Abstract
Surface modification of atomically thin semiconductors enables their electronic, optical, chemical, and mechanical properties to be tailored and allows these nanosheets to be processed in solutions. Here, we report first-principles density functional theory calculations, through which we show chemical functionalization of black phosphorus using phenyl, phenolate, and nitrene species, which were widely investigated for carbon-based materials. We find that covalent functionalization using nitrene-derived species introduces a strong P–N dative bond at the interface without perturbing its intrinsic electronic structure. The Lewis basic and nucleophilic P atom attacks, through a free pair of electrons, the Lewis acidic nitrene species. These results are further compared to other nitrene-derived functional groups on black phosphorus, including N-methylbenzene, N-aminobenzene, and N-nitrobenzene. We find that by tuning the charge redistribution at the interface, the work function of black phosphorus can be tuned by more than 2 eV. These results suggest valuable tunability of the electronic properties of two-dimensional layered black phosphorus by covalent functionalization for future device applications.
Highlights
Two-dimensional (2D) black phosphorus (BP),[1−4] known as single-layer phosphorene, is a member of layered-material family consisting of graphene, 2D hexagonal boron nitride, and transition-metal dichalcogenides, ranging from semimetals to semiconductors and to insulators
We note that the band gap is underestimated using Perdew− Burke−Ernzerhof (PBE) calculations compared to the Heyd−Scuseria−Ernzerhof (HSE) calculations
We have systematically investigated the adsorption of phenyl, phenolate, and nitrene on the basal plane of black phosphorus by means of density functional theory (DFT) computations
Summary
Two-dimensional (2D) black phosphorus (BP),[1−4] known as single-layer phosphorene, is a member of layered-material family consisting of graphene, 2D hexagonal boron nitride, and transition-metal dichalcogenides, ranging from semimetals to semiconductors and to insulators. Covalent functionalization of exfoliated BP remains less explored, it may be more crucial because of its fast degradation upon exposure to ambient conditions.[9−12] Within the context of introducing a protective layer on BP surfaces against ambient degradation, several encapsulation techniques have been proposed, including the encapsulation of BP with transparent poly(methyl methacrylate)[23] and insulating hexagonal boron nitride (h-BN).[24,25] For the same purpose, using trimethylaluminum and H2O as precursors, a thin AlOx film can be deposited onto BP flakes by atomic layer deposition.[26] Very recently, aryl diazonium chemistry, a widely studied chemistry for graphene, has been applied to BP and the functionalized samples have shown enhanced semiconductor performance and improved chemical stability resulting from the surface passivation.[27] the aryl group may introduce a flat energy band within the band gap of BP, leading to reduced hole mobility, as shown recently in first-principles calculations.[28] stable covalent functionalization of BP to modify its chemical stability and solubility without diminishing its desirable electronic properties still remains to be developed
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