Susceptible Detection\nof Organic Molecules Based on\nC<sub>3</sub>B/Graphene and C<sub>3</sub>N/Graphene van der Waals\nHeterojunction Gas Sensors

Constructing van der Waals (vdW) heterostructures is\na prospective\napproach that is essential for developing a new generation of functional\ntwo-dimensional (2D) materials and designing new conceptual nanodevices.\nUsing density-functional theory combined with a nonequilibrium Green’s\nfunction approach allows for the theoretical and systematic exploration\nof the electronic structure, transport properties, and sensitivity\nof organic small molecules adsorbed on 2D C<sub>3</sub>B/graphene\n(Gra) and C<sub>3</sub>N/Gra vdW heterojunctions. Calculations show\nthe metallic properties of C<sub>3</sub>B/Gra and C<sub>3</sub>N/Gra\nafter the formation of heterojunctions. Interestingly, the heterojunctions\nC<sub>3</sub>B/Gra (C<sub>3</sub>N/Gra) for the adsorption of small\norganic molecules (C<sub>2</sub>H<sub>2</sub>, C<sub>2</sub>H<sub>4</sub>, CH<sub>3</sub>OH, CH<sub>4</sub>, and HCHO) at the C<sub>3</sub>B (C<sub>3</sub>N) side are sensitive to the chemisorption\nof C<sub>2</sub>H<sub>2</sub> and C<sub>2</sub>H<sub>4</sub>. Similarly,\nthe Gra/C<sub>3</sub>B is chemisorbed for both C<sub>2</sub>H<sub>2</sub> and C<sub>2</sub>H<sub>4</sub> when adsorbed on Gra side,\nwhile it is only chemisorbed for C<sub>2</sub>H<sub>2</sub> in Gra/C<sub>3</sub>N. Interestingly, all heterojunctions on different sides are\nphysisorbed for CH<sub>3</sub>OH, CH<sub>4</sub>, and HCHO. Furthermore,\nthe calculated <i>I–V</i> curves demonstrate that\nthe devices based on the adsorption of C<sub>2</sub>H<sub>2</sub> and\nC<sub>2</sub>H<sub>4</sub> at each side of the heterojunction have\nremarkable anisotropy, in with the current being considerably greater\nin the zigzag direction than in the armchair direction. More specifically,\nwith C<sub>2</sub>H<sub>2</sub> adsorbed on the Gra side, the sensitivity\nalong the armchair direction is up to 85.0% for Gra/C<sub>3</sub>B\nand close to 100% for Gra/C<sub>3</sub>N. This study reveals that\nC<sub>3</sub>B/Gra (C<sub>3</sub>N/Gra) heterojunctions with high\nselectivity, high anisotropy, and excellent sensitivity are highly\nprospective 2D materials for applications, which further contributes\nnew insights into the development of future electronic nanodevices.