Intrinsic Force Standards Based on Atomic and Molecular Interactions
Physical Measurement Laboratory, Quantum Measurement Division
NIST only participates in the February and August reviews.
The intrinsic forces project aims to establish the capability to traceably measure picoforces using intrinsic molecular forces obviating the need for calibration of transfer artifacts. In the realm of piconewton to nanonewton forces, there are a handful of phenomena already referred to as “force standards” in the single-molecule, bioforce literature. We intend to put these phenomena to the test; measuring and assigning SI values to a selection of atomic and molecular forces that are archetypes of the various interactions (bonding, binding, and conformation change). We are installing a UHV cryogenic AFM/STM equipped with a tuning fork style probe for dynamic force spectroscopy. This system will be used to explore single atom break junctions where we attempt to accurately measure the rupture force of a single gold atomic bond. A high resolution force sensor is being developed that can mount as a sample in the UHV environment to serve as a calibration reference for the experiment. Along with atomic bond rupture, we are exploring DNA as a metrology standard for force measurements. The overstretching-induced conformation of DNA occurs under a tensile force level of approximately 65 pN, as measured using both SPM and optical trapping instruments. We are seeking to develop procedures for traceably recording this force interaction using a general purpose AFM that we will equip with a custom force sensor, such as a focus ion beam milled micro cantilever.