Abstract. The d(d,n)3He and d(d,p)t fusion reactionshave been studied at center-of-mass energies E = 1.6 to 130 keV using intense beam currents from 30, 100, and 450 kV accelerators in combination with detectors in close and far geometry. The cross sesction ratio, (d,p), approaches unity (within 2%) at low energies; thus there is no experimental evidence for the Oppenheimer-Phillips effect at subcoulomb energies. R(E)=a(d,n)/cr The cross sections of d(d,p)t at E<10 keV show clearevidence for electron screening effects. However, the observed cross section enhancement is significantly larger than can be accounted for from available atomic physics models.

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Cross section measurements of the d(3He, p)4He reaction have been extended to an energy as low as E cm =5.4 keV. The data have an improved accuracy compared with previous work and confirm the existence of electron screening. The combined analysis of the present and previous data leads to an electron screening potential of U e =123 ± 9 eV. A similar analysis of previous data for3He( d, p)4He leads to U e =186 ± 9 eV. Both screening potentials differ due to the molecular and atomic aggregate state of the targets involved in these investigations and are significantly larger than expected from available atomic physics models, supporting the general trend in studies of electron screening

The transport of Si atoms during thermal growth of silicon-oxide films on silicon in dry O 2 was investigated by isotopic substitution of Si. The experiment consisted of depositing a 7.6-nm-thick epitaxial layer of 29 Si on a Si͑111͒ substrate and determining the 29 Si profiles, with subnanometric depth resolution, before and after oxidation in 50 mbar of dry O 2 at 1000°C for 60 min. The results constitute an experimental confirmation of a widely held belief that Si does not diffuse through the growing oxide to react with oxygen at the gas/oxide interface, leaving O 2 as the only mobile species.

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