  We present an experimental investigation of a new polymorphic 2D single layer
of phosphorus on Ag(111). The atomically-resolved scanning tunneling microscopy
(STM) images show a new 2D material composed of freely-floating phosphorus
pentamers organized into a 2D layer, where the pentamers are aligned in
close-packed rows. The scanning tunneling spectroscopy (STS) measurements
reveal a semiconducting character with a band gap of 1.20 eV. This work
presents the formation at low temperature (LT) of a new polymorphic 2D
phosphorus layer composed of a floating 2D pentamer structure. The smooth
curved terrace edges and a lack of any clear crystallographic orientation with
respect to the Ag(111) substrate at room temperature indicates a smooth
potential energy surface that is reminiscent of a liquid-like growth phase.
This is confirmed by density functional theory (DFT) calculations that find a
small energy barrier of only 0.17 eV to surface diffusion of the pentamers (see
Supplemental Material). The formation of extended, homogeneous domains is a key
ingredient to opening a new avenue to integrate this new 2D material into
electronic devices.
