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SUMMARY:The Negative Stiffness and Positive Damping of Air Beneath AFM Can
 tilevers (and other AFM Activities at WPI)
DTSTART:20150612T150000
DTSTAMP:20260916T064125Z
UID:08cae5054086681d8496dc7203ea630e3e289afe317d4b2b63f0a492
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Nancy A. Burnham\, Worcester Polytechnic Institute\, Wor
 cester\, MA (USA)\nJOINT MICRO- and BIONGINEERING SEMINARAbstract:\nThe sp
 eaker 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 instrum
 entation\, as a step towards making more quantitative dynamic AFM measurem
 ents in air.\nWhen an AFM cantilever is vibrated with an amplitude of abou
 t 100 nm in air and brought from a distance greater than 50 µm towards th
 e sample\, its amplitude drops by 20%.  This is a non-negligible change i
 f quantitative interpretation of AFM data is desired.  Furthermore\, if t
 he 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 equi
 valent-circuit model of Veijola [1].  The intriguing “negative stiffnes
 s” was found to be a result of the phase lead of the damping of the sque
 ezed film of air.  This progress in modeling air damping will be applied 
 to dynamic measurements of viscous\, compliant materials using the recentl
 y introduced loss-tangent mode [2].\n1. Veijola\, Timo. "Compact models fo
 r squeezed-film dampers with inertial and rarefied gas effects." Journal o
 f Micromechanics and Microengineering 14.7 (2004): 1109.\n2. Proksch\, Rog
 er\, and Dalia G. Yablon. "Loss tangent imaging: Theory and simulations of
  repulsive-mode tapping atomic force microscopy." I 100.7 (2012): 073106.B
 io:\nNancy Burnham graduated from the University of Colorado at Boulder in
  1987 with a Ph.D. in Physics.  Her dissertation concerned the surface an
 alysis of photovoltaic materials. As a National Research Council Postdocto
 ral Fellow at the Naval Research Laboratory\, she became interested in sca
 nning probe microscopy\, in particular its application to detecting materi
 al properties at the nanoscale.  After three years as a von Humboldt Fell
 ow in Germany at Forschungszentrum Juelich\, she spent another six years i
 n Europe\, principally at the Ecole Polytechnique Federale de Lausanne in 
 Switzerland\, all the while pursuing the mechanical properties of nanostru
 ctures and instrumentation for nanomechanics.  Her international experien
 ce also includes sejours at the University of Bordeaux\, Tokyo Institute o
 f Technology\, and the Royal Institute of Technology in Stockholm.  She b
 ecame an Associate Professor of Physics at WPI in January of 2000 and affi
 liated 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 Nanosc
 ience and Technology Division of the AVS.  She was the recipient of the 2
 001 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 20
 14.
LOCATION:GC A 330 http://map.epfl.ch/?room=gca330
STATUS:CONFIRMED
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