Ag Films Research Articles

Tunable Resonant‐Photopyroelectric Detector Using Chalcogenide−Metal−Fluoropolymer Nanograting

AbstractPyroelectric detectors are often broadband and require external filters for wavelength‐specific applications. This paper reports a tunable, narrowband, and lightweight pyroelectric infrared detector built upon a flexible membrane of As2S3−Ag−P(VDF‐TrFE) with subwavelength grating, which is capable of both on‐chip filtering and photopyroelectric energy conversion. The top surface of this hybrid membrane is a corrugated As2S3−Ag film contributing to narrowband light absorption in the near‐infrared (NIR) regime, and the bottom part is a polyvinylidene fluoride‐trifluoroethylene (PVDF‐TrFE) membrane for the conversion of the absorbed light to an electrical signal. Uniquely, applying a bias voltage to the PVDF‐TrFE membrane enables the tuning of the device's absorption and pyroelectric characteristics owing to the piezoelectrically induced mechanical bending. The resonator exhibited a resonant absorption coefficient of 80% and a full‐width‐half‐maximum of 15 nm within the NIR, a responsivity of 1.4 mV mW−1, and an equivalent noise power of 13 µW Hz−1/2 at 1560 nm. By applying a 15‐V bias to the PVDF‐TrFE membrane, the absorption coefficient decreased to 18% due to the change in the grating period and incident angle. The narrowband and tunable features of the As2S3−Ag−P(VDF‐TrFE) pyroelectric detector will benefit a variety of potential applications in sensors, optical spectroscopy, and imaging.

Structural, Morphology and Optical properties of Ag-doped Nanostructured CdS thin films

Chemical Spray Pyrolysis (CSP) method is employed to deposit CdS and Silver (Ag)-doped CdS films. The effect of Ag doping at 1, and 3 wt-% levels is considered. The principal X-ray diffraction peak was along (020) plane. Maximum grain size was observed at the (CdS:3% Ag) films. The dislocation density parameter increased from 53.04 to 37.08, whereas the strain(%) parameter decreases from 25.23 to 21.10. Atomic force Microscope (AFM) images indicate a polycrystalline structure, and reveal that the undoped CdS and doped CdS:Ag films have discontinuous surfaces with spherically grains decreased from (58.05 to 45.77 nm) with the increase of doping from 0% to 3%. Root-mean square (Rrms) roughness of surface is about (9.81-5.42) nm. Also, there was a clear decrement in transmittance as Ag increment. The optical energy bandgap Eg has been decreased from 2.47 to 2.37 eV due to increase in Ag content. The absorption coefficients with photon energy increase with increasing concentration doping in Ag.

The effect of vacuum and air annealing in the physical characteristics and photocatalytic efficiency of In2S3:Ag thin films produced by spray pyrolysis

Indium sulfide thin films, doped with silver, were synthesized by spray pyrolysis technique. These samples were subsequently annealed in air and in vacuum, at the temperature of 400 °C, for 2 h. This work reports the effect of the thermal treatments on the structure, morphology and optical characteristics of the films, but also the study of the photodegradation efficiency of methylene blue solution. The as-produced films are polycrystalline, exhibiting the tetragonal β-phase structure of In 2 S 3 . The annealing treatments cause an increase of 27% and 74% of the crystallite size, and of the roughness of the films (20% and 56%), for the vacuum and air annealed samples, respectively, but provoke a significant decrease of the optical transmittance. The optical band gap decreases from 2.71 eV in the as-produced film, to 2.45 eV and 2.39 eV in the vacuum and air-annealed films, respectively. The photodegradation efficiency of the methylene blue solution increases from 83.0% for the as-produced film to around 95.4%, regardless the type of annealing. • Optimized polycrystalline In 2 S 3 :Ag thin films were produced by spray pyrolysis. • Annealing of the films, in vacuum and air, caused changes in the physical characteristics of In 2 S 3 :Ag films. • The optical band gap of the annealed films decreases relatively to the as-prepared films. • Annealed films exhibit significant increase of the efficiency of the photodegradation of Methylene Blue.

Preparation of CuO/Ag rough nanostructures as SERS-active substrates

In this paper, CuO nanostructures with nanometer roughness were firstly prepared by electrochemical anodic oxidation method, and then CuO/Ag composite nanostructures were prepared by magnetron sputtering method on the surface of CuO substrate. The successful deposition of Ag films on CuO was confirmed by XRD, UV-Vis and SEM. In addition, the effects of different Ag sputtering time on substrate morphology and SERS properties were studied. Due to the many gaps between the rough CuO/Ag nanomorphology, the substrate has many “hot spots” and adsorption sites, which can effectively improve the SERS performance of the substrate. We selected R6G dye molecule as the probe molecule to evaluate the SERS performance of the substrate. The final experimental results show that the preparation method of CuO/Ag rough nanostructure is simple, and it has significant SERS performance improvement. The substrate’s detection limit for R6G can even reach 10-11M.

Effect of a subnanometer thin insulator layer at the Ag/Si(111) interface through the observation of quantum well states

The ``two-step'' growth technique has been used to grow atomically uniform Ag films on $7\ifmmode\times\else\texttimes\fi{}7$ Si(111) and $8\ifmmode\times\else\texttimes\fi{}8 \ensuremath{\beta}{\text{-Si}}_{3}{\text{N}}_{4}$(0001)/Si(111) surfaces. Angle-resolved photoemission spectroscopy reveals the formation of $sp$ quantum well states in the Ag films with distinct properties in the two cases. It is shown that the valence electrons in silver can be confined in the fundamental gap of a less than 1-nm-thin nitride layer, effectively decoupling the Ag and Si states.

Improvement of Ag films with highly (111) surface orientation for metal direct bonding technique: Nanotwinned structure and ion bombardment effect

High-density nanotwinned structure are introduced into Ag films with over 95% of (111) surface orientation. Different substrate biases were applied to the nanotwinned Ag films during the deposition process in order to optimize the nanostructure and properties of nanotwinned Ag films, while maintain the strong (111) surface orientation. The formation of undesirable transition region, which is consisted of random-oriented nanocrystalline structure, can be sufficiently depressed by increasing applied substrate bias. The effect of Ar+ ion bombardment on the nanostructure and properties of nanotwinned (111) Ag films was discussed in this study. With moderate applied substrate bias, the nanotwinned (111) Ag film reveals very low resistivity of 1.84 μΩ cm and high hardness over 2 GPa. This study provides a concept to optimize both the nanostructure and properties of sputtered Ag film with strong (111) surface orientation for metal direct bonding applications.

Fluorescence Enhancement via Dual Coupling of Dye Molecules with Silver Nanostructures

We demonstrate the enhancement of fluorescence emitted from dye molecules coupled with two surface plasmons, i.e., silver nanoparticles (AgNPs)-induced localized surface plasmons (LSP) and thin silver (Ag) film supported surface plasmons. Excitation light is illuminated to a SiO2 layer that contains both rhodamine 110 molecules and AgNPs. AgNPs enhances excitation rates of dye molecules in their close proximity due to LSP-induced enhancement of local electromagnetic fields at dye excitation wavelengths. Moreover, the SiO2 layer on one surface of which a 50 nm-thick Ag film is coated for metal cladding (air on the other surface), acts as a waveguide core at the dye emission wavelengths. The Ag film induces the surface plasmons which couple with the waveguide modes, resulting in a waveguide-modulated version of surface plasmon coupled emission (SPCE) for different SiO2 thicknesses in a reverse Kretschmann configuration. We find that varying the SiO2 thickness modulates the fluorescent signal of SPCE, its modulation behavior being in agreement with the theoretical simulation of thickness dependent properties of the coupled plasmon waveguide resonance. This enables optimization engineering of the waveguide structure for enhancement of fluorescent signals. The combination of LSP enhanced dye excitation and the waveguide-modulated version of SPCE may offer chances of enhancing fluorescent signals for a highly sensitive fluorescent assay of biomedical and chemical substances.

Enhancement of light-induced resistance effect in the nanostructure of Ag/graphene based on the n-type silicon

The direct coupling of material properties across a nanoscale interface is a promising route to achieve the functionality unavailable in bulk materials. Graphene is a kind of sp2 hybridized carbon monolayer and has been investigated in many applications due to its high charge-carrier mobility. In this paper, a type of enhanced light-induced resistance effect (LRE) is observed in the structure of Ag/graphene/n-type Si. This effect features a remarkable linear resistance change with a sensitivity of 4.39 kΩ/mm when a laser moves along the surface of the structure. With the optimal thickness of the Ag film, the resistance change ratio of LRE can reach 472%, which is significantly higher than the Ag/Si control sample (6.4%), showing an obvious graphene-induced enhancement. Photocarriers' diffusion and recombination at the heterojunction interface are crucial for the enhancement. These findings offer an effective way to study the carrier dynamics at the heterojunction interface and will be useful in the development of graphene-based optoelectronic devices, such as laser-controlled variable resistors, laser-induced diodes, and storage devices.

An intensity modulated fiber-optic carbon monoxide sensor based on Ag/Co-MOF in-situ coated thin-core fiber

Abstract An intensity modulated fiber-optic carbon monoxide (CO) sensor by integrating in-situ solvothermal-growth Ag/Co-MOF sensing film is fabricated and evaluated. The Michelson interference sensing structure is composed of single-mode fiber (SMF), enlarged taper, thin-core fiber (TCF), and Ag film as the reflector. Ag/Co-MOF was coated on the cladding of the TCF as the sensing material, and the enlarged taper is located between TCF and SMF as the coupler. The structure, morphology, compositions and thermal stability of the Ag/Co-MOF sensing film were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), etc. The sensitivity of the sensor is 0.04515 dB/ppm, and the fitting parameter of the CO concentration is 0.99876. In addition, the sensor has the advantages of good selectivity, good signal and temperature stability, and it has potential application in trace CO detection.

Oxygen reduction reaction of vertically-aligned nanoporous Ag nanowires

Improving the activity of Ag-based catalysts for oxygen reduction reaction (ORR) is a challenge for achieving economic alkaline-based fuel cells. Here, vertically-aligned nanoporous Ag nanowires (NWs) are developed as electrocatalysts for the ORR. Electrochemical reduction of vertically-aligned AgCl NWs eliminate Cl− ions from the NWs, and thereby reduces Ag+ cations to metallic Ag atoms, to yield nanoporous Ag NWs with a large amount of catalytic active Ag (110) surfaces. The gap between Ag NWs can be a pathway for the electrolyte and increase mass transport of dissolved oxygen to the electrode surface. Consequently, the Ag NWs have 36.4 times higher electrochemical surface area but less than 0.08 times as much charge-transfer resistance as Ag film. As a result, the Ag NWs achieve an ORR-onset potential of 0.97 VRHE and a good long-term stability with only 50 mV decrease in ORR-onset potential even after 30,000 cycles (480,000 s).

Ionic Liquid Electrolyte-Based Switchable Mirror with Fast Response and Improved Durability.

Electrochemically tunable devices based on reversible metal electrodeposition have attracted extensive attention for energy-saving smart windows, information displays, digital signage, and variable reflectance mirrors, owing to their excellent optical modulation characteristics, low operation voltage, and superb electrochemical stability. Here, we study the effects of ionic liquid (IL)-based electrolytes on electrodeposition of the reversible electrochemical mirrors (REMs) by changing the organic cations of the ILs to obtain devices with the desired spectroelectrochemical and electrodeposited properties. Spectroelectrochemical measurements and scanning electron microscopy images show that organic cations drastically affect the switching speed and cycling durability, which we proposed on the basis of the difference in the absorption energies between cations and Ag(111) surfaces. Higher adsorption energy indicates strong adhesion between organic cations and Ag(111) surfaces, and this strong adsorption would prevent aggregation and agglomeration during the nucleation of Ag nanoparticles (AgNPs), leading to a denser and more compact electrodeposited Ag film and faster switching speeds (3.3 s for coloring and 14.3 s for bleaching). These findings allow us to fabricate dynamic devices that exhibit reversibly switchable light modulation at fast switching speeds and excellent cycling stability over thousands of cycles without attenuation. The combination of rapid switching and durable cycling stability enables tunable windows, which are based on reversible electrodeposition of metal Ag and IL-based electrolytes, make REM devices a competitive and promising alternative to traditional intelligent response materials.

In Situ Growth of Silver Film on Polyimide with Tuned Morphologies for Flexible Electronics.

In this work, the silver films with tuned morphologies have been fabricated on flexible polyimide substrate by in situ direct-ion-exchange technique. The morphology of Ag films with loose nanoparticles, dense polyhedrons, aggregated nanoparticle clouds, and dendrite structure can be obtained by a controlled reduced process as illustrated by scanning electron microscopy (SEM) and optical microscopy, respectively. All of the Ag films show good crystalline and high conductivity, which is confirmed by X-ray diffraction (XRD) and four-point probe resistance measurements. Infrared (IR) spectra demonstrate the occurrence of the polyimide surface metallization, which favors good adhesion between the Ag films and the flexible substrate. The adhesion test proves the strong adhesion of these Ag films, especially for the Ag films with the dendritic structure. Moreover, the mechanical properties of these Ag/PI films have been investigated as well. It can be found that all of the Ag/PI films exhibit low sensitivity to the bending test. However, the strain sensitivity strongly depends on the morphology of the Ag films, which can be applied for diverse flexible electronics.

Superior electrical contact characteristics of Ag/CNT composite films formed in a cyanide-free plating bath and tested against corrosion by H2S gas

The electrical contact resistance of a Ag/carbon nanotube (CNT) composite plating film prepared using a cyanide-free bath was evaluated against a H2S gas corrosion test. After the corrosion test, the Ag/CNT composite plating film exhibited a lower electrical contact resistance than a Ag plating film evaluated for comparison. The mechanism of the superior electrical contact characteristics of the Ag/CNT composite plating film was investigated using various methods. Scanning electron microscopy observations and X-ray diffraction analyses revealed that the amount of silver sulfide (Ag2S) generated on the Ag/CNT composite film was smaller than that on the Ag film. Electrochemical measurements clarified that the sulfidation resistances of the Ag/CNT composite film and the Ag film were approximately the same. However, the contact angle of the Ag/CNT composite film against water was remarkably greater than that of the Ag film. This high hydrophobicity of the Ag/CNT film likely suppressed Ag2S production by corrosion, resulting in the observed superior electrical contact characteristics after the H2S gas corrosion test.

Noble Metals for Modern Implant Materials: MOCVD of Film Structures and Cytotoxical, Antibacterial, and Histological Studies.

This work is aimed at developing the modification of the surface of medical implants with film materials based on noble metals in order to improve their biological characteristics. Gas-phase transportation methods were proposed to obtain such materials. To determine the effect of the material of the bottom layer of heterometallic structures, Ir, Pt, and PtIr coatings with a thickness of 1.4–1.5 μm were deposited by metal–organic chemical vapor deposition (MOCVD) on Ti6Al4V alloy discs. Two types of antibacterial components, namely, gold nanoparticles (AuNPs) and discontinuous Ag coatings, were deposited on the surface of these coatings. AuNPs (11–14 nm) were deposited by a pulsed MOCVD method, while Ag films (35–40 nm in thickness) were obtained by physical vapor deposition (PVD). The cytotoxic (24 h and 48 h, toward peripheral blood mononuclear cells (PBMCs)) and antibacterial (24 h) properties of monophase (Ag, Ir, Pt, and PtIr) and heterophase (Ag/Pt, Ag/Ir, Ag/PtIr, Au/Pt, Au/Ir, and Au/PtIr) film materials deposited on Ti-alloy samples were studied in vitro and compared with those of uncoated Ti-alloy samples. Studies of the cytokine production by PBMCs in response to incubation of the samples for 24 and 48 h and histological studies at 1 and 3 months after subcutaneous implantation in rats were also performed. Despite the comparable thickness of the fibrous capsule after 3 months, a faster completion of the active phase of encapsulation was observed for the coated implants compared to the Ti alloy analogs. For the Ag-containing samples, growth inhibition of S. epidermidis, S. aureus, Str. pyogenes, P. aeruginosa, and Ent. faecium was observed.

Transfer matrix based reverse engineering approach to analyse annealing induced changes in optical transmission of TiO2/Ag/TiO2/Ag multilayer

Measured optical transmission spectrum of photonic structure comprising TiO2/Ag/TiO2/Ag multilayer is reverse engineered by employing transfer matrix method with three different multilayer models to analyse the factors responsible for the annealing induced changes in the transmission. The multilayer is made to have a single peak or a passband in the visible region, so that the spectral changes due to annealing can be observed more vividly. Prior to the multilayer deposition, single layer thin film of Ag and TiO2 are prepared using asymmetric bipolar pulsed dc sputtering and their optical constants such as refractive index and extinction co-efficient are determined. The multilayer is prepared by four-layer sequential deposition of Ag and TiO2 on BK7 glass substrate. The deposited TiO2/Ag/TiO2/Ag multilayer is annealed in the temperature range 100–300 °C. The optical transmission of the annealed multilayers is measured using spectrophotometer. The measured peak transmission and spectral bandwidth of the multilayer filter decreases with annealing, which is ascribed to inter-diffusion at the interfaces, and increasing absorption at the interfaces and in the silver layers of the multilayer. The ascription is resolved from the layers properties and interface parameters obtained by reverse engineering the measured transmission spectra. The rough interfaces in the multilayer are modeled as thin homogeneous layers following Bruggeman effective medium approximation, and the interface parameters are found to be varying with annealing.

High‐Performance Upscaled Indium Tin Oxide–Free Organic Solar Cells with Visual Esthetics and Flexibility

Organic solar cells (OSCs) show great promise for future applications due to their merits of low cost, flexibility, and vivid colors, etc. However, the “conventional” device architecture with a brittle and expensive glass/indium tin oxide (ITO) transparent electrode weakens these potential advantages and restricts it to small areas for high performance. Herein, a device architecture simultaneously combining the advantages of high performance, superior flexibility, diverse colors, and low‐cost upscaling production is developed. The device structure features a top‐illumination geometry with a thermally evaporated ultrathin Ag film as transparent electrode for ITO replacement. The formation of optical microcavity and high conductance of ultrathin Ag enables high performance for upscaled OSCs. Moreover, this device architecture further enables diverse colors via tuning the TeO2 layer atop of the ultrathin Ag transparent electrode. This top‐illumination structure is more tolerant for substrates and enables wider flexible substrates. As a result, the flexible OSCs with upscaled areas of 1.05 cm2 exhibit a best performance of 13.09% (certified 11.9%) with superior flexibility, diverse colors, representing one of the best ITO‐free upscaled flexible OSCs. This work provides a versatile device structure to highlight the merits of OSCs, and paves the way for the future commercialization and practical applications.

Electroless Ag films for ionic liquid lubricated electrical contact

Two kinds of plating solutions, i.e. a standard plating solution and a commercially available plating solution, are employed for the preparation of electroless Ag film. The commercially available plating solution enables fast film deposition within several minutes and is highly selective for deposition onto Cu substrate, and cost-effective (reusable solution, and much less Ag consumption) compared to the standard plating solution. Both electroless Ag films prepared have distinct microstructure, surface chemistry, and bulk chemistry. The film from standard plating solution is composed of nano-grains with an average grain size of 300 nm and homogeneity. The film prepared with commercially available plating solution is composed of equiaxed grains (140 nm in size), and ribbon fish-like grains (80 nm in size and 0.5-2 μm in length) and shows microstructural inhomogeneity. The tribological properties of these electroless Ag films in presence of flooded 1-methyl-3-octylimidazolium hexafluorophosphate are investigated on a reciprocating tribometer with a pin-on-disk configuration under electrical contact. The results demonstrate that both electroless Ag films show better tribological property than Cu-on-Cu contact. Due to their dissimilar microstructure the tribological properties of the two electroless Ag films are quite different. For the standard plated film, local adhesion and tear-up in an annular shape on pin result in many plate-like wear debris in the early stage of the sliding test. For commercially the plated film from a commercial solution, compact and thin tribo-film on the worn surfaces of pin and disk as well as little or no wear debris are observed. The microstructural effect also has an influence on the design of the tribo-interface.

Control of localized surface plasmon resonance of Ag nanoparticles by changing its size and morphology

Ag thin-films with thicknesses of 5, 10, 15, 20, and 25 nm are deposited by thermal vacuum evaporation, and the obtained films are subsequently annealed at 400 °C for 1 h to form the Ag nanoparticles (NPs). The averaged diameters of the resultant Ag NPs are increased from 50 to 300 nm as increasing the initial Ag deposition thickness, according to the morphological observation using scanning electron microscopy (SEM). The significant red-shift of the extinction peak depending on the particle size of the Ag NPs, which can be assigned to the localized surface plasmon resonance of the Ag NPs. The organic emitter, tris(8-hydroxyquinolinato)aluminum (Alq3) film is overcoated on the Ag NPs. About 4-fold enhancement of the photoluminescence of Alq3 was observed in combination with the larger size Ag NPs fabricated from the 15–25 nm thick Ag films, which can be applied for the improvement of the light-extraction efficiency of the organic light-emitting devices.

High sensitivity and ultra compact fiber-optic microtip SPR thermometer coated with Ag/PDMS bilayer film

In this paper, we report an ultra-compact reflective SPR microtip temperature probe, which can achieve 2-D spatial resolution of several microns. The pencil-shaped all-fiber microtip proposed by us is a SO2 cone-cylinder with a length of 40 μm and a gradient diameter of 2 μm-10 μm, which can be used to develop multi-type tiny functionalized sensors. Due to the strong evanescent field of the ultra-fine microtip, the surface plasmon resonance (SPR) can be effectively stimulated by depositing nano-silver (Ag) film on its surface. Owing to the high refractive index (RI) sensitivity of SPR effect and the high thermo-optic coefficient (TOC) of polydimethylsiloxane (PDMS), the temperature sensitivity of microtip SPR probe coated with PDMS micron-film can reach to 1.985 nm/°C. Teflon 1600 nano-film on the surface of the SPR thermometer can effectively enhance the non-stickiness, moisture-proof and wear resistance. The test results show that the probe is hardly disturbed by humidity. This new sensing platform can be demonstrated by assembling high-performance sensing materials and ultra-compact fiber-optic structures.

Low-Temperature Oxide/Metal/Oxide Multilayer Films as Highly Transparent Conductive Electrodes for Optoelectronic Devices

Transparent conductors are essential for optoelectronic devices and flexible electronic devices. Oxide/metal/oxide (OMO) multilayer films with outstanding photoelectric performance have become a promising alternative for traditional transparent conductive oxides (TCOs). Most of the oxide films in OMO are deposited by magnetron sputtering or thermal evaporation processes, while the strong ion bombardment or high temperatures would deteriorate the device performance. For example, to fabricate a semitransparent solar cell, a top OMO will need to be deposited on the top of the semiconductor layer. Great care needs to be taken to reduce the damage to the semiconductor material to reduce the possible trapping of photogenerated charges. Recently, Mg and Ga codoped ZnO (MGZO) has been developed because of its wider spectral transmittance and less damage to the underlying functional layers in optoelectronics. However, the conductivity of MGZO remains limited. To produce low sheet resistance, the layer thickness needs to be several hundred nanometers. Here, we present high-quality MGZO films that are deposited by the reactive plasma deposition (RPD) technique with a soft growth process at room temperature (without intentional heating), providing broadband transmission and ultrathin pure Ag films prepared by magnetron sputtering at room temperature. Compared with the single MGZO, MGZO/Ag/MGZO multilayers effectively improve thin-film conductivity while maintaining high transmittances. The transfer matrix method (TMM) is used to determine the optimum thickness of each layer in OMO, and there is an excellent agreement between the simulation and experimental results. An MGZO/Ag/MGZO (40/9.5/45 nm) transparent electrode on a glass substrate presents an average transmittance of 87% (including glass) over a spectral range of 400–800 nm (relative transmittance, 94.7%), and sheet resistance (10 Ω sq–1). A semitransparent perovskite solar cell with an OMO top electrode exhibits a photoelectric conversion efficiency of about 11%. This work provides an insight to grow high-quality OMO films combining the RPD-TCO technique of high-rate deposition and low ion bombardment with ultrathin Ag films at room temperature, which pushes OMO forward to practical applications in more diverse optoelectronic devices.