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Physical Review A

Quantum reflection of He * on silicon

H. Oberst, Yoshihisa Tashiro, Kazuko Shimizu, Fujio Shimizu

Published May 11, 2005• 97 citations
Publisher

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.

DOI
10.1103/physreva.71.052901

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We have experimentally demonstrated a material-independent mirror for atomic waves that uses the Fresnel diffraction at an array of parallel ridges. He* (2 (3)S(1)) and Ne* (1s(3)) atomic waves were reflected coherently on a silicon plate with a microfabricated grating structure, consisting of narrow wall-like ridges. We measured the reflectivity at grazing incidence as a function of the incident velocity and angle. Our data show that the reflectivity on this type of mirror depends only on the distance between the ridges, the wavelength, and the incident angle, but is insensitive to the material of the grating structure. The reflectivity is observed to increase by 2 orders of magnitude, compared to that of a flat polished silicon surface, where the reflection is caused by the attractive surface potential. For He* atoms, the measured reflectivity exceeds 10% for normal incident velocities below about 25 cm/s.
We report on the non-destructive scattering and diffraction of He, He2 and He3 from a plane ruled reflection grating. At grazing incidence the normal component of the particle’s wave-vector is sufficiently small to allow for quantum reflection at the attractive Casimir–van der Waals particle–surface interaction potential. Quantum reflection occurs tens of nanometres in front of the surface, before the dimers and trimers reach the region where the surface-induced forces would inevitably cause the breakup of the fragile bonds. The reflected particles are identified via their mass-dependent diffraction angles and by mass spectrometry. The intensity distributions of the observed diffraction patterns are discussed in terms of the grating’s blaze angle.