Activation energies for 3He adsorbed on hexagonal boron nitride

We present a series of measurements of the sub-monolayer activation energies of He-3 adsorbed on hexagonal boron nitride deduced from measurements of T-2 as a function of temperature. These yield the energy of formation of thermally activated vacancies prior to melting and the energy associated with the desorption process. The T-2 data indicate that in the 2D solid the dipolar relaxation mechanism is dominant. At intermediate temperatures a non-dipolar mechanism appears, due to motion in the fluid him, while at higher temperatures dipolar relaxation again becomes dominant, associated with desorption of the He-3 atoms. (C) 2000 Elsevier Science B.V. All rights reserved.