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Germanium Sulfide Nano-Optics Probed by STEM-Cathodoluminescence Spectroscopy
journal contribution
posted on 2018-06-08, 00:00 authored by Peter Sutter, Christos Argyropoulos, Eli SutterNano-optical
studies of confined modes in planar waveguides have
attracted significant interest as a means to probe exciton-polaritons
and other hybrid light-matter quasiparticles in layered semiconductors,
such as transition metal dichalcogenides or boron nitride. There is
a need to broaden such studies to other materials and to identify
alternatives to scanning near-field optical microscopy for exciting
and measuring confined waveguide modes. Here, we establish an approach
for probing the dispersion of traveling waveguide modes by cathodoluminescence
spectroscopy excited by the focused electron beam in scanning transmission
electron microscopy (STEM-CL) and apply it to solid-state resonators
consisting of mesoscale monocrystalline prisms and plates composed
of GeS, an anisotropic layered semiconductor with direct bandgap in
the near-infrared spectral range. Structure, crystallography, and
chemical composition of the mesostructures are analyzed by analytical
electron microscopy. STEM-CL maps and spectra show pronounced interference
effects and sharp emission peaks at photon energies below the fundamental
bandgap of GeS. Our analysis demonstrates that locally excited light
emission in STEM-CL launches in-plane waveguide modes in the mesoscale
GeS structures, which are internally reflected by highly specular
GeS edges to cause interference of the waveguide modes. Reabsorption
and secondary luminescence give rise to the intensity modulations
detected in the far field. Our results highlight avenues for probing
light-matter interactions below the diffraction limit in a wide range
of quantum materials and open up the possibility of tuning light emission
geometrically using interference rather than by the conventional bandgap
engineering.
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bandgapwaveguide modestransition metal dichalcogenidesmaterialGermanium Sulfide Nano-Optics Probedlight-matterinterferencesemiconductorlight emissionin-plane waveguide modesmesoscale monocrystalline prismsspecular GeS edgesmesoscale GeS structuresscanning transmission electron microscopySTEM-CLSTEM-Cathodoluminescence Spectroscopy Nano-optical studies
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