Near-infrared optical properties and proposed phase-change usefulness of transition metal disulfides

TL;DR

This study measures the near-infrared optical constants of select transition metal dichalcogenides and proposes their potential use as phase-change materials in photonic applications, supported by experimental and theoretical analysis.

Contribution

It provides the first detailed optical constant measurements of sulfide TMDs in the NIR and suggests their novel application as phase-change materials for photonics.

Findings

Measured complex optical constants of MoS2, TiS2, ZrS2 in NIR

Identified giant birefringence in TMDs

Proposed TMD alloys for phase-change photonic devices

Abstract

The development of photonic integrated circuits would benefit from a wider selection of materials that can strongly-control near-infrared (NIR) light. Transition metal dichalcogenides (TMDs) have been explored extensively for visible spectrum opto-electronics, but the NIR properties of these layered materials have been less-studied. The measurement of optical constants is the foremost step to qualify TMDs for use in NIR photonics. Here we measure the complex optical constants for select sulfide TMDs (bulk crystals of MoS2, TiS2 and ZrS2) via spectroscopic ellipsometry in the visible-to-NIR range. Through Mueller matrix measurements and generalized ellipsometry, we explicitly measure the direction of the ordinary optical axis. We support our measurements with density functional theory (DFT) calculations, which agree with our measurements and predict giant birefringence. We further propose that TMDs could find use as photonic phase-change materials, by designing alloys that are thermodynamically adjacent to phase boundaries between competing crystal structures, to realize martensitic (i.e. displacive, order-order) switching.