Uniform Metal Layer Research Articles

Dual-Mode Comb Plasmonic Optical Fiber Sensing.

Surface plasmon (SP) excitation in metal-coated tilted fiber Bragg gratings (TFBGs) has been a focal point for highly sensitive surface biosensing. Previous efforts focused on uniform metal layer deposition around the TFBG cross section and temperature self-compensation with the Bragg mode, requiring both careful control of the core-guided light polarization and interrogation over most of the C + L bands. To circumvent these two important practical limitations, we studied and developed an original platform based on partially coated TFBGs. The partial metal layer enables the generation of dual-comb resonances, encompassing highly sensitive (TM/EH mode families) and highly insensitive (TE/HE mode families) components in unpolarized transmission spectra. The interleaved comb of insensitive modes acts as wavelength and power references within the same spectral region as the SP-active modes. Despite reduced fabrication and measurement complexity, refractometric accuracy is not compromised through statistical averaging over seven individual resonances within a narrowband window of 10 nm. Consequently, measuring spectra over 60 nm is no longer needed to compensate for small temperature or power fluctuations. This sensing platform brings the following important practical assets: (1) a simpler fabrication process, (2) no need for polarization control, (3) limited bandwidth interrogation, and (4) maintained refractometric accuracy, which makes it a true game changer in the ever-growing plasmonic sensing domain.

Integrated Gas Diffusion Electrode with High Conductivity Obtained by Skin Electroplating for High Specific Power Density Fuel Cell.

Smaller volume/weight and higher output power/energy density are always the goals of electrochemistry energy devices. Here, a simple strategy is proposed to prepare an integrated gas diffusion electrode (GDE) with high conductivity through skin electroplating. The skin electroplating is the combination of magnetron sputtering and spatial confinement electroplating. The electroplated metal obtained by skin electroplating is uniformly, continuously, and tightly attached to the surface of carbon paper like a layer of skin. Uniform and continuous electroplating metal layer endows the integrated electrode excellent conductivity with the square resistance as low as 27mΩsq-1 . In application, the self-breathing fuel cell with 1cm2 active area can harvest ultrahigh volume specific power density (20.9kWL-1 ). Additionally, the weight of the fuel cell stack (23W) with the integrated electrode is only 20g, which is only 7% of the commercial stack with the same power. The mass specific power density reaches 1150Wkg-1 , which is 15 times of the commercial stack. Outstandingly, the stack can charge 4 mobile phones at the same time. More importantly, the skin electroplating provides an effective strategy to improve the specific power density of other energy devices including Zn-air batteries, Li-air batteries, and so on.

Highly conductive and transparent thin metal layer for reducing microcavity effect in top-emitting white organic light-emitting diode

The optical and electrical properties of the top electrode are crucial for the structural design of top-emitting organic light-emitting diodes (OLEDs). A uniform metal layer, if obtainable, can be electrically excellent and optically well-tuned. In this study, Ag deposited with Mg at a concentration of 9:1 to form a metal thin film exhibits higher conductivity and higher transmittance than those of a neat Ag thin film within a thickness of 10 nm or less. In addition, the thin Mg:LiF (1:1) layer renders the Mg:Ag metal film more uniform and enhances its electron injection property. If a Mg:LiF/Mg:Ag thin film is applied to top-emitting white OLEDs, the driving voltage is lowered and the efficiency is improved. In addition, color shifts for viewing angles are reduced, and the emission characteristics are close to Lambertian. • 10-nm-thick Mg:Ag (1:9) metal forms a more uniform film compared with neat Ag thin metal of the same thickness. • Thin Mg:LiF (1:1) layer improves the optical and electrical properties of the Mg:Ag thin film. • Top-emitting white OLED device with thin Mg:Ag shows higher efficiency and superior angular emission characteristics.

Interphase Control for Electrodeposition of Thin Lithium Films for Lithium Metal Batteries

Rechargeable lithium metal batteries including Li-S batteries, need a thin lithium anode with high purity for high energy density and long cycle life. Today, lithium metal is typically produced from Li2CO3. In contrast to the price of Li2CO3, which is often used for benchmarking, pure lithium metal is actually a costly component. In addition, it has quite some CO2 footprint as it needs significant amounts of energy to produce. Lithium foils of few hundred micron thick are produced by lithium extrusion and cold rolling. To limit cost and to increase energy density, maximum only a few tens of microns is. However, due to the soft nature of lithium, foils of few tens of micrometers are very difficult to manufacture at large volumes and too expensive for cost competitive high energy density Li-metal based cells. Hence, the production of thin lithium foils is currently a bottleneck.The electrodeposition of thin lithium films directly on copper current collector foils could be a cost effective and elegant method, where it not for the high reactivity of lithium with the electrolyte solution and the poor control of lithium morphology. Recently, several approaches have been pursued on lithium electrodeposition by stabilizing the lithium metal-electrolyte interface with the use of solid electrolytes and polymer coatings on electrode [1], however a poor quality of solid electrolyte interphase (SEI) and lithium metal deposition remain as a challenge.Among the various solid-state electrolytes, nitrogen doped lithium phosphate glass or LiPON has been evaluated as solid-electrolyte coatings on electrode particles as buffer layer between active material and the bulk electrolyte [2]. Previously, we investigated the stability of 100 nm down to 10 nm LiPON thin-films as artificial solid-electrolyte interphase for lithium plating and stripping on copper current collectors. We demonstrated the reversible plating/stripping of 150 nm lithium layer for over 100 cycles, indicating formation of a uniform lithium metal layer in-between substrate and LiPON layer [3].In the present work, we further investigated the effect of artificial solid electrolyte interphase, such as LiPON and poly(ethylene) glycol (PEG) coatings, on the deposition behavior of lithium to fabricate micro-meter thick lithium layer which is desirable for negative electrode in next-generation battery application. With a thin LiPON (<150 nm) layer, lithium layer uniformly grew up to 1 μm between substrate and LiPON without breaking of LiPON layer. However, the breakage of the thin LiPON layer was observed with further growth of lithium layer leading to dendrite growth. On the other hand, with a thick PEG coating (> 1 μm) dendrite growth was mitigated by increasing the molar mass of PEG from 8000 to 600,000 g/mol. Furthermore, addition of PEG into the carbonate-based electrolyte resulted in a denser lithium film with a thickness of 2-5 μm without dendrites. In the presentation, effect of molar mass, concentration of PEG on growth behavior of lithium will be further discussed.

Doctor‐Blade Casting Fabrication of Ultrathin Li Metal Electrode for High‐Energy‐Density Batteries

AbstractThe employment of ultrathin Li metal electrodes with matched capacity with current cathodes and improved electrochemical stripping/plating behaviors plays a key role in the realization of high‐energy‐density batteries. However, their fabrication remains challenging using regular cold rolling processing due to inferior processibility of metallic Li. Herein, a facile molten metal doctor‐blade casting approach is explored to fabricate uniform metallic Li layers with thickness ranging from 10 to 50 µm on regular battery Cu current collectors with a lithiophilic Sn interphase layer. The enhanced surface wettability between Li and the spontaneously formed Li–Sn alloy helps to realize uniform spreading, and formation of an ultrathin and uniform metallic Li layer. The existence of the Li–Sn alloy in the bulk of metallic Li electrode helps to reduce the nucleation barrier and improve the electrochemical performance of the Li metal. With a cathode areal capacity of 2.8 mA h cm−2 the LiCoO2||Li/Li–Sn full cell shows improved capacity retention from 58% to 77% after 100 cycles at a lower Negative/Positive ratio of 2/1, offering a high energy density of 662.4 W h kg−1. The enhanced electrochemical performance of the as‐fabricated ultrathin Li metal electrode with high energy density opens up a promising pathway for realizing next‐generation high‐energy‐density batteries.

A Dendrite-Free Lithium/Carbon Nanotube Hybrid for Lithium-Metal Batteries.

Lithium (Li) metal is promising in the next-generation energy storage systems. However, its practical application is still hindered by the poor cycling performance and serious safety issues for the consequence of dendritic Li. Herein, a dendrite-free Li/carbon nanotube (CNT) hybrid is proposed, which is fabricated by direct coating molten Li on CNTs, for Li-metal batteries. The favorable thermodynamic and kinetic conditions are the powerful force to drive the rapid lift upwards and infusion of molten Li into CNTs network, which is the key to form a uniform metallic layer in Li/CNTs hybrid. The obtained hybrid indicates super-stable functions even at an ultrahigh current density of 40mA cm-2 for 2000 cycles with a stripping/plating capacity of 2 mAh cm-2 in symmetric cells. Subsequently, this hybrid also demonstrates a significantly decreased resistance, excellent cycling stability at high current density and flexibility in the full Li-S battery. This work provides valuable concepts in fabricating Li anodes toward Li-metal batteries and beyond for their high-level services.

Interface modification of electrodes through polyethylene glycol in rechargeable zinc-nickel batteries

Suppressing spongy zinc growth is a critical challenge in the development of alkaline zinc-based batteries. However, most surfactants strongly adsorb on the surface of anodes and depress the kinetic of zinc electrodeposition and dissolution. Here, we demonstrate an effective additive (polyethylene glycol, PEG200) to suppress spongy zinc growth in zinc-nickel flow batteries (ZNFBs) and systematically investigate the effect of PEG200 on zinc morphologies and kinetics of zinc anodes and nickel cathodes. We surprisingly find that 2 × 10−5 mol L−1 PEG200 not only induces a uniform and dense metallic zinc layer without markedly enlarging the overpotential of zinc electrodeposition, but also increases the transfer rate of protons at the interfaces of nickel cathodes. Consequently, the cycle life of ZNFBs is promoted together with the increase of energy efficiency from 75% to 77.5% at 80 mA cm−2.

Narrow Absorption in ITO-Free Perovskite Solar Cells for Sensing Applications Analyzed through Electromagnetic Simulation

This work reports on a computational analysis of how a modified perovskite cell can work as a refractometric sensor by generating surface plasmon resonances at its front surface. Metal-dielectric interfaces are necessary to excite plasmonic resonances. However, if the transparent conductor (ITO) is replaced by a uniform metal layer, the optical absorption at the active layer decreases significantly. This absorption enhances again when the front metallic surface is nanostructured, adding a periodic extruded array of high aspect-ratio dielectric pyramids. This relief excites surface plasmon resonances through a grating coupling mechanism with the metal surface. Our design allows a selective absorption in the active layer of the cell with a spectral response narrower than 1 nm. The photo-current generated by the cells becomes the signal of the sensor. The device employs an opto-electronic interrogation method, instead of the well-known spectral acquisition scheme. The sensitivity and figure of merit (FOM) parameters applicable to refractometric sensors were adapted to this new situation. The design has been customized to sense variations in the index of refraction of air between 1.0 and 1.1. The FOM reaches a maximum value of 1005 RIU − 1 , which is competitive when considering some other advantages, as the easiness of the acquisition signal procedure and the total cost of the sensing system. All the geometrical and material parameters included in our design were selected considering the applicable fabrication constrains.

Smart Golden Leaves Fabricated by Integrating Au Nanoparticles and Cellulose Nanofibers

AbstractA simple processing technology based on spontaneous arrangement of gold nanoparticles (AuNPs) on cellulose nanofibers (CNFs) makes it possible to form a gold leaf with superior mechanical, chemical and electrical characteristics with a small amount of gold (&lt;15 vol.%). The electrical resistivity of the AuNP/CNF hybrid film reached 8.7×10−6 Ω cm at 13 vol.% corresponding to that of a gold plate (2.9×10−6 Ω cm) through a distribution of AuNP inside the film in the form of a band. The AuNPs work not only as linkers between various CNFs in the hybrid structure but also as scaffolds. Self‐assembly allows the formation of leaves on three‐dimensional micrometer‐sized substrates, on which it is impossible to form a uniform flexible metallic layer using conventional techniques such as sputtering, vapor deposition, and electroless plating. The hybrid film holds great promise as a novel gold leaf for a wide range of applications, including coatings, smart papers, electronic skins, and wearable devices owing to its unique combination of superior properties, as well as good productivity, processability, and renewability.

Approaches toward lithium metal stabilization

Abstract

Creating metamaterial building blocks with directed photochemical metallization of silver onto DNA origami templates

DNA origami can be used to create a variety of complex and geometrically unique nanostructures that can be further modified to produce building blocks for applications such as in optical metamaterials. We describe a method for creating metal-coated nanostructures using DNA origami templates and a photochemical metallization technique. Triangular DNA origami forms were fabricated and coated with a thin metal layer by photochemical silver reduction while in solution or supported on a surface. The DNA origami template serves as a localized photosensitizer to facilitate reduction of silver ions directly from solution onto the DNA surface. The metallizing process is shown to result in a conformal metal coating, which grows in height to a self-limiting value with increasing photoreduction steps. Although this coating process results in a slight decrease in the triangle dimensions, the overall template shape is retained. Notably, this coating method exhibits characteristics of self-limiting and defect-filling growth, which results in a metal nanostructure that maps the shape of the original DNA template with a continuous and uniform metal layer and stops growing once all available DNA sites are exhausted.

Effect of SiC particle morphology on Co–P electroless coating characteristics

In this study, two kinds of micrometre sized SiC powders (as received and ball milled) were used as the starting materials to investigate the effect of ceramic surface morphology on the coating characteristics. Determined optimised electroless deposition bath values of pH (9) and bath temperature (70°C) were used. It was found that etching pretreatment was very effective on the coating quality for both types of SiC powders. The experimental results indicated that milling of the powders led to the formation of multimodal sized ceramic powders with sharp edges and rough surfaces, which resulted in a uniform adhesive metallic layer on the powders without any crack formation. Finally, the effect of cobalt coating on the incorporation of ceramic particles into the molten aluminium during fabrication of aluminium matrix composite was studied, and it was revealed that a significant improvement in incorporation could be obtained using cobalt coated ceramic particles.

Preparation of conductive silk fabric with antibacterial properties by electroless silver plating

To obtain an efficient approach to metalize silk fabric, a novel method was explored and silver-plated silk was prepared. In this study, tris (2-carboxyethyl) phosphine (TCEP) was utilized as a reducing agent to generate thiol groups on the silk surface. These thiol groups react with silver ions to form metal complexes, which were used as catalytic seeds and successfully initiated electroless silver plating. A variety of methods, including Raman, XRD, TG, SEM and EDS were used to characterize the intermediates and final products. The results showed that a uniform and smooth metal layer could be obtained when compared with that without TCEP pretreatment. The silver-plated silk fabric exhibited good electrical conductivity and high anti-bacterial properties. These attractive features enable this conductive silk fabric to be a good candidate as a biomedical material.

Near-perfect absorber with ultrawide bandwidth in infrared region using a periodically chirped structure

We propose a near-perfect absorber with ultrawide bandwidth in infrared region using a periodically chirped subwavelength structure implemented in both one-dimensional (1D) and two-dimensional (2D) schemes. The structure is composed of an array of chirped metal–insulator–metal resonators made of a metal/dielectric two-layer grating sitting on a uniform metal layer. Each resonator harvests the photon via the SPP localization at its own resonance wavelength which exhibits linear distribution due to the linearly chirped structure. A near-perfect absorption in wide bandwidth is realized with an appropriate design under the restriction of phase-matching and subwavelength dimension. A stop-band with a FWHM of 3μm at central wavelength of ∼9μm and a high absorption efficiency of up to 92% is achieved simultaneously. This provides a novel method in designing and implementing flexible thin-film devices with wide bandwidth and high absorption efficiency.

Cobalt Nanoparticles Growth on a Block Copolymer Thin Film: A Time-Resolved GISAXS Study

Cobalt sputter deposition on a nanostructured polystyrene-block-poly(ethylene oxide), P(S-b-EO), template is followed in real time with grazing incidence small-angle X-ray scattering (GISAXS). The polymer template consists of highly oriented parallel crystalline poly(ethylene oxide) (PEO) domains that are sandwiched between two polystyrene (PS) domains. In-situ GISAXS shows that cobalt atoms selectively decorate the PS domains of the microphase-separated polymer film and then aggregate to form surface metal nanopatterns. The polymer template is acting as a directing agent where cobalt metal nanowires are formed. At high metal load, the characteristic selectivity of the template is lost, and a uniform metal layer forms on the polymer surface. During the early stage of cobalt metal deposition, a highly asymmetric nanoparticles agglomeration is dominating structure formation. The cobalt nanoparticles mobility in combination with the high tendency of the nanoparticles to coalescence and to form immobile large-sized particles at the PS domains are discussed as mechanisms of structure formation.

Nanoantenna Absorbers for Thermal Detectors

We present a mid-infrared absorber based on the nanoantennas for thermal infrared detectors. Our design utilizes a fraction of the noble metal used in conventional absorbers and is only one layer thick, which allows for extremely small thermal conductance leading potentially to very low thermal detector noise. In this numerical study, we demonstrate that the proposed nanoantenna absorber having an areal coverage of only 2.5% can absorb 10 times more efficiently than a single uniform metal layer of the same thickness.

An improved transfer-matrix model for optical superlenses

The use of transfer-matrix analyses for characterizing planar optical superlensing systems is studied here, and the simple model of the planar superlens as an isolated imaging element is shown to be defective in certain situations. These defects arise due to neglected interactions between the superlens and the spatially varying shadow masks that are normally used as scattering objects for imaging, and which are held in near-field proximity to the superlenses. An extended model is proposed that improves the accuracy of the transfer-matrix analysis, without adding significant complexity, by approximating the reflections from the shadow mask by those from a uniform metal layer. Results obtained using both forms of the transfer matrix model are compared to finite element models and two example superlenses, one with a silver monolayer and the other with three silver sublayers, are characterized. The modified transfer matrix model gives much better agreement in both cases.

Ultrathin platinum-group metal coated hierarchical flowerlike gold microstructure: Electrochemical design and characterization

The deliberate tailoring of hierarchical flowerlike gold microstructure (HFGMs) at the ultrathin level is an ongoing challenge and could introduce opportunities for new fabrication and application in many fields. In this paper, a templateless, surfactantless, electrochemical strategy for fabrication of ultrathin platinum-group metal coated HFGMs is proposed. HFGMs were prepared by simple electrodeposition on an indium tin oxide (ITO) substrate. The resulting HFGMs enables the deposition of an ultrathin overlayer through copper underpotential deposition (UPD), followed by spontaneous replacement of the copper with the platinum-group metal to yielded a uniform and ultrathin Pt-group metal layer on the HFGMs surface. Thus prepared bimetallic “core-shell” sample has been characterized by cyclic voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray maps and X-ray diffraction (XRD). This is a very general and powerful technique for the fabrication of hierarchical, ultrathin coating, bimetallic “core-shell” microstructure, which, in turn, opens up the possibility of building more complex multicomponent hierarchical microstructure with potential application, such as electrocatalysis, biosensors and nanodevices, etc.

A comparison of two methods for metallizing fly-ash cenosphere particles: electroless plating and magnetron sputtering

A dense and uniform metal layer was completely coated on the surface of fly-ash cenosphere particles by either electroless plating or magnetron sputtering technique. The surface morphology and characteristics of the electroless and sputtered metal coatings have been compared and investigated by various characterization methods, including scanning electron microscopy, energy dispersion x-ray spectrum, x-ray photoelectron spectroscopy, optical microscopy and atomic force microscopy. The results indicate that the electroless plating process has a faster deposition rate as compared with the sputtering process, and the metal coating fabricated by electroless plating is rough as compared with the metal coating fabricated by magnetron sputtering. The Cu-coated fine cenospheres could be fabricated by the electroless plating technique.

MEMS switch based serial reconfigurable OADM

A micro-electromechanical systems (MEMS) switch based serial optical add/drop multiplexer (OADM) is demonstrated. This OADM consists of a few cascaded cells, each of which includes one 2 × 2 MEMS optical switch, a tunable fiber Bragg grating (FBG) filter and an optical circulator. Each cell can handle four consecutive channels with 100 GHz spacing. The modularization makes the network upgrading easy. Power consumption of such system is several milli-watts and the isolation between any two channels is greater than 30 dB. The in-plane MEMS optical switches are integrated on single chip and fabricated by deep reactive ion etching technology, whose driving voltage is only 30 V. A uniform metal layer is coated on the FBG by using sputter to obtain 2.9 nm center wavelength tuning range with a maximum injecting current of 12 mA. The MEMS technology makes the coupling and assembly of the switch, filter and circulator easy, precise, and reliable due to the fiber grooves. Various data formats can be added and/or dropped by the proposed OADM because it is bit-rate independent.