Figure 6.

MBE growth of doped and alloyed 2D TMDs. a) MBE growth pathway of Nb doped WSe₂ at 550 °C. At step 3, niobium sources and selenium sources are introduced to form NbSe₂ around the outmost Nb‐WSe₂ and smoothen the surface. Reproduced with permission.^{[ 100 ]} Copyright 2020, Springer Nature. b) ADF‐STEM image of mirror twin boundary (MTB) loop comprised of three MTBs, I, II, and III. Green circles indicate Nb dopants. The scale bar is 1 nm. Reproduced with permission.^{[ 100 ]} Copyright 2020, Springer Nature. c) Atomic structure of 4|4‐Se MTBs marked in (b) indicates the local Nb doping concentration inside the boundary. Reproduced with permission.^{[ 100 ]} Copyright 2020, Springer Nature. d) Simulated STM images and comparison to experimental images for Te vacancy in the negative charge states. Reproduced with permission.^{[ 101 ]} Copyright 2019, Wiley‐VCH. e) Simulated STM images for V at Te site and V interstitial. Their corresponding atomic structures are shown below. Reproduced with permission.^{[ 101 ]} Copyright 2019, Wiley‐VCH. f_1–5) Atomic resolution STM images (15 × 15 nm²) of MoSe₂, V_0.26Mo_0.74Se₂, V_0.55Mo_0.45Se₂, V_0.78Mo_0.22Se₂, and VSe₂ grown by MBE on graphite. Reproduced with permission.^{[ 65 ]} Copyright 2020, American Chemical Society. g_1–5) Corresponding STS curves to each alloy shown in (f). (Set points: f₁ 1.6 V, 44 pA; f₂, 1.2 V, 511 pA; f₃, 0.5 V, 130 pA; f₄, 0.3 V, 103 pA; and f₅, −0.02 V, 200 pA.)Reproduced with permission.^{[ 65 ]} Copyright 2020, American Chemical Society. h) Evolution of (top) thermal stability and (bottom) electronic character of 2D V_xMo_{1− x} Se₂ as a function of x. The narrow “stable” region in the top figure means that the thermally stable phase might exist when x < 0.05. In (bottom), for x ≤ 0.44, the 2D alloys are composed of semiconducting MoSe₂ domains with metallic MTBs as well as homogeneous, metallic alloy domains. Reproduced with permission.^{[ 65 ]} Copyright 2020, American Chemical Society.