Jan 17, 2008
Nanoneedle grows into force sensor
Flexible metal nanowires that can be individually grown on microdevices can elastically buckle without kinking. These buckling springs when viewed in cross-section provide a direct measure of the applied force.
Researchers at the University of Louisville are studying room temperature directed self-assembly strategies to fabricate suspended and freestanding polymer nanofibers and nanowires. A method of selectively crystallizing intermetallic Ag2Ga nanowires on the end of AFM cantilevers provides a remarkably flexible, long and constant diameter needle. These properties, together with the ability to grow the needle in a chosen orientation with respect to the cantilever and the strong and secure attachment of the needle to the cantilever, suggest the application of the needle as a force sensor.
As shown in the figure, the bending of a needle is compared with the deflection of a polymer fiber air-bridge. From multiple deflections of the nanofiber it is possible to determine the elastic modulus and residual tension of the fiber. The mechanical model of buckling that was used, referred to as generalized elastica, permits the force to be estimated for various angles of approach to the nanostructure under test. Additionally the long needle suggests the potential to contact objects underneath liquids while keeping the cantilever (which can disturb measurements through excessive wetting) outside the liquid. This property will be employed for future measurements of elastic properties of certain biopolymers in their native wet state. It should be noted that the buckled shape of the needle can be seen in a light microscope. The high aspect ratio of the needle is also useful for contacting nanostructures on high aspect ratio devices.
About the author
Vladimir V. Dobrokhotov, PhD is a Research Engineer in the R. W. Cohn group at the ElectroOptics Research Institute and Nanotechnology Center, University of Louisville, Kentucky, USA. He currently is exploring directed self-assembly of high aspect ratio nanostructures, together with measurement and application of the resulting nanostructures.