Magnetic Properties of Surface Layers of Helium-3 and Methane on Porous Silicon

Porous silicon has been used as a new homogeneous substrate system to study magnetic surface behavior of nuclear spin coupling and dynamic effects at low temperatures. Spin-lattice relaxation time T 1 measurements of methane ( 1 H spin) physisorbed on porous silicon have been studied as a function of temperature and coverage. The temperature dependence of T 1 in the range of 4-16 K displays a double minima feature similar to previous observations of methane coverages on graphite systems. However, for high coverages of methane on clean porous silicon, the T 1 values are in the neighborhood of tens of minutes at 4.0 K, while those of the methane-graphite system are considerably shorter. Preliminary measurements of 3 He layers on porous silicon have also been done.