Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFingerprints of the Strong Interaction between Monolayer MoS2 and Gold
243
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Gold-mediated exfoliation of MoS2 has attracted considerable interest in the recent years. A strong interaction between MoS2 and Au facilitates preferential production of centimeter-sized monolayer MoS2 with near-unity yield and provides a heterostructure system noteworthy from a fundamental standpoint. However, little is known about the detailed nature of the MoS2-Au interaction and its evolution with the MoS2 thickness. Here, we identify specific vibrational and binding energy fingerprints of such strong interaction using Raman and X-ray photoelectron spectroscopy, which indicate substantial strain and charge-transfer in monolayer MoS2. Near-field tip-enhanced Raman spectroscopy reveals heterogeneity of the MoS2-Au interaction at the nanoscale, reflecting the spatial non-conformity between the two materials. Far-field micro-Raman spectroscopy shows that this interaction is strongly affected by the roughness and cleanliness of the underlying Au. Our results elucidate the nature of the strong MoS2-Au interaction and provide guidance for strain and charge doping engineering of MoS2.
rate research
Read More
The electronic structure of an atomic-layer-deposited MoS2 monolayer on SiO2 was investigated using X-ray absorption spectroscopy (XAS) and synchrotron X-ray photoelectron spectroscopy (XPS). The angle-dependent evolution of the XAS spectra and the photon-energy-dependent evolution of the XPS spectra were analyzed in detail using an ab-initio electronic structure simulation. Although similar to the theoretical spectra of an ideal free-standing MoS2 ML, the experimental spectra exhibit features that are distinct from those of an ideal ML, which can be interpreted as a consequence of S-O van der Waals (vdW) interactions. The strong consensus among the experimental and theoretical spectra suggests that the vdW interactions between MoS2 and adjacent SiO2 layers can influence the electronic structure of the system, manifesting a substantial electronic interaction at the MoS2-SiO2 interface.
We show that the lack of inversion symmetry in monolayer MoS2 allows strong optical second harmonic generation. Second harmonic of an 810-nm pulse is generated in a mechanically exfoliated monolayer, with a nonlinear susceptibility on the order of 1E-7 m/V. The susceptibility reduces by a factor of seven in trilayers, and by about two orders of magnitude in even layers. A proof-of-principle second harmonic microscopy measurement is performed on samples grown by chemical vapor deposition, which illustrates potential applications of this effect in fast and non-invasive detection of crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size of atomically thin films of MoS2 and similar materials.
Strong interactions between surface plasmons in ultra-compact nanocavities and excitons in two dimensional materials have attracted wide interests for its prospective realization of polariton devices at room temperature. Here, we propose a continuous transition from weak coupling to strong coupling between excitons in MoS2 monolayer and highly localized plasmons in ultra-compact nanoantenna. The nanoantenna is assembled by a silver nanocube positioned over a gold film and separated by a dielectric spacer layer. We observed a 1570-fold enhancement in the photoluminescence at weak coupling regime in hybrid nanocavities with thick spacer layers. The interaction between excitons and plasmons is then directly prompted to strong coupling regime by shrinking down the thickness of spacer layer. Room temperature formation of polaritons with Rabi splitting up to 190 meV was observed, which is the largest plasmon-exciton Rabi splitting reported in two dimensional materials. Numerical calculations quantified the relation between coupling strength, local density of states and spacer thickness, and revealed the transition between weak coupling and strong coupling in nanocavities. The findings in this work offer a guideline for feasible designs of plasmon-exciton interaction systems with gap plasmonic cavities.
Metal contacts are a key limiter to the electronic performance of two-dimensional (2D) semiconductor devices. Here we present a comprehensive study of contact interfaces between seven metals (Y, Sc, Ag, Al, Ti, Au, Ni, with work functions from 3.1 to 5.2 eV) and monolayer MoS2 grown by chemical vapor deposition. We evaporate thin metal films onto MoS2 and study the interfaces by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and electrical characterization. We uncover that, 1) ultrathin oxidized Al dopes MoS2 n-type (> 2x10^12 1/cm^2) without degrading its mobility, 2) Ag, Au, and Ni deposition causes varying levels of damage to MoS2 (broadening Raman E peak from <3 1/cm to >6 1/cm), and 3) Ti, Sc, and Y react with MoS2. Reactive metals must be avoided in contacts to monolayer MoS2, but control studies reveal the reaction is mostly limited to the top layer of multilayer films. Finally, we find that 4) thin metals do not significantly strain MoS2, as confirmed by X-ray diffraction. These are important findings for metal contacts to MoS2, and broadly applicable to many other 2D semiconductors.
Dislocations govern the properties of any crystals. Yet, how dislocation of pentagonheptagon (5|7) in grain boundaries (GBs) affects the mechanical properties of two-dimensional MoS2 crystals remains poorly known. Using atomistic simulations and continuum disclination dipole model, we show that, depending on the tilt angle and 5|7 dislocation arrangement, MoS2 GB strength can be enhanced or reduced with tilt angle. For zigzag-tilt GBs primarily composed of Mo5|7+S5|7 dislocations, GB strength monotonically increases as the square of tilt angle. For armchair-tilt GBs with Mo5|7 or S5|7 dislocations, however, the trend of GB strength breaks down as 5|7 dislocations are non-evenly spaced. Moreover, mechanical failure initiates at the bond shared by 5|7 rings, in contrast to graphene where failure occurs at the bond shared by 6|7 rings. This work provides new insights into mechanical design of synthetic transition metal dichalcogenide crystals via dislocation engineering.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
