Structural, Electronic, and Vibrational Properties of a Two-Dimensional Graphdiyne-like Carbon Nanonetwork Synthesized on Au(111): Implications for the Engineering of sp-sp2 Carbon Nanostructures.

Andi Rabia,Qiang Sun,Andrea Li Bassi,Giovanni Onida,Carlo S Casari,Nicolò Bassi,Valeria Russo,Nicola Manini,Guido Fratesi,Francesco Tumino,Simona Achilli,Andrea Lucotti,Wei Xu,Alberto Milani

doi:10.1021/acsanm.0c02665

Abstract

Graphdiyne, atomically thin two-dimensional (2D) carbon nanostructure based on sp-sp2 hybridization is an appealing system potentially showing outstanding mechanical and optoelectronic properties. Surface-catalyzed coupling of halogenated sp-carbon-based molecular precursors represents a promising bottom-up strategy to fabricate extended 2D carbon systems with engineered structure on metallic substrates. Here, we investigate the atomic-scale structure and electronic and vibrational properties of an extended graphdiyne-like sp-sp2 carbon nanonetwork grown on Au(111) by means of the on-surface synthesis. The formation of such a 2D nanonetwork at its different stages as a function of the annealing temperature after the deposition is monitored by scanning tunneling microscopy (STM), Raman spectroscopy, and combined with density functional theory (DFT) calculations. High-resolution STM imaging and the high sensitivity of Raman spectroscopy to the bond nature provide a unique strategy to unravel the atomic-scale properties of sp-sp2 carbon nanostructures. We show that hybridization between the 2D carbon nanonetwork and the underlying substrate states strongly affects its electronic and vibrational properties, modifying substantially the density of states and the Raman spectrum compared to the free standing system. This opens the way to the modulation of the electronic properties with significant prospects in future applications as active nanomaterials for catalysis, photoconversion, and carbon-based nanoelectronics.

Highlights

The on-surface synthesis mechanism can be sketched in three steps[40], which take place simultaneously: (i) adsorption of the molecules on the Au(111) surface, (ii) cleavage of C−Br bonds followed by the diffusion of radicals on the 2D template, and (iii) coupling of the sp carbon chains through gold adatoms
In the context of graphdiyne-like materials, these results show the relevance of Raman spectroscopy as a characterization technique suitable to investigate and discriminate between sp-sp[2] hybrid carbon systems consisting of different topologies
Highresolution scanning tunneling microscopy (STM) imaging combined with Raman spectroscopy allowed us to identify the metalated nanostructure formed right after the deposition and the subsequent formation of spsp2 2D nanonetwork upon annealing in ultra-high vacuum (UHV)

Summary

■ INTRODUCTION

Two-dimensional (2D) carbon systems with mixed sp-sp[2] hybridization, i.e., graphyne and graphdiyne, aroused great interest in the scientific community over the past 30 years as novel 2D carbon structures,[1−3] paving the way for the ultimate goal of fabricating sp-hybridized carbon fragments, whose structural, optical, and transport properties were deeply explored.[3−6] These systems can form a variety of 2D crystals with a different structure, sp/sp[2] ratio, density, and porosity and have been predicted to possess peculiar electronic properties, such as multiple Dirac cones in graphyne.[7]. We report on the nanoscale structure and electronic and vibrational properties of a carbon monolayer nanonetwork whose structure resembles γ- or α-graphdiyne, while differing by the presence of aromatic rings with threefold hydrogen terminated bonds This 2D carbon nanonetwork, characterized by sp-sp[2] hybridization, was grown on Au(111) under UHV conditions, through the exposition to to an organic molecular precursor with three alkynyl bromide groups.[45] By a combination of high-resolution STM imaging, Raman spectroscopy, and DFT simulations, we unveil the structure at different stages of the formation, i.e., from metal organic nanostructure comprising Au adatoms to the pure sp-sp[2] carbon nanonetwork obtained after the release of Au atoms by thermal annealing. Nanomaterials, photoconversion, and photovoltaics as well as carbon-based nanoelectronic devices and sensors

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES