Abstract
A cold beam of ${\mathrm{He}}^{*}\phantom{\rule{0.3em}{0ex}}(2\phantom{\rule{0.2em}{0ex}}^{3}S_{1})$ atoms is used at grazing incidence to study the quantum reflection on a flat polished silicon surface. We measure the reflectivity as a function of the normal incident velocity component between 3 and $30\phantom{\rule{0.3em}{0ex}}\mathrm{cm}∕\mathrm{s}$. Our result is in reasonable agreement with a calculation of the attractive van der Waals surface potential using the dielectric function of Si and the dipole polarizability of ${\mathrm{He}}^{*}$. We discuss the influence of the conductivity and of a thin oxide layer on the potential. By comparing our data to those previously measured with ${\mathrm{Ne}}^{*}$ atoms, we are also able to confirm the scaling of the reflectivity with atomic mass.
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