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تسجيل مستخدم جديدFrom Point Defects in Graphene to Two-Dimensional Amorphous Carbon
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While crystalline two-dimensional materials have become an experimental reality during the past few years, an amorphous 2-D material has not been reported before. Here, using electron irradiation we create an sp2-hybridized one-atom-thick flat carbon membrane with a random arrangement of polygons, including four-membered carbon rings. We show how the transformation occurs step-by-step by nucleation and growth of low-energy multi-vacancy structures constructed of rotated hexagons and other polygons. Our observations, along with first-principles calculations, provide new insights to the bonding behavior of carbon and dynamics of defects in graphene. The created domains possess a band gap, which may open new possibilities for engineering graphene-based electronic devices.
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Defects are inevitably present in two-dimensional (2D) materials and usually govern their various properties. Here a comprehensive density functional theory-based investigation of 7 kinds of point defects in a recently produced {gamma} allotrope of 2
D phosphorus carbide ({gamma}-PC) is conducted. The defects, such as antisites, single C or P, and double C and P and C and C vacancies, are found to be stable in {gamma}-PC, while the Stone-Wales defect is not presented in {gamma}-PC due to its transition metal dichalcogenides-like structure. The formation energies, stability, and surface density of the considered defect species as well as their influence on the electronic structure of {gamma}-PC is systematically identified. The formation of point defects in {gamma}-PC is found to be less energetically favourable then in graphene, phosphorene, and MoS2. Meanwhile, defects can significantly modulate the electronic structure of {gamma}-PC by inducing hole/electron doping. The predicted scanning tunneling microscopy images suggest that most of the point defects are easy to distinguish from each other and that they can be easily recognized in experiments.
The structure of amorphous materials-continuous random networks (CRN) vs. CRN containing randomly dispersed crystallites-has been debated for decades. In two-dimensional (2D) materials, this question can be addressed more directly. Recently, controll
ed experimental conditions and atomic-resolution imaging found that monolayer amorphous carbon (MAC) is a CRN containing random graphene nanocrystallites. Here we report Monte Carlo simulations of the structure evolution of monolayer amorphous boron nitride (ma-BN) and demonstrate that it also features distorted sp2-bonding, but it has a purely CRN structure. The key difference is that, at low temperatures, C atoms easily form hexagons, whereas the probability to form canonical B-N-B-N-B-N hexagons is very low. On the other hand, hexagons have lower energy than non-hexagons, which results in hexagonal CRN regions that grow much like nanocrystallites in MAC. The net conclusion is that two distinct forms of amorphous structure are possible in 2D materials. The as-generated ma-BN is stable at room-temperature and insulating.
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Graphene is considered one of the most promising materials for future electronic. However, in its pristine form graphene is a gapless material, which imposes limitations to its use in some electronic applications. In order to solve this problem many
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