Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018)
    Thin Films Wednesday Sessions
       Session TF-WeE

Paper TF-WeE10
Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides

Wednesday, December 5, 2018, 8:40 pm, Room Naupaka Salons 4

Session: Emerging Topics: Growth and Properties of Electronic Materials, 2D Layers, and Metallic-glass Thin Films
Presenter: Shaul Aloni, Lawrence Berkeley National Laboratory
Authors: S. Aloni, Lawrence Berkeley National Laboratory
A.M. Schwartzberg, Lawrence Berkeley National Laboratory
C.T. Chen, Lawrence Berkeley National Laboratory
C. Kastl, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Materials for nanophotonic devices ideally combine ease of deposition, very high refractive index, and facile pattern formation through lithographic templating and/or etching. In this work, we present a scalable method for producing high refractive index WS2 layers by chemical conversion of WO3 synthesized via atomic layer deposition (ALD). These conformal nanocrystalline thin films demonstrate a surprisingly high index of refraction (n > 3.9), and structural fidelity compatible with lithographically defined features down to ~10 nm. Although this process yields highly polycrystalline films, the optical constants are in agreement with those reported for single crystal bulk WS2. Subsequently, we demonstrate three photonic structures - first, a two-dimensional hole array made possible by patterning and etching an ALD WO3 thin film before conversion, second, an analogue of the 2D hole array first patterned into fused silica before conformal coating and conversion, and third, a three-dimensional inverse opal photonic crystal made by conformal coating of a self-assembled polystyrene bead template. These results can be trivially extended to other transition metal dichalcogenides, thus opening new opportunities for photonic devices based on high refractive index materials.