Helium Film Formed in 1.2 nm Pore in Zeolite Templated Carbon
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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/m2. 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.