High-quality bottom-up grown van der Waals phonon polariton systems

In the infrared range, van der Waals materials have emerged as an exciting class of materials due to their ability to support high-quality phonon polariton excitations.  The ability to localize and guide light in extremely deep subwavelength leads to fundamental light-matter interactions and functional applications such as sensing and waveguiding in ultracompact devices.  In this study, we demonstrate that bottom-up synthesized α-MoO₃ micro- and nano-structures are ultrahigh quality hyperbolic phonon polaritonic systems through material characterization and near-field optical measurement.  No lithography or ion milling is needed to define the structures, and thus fabrication-induced damage or contamination on the vdW material or the substrate material can be voided.  Based on systematic improvement of the sample preparation, we have achieved ultrabroadband visualization of the Fabry-Pérot resonances over four Reststrahlen bands and revealed high quality factors in an α-MoO₃ nanoresonator.  The mode figure of merit analysis confirms that α-MoO₃ structures on ultrasmooth gold is good material combination for high-mode-compression and low-loss polaritonics.