Realization of smaller and faster coherent light sources is critically important for the emerging applications in nanophotonics and information technology. Semiconductor lasers are arguably the most suitable candidate for such purposes. However, the minimum size of conventional semiconductor lasers utilizing dielectric optical cavities for sustaining laser oscillation is ultimately governed by the diffraction limit ((λ/2n)3 for three-dimensional (3D) cavities, where λ is the free-space wavelength and n is the refractive index). Here, we demonstrate the 3D subdiffraction-limited laser operation in the green spectral region based on a metal–oxide–semiconductor (MOS) structure, comprising a bundle of green-emitting InGaN/GaN nanorods strongly coupled to a gold plate through a SiO2 dielectric nanogap layer. In this plasmonic nanocavity structure, the analogue of MOS-type “nanocapacitor” in nanoelectronics leads to the confinement of the plasmonic field into a 3D mode volume of 8.0 × 10–4 μm3 (0.14(λ/2n)3).
Far-Field Optical Imaging of a Linear Array of Coupled Gold Nanocubes: Direct Visualization of Dark Plasmon Propagating Modes
Plasmonic nanoantenna arrays hold great promise for diffraction-unlimited light localization, confinement, and transport. Here, we report on linear plasmonic nanoantenna arrays composed of colloidal gold nanocubes precisely assembled using a nanomanipulation technique. In particular, we show the direct evidence of dark propagating modes in the plasmon coupling regime, allowing for transport of guided plasmon waves without far-field radiation losses. Additionally, we demonstrate the possibility of plasmon dispersion engineering in coupled gold nanocube chains. By assembling a nanocube chain with two sections of coupled nanocubes of different intercube separations, we are able to produce the effect of a band-pass nanofilter.
Layer-by-Layer Assembly of Three-Dimensional Colloidal
We present a simple and efficient method for synthesizing large-area (>1 cm2), three-dimensional (3D) gold and silver nanoparticle supercrystal films. In this approach, Janus nanoparticle (top face solvent-phobic and bottom face solvent-philic) films with an arbitrary number of close-packed nanoparticle monolayers can be formed using layer-by-layer (LbL) assembly from suspensions of thiolate-passivated gold or silver colloids. Furthermore, we demonstrate that these films can act as true 3D plasmonic crystals with strong transverse (intralayer) and longitudinal (interlayer) near-field coupling. In contrast to conventional polyelectrolyte-mediated LbL assembly processes, this approach allows multiple longitudinal coupling modes with a conspicuous spectral dependence on the layer number. We have found a universal scaling relation between the spectral position of the reflectance dips related to the longitudinal modes and the layer number. This relation can be understood in terms of the presence of a plasmonic Fabry−Pérot nanocavity along the longitudinal direction that allows the formation of standing plasmon waves under plasmon resonance conditions. The realization of 3D plasmonic coupling enables broadband tuning of the collective plasmon response over a wide spectral range (visible and near-IR) and provides a pathway to designer plasmonic metamaterials.
III-Nitrides
Single InGaN nanodisk light emitting diodes as full-color subwavelength light sources
Yu-Jung Lu (呂宥蓉), Hon-Way Lin (林弘偉), Hung-Ying Chen (陳虹穎), Yu-Chen Yang (楊右丞), and Shangjr Gwo (果尚志)
Subwavelength electroluminescent sources with spatial, spectral, and polarization controlling capabilities are critical elements for optical imaging and lithography beyond the diffraction limit. Here, we show that the electroluminescence from single, strain-free InGaN nanodisks embedded in self-assembled GaN p-n nanorods can span the entire visible spectrum with a large linear polarization ratio ( ∼ 0.85). Furthermore, this unique nanodisk-in-nanorod geometry enables the realization of the ultrasmall footprint light-emitting diodes (LEDs) to be used as subwavelength light sources. Using these nano-LEDs, we are able to demonstrate near-field, subwavelength photolithography by controlling the exposure time and light intensity from single InGaN nanodisks at chosen wavelengths.
Cheng-Tai Kuo (郭承泰), Shih-Chieh Lin (林詩傑), Kai-Kuen Chang (張凱焜), Hung-Wei Shiu (許紘瑋), Lo-Yueh Chang (張羅嶽), Chia-Hao Chen (陳家浩), Shu-Jung Tang (唐述中), and Shangjr Gwo (果尚志)
Recent experiments indicate the universality of electron accumulation and downward surface band bending at as-grown InN surfaces with polar or nonpolar orientations. Here, we demonstrate the possibility to prepare flatband InN 0001¯ surfaces. We have also measured the surface stoichiometry of InN surfaces by using core-level photoelectron spectroscopy. The flatband InN 0001¯ surface is stoichiometric and free of In adlayer. It implies that the removal of In adlayer at the InN 0001¯ surface leads to the absence of downward surface band bending. On the other hand, the stoichiometric InN 0001 surface still exhibits surface band bending due to the noncentrosymmetry in the wurtzite structure.
InGaN/GaN nanorod array white light-emitting diode
Hon-Way Lin (林弘偉), Yu-Jung Lu (呂宥蓉), Hung-Ying Chen (陳虹穎), Hong-Mao Lee (李弘
貿), and Shangjr Gwo (果尚志)
Conventional InGaN/GaN light-emitting diodes based on planar quantum well structures do not allow for efficient long-wavelength operation beyond the blue region due to a strong quantum confined Stark effect in lattice-mismatched polar InGaN quantum wells. Here we overcome the limitation by using self-assembled GaN nanorod arrays as strain-free growth templates for thick InGaN nanodisks. In combination with enhanced carrier localization and high crystalline quality, this approach allows us to realize full-color InGaN nanodisk emitters. By tailoring the numbers, positions, and thicknesses of polychromatic nanodisk ensembles embedded vertically in the GaN nanorodp-njunction, we are able to demonstrate natural white (color temperature∼ 6000 K) electroluminescence from InGaN/GaN nanorod arrays.
Surface biochemical functionalization of group-III nitride semiconductors has recently attracted much interest because of their biocompatibility, nontoxicity, and long-term chemical stability under demanding physiochemical conditions for chemical and biological sensing. Among Ill-nitrides, aluminum nitride (AlN) and aluminum gallium nitride (AlGaN) are particularly important because they are often used as the sensing surfaces for sensors based oil field-effect transistor or surface acoustic wave (SAW) sensor structures. To demonstrate the possibility of site-selective biofunctionalization oil AlN surfaces, we have fabricated two-dimensional antibody micropatterns oil AlN surfaces by using patterned self-assembled monolayer (SAM) templates. Patterned SAM templates are composed of two types of organosilane molecules terminated with different functional groups (amino and methyl), which were fabricated oil AlN/sapphire substrates by combining photolithography, lift-off process, and self-assembly technique. Because the patterned SAM templates have different surface properties oil the same Surface, clear imaging contrast of SAM micropatterns can be observed by field-emission scanning electron microscopy (FF-SEM) operating at a low accelerating voltage in the range of 0.5-1.5 kV. Furthermore, the contrast in surface potential of the binary SAM microstructures was confirmed by selective adsorption of negatively charged colloidal gold nanoparticles (AuNPs). The immobilization of AuNPs was limited oil the positively charged amino-terminated regions, while they were scarcely found oil the surface regions terminated by methyl groups. In this work, selective immobilization of green fluorescent protein (G FP) antibodies was demonstrated by the specific protein binding of enhanced GFP (EGFP) labeling. The observed strong fluorescent signal front antibody functionalized regions oil the SAM-patterned AlN surface indicates the retained biological activity of specific molecular recognition resulting from the antibody-EGFP interaction. The results reported here show that micropatterning of organosilane SAMs by the combination of photolithographic process and lift-off technique is a practical approach for the fabrication of reaction regions oil AlN-based bioanalytical microdevices.
