Researchers from the National Institute of Standards and Technology, Gaithersburg, Md., and the University of North Carolina, Chapel Hill, have demonstrated a new design for an instrumented nanoscale indenter that makes sensitive measurements of the mechanical properties of thin films. The NIST solution is a touchless surface detector in which the frequency of a pair of tiny quartz tuning forks changes as they get close to the test surface. The nanoindenter senses the frequency shift and locks the indenter mechanism at a fixed distance from the test surface, but without exerting any detectable force on the surface itself.
The NIST nanoindenter can apply forces up to 150 millinewtons, taking readings a thousand times a second. Results have an uncertainty lower than 2 micronewtons, while measuring tip penetration up to 10 micrometers to within about 0.4 nanometers. All of this in done in a way that can be traceably calibrated against basic SI units for force and displacement in a routine manner.
The instrument is well suited for high-precision measurements of hardness, elasticity, and creep. It is useful for a wide range of materials, including often difficult-to-measure soft materials such as polymer films. One of its primary applicationss will be in the development of reference materials that can be used to calibrate other instrumented indenters. “There still are no NIST standard reference materials for this class of instruments because we wanted to have an instrument that was better than the commercial instruments for doing that,” explains NIST researcher Douglas Smith.
