  Do van der Waals interactions determine the smallest nanostructures that can
be used for atom optics? This question is studied with regard to the problem of
designing an atom interferometer with optimum sensitivity to de Broglie wave
phase shifts. The optimum sensitivity to acceleration and rotation rates is
also considered. For these applications we predict that nanostructures with a
period smaller than 40 nm will cause atom interferometers to perform poorly
because van der Waals interactions adversely affect how nanostructure gratings
work as beam-splitters.
