Helium film formed in 1.2 nm pore in zeolite templated carbon

We have measured the vapor pressure of ⁴He adsorbed in zeolite templated carbon (ZTC) at 4.2 K, in order to examine ⁴He film growth in the nanopore. ZTC has a framework made of non-stacked graphene, and has a relatively uniform 1.2 nm pore with three-dimensional (3D) periodicity of 1.4 nm. The nanoporous substrate is a candidate to realize superfluid ⁴He film with closer 3D connectivity than those studied so far. From the vapor pressure, coverage dependences of the thickness and the two-dimensional (2D) isothermal compressibility of ⁴He film were derived using thermodynamic equations. The 2D compressibility indicates the onset coverage n ₁ of the second adsorption layer around 20 μmol/m ². It is confirmed that the ⁴He film in the 1.2 nm pores grows uniformly at least up to 1.3-1.5 n ₁.