We present a measurement scheme for creating reference electrostatic forces that are traceable to the International System of Units (SI). This scheme yields references forces suitable for calibrating the force sensitivity of instrumented indentation machines and atomic force microscopes (AFMs). Forces ranging between 10 micronewtons and 200 micronewtons were created and expressed in terms of the voltage, length, and capacitance between a pair of interacting electrodes. The electrodes were comprised of an electrically conductive spherical probe mounted as a tip on an instrumented indentation sensor, and a planar counter electrode fixed to a sample stage in close proximity to the probe. For comparison, we applied mechanical forces of similar magnitudes ?first using deadweights and then using a reference force cell. The deflection of the sensor due to the various applied forces was measured using an interferometer. A spring constant for the sensor was computed from the observed records of force versus displacement. Each procedure yielded a relative standard uncertainty of approximately 1 %; however, the electrostatic technique is scaleable a d could provide traceable reference forces as small as a few hundred piconewtons, a range far below anything yet achieved using deadweights.
Citation: Review of Scientific Instruments
Pub Type: Journals
Calibration, Electrostatic force, Instrumented indentation, SI traceability