Scalable and Transfer-Free Fabrication of MoS2/SiO2 Hybrid Nanophotonic Cavity Arrays with Quality Factors Exceeding 4000

We report the fully-scalable fabrication of a large array of hybrid molybdenum disulfide (MoS2) -silicon dioxide (SiO2) one-dimensional, free-standing photonic-crystal cavities capable of enhancement of the MoS2 photoluminescence at the narrow cavity resonance. We demonstrate continuous tunability of the cavity resonance wavelength across the entire emission band of MoS2 simply by variation of the photonic crystal periodicity. Device fabrication started by substrate-scale growth of MoS2 using chemical vapor deposition (CVD) on non-birefringent thermal oxide on a silicon wafer;it was followed by lithographic fabrication of a photonic crystal nanocavity array on the same substrate at more than 50% yield of functional devices. Our cavities exhibit three dominant modes with measured linewidths less than 0.2 nm, corresponding to quality factors exceeding 4000. All experimental findings are found to be in excellent agreement with finite difference time domain (FDTD) simulations. CVD MoS2 provides scalable access to a direct band gap, inorganic, stable and efficient emitter material for onchip photonics without the need for epitaxy and is at CMOS compatible processing parameters even for back-end-of-line integration;our findings suggest feasibility of cavity based line-narrowing in MoS2-based on-chip devices as it is required for instance for frequency-multiplexed operation in on-chip optical communication and sensing

Testbeds for Transition Metal Dichalcogenide Photonics: Efficacy of Light Emission Enhancement in Monomer vs. Dimer Nanoscale Antennae

Monolayer transition metal dichalcogenides are uniquely-qualified materials for photonics because they combine well defined tunable direct band gaps and selfpassivated surfaces without dangling bonds. However, the atomic thickness of these 2D materials results in low photo absorption limiting the achievable photo luminescence intensity. Such emission can, in principle, be enhanced via nanoscale antennae resulting in; a. an increased absorption cross-section enhancing pump efficiency, b. an acceleration of the internal emission rate via the Purcell factor mainly by reducing the antennas optical mode volume beyond the diffraction limit, and c. improved impedance matching of the emitter dipole to the freespace wavelength. Plasmonic dimer antennae show orders of magnitude hot-spot field enhancements when an emitter is positioned exactly at the midgap. However, a 2D material cannot be grown, or easily transferred, to reside in mid-gap of the metallic dimer cavity. In addition, a spacer layer between the cavity and the emissive material is required to avoid non-radiative recombination channels. Using both computational and experimental methods, in this work we show that the emission enhancement from a 2D emitter- monomer antenna cavity system rivals that of dimers at much reduced lithographic effort. We rationalize this finding by showing that the emission enhancement in dimer antennae does not specifically originate from the gap of the dimer cavity, but is an average effect originating from the effective cavity crosssection taken below each optical cavity where the emitting 2D film is located. In particular, we test an array of different dimer and monomer antenna geometries and observe a representative 3x higher emission for both monomer and dimer cavities as compared to intrinsic emission of Chemical Vapor Deposition synthesized WS2 flakes.Comment: 31 pages, 5 figure

Gold Dispersion and Activation on the Basal Plane of Single-Layer MoS₂

Gold islands are typically associated with high binding affinity to adsorbates and catalytic activity. Here we present the growth of dispersed nanoscale gold islands on single layer MoS₂, prepared on an inert SiO₂/Si support by chemical vapor deposition. This study offers a combination of growth process development, optical characterization, photoelectron spectroscopy at submicron spatial resolution, and advanced density functional theory modeling for detailed insight into the electronic interaction between gold and single-layer MoS₂. In particular, we find the gold density of states in Au/MoS₂/SiO₂/Si to be far less well-defined than Au islands on other 2-dimensional materials such as graphene, for which we also provide data. We attribute this effect to the presence of heterogeneous Au adatom/MoS₂-support interactions within the nanometer-scale gold cluster. Theory predicts that CO will exhibit adsorption energies in excess of 1 eV at the Au cluster edges, where the local density of states is dominated by Au 5d_<i>z</i>2 symmetry