Sub-100-nm sized silver split ring resonator metamaterials with fundamental magnetic resonance in the middle visible spectrum

Split ring resonator (SRR) metamaterials working in the visible spectrum have great potential applications, but their fabrication is challenging due to the stringent requirements in the feature size and critical dimension. This paper reports fabrication and systematic characterization of silver SRRs with sub-100-nm sizes that can have magnetic resonance entering into the visible frequency spectrum. SRR size as small as ∼60 nm and fundamental magnetic resonance (LC-resonance) as short as ∼604 nm have been successfully demonstrated, which to the best of our knowledge represent the smallest fabricated SRR and the shortest LC-resonance based on SRR geometry. The resonance wavelengths of the LC and plasmon modes of the sub-100-nm SRRs are found to linearly decrease with SRR size. Excellent agreement between LC-model and experimental data is obtained when the capacitance of the sub-100-nm SRRs is interpreted as capacitance between two spheres instead of between two parallel plates

Observation of the Kinetic Inductance Limitation for the Fundamental Magnetic Resonance in Ultrasmall Gold v-Shape Split Ring Resonators

The achievable fundamental magnetic resonance in split ring resonators (SRR) is limited by the electron plasma oscillation in the metal. This so-called kinetic inductance limitation was predicted many years ago, but its experimental verification has been hindered due to nanofabrication challenges. Here, the first experimental demonstration of magnetic resonance frequency saturation is reported at 520 THz in ultrasmall v-shape gold SRRs.Accepted versio

Experimental verification of finesse enhancement scheme in two-ring resonator system

We propose a finesse enhancement scheme by a simple two-ring system, in which the resonance finesse is dependent on the relative intensity buildup of the second ring with respect to the first. In lossless case, it is possible to obtain finesse two orders of magnitude higher than that of the single ring system. The two-ring system is fabricated in silicon-on-insulator using deep UV (DUV) lithography and shown to exhibit the finesse of 100 to 300. The associated finesse enhancement of 20 is in a good agreement with the theory

A Simple Method for the Growth of Very Smooth and Ultra-Thin GaSb Films on GaAs (111) Substrate by MOCVD

We present a simple thermal treatment with the antimony source for the metal–organic chemical vapor deposition of thin GaSb films on GaAs (111) substrates for the first time. The properties of the as-grown GaSb films are systematically analyzed by scanning electron microscopy, atomic force microscopy, x-ray diffraction, photo-luminescence (PL) and Hall measurement. It is found that the as-grown GaSb films by the proposed method can be as thin as 35 nm and have a very smooth surface with the root mean square roughness as small as 0.777 nm. Meanwhile, the grown GaSb films also have high crystalline quality, of which the full width at half maximum of the rocking-curve is as small as 218 arcsec. Moreover, the good optical quality of the GaSb films has been demonstrated by the low-temperature PL. This work provides a simple and feasible buffer-free strategy for the growth of high-quality GaSb films directly on GaAs substrates and the strategy may also be applicable to the growth on other substrates and the hetero-growth of other materials.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio

Azimuthally Polarized, Circular Colloidal Quantum Dot Laser Beam Enabled by a Concentric Grating

Since optical gain was observed from colloidal quantum dots (CQDs), research on CQD lasing has been focused on the CQDs themselves as gain materials and their coupling with optical resonators. Combining the advantages of a CQD gain medium and optical microcavity in a laser device is desirable. Here, we show concentric circular Bragg gratings intimately incorporating CdSe/CdZnS/ZnS gradient shell CQDs. Because of the strong circularly symmetric optical confinement in two dimensions, the output beam CQD-based circular grating distributed feedback laser is found to be highly spatially coherent and azimuthally polarized with a donut-like cross section. We also observe the strong modification of the photoluminescence spectrum by the grating structures, which is associated with modification of optical density of states. This effect confirmed the high quality of the resonator that we fabricated and the spectral overlap between the optical transitions of the emitter and resonance of the cavity. Single mode lasing has been achieved under a quasi-continuous pumping regime, while the position of the lasing mode can be conveniently tuned via adjusting the thickness of the CQD layer. Moreover, a unidirectional output beam can be observed as a bright circular spot on a screen without any collimation optics, presenting a direct proof of its high spatial coherence

Controlling spontaneous emission from perovskite nanocrystals with metal–emitter–metal nanostructures

We show the increase of the photoluminescence intensity ratio (PLR) and the emission rate enhancement of perovskite cesium lead bromide (CsPbBr3 ) and formamidinium lead bromide (FAPbBr3 ) nanocrystals (NCs) in the presence of single and double gold layer cavities, which we refer to as Metal-Emitter (ME) and Metal-Emitter-Metal (MEM) nanostructures. Up to 1.9-fold PLRs and up to 5.4-fold emission rate enhancements were obtained for FAPbBr3 NCs confined by double gold layers, which are attributed to plasmonic confinement from the gold layers. The experimentally obtained values are validated by analytical calculations and electromagnetic simulations. Such an effective method of manipulation of the spontaneous emission by simple plasmonic nanostructures can be utilized in sensing and detection applications.Ministry of Education (MOE)Published versionThis research was funded by Ministry of Education, Singapore, grant nos. MOE2016-T2-1-052 and MOE2019-T1-002-063

Room temperature plasmon-enhanced InAs0.91Sb0.09-based heterojunction n-i-p mid-wave infrared photodetector

Middle wavelength infrared (MWIR) photodetectors have a wide range of applications, but almost all of them operate at low temperature due to the limit of materials and device structures. The capability of plasmonic structures to localize electromagnetic wave on the deep subwavelength scale provides the possibility for MWIR photodetectors operating at room temperature. Here, we report a high sensitivity room temperature MWIR photodetector which is an InAs0.91Sb0.09-based heterojunction n-i-p photodiode integrated with a Au-based two-dimensional subwavelength hole array (2DSHA). A room temperature detectivity of 0.8 × 1010 cm Hz1/2 W−1 and a response time of 600 ns are achieved. The non-cooling high performance of 2DSHA-InAs0.91Sb0.09 based heterojunction photodetectors will make their applications easier, broader, and economic.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)EDB (Economic Devt. Board, S’pore)Published versio