Lithographically fabricated gold nanowire waveguides for plasmonic routers and logic gates

Monolayer Capping Provides Close to Optimal Resistance to Laser Dewetting of Au Films

Next-generation heat-assisted magnetic recording (HAMR) relies on fast, localized heating of the magnetic medium during the write process. Au plasmonic near-field transducers are an attractive solution to this challenge, but increased thermal stability of Au films is required to improve long-term reliability. This work compares the effect of nanoscale Al, AlOx, and Ta capping films on Au thin films with Ti or Ta adhesion layers for use in HAMR and other high-temperature plasmonic applications. Thermal stability is investigated using a bespoke laser dewetting system, and SEM and AFM are extensively used to interrogate the resulting dewet areas. The most effective capping layers are found to be 0.5-1 nm of Al or AlOx, which can eliminate dewetting under certain conditions. Even one monolayer of AlOx is shown to be highly effective in reducing dewetting. In the case of thicker capping layers of Ta and AlOx, the Au film can easily dewet underneath, leaving an intact capping layer. It is concluded that thinner capping layers are most effective against dewetting as the Au cannot dewet without breaking them and pulling them apart during the dewetting process. A simple model based on energetics considerations is developed, which explains how thinner capping layers can more effectively protect the metal from pore or fissure creation. The model provides some convenient guidelines for choosing both the substrate and capping layer, for a given metal, to maximize the resistance to laser-induced damage.

Multifunctional and wavelength division multiplexing all-optical logic gates based on four-port metal-insulator-metal waveguides coupled with a ring resonator

In the past few years, designing multifunctional all-optical logic devices has attracted more and more attention in integrated optical computing. We report a metal-insulator-metal based four-port all-optical logic gate device containing two parallel straight waveguides and a ring resonator. We employ the scattering matrix method to analyze the coupling mechanisms of the hybrid waveguide and adopt the finite-difference time-domain method to design four fundamental logic functions of AND, OR, XOR, and NOT based on the all-optical coherent control of the four-port system under three symmetrically incident conditions. We demonstrate that these logic functions can be freely modulated by changing the phase difference of the input light at two resonant wavelengths or in a broad band. The logic gate device proposed shows a simple structure with multiple functions, multiple channels, and convenience in fabrication, and can be applied in parallel optical computing based on wavelength division multiplexing technology.

Elastocapillary Force Induced Alignment of Large Area Planar Nanowires

Achieving large scale precise positioning of the vapor-liquid-solid (VLS) nanowires is one of the biggest challenges for mass production of nanowire-based devices. Although there have been many noteworthy progresses in postgrowth nanowire alignment method development over the past few decades, these methods are mostly suitable for low density applications only. For high density applications such as transistors, both high yield and density are required. Here, we report an elastocapillary force-induced nanowire-aligning method that is extremely simple, clean, and can achieve single/multiple nanowire arrays with up to 98.8% yield and submicron pitch between the nanowires.

Gold Nanowires from Nanorods

Gold nanowires (AuNWs) possess strong potential application in micro- and nanoelectronics as well as in plasmonic waveguides because of their low electrical resistance. However, the synthesis of pure solvent-dispersible AuNWs with full control over their length still remains a challenge. All the previously reported methods produce AuNWs with other impurities such as smaller nanorods, platelets, and spherical particles and are limited to a certain length (typically below 10 μm). This article describes a one-step synthesis of extremely long AuNWs (up to 25 μm) with great control over their dimensions by using pentahedrally twinned gold nanorods (AuNRs) as seed particles. To induce the AuNW growth, the reduction of Au(I) to Au(0) was carried out on the surface of AuNRs at a very low pH by introducing HCl into the growth solution. The slow conversion of Au(I) to Au(0) due to the increase in reduction potential at lower pH promoted the preferential deposition of metallic gold on the more reactive tips of AuNRs compared to their sides, resulting in the formation of AuNWs. In analogy to the "living" polymerization reaction, the length of the AuNWs was proportional to the amount of Au(I) added to the growth solution; thus, the desired length of AuNWs was achieved by controlling the supply of Au(I) ions in the reaction mixture. The AuNWs longer than 6 μm were found to be responsive to microwave radiation. When an aqueous solution of AuNWs was exposed to microwaves, the formation of sharp kinks was observed in several locations of AuNWs without their disintegration into smaller pieces.

Multifunctional and multichannel all-optical logic gates based on the in-plane coherent control of localized surface plasmons

In this Letter, we report a scheme to design multifunctional and multichannel all-optical logic gates based on the in-plane coherent control of localized surface plasmons in an Au nanorod (NR) array on the Si substrate. By using theoretical analysis and structural optimization, we numerically demonstrate a four-channel all-optical logic gate device that can switch three basic logic operations on each NR only by controlling the phase differences of incident beams. This device is ultra-compact in size and shows high extensibility for parallel logic operations, which may be applied in future high-speed on-chip integrated optical computing.

Plasmonics for Telecommunications Applications

Plasmonic materials, when properly illuminated with visible or near-infrared wavelengths, exhibit unique and interesting features that can be exploited for tailoring and tuning the light radiation and propagation properties at nanoscale dimensions. A variety of plasmonic heterostructures have been demonstrated for optical-signal filtering, transmission, detection, transportation, and modulation. In this review, state-of-the-art plasmonic structures used for telecommunications applications are summarized. In doing so, we discuss their distinctive roles on multiple approaches including beam steering, guiding, filtering, modulation, switching, and detection, which are all of prime importance for the development of the sixth generation (6G) cellular networks.

Graphene-coated nanowire dimers for deep subwavelength waveguiding in mid-infrared range

In this paper, we show that the graphene-coated nanowire dimers could enable outstanding waveguiding performance in the mid-infrared range. The propagating properties of the fundamental graphene plasmon mode and their dependence on the nanowire radius, gap distance, nanowire permittivity and chemical potential of graphene are revealed in detail and compared with the graphene-coated circular nanowire. By improving the geometric parameters and the surface conductivity of graphene, the propagation length could reach about 9 μm, which is larger than that of the graphene-coated circular nanowire plasmon mode. Meanwhile, the effective mode area is only 10^-4A₀, which is one order of magnitude smaller than that of the graphene-coated circular nanowire plasmon mode. Theoretically, the propagation length could be further enhanced by increasing the chemical potential. Besides, the proposed graphene-coated nanowire dimers show quite good fabrication tolerance. The manipulation of mid-infrared waves at the deep subwavelength scale using graphene plasmons may offer potential applications in tunable integrated nanophotonic devices and infrared sensing.

Theoretical investigation on the electronic structure of one dimensional infinite monatomic gold wire: insights into conducting properties

Mixed-valence metal–organic nanostructures show unusual electronic properties. In our pervious investigation, we have designed and predicted a unique one-dimensional infinite monatomic gold wire (1D-IMGW) with excellent conductivity and the interesting characteristic of mixed valency (Au_c³⁺ and Au⁰_i). For further exploring its conduction properties and stability in conducting state, here we select one electron as a probe to explore the electron transport channel and investigate its electronic structure in conducting state. Density functional theory (DFT) calculations show the 1D-IMGW maintains its original structure in conducting state illustrating its excellent stability. Moreover, while adding an electron, 1D-IMGW is transformed from a semiconductor to a conductor with the energy band mixed with Au_c (5d) and Au_i (6s) through the Fermi level. Thus 1D-IMGW will conduct along its gold atom chain demonstrating good application prospect in nanodevices.

The electron transport is along the energy band mixed with Au_c (5d) and Au_i (6s) through the Fermi level for [1D-IMGW]⁻.