LOW-TEMPERATURE RADIO-FREQUENCY SHIELDING OF EXFOLIATED GRAPHITE

The results of experiments using exfoliated graphite as a low temperat ure substrate for NMR studies of physisorbed molecules at ultra-high f requencies (100-300 MHz) are reported. The radio frequency shielding w as observed to be anomalously high at very high frequencies for the gr aphite samples studied and precluded the use of this material for NMR studies requiring high sensitivity in this frequency range at liquid h elium temperatures. It is shown that this behaviour can be understood in terms of the in- and out-of-plane conductivities and the capacitive coupling of the microcrystalline structure of the graphite.