Gratings and step height standards are useful transfer standards for lateral and vertical length scale calibration of atomic force microscopes (AFMs). In order to have traceability to the SI-meter, the standards must have been calibrated prior to use. Metrological AFMs (MAFMs) with online laser interferometric position measurements are versatile instruments for the calibrations. The developed task-specific measurement strategies for step height and pitch calibrations with the Centre for Metrology and Accreditation's (MIKES's) metrological AFM are described. The strategies were developed to give high accuracy and to reduce measurement time. Detailed uncertainty estimations for step height and grating pitch calibrations are also given. Standard uncertainties are 0.016 and 0.018 nm for 300 and 700 nm pitch standards, respectively, and 0.21 and 0.44 nm for 7 and 1000 nm step height standards.
Gratings and step height standards are useful transfer standards for lateral and vertical length scale calibration of AFMs.
In order to have traceability to the SI-metre, the standards must have been calibrated prior to use. Metrological AFMs
(MAFMs) with online laser interferometric position measurements are versatile instruments for the calibrations. The
developed task specific measurement strategies for step height and pitch calibrations with MIKES metrological AFM are
described. The strategies were developed to give high accuracy and to reduce the measurement time. Detailed
uncertainty estimations for step height and grating pitch calibrations are also given.
An acoustic method for the measurement of the effective temperature and refractive index of air for precision length interferometry is described. The method can be used to improve the accuracy of interferometric length measurements outside the best laboratory conditions and also in industrial conditions. The method is based on the measurement of speed of 50-kHz ultrasound over the same distance measured with a laser interferometer. The measured speed of ultrasound is used to define the effective temperature or the refractive index of air along the laser beam path using the equations presented. The measured speed of sound, Cramer equation, dispersion correction, and Edlén equations are used in the fitting of new equations for the effective air temperature and refractive index of air as a function of speed of 50-kHz ultrasound. The standard uncertainties of the effective temperature and the refractive index of air equations are 15 mK and 1.7×10–8, respectively. The uncertainties of the effective temperature and refractive index of air measured with the test setup for distances of about 5 m are 25 mK and 2.6×10–8, respectively.
An acoustic method for measurement of the effective temperature and refractive index of air along a laser beam path is described. The method can be used to improve the accuracy of interferometric length measurements outside the best laboratories, and even in severe environmental conditions. The method is based on the measurement of the speed of ultrasound over the same distance measured with a laser interferometer. The effectiveness of the method derives from the fact that the relative effect of a change in air temperature is about two thousand times greater on the speed of sound than on the refractive index of air. Experimental equations for the effective temperature or refractive index of air as a function of the speed of sound, pressure, humidity and CO2 concentration are fitted using the measured speed of sound, the Cramer equation, the dispersion correction and Edlén equations. The standard uncertainties of the effective temperature and the refractive index of air equations are estimated to be 15 mK and 1.7×10-8, respectively. The uncertainties of the effective temperature and refractive index of air measured with the test setup were 25 mK and 2.6×10-8 (for L = ~5 m), respectively.
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