▎ 摘　　要

The experimental realization of two-dimensional materials such as graphene, silicene and germanene has attracted incredible interest ranging from understanding their physical properties to device applications. During the fabrication and processing of these two-dimensional materials, structural defects such as vacancies may be produced. In this work we have systemically investigated the formation energies, electronic and magnetic properties of graphene, silicene and germanene with vacancies in the framework of spin polarized density functional theory. It is found that the magnetic moment of graphene and silicene with vacancies decreases with the increase in the concentration of vacancies. However, germanene remains non-magnetic irrespective of the vacancy concentration. Low-buckled silicene and germanene with vacancies may possess remarkable band gaps, in contrast to planar graphene with vacancies. With the formation of vacancies silicene and germanene demonstrate a transition from semimetal to semiconductor, while graphene turns to be metallic. (C) 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).