Ag Bilayer Research Articles

High-Linearity Ta2O5 Memristor and Its Application in Gaussian Convolution Image Denoising.

In the image Gaussian filtering process, convolving with a Gaussian matrix is essential due to the numerous arithmetic computations involved, predominantly multiplications and additions. This can heavily tax the system's memory, particularly with frequent use. To address this issue, a W/Ta2O5/Ag memristor was employed to substantially mitigate the computational overhead associated with convolution operations. Additionally, an interlayer of ZnO was subsequently introduced into the memristor. The resulting Ta2O5/ZnO heterostructure layer exhibited improved linearity in the pulse response, which enhanced linearity facilitates easy adjustment of the conductance magnitude through a linear mapping of the number of pulses and the conductance. Subsequently, the conductance of the W/Ta2O5/ZnO/Ag bilayer memristor was employed as the weights for the convolution kernel in convolution operations. Gaussian noise removal in image processing was achieved by assembling a 5 × 5 memristor array as the kernel. When denoising was performed using memristor arrays, compared to denoising achieved through Gaussian matrix convolution, an average loss of less than 5% was observed. The provided memristors demonstrate significant potential in convolutional computations, particularly for subsequent applications in convolutional neural networks (CNNs).

Enhanced control over size, areal density, and shape of substrate-supported Au and Ag nanoparticles by solid-state dewetting and alloying

The ability to manipulate the dimensions, areal density, and form of substrate-supported Au and Ag nanoparticles (NPs) is highly desirable for utilizing their plasmonic properties in biosensing, photovoltaics, and nanophotonic applications. The transformation of thin films into the substrate-supported nanostructures by solid-state dewetting (SSD), provides an avenue to manipulate the dimensional aspects of nanostructures simply and cost-effectively on a large scale. However, spontaneous agglomeration of the film produces randomly distributed and non-uniform nanostructures that must be controlled. Here, we have systematically studied the effect of annealing temperature, between 200 °C and 750 °C, on the dewetting morphology evolution of Au, Ag, and Au–Ag bilayer ultrathin films sputter deposited on the c-plane (0001) sapphire substrates. Regardless of the film thickness, Ag films dewet faster than Au films and produce spherical NPs, compared to faceted Au NPs, with broader size distribution. Whereas, by the SSD of Au–Ag bilayer ultrathin films, highly spherical and monodisperse AuAg bimetallic NPs can be fabricated. Furthermore, we have shown the possibility of fabricating the AuAg bimetallic NPs of varying compositions by adjusting the thickness of individual layers, thus enabling us to smoothly tune the spectral location of plasmonic resonance within the visible range.

Dry synthesis of bi-layer nanoporous metal films as plasmonic metamaterial

Abstract Nanoporous metals are a class of nanostructured materials finding extensive applications in multiple fields thanks to their unique properties attributed to their high surface area and interconnected nanoscale ligaments. They can be prepared following different strategies, but the deposition of an arbitrary pure porous metal is still challenging. Recently, a dry synthesis of nanoporous films based on the plasma treatment of metal thin layers deposited by physical vapour deposition has been demonstrated, as a general route to form pure nanoporous films from a large set of metals. An interesting aspect related to this approach is the possibility to apply the same methodology to deposit the porous films as a multilayer. In this way, it is possible to explore the properties of different porous metals in close contact. As demonstrated in this paper, interesting plasmonic properties emerge in a nanoporous Au–Ag bi-layer. The versatility of the method coupled with the possibility to include many different metals, provides an opportunity to tailor their optical resonances and to exploit the chemical and mechanical properties of components, which is of great interest to applications ranging from sensing, to photochemistry and photocatalysis.

Tailoring Microenvironment in Bilayer Electrode with Copper and Silver Nanocatalysts for Bicarbonate Electroreduction to Multicarbon Products

As compared with CO2 electrolyzers, bicarbonate electrolyzers can achieve direct conversion of CO2 captured solutions to higher-valued chemicals, that can bypass energy-intensive steps of CO2 regeneration and pressurization processes. However, most previous studies have only reported single carbon chemicals (i.e., CO, formate, CH4) as the major products so far. In this presentation, we will present direct electro-reduction of potassium bicarbonate (KHCO3) to multicarbon (C2+) products (i.e., acetate, ethylene, ethanol, propanol) using rationally designed bilayer of Cu and Ag nanosized catalysts. The in-situ generated CO2 was first reduced to CO on the Ag layer, followed by CO reduction to C2+ products on the Cu layer benefiting from locally high concentration of CO. Through optimizing the configurations, compositions, ionomer types, and local hydrophobicity of the bilayer electrode, we have created the favorable microenvironment (high local pH, low water content, etc.) to increase bicarbonate conversion to C2+ products with a largely suppressed hydrogen evolution reaction, and a remarkable C2+ FE of 41.6% at a current density of 100 mA cm−2 was achieved.

Multilevel resistive switching in solution-processed CuFe2O4/TiO2 heterostructure

Low-cost, stable, and easy-to-fabricate resistive switching memory (RSM) devices are highly desirable for next-generation nonvolatile memories. Spinel-structured CuFe2O4 (CFO), composed of earth-abundant, environmentally friendly elements, is a multifunctional material mainly featuring super-paramagnetism. This work explores the potential of spin-coated CFO thin films as an active material in RSM. A simple fluorine-doped tin oxide (FTO)/CFO/Ag device shows a bipolar resistive switching behavior with the problems like scattered SET and RESET voltages and endurance deterioration. Adding a TiO2 layer in the conventional device, we overcame the above limitations and achieved additional advantages of multilevel switching and improved temperature stability. The solution-processed FTO/TiO2/CFO/Ag bilayer device shows stable endurance with a maximum ON/OFF ratio of 100 with the ability to have multiple high resistance states and exhibits excellent temperature stability up to 250 °C. Our results further enhance the multifunctionality of CFO with the potential of being low-cost multilevel RSM.

Antiferromagnetic ordering and signatures of enhanced spin-frustration in honeycomb-layered tellurates with Ag bilayers

We report the magnetic and spin frustration properties of Ag-based honeycomb layered tellurates with magnetic honeycomb slabs separated by Ag bilayers.

Atomic-Scale Friction Study by EC-AFM: Underpotential Deposition (UPD) of Ag on I-Modified Au(111) and Its Tip Penetration

The underpotential deposition (UPD) of Ag on an I-modified Au(111) surface is examined in perchloric acid solution by electrochemical lateral force microscopy (LFM). The transitions of ordered structures are observed as potential is swept and normal load changes. At low normal load, the structural changes with potential indicate that the iodine structure is very sensitive to the coverage of silver. At potentials positive of the 1st Ag UPD peak, the iodine forms a ( × R30°) structure (θ I = 0.33) on Au(111). The structural transition to a 1 × 1 structure observed as the normal load increases demonstrates that the AFM tip penetrates the iodine adlayer. As the potential passes the 1st Ag UPD peak, the iodine forms a p(3 × 3) (θ I = 0.44) structure and also silver seems to form a p(3 × 3) (θ Ag = 0.44) structure, as suggested by LFM images at high load. At even higher load, also this Ag layer is penetrated and the 1 × 1 structure of the substrate is observed. At potentials slightly negative of the 2nd Ag UPD peak, even though the iodine structure is maintained as a p(3 × 3) (θ I = 0.44) structure, the atomic corrugations observed at high normal load indicate that silver completes a monolayer. The large-scale images clearly show that an Ag bilayer is formed at the 3rd Ag UPD peak. When the Ag bilayer completes, the iodine forms a ( × R30°) (θ I = 0.33).

Advanced characterization of organic–metal and organic–organic interfaces: from photoelectron spectroscopy data to energy-level diagrams

Organic–metal and organic–organic interfaces account for the functionality of virtually all organic optoelectronic applications and the energy-level alignment is of particular importance for device performance. Often the energy-level alignment is simply estimated by metal work functions and ionization energies and electron affinities of the organic materials. However, various interfacial effects such as push back, mirror forces (also known as screening), electronic polarization or charge transfer affect the energy-level alignment. We perform x-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) measurements on copper-hexadecafluorophthalocyanine (F16CuPc) and titanyl-phthalocyanine (TiOPc) thin films on Ag(111) and use TiOPc bilayers to decouple F16CuPc layers from the metal substrate. Even for our structurally well-characterized model interfaces and by stepwise preparation of vacuum-sublimed samples, a precise assignment of vacuum-level and energy-level shifts remains challenging. Nevertheless, our results provide guidelines for the interpretation of XPS and UPS data of organic–metal and organic–organic interfaces.

Ultrathin Layered Hyperbolic Metamaterial-Assisted Illumination Nanoscopy.

Metamaterial-assisted illumination nanoscopy (MAIN) has been proven to be a promising approach for super-resolution microscopy with up to a 7-fold improvement in imaging resolution. Further resolution enhancement is possible in principle, however, has not yet been demonstrated due to the lack of high-quality ultrathin layered hyperbolic metamaterials (HMMs) used in the MAIN. Here, we fabricate a low-loss composite HMM consisting of high-quality bilayers of Al-doped Ag and MgO with a nominal thickness of 2.5 nm, and then use it to demonstrate an ultrathin layered hyperbolic metamaterial-assisted illumination nanoscopy (ULH-MAIN) with a 14-fold imaging resolution improvement. This improvement of resolution is achieved in fluorescent beads super-resolution experiments and verified with scanning electron microscopy. The ULH-MAIN presents a simple super-resolution imaging approach that offers distinct benefits such as low illumination power, low cost, and a broad spectrum of selectable probes, making it ideal for dynamic imaging of life science samples.

Transparent and flexible heaters using plasma polymer fluorocarbon/silver bilayer thin films

In this study, a transparent and flexible heater is fabricated using plasma polymer fluorocarbon (PPFC)/silver (Ag) bilayer thin films. Compared with polymer/metal/polymer trilayer thin film structures, the polymer/metal bilayer thin film structure allows a simple process while improving the optical transmittance in the visible light range. The optimized PPFC/Ag bilayer thin film demonstrates an optical transmittance of 0.80 at a wavelength of 440 nm, a sheet resistance of 6.67 Ω·sq–1, and a deionized water contact angle of 103.44°. Results from various mechanical flexibility tests indicate that the heater can be used in flexible and rollable devices without severe performance degradation. This study provides insights into the use of transparent and flexible heaters in the exterior walls of buildings, flexible devices, and automobile glasses for preventing frosting and fogging.

Improved Operational Stability of Perovskite Solar Cells via Au Barrier Layer Incorporation

Metal electrode corrosion by halogen species from perovskites causes severe degradation in perovskite solar cells (PSCs). By employing the Au–Ag bilayer top electrode, we show improved operational stability for PSCs compared to devices with a single metal electrode. The optoelectronic property of bilayer electrodes and their influence on device parameters and operational stability are characterized and discussed. Significantly enhanced operational stability (T80 > 200 h) is demonstrated compared to pure Ag metal electrode devices (T40 ≈ 200 h), under maximum power point conditions. The applicability of this strategy is further confirmed by the Au–Al bilayer electrode system. The work not only demonstrates an effective method to prevent metal electrode corrosion and perovskite decomposition but also provides insights into the working principle and degradation of PSCs.

In situ friction study of Ag Underpotential deposition (UPD) on Au(111) in aqueous electrolyte.

The electrodeposition of silver on Au(111) was investigated using lateral force microscopy (LFM) in Ag+ containing sulfuric acid. Friction force images show that adsorbed sulfate forms 3×7R19.1∘ structure (θsulfate=0.2) on Au(111) prior to Ag underpotential deposition (UPD) and (3×3R30∘) structure (θsulfate=0.33 ) on a complete monolayer or bilayer of Ag. Variation of friction with normal load shows a non‐monotonous dependence, which is caused by increasing penetration of the tip into the sulfate adlayer. In addition, the friction force is influenced by the varying coverage and mobility of Ag atoms on the surface. Before Ag coverage reaches the critical value, the deposited silver atoms may be mobile enough to be dragged by the movement of AFM tip. Possible penetration of the tip into the UPD layer at very high loads is discussed as a model for self‐healing wear. However, when the coverage of Ag is close to 1, the deposited Ag atoms are tight enough to resist the influence of the AFM tip and the tip penetrates only into the sulfate adlayer.

Electron-Induced Modification of Self-Assembled Monolayers of Aromatic Carboxylic Acids

The effects of low-energy electrons on aromatic self-assembled monolayers (SAMs) with carboxylic acid (CA) docking groups were studied with a focus on the dose range below 5 mC/cm2. The SAMs were prepared on an underpotentially deposited Ag bilayer and comprised nonsubstituted and CA-substituted monolayers with a rod-like biphenyl backbone and a monolayer of a Y-shaped, CA-substituted molecule, 1,3,5-benzenetribenzoic acid (H3BTB), formed either as a single-component film or as a binary one by mixing with adamantane-CA (Ad-CA). X-ray photoelectron and near-edge X-ray absorption fine structure spectra suggest high proneness of the CA groups to electron irradiation at both SAM/substrate and SAM/ambient interfaces. Cleavage of the carboxylate-substrate bond results in substantial molecular desorption at the initial stage of irradiation until electron-induced cross-linking gradually takes over. The CA groups at the outer SAM interface undergo substantial chemical changes, indicating that they participate in the cross-linking chemistry. The electron-induced processes are accompanied by molecular reorientation. Disordering for the SAMs formed by the rod-like molecules is contrasted by the H3BTB-based systems where changes also occur but some molecular order is preserved as explained by a proposed model invoking conformational changes. In SAMs of H3BTB mixed with Ad-CA, the latter shows higher proneness to irradiation-induced desorption than the former, as well as an influence on the cross-linking chemistry. The results of the present study suggest that CA-based SAMs on Ag offer additional options for cross-linking in SAMs and, as exemplarily demonstrated by the generation of Cu patterns on structured H3BTB templates, can be efficiently used for lithography and nanofabrication.

Enhancing the operational stability of unencapsulated perovskite solar cells through Cu–Ag bilayer electrode incorporation

Incorporation of bilayer electrodes (Cu:Ag) significantly reduces electrode corrosion and device degradation in perovskite solar cells operating in air. A symbiosis exists whereby Ag inhibits Cu oxidation and Cu prevents interfacial reactions between the perovskite (MAPbI3) and Ag.

Tunable Fano resonances and improved sensitivity in waveguide-coupled surface plasmon resonance sensors with a bimetallic layer

A multilayer structure consisting of Au–Ag bimetal and dielectric layers which allows coupling between surface plasmon polaritons and waveguide modes is studied by calculating reflectivity curves of incident light. The coupling results in asymmetric resonance modes, which can be attributed to Fano resonances (FR). The variation trend of FR is investigated in detail by fitting numerical results with an analytic model when changing both waveguide widths and silver thicknesses. It is demonstrated that changing the thickness ratio of Au–Ag bilayers can tune the coupling strength and the line shape of FR. We build the resonant mode diagram according to the different asymmetric line shape which can be depicted by the sign of the fitting Fano constant q. At a critical Ag thickness, the coupling gives rise to a q = 0 symmetrical resonance state (plasma induced transparency). Finally, the best optimized thickness combination (Ag/Au) in the structure is found when the refractive index of the sensing layer medium changes. The sensitivity of the optimized sensor is twice as high as that of the single Au film structure.

Molecular dynamics simulation of plastic deformation and interfacial delamination of NiTi/Ag bilayer by cyclic-nanoindentation: Effects of crystallographic orientation of substrate

This paper presents a comparative study of plasticity and fracture behavior of the NiTi/Ag bilayer for the different crystallographic orientations of the substrate. Molecular dynamic (MD) simulation was used to determine the deformation mechanism, dislocation density, plastic energy dissipation and delamination of the NiTi/Ag bilayers near the interface, when NiTi aligned at (1 0 0), (1 1 1), (1 1 0), (3 2 1), (2 1 0) and (2 1 1) faces during the cyclic-nanoindentation test. The Griffith energy balance model was used to estimate the energy release associated with the delamination. The results of the simulation are suggested the dependence of deformation mechanism, energy release rate (Gin), interfacial toughness (Kin) and average plastic energy dissipation per unit cycle (Eplastic) of NiTi/Ag bilayer on the crystallographic orientation of the NiTi substrate. Prismatic dislocation loop and the nest-like organization of the twins were responsible for the plastic deformation of the NiTi/Ag bilayers when NiTi aligned at (211,010,111) and (100,210,321) faces, respectively. The values of Gin and Kin of the bilayers were in the range of 64.27–147.71 J/m2 and 77–192 J/m2, respectively. The values of Eplastic is increased in the following order: NiTi (2 1 1) < NiTi (3 2 1) < NiTi (1 0 0) < NiTi (2 1 0) < NiTi (1 1 1) < NiTi (0 1 0). The average dislocation densities produced for the indenter radius of 30 Å were in the range of 1.23 × 1019–1.84 × 1019 m−2. The results show that the NiTi (0 1 0)/Ag case has the larger dislocation density than other bilayers. Both of hardness and the interfacial toughness of the NiTi/Ag at different crystallographic orientations were consistent with the free energy data obtained from Jarzynski’s equality for nanoindentation results, which were in the range of 3.35 × 10−4−7.81 × 10−4 eV/atom. Due to high interfacial toughness and hardness plus lower plastic energy dissipation, the NiTi (2 1 1)/Ag bilayer may show the better results for engineering and medical applications.

H2 Adsorption on Wurtzite ZnO and on ZnO/M(111) (M=Cu, Ag and Au) Bilayer Films

AbstractThe dissociative adsorption of H2 on the wurtzite ZnO (10 0) surface and on ZnO/M(111) (M=Cu, Ag and Au) bilayer films has been investigated by mean of DFT+U calculations. On ZnO wurtzite and free‐standing ZnO bilayer, H2 prefers to dissociate heterolytically, forming a proton adsorbed on an O atom and an hydride atom sitting on a Zn cation. While this adsorption mechanism is exothermic on the wurtzite ZnO (10 0) surface, an endothermic process is observed on a free‐standing, unsupported ZnO bilayer. The trend is completely reversed when H2 is adsorbed and dissociated on a metal supported ZnO bilayer. Here the homolytic dissociation mechanism is exothermic and preferred over the heterolytic dissociation. This is due to the effect of the metal support which acts as an electron reservoir to accept extra electrons accompanied to homolytic dissociation of H2 molecule (two electrons are transferred to the metal support with formation of two H+ ions). The study of the reaction pathway for dissociative adsorption of H2 on ZnO/Cu(111) shows that the reaction occurs via (a) heterolytic splitting and (b) the displacement of an H atom from a Zn site to the neighboring O site, forming the final product of homolytic dissociation.

Femtosecond laser generation of microbumps and nanojets on single and bilayer Cu/Ag thin films.

The formation mechanisms of microbumps and nanojets on films composed of single and double Cu/Ag layers deposited on a glass substrate and irradiated by a single 60 fs laser pulse are investigated experimentally and in atomistic simulations. The composition of the laser-modified bilayers is probed with the energy dispersive X-ray spectroscopy and used as a marker for processes responsible for the modification of the film morphology. For the bilayer with the top Ag layer facing the laser, the increase in fluence is found to result in a sequential appearance of a Ag microbump, the exposure of the Cu underlayer by removal of the Ag layer, a Cu microbump, and a frozen nanojet. The Cu on Ag bilayer exhibits a partial spallation of the top Cu film, followed by the generation of surface structures that mainly consist of Ag at higher fluences. The experimental observations are explained with atomistic simulations, which reveal that the stronger electron-phonon coupling of Cu results in the confinement of the deposited laser energy in the top Cu layer in the Cu on Ag case and channelling of the energy from the top Ag layer to the underlying Cu layer in the Ag on Cu case. This difference in the energy (re)distribution directly translates into differences in the morphology of the laser-modified bilayers. In all systems, the generation of microbumps and nanojets occurs in the molten state. It is driven by the dynamic relaxation of the laser-induced stresses and, at higher fluences, the release of vapor at the interface with the substrate. The resistance of the colder periphery of the laser spot to the ejection of spalled layers as well as the rapid solidification of the transient molten structures are largely defining the final shapes of the surface structures.

Catalytic Activities of Mono- and Bimetallic (Gold/Silver) Nanoshell-Coated Gold Nanocubes toward Catalytic Reduction of Nitroaromatics.

A new class of core-shell metallic nanostructures with tunable near-surface composition and surface morphology with excellent catalytic activity is reported. Very thin shells of metal nanoassemblies such as monolayer (Ag and Au), bilayer of Ag or Au, and AgAu alloy layer with controlled size and morphology were deposited onto a gold nanocube (AuNC) core. UV-vis absorption spectroscopy and high-resolution transmission electron microscopy analyses along with selected-area electron diffraction, energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometer, and X-ray diffraction techniques were used to characterize the prepared core-shell nanocubes. High-angle annular dark field scanning transmission electron microscopy-energy dispersive X-ray spectroscopy mapping images were recorded for the bilayer shell and alloy layer shell in the core-shell nanostructures. Reduction of 4-nitroaniline in the presence of sodium borohydride was chosen to validate the catalytic activity of the prepared core-shell metal nanocubes. Interestingly, the AgAu alloy shell layer over the AuNC (AuNC1@Ag0.25Au0.25) showed excellent catalytic activity compared with the pristine AuNC and monolayer and bilayer core-shell nanostructures.

Thermal and Plasmonic Stabilization of Silver Nanostructures Using a Bilayer Anchoring Technique.

In this work, we demonstrate how to suppress the shape instability of silver (Ag) nanotriangular pyramids following high-temperature annealing without a coating or encapsulation, thus producing a more stable optical plasmonic system. Nanosphere lithography (NSL) was used to fabricate large-area arrays of nanotriangular pyramids of Ag on glass substrates. By using a combination of morphology and spectroscopic studies it was found that exposure of this system to high temperatures of 473 K and beyond in air led to a rapid change in nanostructure shape, and thus, the surface area, with a substantial change to the original plasmonic character. On the other hand, NSL nanotriangular pyramids made from bilayers of Ag on Co or Co on Ag showed much smaller changes in shape and area following annealing up to 573 K in air. In the case of pure Ag, the NSL nanotriangular pyramid changed into a more spherical shape with an overall decrease of ∼24% in its surface area following annealing at 573 K. This lead to a large blue shift of over ∼287 nm or ∼39% in the location of the dipolar plasmonic resonance. On the other hand, the triangular shape of Ag was retained in both the metal bilayer cases, with much smaller area changes of ∼10 and ∼9%, for the Ag deposit when on Co and when under Co, respectively. Consequently, the plasmonic shifts were substantially smaller, of ∼65 nm or about 9%, in these bilayer systems. The mechanism for this stabilization was attributed to the higher surface energy of Co and much lower diffusivity of Co as well as Ag on Co that resulted in an anchoring of the Ag shape to its original state. The plasmonic quality factor for the bimetal NSL nanotriangular pyramids also showed substantially improved stability over pure Ag, further indicating that this anchoring approach is a viable pathway to produce pristine Ag surfaces for high-temperature plasmonic applications.