posted on 2020-11-25, 22:46authored byZechao Yang, Tim Sander, Julian Gebhardt, Tobias A. Schaub, Jörg Schönamsgruber, Himadri R. Soni, Andreas Görling, Milan Kivala, Sabine Maier
Graphyne-based
two-dimensional (2D) carbon allotropes feature extraordinary physical
properties; however, their synthesis as crystalline single-layered
materials has remained challenging. We report on the fabrication of
large-area organometallic Ag−bis-acetylide networks and their
structural and electronic properties on Ag(111) using low-temperature
scanning tunneling microscopy combined with density functional theory
(DFT) calculations. The metalated graphyne-based networks are robust
at room temperature and assembled in a bottom-up approach via surface-assisted dehalogenative homocoupling of terminal
alkynyl bromides. Large-area networks of several hundred nanometers
with topological defects at domain boundaries are obtained due to
the Ag–acetylide bonds’ reversible nature. The thermodynamically
controlled growth mechanism is explained through the direct observation
of intermediates, which differ on Ag(111) and Au(111). Scanning tunneling
spectroscopy resolved unoccupied states delocalized across the network.
The energy of these states can be shifted locally by the attachment
of a different number of Br atoms within the network. DFT revealed that free-standing metal−bis-acetylide networks
are semimetals with a linear band dispersion around several high-symmetry
points, which suggest the presence of Weyl points. These results demonstrate
that the organometallic Ag−bis-acetylide networks feature the
typical 2D material properties, which make them of great interest
for fundamental studies and electronic materials in devices.