Energy-dissipation nanoprobe

Scanning probe microscopy translates the interaction between a flexible cantilever’s supersharp tip and a sample material into topographical images and force measurements at the nanoscale. However, standard single-frequency SPM cannot reveal certain information, such as the local energy dissipation at a single structural defect—that information is embodied in the quality factor Q of the vibrating cantilever. Frequency sweeps using standard lock-in techniques can determine Q, but those techniques are too slow for practical imaging. Now Stephen Jesse and Sergei Kalinin and their collaborators at Oak Ridge National Laboratory, working with Roger Proksch of Asylum Research, have devised a way to excite the cantilever and measure the response over a band of frequencies simultaneously. Known as band excitation (BE), the method is useful for energy-dissipation measurements since the Q factor can be measured directly, even for low Q-factor environments such as liquids. In just about 1 second, the researchers produced force—distance curves of the tip interactions with cleaved mica; a comparable lock-in scan would take around 30 minutes. The team also showed that Q decreased sharply when ferroelectric domains nucleated. In addition, the BE SPM imaged in both amplitude (left image) and phase (right image) the flower-like patterns associated with magnetic domains of yttrium-iron garnet, and detected ring-like energy dissipation centers. The researchers anticipate that the BE method will be a fast and sensitive technique for understanding and mitigating energy losses in magnetic, electrical, and electromechanical processes and technologies. (S. Jesse et al., Nanotechnology 18 , 435503, 2007 http://dx.doi.org/10.1088/0957-4484/18/43/435503 . )