Controlling and Exploiting Defects in Synthetic Two-Dimensional Materials*

Defects including vacancies, dislocations, and grain boundaries play a fundamental role in determining the properties of materials. With fewer degrees of freedom, the effects of defects are particularly significant in two-dimensional (2D) materials [1]. For example, in chemical vapor deposited monolayer MoS₂, the interplay between sulfur vacancies and grain boundaries lowers the barrier for vacancy motion, thus enabling the realization of field-driven vacancy motion. Since sulfur vacancies act as n-type dopants, field-driven vacancy motion leads to reconfigurable doping profiles and memristive charge transport [2]. This memristive charge transport can be further modulated with a gate potential, resulting in a hybrid device that combines the attributes of a memristor and transistor (i.e., a memtransistor) [3]. As a second example, molecular beam epitaxy allows the control of defect structures for 2D boron (i.e., borophene) [4]. In particular, mixed phases of borophene have been achieved that each consist of periodically ordered vacancies [5]. The linear defects in these mixed phases self-assemble into spatially periodic superlattices, which modulate correlated electron phenomena such as charge density waves, as observed at the atomic scale with scanning tunneling microscopy and spectroscopy [6].

[1] X. Liu, et al., Advanced Materials, 30, 1801586 (2018).
[2] V. K. Sangwan, et al., Nature Nanotechnology, 10, 403 (2015).
[3] V. K. Sangwan, et al., Nature, 554, 500 (2018).
[4] A. J. Mannix, et al., Science, 350, 1513 (2015).
[5] A. J. Mannix, et al., Nature Nanotechnology, 13, 444 (2018).
[6] X. Liu, et al., Nature Materials, 17, 783 (2018).