Magnetic actuation enables nanoscale thermal analysis

Jan 12, 2012
This is the atomic force microscope with an integrated heater actuated using Lorentz forces. Credit: William King

Polymer nano-films and nano-composites are used in a wide variety of applications from food packaging to sports equipment to automotive and aerospace applications. Thermal analysis is routinely used to analyze materials for these applications, but the growing trend to use nanostructured materials has made bulk techniques insufficient.

In recent years an atomic force microscope-based technique called nanoscale thermal analysis (nanoTA) has been employed to reveal the temperature-dependent properties of materials at the sub-100 nm scale. Typically, nanothermal analysis works best for soft polymers. Researchers at the University of Illinois at Urbana-Champaign and Anasys Instruments, Inc. have now shown that they can perform nanoscale thermal analysis on stiff materials like epoxies and filled composites.

"This new technique lets us measure temperature and frequency-dependent properties of materials rapidly over a wide bandwidth," noted William King, the College of Engineering Bliss Professor in the Department of Mechanical Science and Engineering at Illinois, who led the research. The technique works by flowing a current around the U-shaped arms of a self-heating (AFM) cantilever and interacting that current with a magnetic field. The magnetic field allows the tip-sample force to be modulated right near the tip of the AFM.

"We are able to achieve nanometer-scale force control that is independent from the heating temperature," according to Byeonghee Lee, first author of the paper.

"Conventional nanothermal analysis has struggled with highly filled, highly crosslinked materials and sub-100 nm . This new technique has allowed us to reliably measure and map and melting transions on classes of materials that were previously very challenging," said Craig Prater, at Anasys Instruments and co-author on the paper.

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More information: "Magnetic Actuation of a Heated Atomic Force Microscope Cantilever using Lorentz Force," Nanotechnology doi:10.1088/0957-4484/23/5/055709

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