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Room-temperature photoluminescence enhancement of molybdenum disulfide (MoS2) monolayers on epitaxial titanium nitride (TiN) thin films grown by molecular-beam-epitaxy as well as magnetron-sputtered TiN films is observed by a confocal laser scanning microscope with excitation wavelengths covering the transition of TiN's macroscopic optical properties from dielectric to plasmonic. The photoluminescence enhancement increases as TiN becomes more metallic, and strong enhancement is obtained at the excitation wavelengths equal to or longer than the epsilon-near-zero (ENZ) wavelength of TiN films. A good agreement is observed between measured and calculated enhancements. The enhancement is attributed to the increased excitation field in MoS2 at TiN's ENZ wavelength and interference effects for thick spacers that separate the MoS2 flakes from TiN films in the metallic regime. This study enriches the fundamental understanding of emission properties on ENZ substrates that could be important for the development of advanced nanoscale lasers/light sources, optical/biosensors, and nano-optoelectronic devices.

This talk will review our recent studies on the nonlinear and emission properties of conducting oxide and metallic nitride epsilon-near-zero (ENZ) materials. I will present a method to engineer the field intensity enhancement of the Al-doped zinc oxide (AZO) ENZ thin films synthesized by atomic layer deposition (ALD) technique. I will then discuss the observation of abnormal nonlinear temporal dynamic of hot electrons and enhanced optical nonlinearity in AZO and ITO ENZ thin films under different pump fluences and excitation angles using a degenerate pump-probe spectroscopy technique. Finally, I will present the first comprehensive study of photoluminescence from a 2D material placed near ENZ films and its dependence on the losses of materials, as well as the spectral response of such emitters with excitation wavelengths across the ENZ regime. This work was supported in part by the National Science Foundation (grant number: 1752295) and AFOSR-AOARD (FA2386-18-1-4099)

Room-temperature photoluminescence enhancement of molybdenum disulfide (MoS

In this talk, I will present our recent development on the “Meta”-optical fiber integrated with optical plasmonic nanocircuits and epsilon-near-zero (ENZ) materials. I will present the integrated plasmonic network (e.g. directional coupler and resonator) powered by the core mode of optical fiber. I will also discuss the first experimental demonstration of optically confined ENZ resonance excitation in an optical fiber waveguide uniformly coated with AZO nanolayer. The integration of plasmonic/ENZ nanocircuits and optical fiber will open the path to revolutionary ultracompact in-fiber optical devices for optical communication, imaging, sensing/laser applications. The authors acknowledge the supports partially by the Air Force Office of Scientific Research (AFOSR, Award number: FA9550-19-1-0274) and Defense Advanced Research Projects Agency (grant number N66001-17-1-4047).

The direct interfacing of photonic crystal fiber to metallic nanoantenna has widespread application in nano-scale imaging, optical lithography, nanoscale lasers, quantum communication, in-vivo sensing and medical surgery. I will present the design, fabrication, and characterization of fiber-plasmonic probes for nanoscale chemical imaging. The proposed Fiber-based Tip-Enhanced Raman Spectroscopy (F-TERS) combines the spatial (

Photoluminescence enhancement of MoS2 monolayers on TiN thin films grown on sapphire by molecular-beam-epitaxy (MBE) is observed. The PL spectra of MoS2 flakes on MBE-grown 58-nm-thick TiN crystalline film and on reference sapphire substrate are obtained at room temperature using a confocal laser scanning microscope with 405, 445, 488 and 561 nm excitation wavelengths. The maximum PL enhancement for B-exciton (6-fold) and A- trion (15-fold) is obtained at the excitation wavelength 488 nm that matches most closely to the epsilon-near-zero wavelength, 473 nm, of TiN film. A good agreement is observed between measured and calculated enhancements. The enhancement is attributed to increased light absorption when excitation wavelength matches the epsilon-near-zero wavelength of TiN film.

We study photoluminescence enhancement of MoS2 monolayers on alumina-coated thin TiN films grown by molecular-beam-epitaxy. The enhancement is due to increased light absorption at excitation wavelengths equal to epsilon-near-zero wavelength of TiN.

We demonstrate the excitation of epsilon-near-zero (ENZ) resonance on a side-polished optical fiber nano-coated with aluminum-doped zinc oxide (AZO) with vanishing permittivity at near-infrared wavelength. The ENZ resonance is caused by the coupling between guided modes supported by optical fiber and the AZO nanolayer.

Metallic nanowires supporting surface plasmon polaritons can localize optical fields at nanoscale for near-field imaging. In this paper, we propose a photonic-plasmonic probe for nanoscale light confinement. The linearly polarized fiber mode is asymmetrically coupled to radial plasmons to create hot-spot at the tip apex.

The direct interfacing of photonic crystal fiber to a metallic nanoantenna has widespread application in nanoscale imaging, optical lithography, nanoscale lasers, quantum communication, in vivo sensing, and medical surgery. We report on the fabrication of a needle-shaped plasmonic nanoantenna on the end facet of a photonic crystal fiber using electron-beam-induced evaporation of platinum. We demonstrate the coupling of light from the fiber waveguide mode to the subwavelength nanoantenna plasmonic mode focusing down to the apex of the plasmonic needle using a polarization-resolved far-field side-scatter imaging technique. Our work provides an important step toward widespread application of optical fibers in nearfield spectroscopic techniques such as tip-enhanced Raman and fluorescence microscopy, single-photon excitation and quantum sensors, nanoscale optical lithography, and lab-on-fiber devices.

Nanoscale spectroscopy and imaging, a hybrid technique that combines a scanning probe microscope (SPM) with spectroscopy, can provide nanoscale topographical, spectral, and chemical information of a sample. In recent years, developments in nanofabrication technology have dramatically advanced the field of nanospectroscopy for applications in various fields including nanoscale materials, electronics, catalysis, and biological systems. However, challenges in nanofocusing of light for excitation and extracting weak signals of individual molecules from the background signal persist in conventional nanoscale spectroscopy including tip-enhanced Raman spectroscopy, scanning near-field microscopy (SNOM/NSOM), and photoluminescence spectroscopy. This article reviews new approaches to design plasmonic SPM probes that improve important aspects of nanospectroscopy such as nanofocusing, far-to-near-field-coupling efficiency, background suppression, and ease of fabrication. The authors survey a diverse range of novel schemes to excite propagating surface plasmon polaritons on the probe surface to attain highly enhanced nanofocused light at the apex for nanoscale spectroscopies. These schemes include grating coupler configurations on the plasmonic SPM probes, aperture and apertureless plasmonic SNOM probes, nanostructured resonators coupled with a high-quality-factor photonic cavity, interfacing of the optical fiber with plasmonic nanowires, and nanoparticle-coupled plasmonic nanowires. These innovative probes merge the field of fiber optics, plasmonics, quantum optics, and nanomaterials. The authors provide a perspective on new approaches that combine the advantages of these probes and have the potential for significant advancement in nanoscale imaging and other types of nanoscale spectroscopies including scanning quantum spin spectroscopy and scanning thermal imaging microscopy.

We present our recent development on the use of tunable transparent conducting oxides to demonstrate electrically tunable epsilon-near-zero (ENZ) optical devices and to excite ENZ resonance in nanostructured optical fiber.