Selective Vertical and Horizontal Growth of 2D WS₂ Revealed by In Situ Thermolysis using Transmission Electron Microscopy

Abstract

Direct observation of the growth dynamics of 2D transition metal dichalcogenides (TMDs) is of key importance for understanding and controlling the growth modes and for tailoring these intriguing materials to desired orientations and layer thicknesses. Here, various stages and multiple growth modes in the formation of WS 2 layers on different substrates through thermolysis of a single solid-state (NH 4 ) 2 WS 4 precursor are revealed using in situ transmission electron microscopy. Control over vertical and horizontal growth is achieved by varying the thickness of the drop-casted precursor from which WS 2 is grown during heating. First depositing platinum (Pt) and gold (Au) on the heating chips much enhance the growth process of WS 2 resulting in an increased length of vertical layers and in a self-limited thickness of horizontal layers. Interference patterns are formed by the mutual rotation of two WS 2 layers by various angles on metal deposited heating chips. This shows detailed insights into the growth dynamics of 2D WS 2 as a function of temperature, thereby establishing control over orientation and size. These findings also unveil the important role of metal substrates in the evolution of WS 2 structures, offering general and effective pathways for nano-engineering of 2D TMDs for a variety of applications.

Elucidating the Critical Role of Ruthenium Single Atom Sites in Water Dissociation and Dehydrogenation Behaviors for Robust Hydrazine Oxidation‐Boosted Alkaline Hydrogen Evolution

“…The corresponding fast Fourier transform (FFT) analysis of HAADF-STEM image in Figure 2j further confirms the expected hexagonal structure characteristic of 2H-WS 2 (Figure 2h,l). [32] In addition, the lattice spacing of 0.276 nm with intersection angle of 60° is indicative of the (100) plane for WS 2 /Ru-450 which implies that the immobilization of Ru SAs onto WS 2 could not change the structure of WS 2 . [32,33] Furthermore, EDS pattern and elemental mappings indicate the uniformly distributed of the W, S, and Ru elements in the entire nanosheets, revealing the homogeneous isolation of Ru SAs onto the WS 2 NSs (Figure 2k; Figures S4 and S5, Supporting Information).…”

“…[32] In addition, the lattice spacing of 0.276 nm with intersection angle of 60° is indicative of the (100) plane for WS 2 /Ru-450 which implies that the immobilization of Ru SAs onto WS 2 could not change the structure of WS 2 . [32,33] Furthermore, EDS pattern and elemental mappings indicate the uniformly distributed of the W, S, and Ru elements in the entire nanosheets, revealing the homogeneous isolation of Ru SAs onto the WS 2 NSs (Figure 2k; Figures S4 and S5, Supporting Information). The existence of atomic Sv in WS 2 was demonstrated by electron paramagnetic resonance (EPR) analysis.…”

Atomic-scale mechanisms on the stepwise growth of MoxW1−xS2 into hexagonal flakes

“…2e summarizes the layer-by-layer growth pattern of Mo x W 1− x S 2 structures at this stage, which is basically similar to previous reports on pure TMDs. 20,23,26 The appearance of vertical clusters rather than horizontal structures at the early stage of TMDs’ growth has been argued to be due to either the energetic factor (these vertical clusters have much stronger bonding with substrates than the horizontal ones) 20,23,27 or steric hindrance (the crowded vertical clusters cause the difficulty in horizontal development); 24,28,29 our observation prefers to support the former, because the density of vertical clusters here is controlled at a low level to avoid overcrowding. Besides, the aforementioned limitation on layer numbers for alloyed clusters is of notable difference to that of the stoichiometric MoS 2 and WS 2 , since the vertical clusters with five or even more layers have been frequently confirmed in previous studies for these TMDs; 27,30 this can be a sign of higher anisotropy in growth of the alloyed structure compared to that for pure TMDs.…”

Thermolysis-Driven Growth of Vanadium Oxide Nanostructures Revealed by In Situ Transmission Electron Microscopy: Implications for Battery Applications

“…50−52 In other experiments, 2D WS 2 vertical and horizontal layers were grown in TEM through thermal decomposition of a single solid-state precursor. 53,54 Metal oxide nanomaterials were also observed to grow during in situ TEM experiments. 55−57 In this work, with the combination of in situ TEM heating and thermolysis of ammonium metavanadate (NH 4 VO 3 ) inside the TEM, we have observed the real-time growth of crystalline V 2 O 5 nanostructures on the SiN x membrane of the heating chip.…”