Physisorption at ultra-low temperatures
Having a gaseous many-body groundstate,
spin-polarized atomic hydrogen is
very well suited to study collisional phenomena in the limit of ultra-low
energies. In previous research we investigated, within the thesis project of
J.J. Berkhout, mostly experimentally, atom-surface scattering
phenomena, in particular surface adsorption and specular reflection at the
surface of liquid helium films. The experiments
were done at temperatures down to about 100 mK. It was established that
surface adsorption is the dominant inelastic scattering channel at
temperatures below about 0.5 K and that the adsorption probability is
vanishing with temperature to yield complete specular reflection in the
zero temperature (in accordance with existing theory ). This was
demonstrated by focusing of atomic beams of H with a superfluid-He covered
we contributed to some new
developments which have taken place since the publication of our
experimental findings. Doyle et al.  observed the
adsorption probability to increase with decreasing temperature for
T < 20 mK. This result was puzzling as it was found to be consistent with a
result obtained previously by Goldman  using a Van der Waals
coefficient four times bigger than the known coefficient for the He-H
system. We could explain this unexpected rise as a resonantly
enhanced adsorption probability induced by the substrate beneath the helium
film (see ). This conjecture received support from a more
detailed calculation by Carraro and Cole . Recent measurements
by Yu et al.  have confirmed our explanation by
demonstrating that the adsorption probability could be reduced by almost two
orders of magnitude using bulk helium rather that a helium film, thus
regaining the picture of a vanishing adsorption probability.
The progress on this topic has been very rewarding. Currently superfluid
mirrors start to be applied in polarized proton sources .
 D.S. Zimmerman and A.J. Berlinsky, Can. J. Phys.
61, 50 (1983) 50; Yu. Kagan and G.V. Shlyapnikov,
Phys. Lett. 95A, 309 (1983).
 J.M. Doyle, J.C. Sandberg, I.A. Yu, C.L. Cesar, D.
Kleppner, and T.J. Greytak, Phys. Rev. Lett. 67, 603
 V.V. Goldman, Phys. Rev. Lett. 56, 612
 T.W. Hijmans, J.T.M. Walraven en G.V. Shlyapnikov:
Influence of the substrate on the low-temperature limit of the sticking
probability of hydrogen atoms on He films, Phys. Rev. B 45, 2561 (1992).
 C. Carraro and M.W. Cole, Phys. Rev. B
45, 12930 (1992).
 I.A. Yu, J.M. Doyle, J.C. Sandberg, C.L. Cesar, D. Kleppner,
and T.J. Greytak, Phys. Rev. Lett. 71, 1589 (1993).
 V.G. Luppov, W.A. Kaufman, K.M. Hill, R.S. Raymond, and
A.D. Krisch, Phys. Rev. Lett. 71, 2405 (1993).
Quantum gases home page