The Negative Stiffness and Positive Damping of Air Beneath AFM Cantilevers (and other AFM Activities at WPI)
Event details
| Date | 12.06.2015 |
| Hour | 15:00 |
| Speaker | Prof. Nancy A. Burnham, Worcester Polytechnic Institute, Worcester, MA (USA) |
| Location | |
| Category | Conferences - Seminars |
JOINT MICRO- and BIONGINEERING SEMINAR
Abstract:
The speaker will provide an overview of nanoscience and atomic-force-microscopy (AFM) activities at Worcester Polytechnic Institute. She will then focus on the following project related to nanotechnology and biomedical instrumentation, as a step towards making more quantitative dynamic AFM measurements in air.
When an AFM cantilever is vibrated with an amplitude of about 100 nm in air and brought from a distance greater than 50 µm towards the sample, its amplitude drops by 20%. This is a non-negligible change if quantitative interpretation of AFM data is desired. Furthermore, if the vibration frequency is right at the cantilever’s free resonance, the phase lag changes from 90o to about 95o, indicating negative stiffness, that is, an attractive interaction between the cantilever and sample. We found that the data fit the resistance and capacitive terms of the equivalent-circuit model of Veijola [1]. The intriguing “negative stiffness” was found to be a result of the phase lead of the damping of the squeezed film of air. This progress in modeling air damping will be applied to dynamic measurements of viscous, compliant materials using the recently introduced loss-tangent mode [2].
1. Veijola, Timo. "Compact models for squeezed-film dampers with inertial and rarefied gas effects." Journal of Micromechanics and Microengineering 14.7 (2004): 1109.
2. Proksch, Roger, and Dalia G. Yablon. "Loss tangent imaging: Theory and simulations of repulsive-mode tapping atomic force microscopy." I 100.7 (2012): 073106.
Bio:
Nancy Burnham graduated from the University of Colorado at Boulder in 1987 with a Ph.D. in Physics. Her dissertation concerned the surface analysis of photovoltaic materials. As a National Research Council Postdoctoral Fellow at the Naval Research Laboratory, she became interested in scanning probe microscopy, in particular its application to detecting material properties at the nanoscale. After three years as a von Humboldt Fellow in Germany at Forschungszentrum Juelich, she spent another six years in Europe, principally at the Ecole Polytechnique Federale de Lausanne in Switzerland, all the while pursuing the mechanical properties of nanostructures and instrumentation for nanomechanics. Her international experience also includes sejours at the University of Bordeaux, Tokyo Institute of Technology, and the Royal Institute of Technology in Stockholm. She became an Associate Professor of Physics at WPI in January of 2000 and affiliated Associate Professor of Biomedical Engineering in 2012. Invited, tutorial, or plenary speaker at over 40 conferences, author or co-author of over 70 publications with over 8000 citations (h-index 32), she is as well active in professional societies as, e.g., Treasurer of the Nanoscience and Technology Division of the AVS. She was the recipient of the 2001 Nanotechnology Recognition Award from the latter organization, was a 2002 Institute of Physics of Ireland Lecturer, and became a Fellow of the AVS in 2010. Two of her articles were featured among the 25 highlighted publications for the 25th anniversary of the journal Nanotechnology in 2014.
Abstract:
The speaker will provide an overview of nanoscience and atomic-force-microscopy (AFM) activities at Worcester Polytechnic Institute. She will then focus on the following project related to nanotechnology and biomedical instrumentation, as a step towards making more quantitative dynamic AFM measurements in air.
When an AFM cantilever is vibrated with an amplitude of about 100 nm in air and brought from a distance greater than 50 µm towards the sample, its amplitude drops by 20%. This is a non-negligible change if quantitative interpretation of AFM data is desired. Furthermore, if the vibration frequency is right at the cantilever’s free resonance, the phase lag changes from 90o to about 95o, indicating negative stiffness, that is, an attractive interaction between the cantilever and sample. We found that the data fit the resistance and capacitive terms of the equivalent-circuit model of Veijola [1]. The intriguing “negative stiffness” was found to be a result of the phase lead of the damping of the squeezed film of air. This progress in modeling air damping will be applied to dynamic measurements of viscous, compliant materials using the recently introduced loss-tangent mode [2].
1. Veijola, Timo. "Compact models for squeezed-film dampers with inertial and rarefied gas effects." Journal of Micromechanics and Microengineering 14.7 (2004): 1109.
2. Proksch, Roger, and Dalia G. Yablon. "Loss tangent imaging: Theory and simulations of repulsive-mode tapping atomic force microscopy." I 100.7 (2012): 073106.
Bio:
Nancy Burnham graduated from the University of Colorado at Boulder in 1987 with a Ph.D. in Physics. Her dissertation concerned the surface analysis of photovoltaic materials. As a National Research Council Postdoctoral Fellow at the Naval Research Laboratory, she became interested in scanning probe microscopy, in particular its application to detecting material properties at the nanoscale. After three years as a von Humboldt Fellow in Germany at Forschungszentrum Juelich, she spent another six years in Europe, principally at the Ecole Polytechnique Federale de Lausanne in Switzerland, all the while pursuing the mechanical properties of nanostructures and instrumentation for nanomechanics. Her international experience also includes sejours at the University of Bordeaux, Tokyo Institute of Technology, and the Royal Institute of Technology in Stockholm. She became an Associate Professor of Physics at WPI in January of 2000 and affiliated Associate Professor of Biomedical Engineering in 2012. Invited, tutorial, or plenary speaker at over 40 conferences, author or co-author of over 70 publications with over 8000 citations (h-index 32), she is as well active in professional societies as, e.g., Treasurer of the Nanoscience and Technology Division of the AVS. She was the recipient of the 2001 Nanotechnology Recognition Award from the latter organization, was a 2002 Institute of Physics of Ireland Lecturer, and became a Fellow of the AVS in 2010. Two of her articles were featured among the 25 highlighted publications for the 25th anniversary of the journal Nanotechnology in 2014.
Practical information
- Informed public
- Free