garcia, Appl. Phys. Lett. 84, 449 (2004).
[iv] R. Proksch, Appl. Phys. Lett. 89, 113121 (2006).
[v] A. Labuda et al, Rev. Sci. Instrum. 83, 053702 (2012).
[vi] A. Labuda and R. Proksch, Appl. Phys. Lett. 106 253103 (2015).