Abstract
We perform a systematic first-principles study of phosphorene in the presence of typical monovalent (hydrogen and fluorine) and divalent (oxygen) impurities. The results of our modeling suggest a decomposition of phosphorene into weakly bonded one-dimensional (1D) chains upon single- and double-side hydrogenation and fluorination. In spite of a sizable quasiparticle band gap (2.29 eV), fully hydrogenated phosphorene was found to be dynamically unstable. In contrast, complete fluorination of phosphorene gives rise to a stable structure, which is an indirect gap semiconductor with a band gap of 2.27 eV. We also show that fluorination of phosphorene from the gas phase is significantly more likely than hydrogenation due to the relatively low energy barrier for the dissociative adsorption of F2 (0.19 eV) compared to H2 (2.54 eV). At low concentrations, monovalent impurities tend to form regular atomic rows of phosphorene, though such patterns do not seem to be easily achievable due to high migration barriers (1.09 and 2.81 eV for H2 and F2, respectively). Oxidation of phosphorene is shown to be a qualitatively different process. Particularly, we observe instability of phosphorene upon oxidation, leading to the formation of disordered amorphous-like structures at high concentrations of impurities.
Highlights
Double-side coverage of phosphorene with hydrogen or fluorine monoatomic impurities can be a source of various PxHy (PxFy) metastable structures where impurities form regular 1D rows on phosphorene
Such regular patterns are the most favorable energetically, it appears unlikely to achieve them by dissociating the H2 or F2 molecules from the gas phase, which is due to high energy barriers (42.5 eV), determined by dissociation and by migration of atoms
From the electronic structure point of view, both systems correspond to indirect gap semiconductors with an energy gap of B2.3 eV
Summary
Apart from the negative consequences due to the interaction with impurities, a controlled passivation of black phosphorus might lead to new stable structures as it shows the prominent example of graphene derivatives.[29,30,31] Last but not least, the chemical reactivity of black phosphorus might be exploited for the purpose of gas sensing due to the reported adsorption selectivity.[22,32] Recent theoretical studies discussed the chemical properties of phosphorene in the presence of hydrogen,[23,24] fluorine,[23] and oxygen.[20,25,33] In these studies, the authors discussed either certain single impurities in phosphorene or its stoichiometric derivatives, whereas the mechanism of a step-by-step functionalization is not yet understood. Description of the functionalization process because the existence of desired atomic structures may turn out to be unlikely due to the presence of highly unfavorable intermediate states[34] or high energy barriers of the molecular dissociation upon adsorption Another important aspect of chemical functionalization is the dynamical stability of the reaction products of phosphorene and, its derivatives. We consider atom-by-atom single- and double-side functionalization of phosphorene and find the most favorable adsorption patterns for different impurity concentrations We find that these patterns correspond to a regular surface distribution of hydrogen and fluorine impurities, representing one-dimensional (1D) rows in the zigzag direction of phosphorene. Oxygen impurities tend to form an irregular arrangement of atoms on the phosphorene surface, while at high concentrations a transition to a disordered amorphous-like structure is observed
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