Monolayer MoS₂ Dendrites on a Symmetry‐Disparate SrTiO₃ (001) Substrate: Formation Mechanism and Interface Interaction

Abstract

Dendritic patterns mediated by non-equilibrium growth processes are ubiquitous in all length scales from atomic metal islands [ 1 ] to macroscopic snowfl akes. [ 2 ] These fractal species have attracted great research interests regarding their complex morphologies, unique formation mechanisms, [ 3 ] and more importantly intriguing physical and chemical properties. [ 4 ] A model fractal growth system toward these is metal-on-metal epitaxy [ 5 ] which is usually mediated by a limited diffusion of adatoms along island edges with respect to that on free surfaces, following a diffusion-limited aggregation (DLA) mechanism. [ 6 ] Notably, adatoms in this model have to hop among predefi ned lattice sites of the substrate to achieve effi cient bonding, [ 7 ] and the resultant epilayer usually follows the same lattice symmetry as that of the substrate. However, it remains an open question what would happen if the symmetry of the overlayer differs from that of the substrate. Recently, it is intriguing to see that van der Waals epitaxial growth of compact 2D atomic crystals can be realized on symmetry-different metal substrates (e.g., graphene grown on Cu(001) [ 8 ] ). In this regard, it is imperative to know if the fl ake shape of similar 2D layered materials could be tailored from compact to fractal by the deliberately introduced adlayer-substrate symmetry disparity.Monolayer molybdenum disulfi de (MoS 2 ) has emerged as a star material due to its exceptional electronic [ 9 ] and optoelectronic [ 10 ] properties among the 2D crystal family. Particularly, in recent works, MoS 2 with rich active edges was proved to be an effi cient catalyst in electrochemical hydrogen evolution, [ 11 ] petrochemical hydrodesulfurization, [ 12 ] etc. However, dendritic MoS 2 samples were rarely achieved through chemical vapor deposition (CVD) or any other bottom-up synthesis methods, [ 13 ] with respect to that of the universally derived compact MoS 2 triangles.Herein, we realized the controllable synthesis of 2H-phase monolayer MoS 2 dendrites on a symmetry-disparate SrTiO 3 (STO) (001) substrate via a facile CVD method. With a combination of various characterization techniques, we tried to uncover the coverage-dependent fractal dimension, the crystallinity inside a dendritic fl ake, and fi nally the key factors that induce the dendritic growth behavior. It is expected that the Dendritic patterns generated in non-equilibrium growth processes are prevalent in nature while their formation mechanisms are far from fully understood. Here, we report a coverage-dependent fractal degree evolution of monolayer 2H-MoS 2 dendrites synthesized on a symmetry-disparate substrate of SrTiO 3 (001). Surprisingly, various characterizations have revealed that the monolayer dendrites featured with orthogonal backbones are single crystalline, possessing both peculiar adlayer-substrate interaction and abnormal indirect bandgap on SrTiO 3 (001). Further theoretical calculations indicate that a prominent diffusion anisotropy of monomer precursors, combined w...

Recent Progress in CVD Growth of 2D Transition Metal Dichalcogenides and Related Heterostructures

“…In other words, the growth results can be modulated by utilizing different growth substrates. Therefore, for a deep exploration of the formation mechanism, Zhang et al investigated the growth behavior of dendritic MoS 2 on STO(100) via experimental characterizations and theoretical calculations . Through a standard box‐counting evolution, Figure i presents statistics on the fractal dimensions ( D ) of a series dendritic flakes with an average D of 1.65 ± 0.08 (30 flakes; the left inset is a typical SEM image, and a linear fitting of the fractal dimensions is shown in the right inset of Figure i).…”

Large-Scale Synthesis and Systematic Photoluminescence Properties of Monolayer MoS2 on Fused Silica

“…The fractal-shaped monolayer MoS 2 may find application in sensing, energy storage and transparent optoelectronics, etc. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 / 24 probably mediated by a relatively strong interface interaction and a diffusion-limited-aggregation (DLA) process [31][32] because of the ad-layer-substrate symmetry disparity. Briefly, in the DLA model, adatoms have to hop among predefined lattice sites of a substrate to achieve efficient bonding.…”

Recent Advances in Controlling Syntheses and Energy Related Applications of MX2 and MX2/Graphene Heterostructures

“…[46,47,108] For example, Zhang and colleagues recently reported a unique dendritic growth of monolayer MoS 2 on STO (001) (Figure 3a). [46,47] The MoS 2 dendrites were featured with fractal dimension of ≈1.6 which gradually increased to ≈2 for full coverage MoS 2 (Figure 3b), This was considered to obey a diffusion-limited aggregation (DLA) mechanism. DFT calculations subsequently revealed a prominent diffusion anisotropy of monomer MoS x precursors on STO (001) (Figure 3c,d).…”

“…[38][39][40][41][42][43][44][45][46][47] Particularly, their ultraflat surfaces, along with different interfacial energetics, and possible lattice registry to MX 2 adlayer, enabled additional controllability in a van der Waals epitaxy regime, leading to the formation of largely aligned monolayer domains or uniform complete layers. Liu et al, previously reported on the suitability of fluorophlogopite mica (KMg 3 AlSi 3 O 10 F 2 ) as a substrate for the van der Waals epitaxial growth of monolayer MoS 2 .…”

“…[9,10,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Meanwhile, some insulating single-crystals such as mica, [38,39] sapphire, [38,[40][41][42][43][44][45] and SrTiO 3 (STO) [46,47] were proved to be effective substrates in synthesizing large-domain or large-area, aligned or randomly oriented MX 2 monolayers, owing to their relatively flat surfaces and flexible interfacial binding strengths. [38][39][40][41][42][43][44][45][46][47] Notably, the inert metal of Au was also found to be a suitable substrate for the controlled growth of large-domain/domain size controllable, highquality monolayer MoS 2 and WS 2 . [48][49][50][51][52][53] Intriguingly, the MX 2 / Au foil was confirmed to be an ideal system for studying the electronic structure of monolayer...…”