Читать книгу Defects in Functional Materials - Группа авторов - Страница 23

Intrinsic structural defects emerge inevitably in the sample growth within finite time according to the thermodynamic theory. Hong et al. [19] found the primary point defects in monolayer MoS₂ changed with the growth methods, physical vapor deposition (PVD) [11, 20–22], mechanical exfoliation (ME) [23] and chemical vapor deposition (CVD) [16, 17, 24, 25], as shown in Fig. 3. It is observed that antisite defects Mo_S2 with Mo replacing the S2 sublattice are the dominant point defects in PVD MoS₂, while in ME and CVD monolayers, sulfur vacancies V_S are the most common defects. Different atomic growth mechanisms [19] have been outlined to account for the difference in the primary defect species in the different growth methods.

The predominant defects such as antisite Mo_S2 and Mo_S in PVD samples are statistically analyzed at a density of (2.8 ± 0.3) × 10¹³cm⁻² and 7.0 × 10¹²cm⁻², corresponding to an atom percent of 0.8% and 0.21%, respectively. The dominant point defect V_S vacancy in the CVD samples has a statistical concentration of (1.2 ±0.4) × 10¹³cm⁻². As both concentrations of primary defects (vacancies or antisites) are remarkably high (0.8–0.2%), it is naturally expected that they will considerably tailor the electronic structures [19].

Figure 2. Atomic structures of antisite defects. (a)–(c) High-resolution ADF-STEM images of antisite Mo_S, Mo_S2, and Mo2_S2, respectively. The former two antisites are dominant in PVD-synthesized MoS₂ single layers. Scale bar: 0.5 nm. (d) and (e) Atomic structures of antisite defects S_Mo and S2_Mo, respectively. (f)–(j) Simulated STEM images based on the theoretically relaxed structures of the corresponding point defects in (a)–(e). (k)–(t) Top and side views of DFT-relaxed atomic model of all antisite defects. Light blue: Mo atom; gold: S2 atoms. Reproduced from Jin et al. (2015) with permission.