The Small Force Metrology project supports U.S. instrumentation vendors, academic researchers, government scientists, and a broad spectrum of industrial physicists, physical chemists, biophysicists, and materials scientists who seek accuracy in verifying the forces measured by instrumented indentation equipment and atomic force microscopes (AFM). The forces measured by these instruments range from tens of piconewtons in single-molecule biophysical studies of disease therapies, to tens of millinewtons in studies of new dielectric coatings for metals and semiconductors.
In direct response to these customer needs, this project focuses on creating the means to achieve SI traceability for small force measurement and instrumentation, and includes the development and testing of internationally-accepted primary and secondary standards of force in the regime below 10-3 N, exploration of atomic and single-molecule forces as potential intrinsic standards and references, and the development of new instrument platforms at NIST that are capable of realizing ever smaller values of force in terms of traceably realized SI base units and quantum invariants.
- Demonstrated the first accurate scheme for practically realizing forces below the level of a nanonewton enabling the direct calibration of probes used in single molecule mechanical characterization experiments. The technique, which exploits a calculable electrostatic force between a flat probe tip and a thirty micrometer diameter metallic sphere, has been used as the basis for calibrating both normal and lateral force sensitivities of colloidal probe AFM instruments used at NIST.
- Demonstrated that biological molecules could serve as intrinsic force standards. Biological molecules, in general, and DNA, in particular, exhibit some unique properties that make them excellent candidates for future NIST reference materials. In 2009, reliable methods for performing this complex single molecule experiment were developed and the first traceable measurements of this force were achieved.
- Demonstrated the stable creation and manipulation of single atom chains using a newly-developed instrument for the feedback-stabilized break junction experiment. To achieve this result, we created a fiber interferometer system for the accurate measurement of picoscale displacements.
- Demonstrated a new method for characterizing the sliding friction between an atomic force microscope (AFM) cantilever tip and a compliant surface. The new technique yields the coefficient of friction between the surface and tip and also allows us to correct the results of cantilever-on-cantilever calibrations of AFM sensitivities. The results greatly improve the calibration accuracy (by as much as 20 % in some instances).
- Completed an informal round robin study of small force calibrations with Korea, Germany, and England that was initiated in 2008. This test is a first step in verification that micronewton force instruments and associated practices for dissemination of the micronewton are in agreement among the NMI laboratories that support such measurements. This comparison should also underpin the new ISO standard on cantilever stiffness calibration.
Mechanical engineer Jon Pratt makes an adjustment to the prototype NIST Electrostatic Force Balance designed to measure nanoscale forces.
February 1, 2008
Lead Organizational Unit:
- Asylum Research
- MTS Nanotechnology
- General Motors
- Dow Chemical
- Worchester Polytechnic Institute (WPI)
- University of Florida
Related Programs and Projects: