Ensuring accurate measurements
NPL can supply calibrated artefacts for 2-dimensional and 3-dimensional surface topography measuring instruments. These include step height samples, periodic samples and samples with pseudo random surface texture (for testing the overall performance of the instrument). Similar dimensional standards for atomic force microscopes can also be measured.
2-D surface texture standards
NPL provides traceable calibrations for 2-D surface standards having features ranging from micrometres to millimetres in height. The most accurate calibrations are obtained using the NanoSurf IV instrument. This instrument, developed at NPL, uses laser interferometers to provide accurate displacement measurements in both the vertical and horizontal axes. The high stiffness of the metrology frame and the use of low thermal expansion coefficient materials enable very low uncertainties to be achieved. The instrument can be used to determine all ISO 4287 (1997) surface texture parameters and calibrate Type A to E material artefacts as described in ISO 5436-1 (2000). Step heights of 10 µm can be calibrated with a typical uncertainty of 1.3 nm.
3-D surface texture standards
New standards, e.g. ISO 25178-6, are emerging for 3-dimensional surface topography measurements. Supporting these new measurement requirements, NPL has developed a three-dimensional, or areal, surface texture measurement capability to calibrate standard artefacts for the verification of measurement instruments and provide directly traceable measurements for components such as optical components (e.g. lenses), machined parts (e.g. cylinders liners), industrial coatings, bio-medical devices, wafers for microelectronics and MEMS.
Atomic force microscope standards
Pitch and height standards artefacts, used to calibrate atomic force microscopes can be calibrated using the metrological atomic force microscope (MAFM), developed at NPL, that uses laser interferometers to provide traceable measurement of displacement in all three axes over a measurement range in x and y of 100 micrometres. The typical uncertainties for pitch measurement range between ± 0.2 nm (300 nm pitch) to ±2 nm (10 µm pitch) and for step height measurement range between ± 0.4 nm (10 nm step) to ± 15 nm (0.5 µm step).