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Title: Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides

Abstract

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. Furthermore these results can be trivially extended to other transition metal dichalcogenides, thus opening new opportunities for photonic devices based on high refractive index materials.

Authors:
ORCiD logo [1];  [2];  [1];  [1];  [1];  [1];  [1];  [1]; ORCiD logo [1];  [1];  [1]
  1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Univ. degli Studi di Milano-Bicocca, Milano (Italy)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division
OSTI Identifier:
1503660
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Chen, Christopher T., Pedrini, Jacopo, Gaulding, E. Ashley, Kastl, Christoph, Calafiore, Giuseppe, Dhuey, Scott, Kuykendall, Tevye R., Cabrini, Stefano, Toma, Francesca M., Aloni, Shaul, and Schwartzberg, Adam M. Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides. United States: N. p., 2019. Web. doi:10.1038/s41598-019-39115-3.
Chen, Christopher T., Pedrini, Jacopo, Gaulding, E. Ashley, Kastl, Christoph, Calafiore, Giuseppe, Dhuey, Scott, Kuykendall, Tevye R., Cabrini, Stefano, Toma, Francesca M., Aloni, Shaul, & Schwartzberg, Adam M. Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides. United States. doi:10.1038/s41598-019-39115-3.
Chen, Christopher T., Pedrini, Jacopo, Gaulding, E. Ashley, Kastl, Christoph, Calafiore, Giuseppe, Dhuey, Scott, Kuykendall, Tevye R., Cabrini, Stefano, Toma, Francesca M., Aloni, Shaul, and Schwartzberg, Adam M. Tue . "Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides". United States. doi:10.1038/s41598-019-39115-3. https://www.osti.gov/servlets/purl/1503660.
@article{osti_1503660,
title = {Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides},
author = {Chen, Christopher T. and Pedrini, Jacopo and Gaulding, E. Ashley and Kastl, Christoph and Calafiore, Giuseppe and Dhuey, Scott and Kuykendall, Tevye R. and Cabrini, Stefano and Toma, Francesca M. and Aloni, Shaul and Schwartzberg, Adam M.},
abstractNote = {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. Furthermore these results can be trivially extended to other transition metal dichalcogenides, thus opening new opportunities for photonic devices based on high refractive index materials.},
doi = {10.1038/s41598-019-39115-3},
journal = {Scientific Reports},
number = 1,
volume = 9,
place = {United States},
year = {2019},
month = {2}
}

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Figures / Tables:

Figure 1 Figure 1: Synthesis, optical properties, and comparison of refractive indices of converted WS2 thin films. (a) Thin films of ALD metal oxides are heated in a chalcogen-containing gas environment at high temperatures to yield TMD thin films. (b) Representative thin film Raman spectrum. (c) Refractive index values of WS2 convertedmore » at 650 °C and 850 °C compared to literature values for bulk WS215, Si21, and GaP (Woollam, J.A. GaP tabulated from UNL. Unpublished, CompleteEASE Materials Library.). Extracted refractive index values for thin film have features from the expected excitonic contributions and n > 4 for much of the visible into the IR. (d) Comparison of thin film absorption coefficient to literature values for bulk 3R-WS2, Si, and GaP. The absorption coefficient falls off near the expected indirect gap value of ~1.2 eV for both conversion temperatures.« less

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    Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.