Bottom‐Up On‐Surface Synthesis of Two‐Dimensional Graphene Nanoribbon Networks and Their Thermoelectric Properties

Abstract

Graphene, the one‐atom‐thick two‐dimensional (2D) carbon material, has attracted tremendous interest in both academia and industry due to its outstanding electrical, mechanical, and thermal properties. For electronic applications, the challenging task is to make it as a semiconductor. The bottom‐up synthesis of semiconducting one‐dimensional (1D) nanometer‐wide graphene strips, namely, graphene nanoribbons (GNRs), has attracted much attention owing to its promising electronic, optical, and magnetic properties. In this regard, we report the fabrication of cove‐type 2D GNR networks (GNNs) via the interconnection of 1D self‐assembled GNRs on the surface of Au(111). The cove‐type 2D GNRs networks (GNNs) were fabricated from the GNR, 5‐CGNR‐1‐1, synthesized using the precursor of DBSP. Annealing of high‐density self‐assembled GNRs on the surface of Au(111) through two‐zone chemical vapour deposition (2Z CVD) successfully generated a 2D interconnected structure with high yield via the fusion and ladder coupling reactions of GNR chains. In order to validate the later fusion reaction, we have also synthesized the GNR, 7‐AGNR‐1‐1, using the precursor of DBBA. The GNNs, which consist of hybridized metallic‐like and semiconducting GNRs, are a new class of carbon‐based materials. Further, we applied this material for thermoelectric (TE) applications and found a very low cross‐plane thermal conductivity of 0.11 Wm−1 K−1, which is one of the lowest value among the carbon‐based materials as well as inorganic semiconductors, while maintaining the cross‐plane electrical conductivity of 188 S m−1.

Molecular-Vapor-Assisted Low-Temperature Growth of Graphene Nanoribbons

“…The observed dots in the flat strands after DDQ addition are assigned to unfused phenyl groups in which three types of partially fused structures appear (Figure S3). Eight additions of 0.5 mg of gaseous DDQ alter the LT-STM image to that of stranded structures with regularly cove-shaped edges (Figure d), identical to cove-type GNRs produced by conventional thermal annealing at 500 °C . As a reference, LT-STM images of prepolymers without DDQ show no change before or after annealing at 350 °C (Figure S4).…”

Materials Science Challenges to Graphene Nanoribbon Electronics

“…Toward this end, ref has recently demonstrated the catalyst-independent synthesis of polyaromatic azaullazine chains via polymerization of polycyclic aromatic azomethine ylides on h-BN, and ref has recently shown the synthesis of armchair GNRs on insulating TiO 2 surfaces, both of which are promising breakthroughs motivating further research into engineering monomers that polymerize on nonmetallic surfaces. The use of polymerized GNRs in thin-film transistors, in which the channels are longer than the individual GNRs, necessitates synthesis of longer GNRs and networks of GNRs interlinked via covalent bonds to achieve a satisfactory μ. , Here, it is particularly attractive to use an on-surface polymerized graphene nanomesh as a channel, which is easier to transfer from Au(111) to a target substrate than arrays of isolated GNRs and can exhibit electronic properties ( G on and I on / I off ) comparable to those of individual GNRs. − …”

Graphene Nanoribbon Grids of Sub-10 nm Widths with High Electrical Connectivity

“…Both G s and μ are orders of magnitude larger than the similarly obtained values previously (∼few tens nS·sq, ∼0.02 cm 2 /(V·s)) for GNR networks (see Table S1). − …”