Characterization of Pyrolytic Graphite Sheet: A New Type of Adsorption Substrate for Studies of Superfluid Thin Films

We have measured the surface morphology and gas adsorption characteristics of an uncompressed pyrolytic graphite sheet (uPGS) which is a candidate substrate for AC and DC superflow experiments on monolayers of \(^4\)He below \(T= 1\,\hbox {K}\). The PGS is a mass-produced thin graphite sheet with various thicknesses between 10 and 100 \(\upmu \)m. We employed a variety of measuring techniques such as imagings with optical microscope, SEM and STM, Raman spectroscopy, and adsorption isotherm. PGS has smooth and atomically flat external surfaces with high crystallinity. Although the specific surface area (\(\le 0.1\,\hbox {m}^2/\hbox {g}\)) is rather small, by making use of its smooth external surface, the thinnest uPGS of \(10\,\upmu \hbox {m}\) thick is found to be a promising substrate for future superflow experiments on strictly two-dimensional helium systems.