Nanomechanical Motions of Cantilevers: Direct Imaging in Real Space and Time with 4D Electron Microscopy

• Published in: Nano letters Vol. 9; no. 2; pp. 875 - 881
• Main Authors: Flannigan, David J, Samartzis, Peter C, Yurtsever, Aycan, Zewail, Ahmed H
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-02-2009
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Image Processing, Computer-Assisted; Mechanical and acoustical properties of condensed matter; Mechanical properties of nanoscale materials; Microscopy, Electron; Models, Molecular; Motion; Nanoparticles - chemistry; Nanoparticles - ultrastructure; Physics; Stress, Mechanical; Time Factors; Young modulus; Time dependence; Monocrystals; Imaging; Mechanical properties; Organic semiconductors; Electron microscopy; Real time
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl803770e

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.