posted on 2024-01-18, 13:17authored byIryna Kandybka, Benjamin Groven, Henry Medina Silva, Stefanie Sergeant, Ankit Nalin Mehta, Serkan Koylan, Yuanyuan Shi, Sreetama Banerjee, Pierre Morin, Annelies Delabie
Recently, a step-flow growth mode
has been proposed to break the
inherent molybdenum disulfide (MoS2) crystal domain bimodality
and yield a single-crystalline MoS2 monolayer on commonly
employed sapphire substrates. This work reveals an alternative growth
mechanism during the metal–organic chemical vapor deposition
(MOCVD) of a single-crystalline MoS2 monolayer through
anisotropic 2D crystal growth. During early growth stages, the epitaxial
symmetry and commensurability of sapphire terraces rather than the
sapphire step inclination ultimately govern the MoS2 crystal
orientation. Strikingly, as the MoS2 crystals continue
to grow laterally, the sapphire steps transform the MoS2 crystal geometry into diamond-shaped domains presumably by anisotropic
diffusion of ad-species and facet development. Even though these MoS2 domains nucleate on sapphire with predominantly bimodal
0 and 60° azimuthal rotation, the individual domains reach lateral
dimensions of up to 200 nm before merging seamlessly into a single-crystalline
MoS2 monolayer upon coalescence. Plan-view transmission
electron microscopy reveals the single-crystalline nature across 50
μm by 50 μm inspection areas. As a result, the median
carrier mobility of MoS2 monolayers peaks at 25 cm2 V–1 s–1 with the highest
value reaching 28 cm2 V–1 s–1. This work details synthesis–structure correlations and the
possibilities to tune the structure and material properties through
substrate topography toward various applications in nanoelectronics,
catalysis, and nanotechnology. Moreover, shape modulation through
anisotropic growth phenomena on stepped surfaces can provide opportunities
for nanopatterning for a wide range of materials.