Pyrolytic Graphite Sheet, a New Adsorption Substrate for Superfluid Thin Films

TL;DR

This study evaluates uncompressed pyrolytic graphite sheet as a novel, atomically-flat substrate for superfluid helium films, demonstrating its suitability for two-dimensional superflow experiments due to its surface properties.

Contribution

It introduces uncompressed pyrolytic graphite sheet as a new, effective substrate for superfluid helium experiments, highlighting its surface quality and suitability for 2D helium systems.

Findings

uPGS has atomically-flat, smooth surfaces with high crystallinity.

The thinnest uPGS (10 μm) is suitable for superflow experiments.

Despite low surface area, uPGS's surface quality makes it ideal for 2D helium studies.

Abstract

We have measured surface morphology and gas adsorption characteristics of uncompressed pyrolytic graphite sheet (uPGS) which is a candidate substrate for AC and DC superflow experiments on monolayers of 4He below T = 1 K. The PGS is a mass-produced thin graphite sheet with various thicknesses between 10 and 100 {\mu}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 (<0.1 m$^2$/g) is rather small, by making use of its smooth external surface, the thinnest uPGS of 10 {\mu}m thick is found to be suitable for the superflow experiments on the strictly two-dimensional helium systems.