This
work is focused on the structural control of graphene nanoribbons
(GNRs) and intermediate polymeric wires [poly(p-phenylene),
PPP] during their thermoactivated bottom-up synthesis from room temperature
to 480 °C. The first step of the synthesis relies on the Ullmann
coupling between 4,4″-dibromo-p-terphenyl
(DBTP) molecular precursor units that lead to PPP wires in the temperature
range between 170 and 200 °C. Thermal annealing at higher temperatures
(360–480 °C) triggers the PPP lateral fusion to yield
GNRs. We systematically studied the deposition of DBTP on the three
main low-Miller-index gold surfaces, i.e., Au(100), Au(110), and Au(111),
to elucidate the templating effects of such surfaces due to the pronounced
anisotropy of their reconstructions via a multitechnique approach
(scanning tunneling microscopy, X-ray photoelectron spectroscopy,
and low-energy electron diffraction). The best results are obtained
on Au(100) in terms of (i) GNR length (up to 80 nm), (ii) narrow width
distribution (only 6- and 9-GNRs), (iii) long-range order, and (iv)
excellent alignment along the reconstruction. Au(111) produces longer
GNRs than Au(100) but poorer molecular ordering. Concerning PPP wires,
they are stable within a wide temperature range and exhibit an interesting
improvement of the long-range order with increasing temperature on
Au(100), but the best overall organization and unidirectionality have
been achieved on Au(110).
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