Construction of two-dimensional hydrogen clusters on Au(111) directed by phthalocyanine molecules

Low-dimensional H₂ aggregates have been successfully fabricated on Au(111) surfaces and investigated by means of low temperature scanning tunneling microscopy. We use manganese phthalocyanine (MnPc) molecules anchored on the Au(111) surface to efficiently collect and pin hydrogen molecules. A two-dimensional (2D) molecular hydrogen cluster is formed around the MnPc. The hydrogen cluster exhibits bias-dependent topography and spatial-dependent conductance spectra, which are rationalized by the exponentially decreasing threshold energy with distance from the central MnPc to activate the motion of the H₂ molecules. This exponential drop reveals an interfacial phase behavior in the 2D cluster. [Figure not available: see fulltext.]