Nanomechanical motions of cantilevers: direct imaging in real space and time with 4D electron microscopy
The function of many nano- and microscale systems is revealed when they are visualized in both space and time. Here, we report our first observation, using four-dimensional (4D) electron microscopy, of the nanomechanical motions of cantilevers. From the observed oscillations of nanometer displacements as a function of time, for free-standing beams, we are able to measure the frequency of modes of motion and determine Young's elastic modulus and the force and energy stored during the optomechanical expansions. The motion of the cantilever is triggered by molecular charge redistribution as the material, single-crystal organic semiconductor, switches from the equilibrium to the expanded structure. For these material structures, the expansion is colossal, typically reaching the micrometer scale, the modulus is 2 GPa, the force is 600 μN, and the energy is 200 pJ. These values translate to a large optomechanical efficiency (minimum of 1% and up to 10% or more) and a pressure of nearly 1,500 atm. We note that the observables here are real material changes in time, in contrast to those based on changes of optical/contrast intensity or diffraction.
Additional Information© 2009 American Chemical Society. Received December 13, 2008; Revised Manuscript Received December 23, 2008. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research in the Gordon and Betty Moore Foundation Physical Biology Center for Ultrafast Science and Technology (UST) at Caltech. We thank Dr. Spencer Baskin for his helpful discussions and Dr. Vladimir Lobastov for his effort on automation and software development. Supporting Information Available: Movies of the dynamics of both the microscale (nl803770e_si_001.avi) and nanoscale (nl803770e_si_002.avi) Cu(TCNQ) crystals, as well as movies of the tilt series of the microscale (nl803770e_si_003.avi) crystal showing the orientation relative to the substrate. The frames of the dynamics movies are the basis of the analysis shown in Figures 5 and 6 in the text. The movies show the real-time dynamics slowed by a factor of ~10^6 in order to make their direct visualization amenable. The frames of the tilt series (tomography) were acquired at 1° intervals spanning a 100° range, with essentially equal displacement from the zero degree position in both the clockwise and counterclockwise rotational directions. This material is available free of charge via the Internet at http://pubs.acs.org.
Supplemental Material - Flannigan2009p17910.1021nl803770enl803770e_si_001.avi
Supplemental Material - Flannigan2009p17910.1021nl803770enl803770e_si_002.avi
Supplemental Material - Flannigan2009p17910.1021nl803770enl803770e_si_003.avi