New Imaging System Maps Nanomechanical Properties

An imaging system has been developed that can quickly map the mechanical properties of materials--how stiff or stretchy they are, for example--at scales on the order of billionths of a meter. The new tool can be a cost-effective way to design and characterize mixed nanoscale materials such as composites or thin-film structures.

The nanomechanical mapper, created by scientists from the U.S. National Institute of Standards and Technology (NIST; Gaithersburg, MD, USA), utilizes custom software and electronics to process data acquired by a conventional atomic force microscope (AFM), transforming the microscope's normal topographic maps of surfaces into precise two-dimensional (2D) representations of mechanical properties near the surface. The images enable scientists to see variations in elasticity, adhesion or friction, which may vary in different materials even after they are mixed together. The NIST system, described fully for the first time in an article published in the January 1, 2008, issue of the journal Measurement Science and Technology, can make an image in minutes whereas competing systems might take an entire day.

The images are based on measurements and interpretations of changes in frequency as a vibrating AFM tip scans a surface. Such measurements have typically been made at stationary positions, but until now 2D imaging at many points across a sample has been too slow to be practical. The NIST DSP-RTS system (for digital signal processor-based resonance tracking system) has the special feature of locking onto and tracking changes in frequency as the tip moves over a surface. Mechanical properties of a sample are deduced from calculations based on measurements of the vibrational frequencies of the AFM tip in the air and changes in frequency when the tip contacts the material surface.

NIST materials researchers have used the system to map elastic characteristics of thin films with finer spatial resolution than is possible with other tools. The DSP-RTS can produce a 256 × 256 pixel image with micrometer-scale dimensions in 20 to 25 minutes. The new system also is modular and offers greater flexibility than competing approaches. Adding capability to map additional materials properties can be as simple as updating the software.


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National Institute of Standards and Technology