Identifying different stacking sequences in few-layer CVD-grownMoS2by low-energy atomic-resolution scanning transmission electron microscopy

Abstract

ABSTRACT:Atomically thin MoS 2 grown by chemical vapor deposition (CVD) is a promising candidate for the next-generation electronics due to inherent CVD scalability and controllability. However, it is well-known that the stacking sequence in few-layer MoS 2 can significantly impact the electrical and optical properties. Herein we report different intrinsic stacking sequences in CVD grown few-layer MoS 2 obtained by atomic-resolution annular-dark-field imaging in an aberration-corrected scanning transmission electron microscope operated at 50 keV. Tri-layer MoS 2 displays a new stacking sequence distinct from the commonly observed 2H and 3R phases of MoS 2 . Density functional theory is used to examine the stability of different stacking sequences, and the findings are consistent with our experimental observations.

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

“…[10][11][12][13]16,17 Moreover, the remaining stacking order, such as A (BB…) or AA(BA...), with a false order of either AB(A...) or AA(A...) gives rise to a combination of 2H and 3R-phases. Note that these stacking orientations tune the electronic properties by engineering interlayer distances and structural symmetry.…”

“…[3][4][5]11,16,17 To the best of our knowledge, few studies of stacking-orientation-controlled samples of more than three layers and subsequent characterization with PL and Raman spectroscopy have been conducted. [10][11][12][13]18 Furthermore, studying the nonlinear optical properties, such as SHG or four-wave mixing (FWM), as a function of the layer number and stacking orientation of the multi-stacked crystals grown by CVD have scarcely been sought. [4][5][6] The minute variations of the band structures according to the geometry and order of stacking are sufficient to modulate the nonlinear optical susceptibility, and hence, versatile MoS 2 crystals synthesized by CVD play a crucial role in understanding fundamental optoelectronic properties.…”

“…11 In this process, the temperature was identified as a key parameter affecting the growth kinetics of the CVDbased MoS 2 synthesis with a positive correlation between the growth rate and film thickness. [9][10][11][12][13][14] To date, stacking of up to three layers of MoS 2 with various orientations has only been obtained by CVD at high temperatures (⩾850°C). [11][12][13][14] In conventional CVD synthesis, high-order stacking is only possible at high temperatures.…”

“…[9][10][11][12][13][14] To date, stacking of up to three layers of MoS 2 with various orientations has only been obtained by CVD at high temperatures (⩾850°C). [11][12][13][14] In conventional CVD synthesis, high-order stacking is only possible at high temperatures. In contrast, in this research, our approach involves growing MoS 2 stacked crystals with high stacking orders (AAA and ABA) at the lowest possible temperature.…”

“…Note that these stacking orientations tune the electronic properties by engineering interlayer distances and structural symmetry. 3,11,13 In particular, the spin-orbit coupling (SOC) effect, valley polarization, and representative nonlinear optical properties, such as second-harmonic generation (SHG), are highly affected by the stacking configuration and subsequent structural symmetry. [3][4][5]11,16,17 To the best of our knowledge, few studies of stacking-orientation-controlled samples of more than three layers and subsequent characterization with PL and Raman spectroscopy have been conducted.…”