Thermal expansion coefficient of single-crystal silicon from 7 K to 293 K

We measured the absolute lengths of three single-crystal silicon samples by means of an imaging Twyman-Green interferometer in the temperature range from 7 K to 293 K with uncertainties of about 1 nm. From these measurements we extracted the coefficient of thermal expansion with uncertainties on the order of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}/\mathrm{K}$. To access the functional dependence of the length on the temperature, usually polynomials are fitted to the data. Inst