Multifrequency force microscopy improves sensitivity and resolution over conventional AFM
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The three-dimensional reconstruction of a lithium-ion battery electrode, composed of 1441 individual images captured and aligned by the transmission x-ray microscope, reveals nanoscale structural details to help guide future energy research.
Nano Focus Multifrequency force microscopy improves sensitivity and resolution over conventional AFM
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cience and technology at the nanoscale has benefited greatly from the atomic force microscope (AFM), which provides images by measuring the deflection of a probe—a very sharp tip attached to a flexible cantilever—as it scans across the surface of a sample. In conventional dynamic force microscopy (the most common form of AFM), a specific frequency is used to both vibrate the cantilever and measure the tip’s deflection, but information about the sample that is encoded in the nonlinear deflection at other frequencies is irretrievable. A solution to this problem is found in multifrequency force microscopy, where the excitation and/or deflection measurement is carried out at two or more frequencies. With acquisition times similar to those for conventional AFM, multifrequency force microscopy has the potential to overcome conventional force microscopes’ limitations in spatial resolution. Recently, R. Garcia and E.T. Herruzo from the Instituto de Microelectrónica de Madrid, Madrid,
to capture every possible angle. These separate images were then combined to generate a single 3D construct of the specimen. It is this reconstruction process that has previously limited the widespread application of transmission x-ray microscopy to nanotomography. Traditional methods require manual alignment of each 2D projection, or use software to slowly interpret the shifts. To achieve this, the sample has to have sharp internal features or be marked to provide guidelines, which can place restrictions on the materials that can be studied in this way. Such manual alignment procedures are extremely time-consuming, which limits the number of 2D images that can be employed, leading to reduced resolution of the final 3D images.
With the TXM, the specimen is mounted on top of a platform with three sensors that measure nanometer shifts in any direction as the sample rotates and the microscope takes pictures. The computer recording the images, after calibration using a gold sphere, then automatically compensates for any shifts and accurately assembles the images into the final 3D construct. The process takes only four hours, which owes more to the x-rays available from a synchrotron source than the microscope itself or the computer speed. While this work has focused on alternative energy fuels and storage solutions, the new technology associated with this TXM will undoubtedly lead to its widespread use in examining biological, environmental, and materials samples.
Spain, have reviewed the development of five different types of multifrequency force microscopy—multiharmonic AFM imaging, bimodal AFM, band excitation, torsional harmonic AFM, and nanomechanical holography—and examined their applications in a
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