X-ray Interferometry : Research : Dimensional : Science + Technology : National Physical Laboratory

X-ray Interferometry

X-ray interferometer

An x-ray interferometer can be thought of as a ruler or translation stage where the graduations or steps are equal to the spacing between silicon atoms in a crystal. The interferometer is a monolithic silicon crystal with three lamellae from which x-rays are Bragg diffracted. Two diffracted beams recombine at the third lamella and, as the lamella is translated, give rise to a variation in the x-ray signal is observed with a period equal to the lattice spacing of the planes from which the x-rays were diffracted, d₍₂₂₀₎= 0.192 nm.

NPL led a EU funded project with the Physikalisch-Technische Bundesanstalt (PTB) and Istituto Nazionale di Ricerca Metrologica (INRIM) to develop a Combined Optical and X-ray Interferometer (COXI) for the sub-nanometre calibration of displacement measuring transducers. The instrument was successfully used to measure picometre non-linearity in optical interferometers. This led to work combining the x-ray interferometer with scanning probe microscopes to calibrate SPM transfer standards and look at local variations in the pitches of these standards.

Non-linearity in NPL Plane Mirror Differential Optical Interferometer measured using optical interferometry

NPL is currently participating in the EMRP funded project NANOTRACE that is developing state of the art displacement measuring optical interferometers with target uncertainties of 10 pm. The performance of these interferometers will be evaluated at NPL using x-ray interferometry. The platform for mounting the x-ray interferometer is currently being redesigned to accommodate the various optical interferometers that will be evaluated.

Publications

Yacoot A (2005) Metrological applications of x-ray interferometry in Nanoscale Calibration Standards & Methods: ed Wilkening G & Koenders L, Wiley-VCH 34-44.
Yacoot, A. and Koenders, L. (2003): From Nanometre to Millimetre: A Feasibility Study of the Combination of Scanning Probe Microscopy and Combined Optical and X-ray Interferometry. Meas. Sci. Technol. 14, N59-63.
Yacoot, A. and Cross, N. (2003): Measurements of Picometre non-linearity in an optical grating encoder using x-ray interferometry. Meas. Sci. Technol. 14, 148-152.
Peggs, G.N. and Yacoot, A. (2002): A review of recent work in sub-nanometre displacement measurement using optical and X-ray interferometry. Phil. Trans. R. Soc. Lond. A 360, 953-968.
Yacoot, A., Kuetgens, K., Koenders, L. and Weimann, T. (2001): A combined x-ray interferometer and scanning tunnelling microscope. Meas. Sci. Technol. 12, 1660-1665.
Yacoot, A. and Downs, M.J. (2000): The use of x-ray interferometry to investigate the linearity the NPL Differential Plane Mirror Optical Interferometer. Meas. Sci. Technol. 11, 1126-1130.
Basile, G., Becker, P., Bergamin, A., Cavagnero, G., Franks, A., Jackson, K., Kuetgens, U., Mana, G., Palmer, E.W., Robbie, C.J., Stedman, M., Stümpel, J., Yacoot, A. and Zosi, G. (2000): Combined optical interferometer for high precision dimensional metrology. Proc. Roy. Soc. Lond. A 456, 701-729.