Sunday, June 5

Fundamental improvements in the design of Atomic Force Microscopy (AFM) components benefit a wide variety of applications such as AFM imaging and single molecule pulling. Trends towards high-speed AFM imaging require lower noise and higher bandwidth components, in particular the scanning unit, the force sensing cantilever and the AFM electronics, which also benefits low noise molecular measurements. i) The scanning unit needs not only sub-nanometer resolution and a high bandwidth but also must not show any oscillatory behavior in order to achieve the required position accuracy. To this end we implemented a new mechanical design that uses stack piezos and flexures for the spatial movement while maintaining high resonance frequencies and rigidity. The system is equipped with absolute position readout for accurate scanning and precise pulling. ii) Small cantilevers (10 um wide) show higher resonance frequencies and lower thermal noise at a given spring constant than conventional sized cantilevers. This allows higher imaging speeds through a faster cantilever response. The lower noise and higher bandwidth also allow the measurements of smaller force ruptures with higher temporal resolution. iii) The feedback and piezo drive electronics as well as the data acquisition system (DAQ) have to fulfill low noise and high bandwidth requirements. We developed a fast DAQ system that allows imaging at 30 frames per second at 150x150 pixels. Combining all these improvements, the next generation of AFMs will allow imaging speeds two orders of magnitudes faster than current commercial AFM systems. Acoustic and Piezoelectric Imaging of Biomaterials with Scanning Probe Microscopy A.P. Baddorf,1 A. Gruverman,2 S. Jesse,1 B.J. Rodriguez,2 and Sergei V. Kalinin1 1 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 Scanning Probe Microscopies sensitive to elastic and electromechanical properties offer exciting promise for exploring complex compositions such as biological materials. We describe the principles of Acoustic and Piezoresponse Force Microscopies with emphasis on the nature and implications of the tip-surface interaction, describing the opportunities for quantitative measurements. Application is demonstrated in several biological systems, including bone, tooth, and hair. Mechanical and electromechanical nanostructure of hydroxiapatite platelets and collagen fibrils have been determined with resolution below 10 nm. The local electromechanical response varies widely in functionally different components, for example between enamel, dentin, and pulp in tooth. Microstructural organization is correlated with the directional dependence of the response. This work demonstrates that scanning probes have great potential beyond topography for this class of materials. ORNL is managed by UT-Battelle, LLC under DOE contract DCE-AC05-00OR22725. AG acknowledges financial support of the National Science Foundation grant DMR0235632. Correlated Topographic and Spectroscopic Imaging Beyond Diffraction Limit by AFM Metallic Tip-Enhanced Near-Field Fluorescence Lifetime Microscopy Dehong Hu, Miodrag Micic, Nicholas Klymyshyn, Yung Doug Suh, and H. Peter Lu Fundamental Science Division, Pacific Northwest National Laboratory, P. O. Box 999, Richland, WA 99352, U.S.A. [email protected] Abstract A near-field optical imaging approach is demonstrated for simultaneous topographic and spectroscopic imaging with spatial resolution beyond the optical diffraction-limit. The method combines metallic-tip-based atomic force microscopy (AFM) with fluorescence lifetime imaging microscopy (FLIM). The AFM metallic tip apex generates high local electric field enhancement under laser illumination, which provides a strong electric-field interaction between the AFM tip and the fluorescent molecules under the tip. The tip perturbation of fluorescence gives the fluorescence lifetime changes that provide the AFM-FLIM imaging contrast. The globular Au-coated AFM tip not only gives adequate spatial AFM tapping-mode imaging spatial resolution but also is “environmentally friendly” to soft samples, such as polymeric dye-labeled nano-spheres and even biological specimens such as POPO-3 labeled DNA and bacterial cells.A near-field optical imaging approach is demonstrated for simultaneous topographic and spectroscopic imaging with spatial resolution beyond the optical diffraction-limit. The method combines metallic-tip-based atomic force microscopy (AFM) with fluorescence lifetime imaging microscopy (FLIM). The AFM metallic tip apex generates high local electric field enhancement under laser illumination, which provides a strong electric-field interaction between the AFM tip and the fluorescent molecules under the tip. The tip perturbation of fluorescence gives the fluorescence lifetime changes that provide the AFM-FLIM imaging contrast. The globular Au-coated AFM tip not only gives adequate spatial AFM tapping-mode imaging spatial resolution but also is “environmentally friendly” to soft samples, such as polymeric dye-labeled nano-spheres and even biological specimens such as POPO-3 labeled DNA and bacterial cells.