Visualization of Band Shifting and Interlayer Coupling in WMoS Alloys Using Near-Field Broadband Absorption Microscopy.

Beyond-diffraction-limit optical absorption spectroscopy provides in-depth information on the graded band structures of composition-spread and stacked two-dimensional materials, in which direct/indirect bandgap, interlayer coupling, and defects significantly modify their optoelectronic functionalities such as photoluminescence efficiency. We here visualize the spatially varying band structure of monolayer and bilayer transition metal dichalcogenide alloys by using near-field broadband absorption microscopy. The near-field spectral and spatial information manifests the excitonic band shift that results from the interplay of composition spreading and interlayer coupling.

Near-field spectroscopic imaging of exciton quenching at atomically sharp MoS/WS lateral heterojunctions.

Heterojunctions made by laterally stitching two different transition metal dichalcogenide monolayers create a unique one-dimensional boundary with intriguing local optical properties that can only be characterized by nanoscale-spatial-resolution spectral tools. Here, we use near-field photoluminescence (NF-PL) to reveal the narrowest region (105 nm) ever reported of photoluminescence quenching at the junction of a laterally stitched WS/MoS monolayer. We attribute this quenching to the atomically sharp band offset that generates a strong electric force at the junction to easily dissociate excitons.

Plasmonically Enhanced Enantioselective Nanocolorimetry.

We report on the generation of a super- and homochiral field where linearly polarized incident light is twisted by plasmonic dimeric nanostructure within the gap. The asymmetry in exciting a molecule's chiral polarizability is enhanced, resulting in discriminatory nanocolorimetry. A chromaticity shift is used to discriminate the handedness of chiral molecules which is sensitive, faster, and self-referenced, and requires only a single scan as compared to existing methods.

Nano-colorimetrically determined refractive index variation with ultra-high chromatic resolution.

We develop a front-to-end solution where the shift of chromaticity from scattering of plasmonic nanoparticles is used as the reporter for nano-environmental refractive index variation. By co-projecting possible power combinations of RGB LEDs and digitized color grid density of CCD with various luminance onto the CIE 1931 chromaticity diagram, optimum condition for nanoenvironment sensing can be achieved. The highest resolution for local refractive index change is 0.

Unraveling current hysteresis effects in regular-type C-CHNHPbI heterojunction solar cells.

Comprehensive studies were carried out to understand the origin of the current hysteresis effects in highly efficient C-CHNHPbI(MAPbI) heterojunction solar cells, using atomic-force microscopy, transmittance spectra, photoluminescence spectra, X-ray diffraction patterns and a femtosecond time-resolved pump-probe technique. The power conversion efficiency (PCE) of C-MAPbI solar cells can be increased to 18.23% by eliminating the point (lattice) defects in the MAPbI thin film which is fabricated by using the one-step spin-coating method with toluene washing treatment.

Label-free multi-color superlocalization of plasmonic emission within metallic nano-interstice using femtosecond chirp-manipulated four wave mixing.

We demonstrate an as yet unused method to sieve, localize, and steer plasmonic hot spot within metallic nano-interstices close to percolation threshold. Multicolor superlocalization of plasmon mode within 60 nm was constantly achieved by chirp-manipulated superresolved four wave mixing (FWM) images. Since the percolated film is strongly plasmonic active and structurally multiscale invariant, the present method provides orders of magnitude enhanced light localization within single metallic nano-interstice, and can be universally applied to any region of the random film.