Nuclear Magnetic Resonance Study of the Formation and Structure of an Adsorbed 3He Monolayer
For several years there has been speculation concerning the nature of an adsorbed monolayer of helium atoms, with special interest as to whether the state of this layer is like a liquid, a solid, or a collection of atoms isolated by the potentials of the adsorbent sites.†1 Although the monolayer density corresponds to that of a high-pressure solid, the observed temperature dependences of the specific heat1-3 (C ∝ T 2) and nuclear magnetic susceptibility4 (χ ∝ T -1) are consistent with either solid-like or liquid-like behavior. We present here measurements of the spin-lattice (T 1) and spin-spin (T 2) relaxation times for 3He atoms adsorbed on Vycor glass; from, these results it is possible to estimate both the correlation time τ c, which is related to mobility, and the second moment of the nuclear magnetic resonance line M 2, which depends on the spatial arrangement of the atoms. We find that the configuration of the atoms is strongly dependent on the fractional coverage θ, in particular indicating a solid arrangement for values of θ ≳ 1/2.
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