Silver Thin Films Research Articles

Understanding the Preferred Crystal Orientation of Sputtered Silver in Ar/N2 Atmosphere: A Microstructure Investigation

Silver thin films were prepared by direct current (DC) magnetron sputtering technique in Ar/N2 atmosphere with various N2 volumetric ratios on Si substrates. Silver thin films prepared in pure Ar atmosphere show highly (111) preferred orientation. However, as the N2 content increases, Ag (111) preferred orientation evolves into (100) preferred orientation gradually. When N2 content is more than 12.5 vol.%, silver thin films exhibit highly (100) preferred orientation. Moreover, the average grain size decreases with increasing N2 content. Silver thin films with low relative density are prepared at high N2 content, which results in higher resistivity of films. By analyzing the resistivity and microstructures of silver thin films, the optimum range of N2 content to get compact silver thin films is found to be not more than 33.3 vol.%. Finally, the mechanism of N2 addition on microstructure evolution of silver thin films was proposed.

Initial quantum well states in Ag thin films on the In/Si(111)-[formula omitted] surface

Silver thin films have been formed by room temperature deposition of Ag on In/Si(111)-3×3. The Ag films have been investigated using both angle-resolved photoelectron spectroscopy (ARPES) and scanning tunneling microscopy and spectroscopy (STM/STS). This creates a powerful link between the electronic structures and the film morphology. The valence band spectra show a clear evidence of quantum well state (QWS) formation already for a 2 monolayer (ML) film. This QWS moves towards the Fermi level for the 3 ML film, which also reveals a second QWS. The QWSs’ dispersions have been plotted along the Γ¯M¯ and Γ¯K¯ symmetry lines of the 1×1 surface Brillouin zone (SBZ), where the Γ¯M¯ direction shows the umklapp-mediated QWSs. The valence band spectra for the 3 ML Ag film also show a strong Ag sp band close to the edge of the Ag(111) 1×1 SBZ. In the STS spectrum from 2 ML, two peaks are visible below the Shockley surface state. These peaks are compared with the ARPES data and attributed to different features of the QWS, namely the turning part where the QWS band intersects with the bulk Si valence band region and the local binding energy minimum close to the Γ¯ point.

Electrical percolation threshold evaluation of silver thin films for multilayer WO3/Ag/WO3 transparent conductive oxide

In this work, we developed an algorithm capable of identifying the electrical percolation threshold from AFM images of silver (Ag) thin films with different thickness. The percolation threshold was first determined experimentally using electrical measurements. Subsequently, the AFM images, film thicknesses, and conductivity values were fed to the algorithm to correlate the morphology from the AFM images and determine the existence of electrical conductivity. Then, the algorithm was calibrated using the threshold values found experimentally. Finally, the minimum thickness necessary for electrical percolation of silver thin films was determined to be around 7 nm. This methodology eliminates the urgency to carry out electrical measurements once the morphological ones are available, providing a criterion that allows to decide whether a film is suitable for its use as an intermediate layer in multilayer TCOs. To validate these results, indium free room temperature TCOs multilayer WO3/Ag /WO3 were grown and the Haacke figure of merit (FOM) were calculated. A good quality WO3-based TCO was obtained with a FOM value of 1.11 × 10−2 Ω−1 for WO3(10 nm)/Ag(7 nm)/WO3(20 nm).

Fabrication and characterization of silver thin films using physical vapor deposition, and the investigation of annealing effects on their structures

Silver nanoparticles have attracted increasing interest due to their chemical stability, catalytic activity, localized surface plasma resonance, and high conductivity. In this article, silver thin films with a thickness of ∼20 nm were fabricated on commercial glass (20 mm × 20 mm) substrate using physical vapor deposition technique, through the bombardment of the electron beam. To check the effect of annealing temperature, the fabricated substrates were annealed at the temperature range of 373.15 K to 1073.15 K with the difference of 100 K under a vacuum condition of ∼0.99 bar at constant time of 20 min; in addition, a single sample that had undergone no annealing effect has also been provided as a reference substrate. We investigated the physical and morphology evaluation information of fabricated annealed silver thin films on the glass substrate using the Ultra-Violet and Visible (UV–vis) spectroscopy, x-ray diffraction (XRD) and the field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). The results obtained from this study show that by increasing the annealing temperature of silver thin films, the flat silver thin films changed into rough silver thin films, by further increment change the silver thin films into silver nano-particles. At the annealed temperature of 1073.15 K, the 20 nm silver thin film was completely removed from the glass as well as bending occurred on the glass substrate. In the end, the absorbance spectra of each sample and the referenced sample were also measured.

The retrieval of a thin silver film dielectric constant by resonant approach

The film optical parameters retrieval method based on Otto configuration is considered. The high sensitivity of the method in comparison to the ellipsometry is demonstrated. It is shown that the ellipsometric angles of reflection from the Otto configuration can be used for parameters retrieval. The method allows parameters retrieval without additional assumptions on the dielectric constant, being the reliable self consistent retrieval procedure.

Effects of different gas flow rates and non-perpendicular incidence angles of argon cold atmospheric-pressure plasma jet on silver thin film treatment

In this study, the influences of variations in the gas flow rate and incidence angles of argon cold atmospheric-pressure plasma jet on the morphology and absorption spectra of silver thin films (60 nm, 80 nm, and 100 nm film thickness) are investigated. To evaluate the surface morphology, atomic force microscopy (AFM) was employed on the silver thin film surface before and after plasma processing. To analyze the effect of plasma treatment on the grain size, the one-dimensional AFM surface profiles of Ag thin films are approximated using a Gaussian function. The absorbance of Ag thin films is measured in wavelength range of 190–1100 nm utilizing UV–Vis absorption spectrometer. Compared to the gas flow rates 0.5 standard litter per minute (SLM) and 2 SLM, surface treatment of Ag thin film with gas flow rate of 1 SLM increased the valley depth, the peak valley height, and the distance between two deepest valleys remarkably. A sequential argon plasma treatment (2-min plasma treatment perpendicular to surface was followed by 2-min plasma processing with non-perpendicular incidence angle of 60°) offers considerable improvement in the uniformity of grains and also changes shape of grains, especially the peak height (about 44 times higher than untreated sample) and area of grains (almost 136 times greater than untreated sample) which can be applicable for optical sensing technology.

SERS-Active Substrates Nanoengineering Based on e-Beam Evaporated Self-Assembled Silver Films

Surface-enhanced Raman spectroscopy (SERS) has been intensely studied as a possible solution in the fields of analytical chemistry and biosensorics for decades. Substantial research has been devoted to engineering signal enhanced SERS-active substrates based on semi-continuous nanostructured silver and gold films, or agglomerates of micro- and nanoparticles in solution. Herein, we demonstrate the high-amplitude spectra of myoglobin precipitated out of ultra-low concentration solutions (below 10 μg/mL) using e-beam evaporated continuous self-assembled silver films. We observe up to 105 times Raman signal amplification with purposefully designed SERS-active substrates in comparison with the control samples. SERS-active substrates are obtained by electron beam evaporation of silver thin films with well controlled nanostructured surface morphology. The characteristic dimensions of the morphology elements vary in the range from several to tens of nanometers. Using optical confocal microscopy we demonstrate that proteins form a conformation on the surface of the self-assembled silver film, which results in an effective enhancement of giant Raman scattering signal. We investigate the various SERS substrates surface morphologies by means of atomic force microscopy (AFM) in combination with deep data analysis with Gwyddion software and a number of machine learning techniques. Based on these results, we identify the most significant film surface morphology patterns and evaporation recipe parameters to obtain the highest amplitude SERS spectra. Moreover, we demonstrate the possibility of automated selection of suitable morphological parameters to obtain the high-amplitude spectra. The developed AFM data auto-analysis procedures are used for smart optimization of SERS-active substrates nanoengineering processes.

HiPIMS and DC Magnetron Sputter-Coated Silver Films for High-Temperature Durable Reflectors

High-temperature durable mirrors based on a protected silver sputter coating are attractive for secondary reflector applications in concentrated solar thermal power plants. In this paper, silver films are deposited by high-power impulse magnetron sputtering (HiPIMS) and standard direct current (DC) magnetron sputtering, either as exposed discretely deposited films or in-sequence-deposited thin film systems, where the silver is protected and embedded between adhesion and barrier layers. The unprotected silver films and equivalent protected silver thin film systems are compared and characterized as deposited and after 400 °C oven temperature exposure. The reflectance is measured and grazing incident X-ray diffraction (GIXRD) and scanning electron microscopy (SEM) pictures were taken. The HiPIMS silver film, sputtered with a peak current of 200 A and an approximately equivalent average power density to the DC magnetron sputtered silver, exhibits higher reflectance (and conductivity). Increasing the power density further, yields silver films with lower reflectance, correlating to a reduced grain size. In the protected silver film system, the reflectance does not improve, due to the presence of a less reflective top adhesion layer. The protected film system, with the 200 A HiPIMS, is, however, more durable at 400 °C than the DC magnetron sputtered equivalent.

Fabrication of silver and silver-copper bimetal thin films using co-sputtering for SERS applications

The objective of this work is to tune the surface plasmon resonance (SPR) of thin silver and silver-copper bimetallic films into a strong and broad absorption in the red and near infrared regions for applications in Surface Enhanced Raman Spectroscopy. The SPR tuning was achieved by varying the composition of silver and copper in the films fabricated using magnetron co-sputtering method and also by annealing it under high vacuum condition. Atomic Force Microscope was used to study the film surface morphology and its growth with annealing temperatures. SPR exhibited by the films were directly studied using UV–Visible spectroscopy. Surface Enhanced Raman Scattering studies taken on Methylene Blue drop-casted on film surface shows a threefold increase in the enhancement factor of Ag–Cu films as compared to pure Ag sputtered films.

Dry Transfer of van der Waals Crystals to Noble Metal Surfaces To Enable Characterization of Buried Interfaces

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have been explored for many optoelectronic applications. Most of these applications require them to be on insulating substrates. However, for many fundamental property characterizations, such as mapping surface potential or conductance, insulating substrates are nonideal as they lead to charging and doping effects or impose the inhomogeneity of their charge environment on the atomically thin 2D layers. Here, we report a simple method of residue-free dry transfer of 2D TMDC crystal layers. This method is enabled via noble-metal (gold, silver) thin films and allows comprehensive nanoscale characterization of transferred TMDC crystals with multiple scanning probe microscopy techniques. In particular, intimate contact with underlying metal allows efficient tip-enhanced Raman scattering characterization, providing high spatial resolution (<20 nm) for Raman spectroscopy. Further, scanning Kelvin probe force microscopy allows high-resolution mapping of surface potential on transferred crystals, revealing their spatially varying structural and electronic properties. The layer-dependent contact potential difference is clearly observed and explained by charge transfer from contacts with Au and Ag. The demonstrated sample preparation technique can be generalized to probe many different 2D material surfaces and has broad implications in understanding of the metal contacts and buried interfaces in 2D material-based devices.

Monitoring morphological and chemical properties during silver solid-state dewetting

Solid-state dewetting phenomenon in silver thin films offers a straightforward method to obtain structures having controlled shape or size -this latter in principle spanning several orders of magnitudes- with potentially strong interest in many applications involving high-tech industry and biomedicine. In this work nanostructured and polycrystalline thin films of silver are deposited by pulsed electron ablation technique and the surface modified upon thermal treatments in air at increasing temperatures. Surface chemistry and morphology are then monitored simultaneously by X-ray photoemission spectroscopy and atomic force microscopy; in particular, the power spectral density of surface heights is used to analyze the alteration of the surface texture induced by annealing. It is found that such a combined approach adds a level of information about the surface as concerns the microscopic processes at the basis of the surface reshaping and elucidates the geometrical meaning of the wavelengths brought into play by the annealing process. Our results are presented in the framework of a multidisciplinary approach, advantages and limitations of which are explored and discussed.

Electrochemical Properties of Silver-Zinc Secondary Battery

The forthcoming green energy era strongly demands a next generation energy storage systems with much higher energy/power density, environmental friendliness, stability, etc. In relation to this, much effort has been made to explore the possible use of conventional primary battery in an electrically rechargeable form. Various alkaline batteries have been proposed as a candidate. Among this, silver-oxide battery draws a special attention because it has flat discharge voltage, high energy density (200 Wh/kg, 750 Wh/dm3) and superior rate performance. In addition, it is much safer and easier to recycle, as compared to lithium-ion batteries. A silver-oxide battery is often called a silver-zinc battery when it is designed to be electrically rechargeable. Like its primary form, it is desirable to minimize the content of expensive silver, i.e., the design needs to be cathode-limited. Accordingly, the characteristics of silver-zinc battery might be strongly affected by the behavior of silver cathode. Based on the works on the silver anodization, it has been reported that silver is transformed to Ag2O and then AgO during anodic oxidation and the latter AgO formation needs relatively large driving force. In spite of many data on the anodization process of silver, however, there has been little information about the battery performance of silver-zinc secondary battery. Moreover, as far as we know, the systematic study on its electrochemical characteristics is extremely lacking. The work provides an in-depth investigation of silver-zinc battery. In particular, the electrochemical properties and battery performance were systematically investigated at different charging/discharging rate, operating temperature, state of charge (SoC), etc. For this purpose, cathode-limited silver-zinc battery was fabricated using well-defined silver thin film and was analyzed by a variety of electrochemical techniques such as galvanostatic/potentiostatic methods, cyclic voltammetry, and impedance spectroscopy. From the combination of electrochemical, compositional, and structural analyses, the transformation of silver to Ag2O and AgO, and vice versa process was thoroughly investigated. For example, figure shows the SEM images and the corresponding XRD patterns of silver cathode at different SoCs. Porosity of products (Ag2O, AgO) gets increased with the SoC and the diffraction intensities of substrate and products are accordingly varied. In this presentation, the charging/discharging mechanism of silver-zinc battery will be systematically explored and its uniqueness will be highlighted from the viewpoint of the kinetics of electrochemical reactions. Moreover, the cycling performance and the factors governing the capacity and efficiency degradation will be discussed. Figure 1

Reversible Electrochemical Mirror Devices Using Space Compliant Ionic Liquid Electrolytes

Reversible electrochemical mirror devices function through reversible redox reactions that alternate between deposition of a highly reflective thin metallic film (hence the term mirror) and complete oxidation of the metallic film during the erasure cycle. These devices generally utilize transparent, conductive substrates such as those based on indium tin oxide type films applied to glass or plastic transparent substrates, though other substrate materials could be used in the build of these devices. REM devices may be built to either facilitate reflection and transmission or reflection and absorption of radiation sources depending on the nature of the counter electrode used. REM devices may be used for various applications including auto-dimming mirrors for the automotive industry, electrochromic windows for the aviation industry, smart glass for the architectural industry and mirrors or thermal emitters for deployment on orbital platforms. Conventional REM devices utilize electrolytes based on organic solvents such as gamma-butylrolactone and dimethyl sulfoxide. For space based applications, these electrolytes are unsuitable due to their vapor pressures and potential for evaporation if the cell seal is compromised. Room temperature ionic liquid electrolytes (RTIL) are an attractive alternative to these conventional systems due to their negligible vapor pressure in addition to their excellent chemical and thermal stability and their large electrochemical windows. RTIL base electrolytes may be tailored to deliver specific properties based on their cation and anion species, making the electrolytes tunable for specific applications. RTILs with anionic species such as chloride, bromide and iodide have been evaluated as potential alternatives to the conventional organic electrolytes for REM devices. These systems have shown promise in terms of mirror formation and long cycle life; however, they exhibit high sensitivity to water, including atmospheric moisture, which can limit their usefulness in REM devices. The present work focuses on deposition and stripping of silver thin films from RTIL with relative low moisture sensitivity. Simple, two electrode cells were built using transparent electrodes with electrically conductive films (i.e. indium tin oxide, platinum and silver) and air and moisture stable RTIL electrolytes for electrochemical characterization and plating/stripping cycling experiments. Highly reflective and reproducible silver mirror formation using air and moisture stable RTIL based electrolytes has been demonstrated. In the current work, experiments are being conducted to explore how the cell configuration and cell components influence deposition and oxidation processes as well as device cycling lifetime. Use of pulsed deposition and erasure steps have also been explored in simple REM systems containing RTIL electrolytes. Pulse and pulse reverse processes have the ability to improve the deposition process of reversible silver systems as compared to operation under constant voltage or constant current electric fields, namely the ability to enhance mass transport properties of the system as well as driving nucleation of the silver thin films over grain growth, which is anticipated to help in the stripping of the film from the substrate. Operation under pulse/pulse reverse electric fields is expected to achieve highly reflective metallic mirror films while maximizing the cycling lifetimes and preventing operational degradation of the electrolyte and cell components. This work outlines how cell configuration and device operating conditions influence deposition and erasure reactions as well as device cycle lifetime. Acknowledgement: Funding for this work is gratefully acknowledged from Air Force STTR Contract Number FA9453-17-C-0490. Platinum coated ITO electrodes were prepared by Dr. John Bryan Plumley.

Thin Film Deposition and Carbon Nanotube Synthesis

Carbon nanotubes (CNTs) are a viable product for many different markets. One specific area of promise is the use of CNTs in supercapacitors. The CNT synthesis is a two-step process with the first being the formation of a thin film layer. The thin film substrate is created by means of the Thermal Evaporation Physical Vapor Deposition (TPVD) process. After the thin film substrate is deposited, the CNTs are grown in a Chemical Vapor Deposition (CVD) growth chamber. Analysis of the thin film substrate and CNTs is performed primarily using Scanning Electron Microscopy (SEM). The results show the inclusion of ultrapure water in the CVD process contributed to the success of CNT growth. Multiple prong CNT grow is seen for CVDs trails of silver thin film layer deposited on silicon substrates. The silver nanoparticle had a large diameter with an acute contact angle. The single prong growth indicates the iron nanoparticles formed an obtuse contact angle due to the amorphic surface of alumina substrate. The focus of this project is to explore and investigate different materials and conditions for optimal CNT synthesis in the hopes of creating a uniform forest of vertically aligned carbon nanotubes.

Roughness-dependent wetting behavior of vapor-deposited metallic thin films.

We studied the wetting behavior of silver and copper thin films versus their kinetic roughening upon deposition at room temperature on glass substrates. Time-dependent height-height correlation functions were extracted from atomic force microscopy images, and they demonstrated a nonstationary growth front of the film roughness associated with a temporal evolution of the local surface slope. As a result, we tried to correlate the roughness statistical properties such as the root-mean-square (rms) roughness σ, the correlation length ξ, and the local surface slope (ρ≈σ/ξ) with the wetting behavior of the films' surfaces. The contact angle behavior was also studied by analyzing the variation of the energy of the system with water penetrating into the surface cavities, and the associated Laplace pressure induced by the local surface curvature. Hence, it was demonstrated that the wetting transition from a metastable Cassie-Baxter state to a Wenzel state as well as the penetration of a droplet into the surface crevices occur at the smaller local surface slopes for the higher surface energy material.

Retraction notice to "Investigation of plasmonic studies on morphology of deposited silver thin films having different thicknesses by soft computing methodologies—A comparativestudy" [ Physica E 63 (2014) 317–323

Retraction notice to "Investigation of plasmonic studies on morphology of deposited silver thin films having different thicknesses by soft computing methodologies—A comparativestudy" [ Physica E 63 (2014) 317–323

Stabilizing Silver Window Electrodes for Organic Photovoltaics Using a Mercaptosilane Monolayer

A single layer of the bifunctional molecule 3-mercaptopropyltrimethoxysilane is shown to be remarkably effective at improving the stability of optically thin silver film electrodes towards spontaneous morphological change and oxidation by airborne sulfur. Inclusion of this layer in the novel transparent electrode; WO3 (30 nm) / silver (13 nm) / sol-gel ZnO (27 nm), at the silver / ZnO interface improves the efficiency of organic photovoltaic devices using this electrode by 20%, such that the power conversion efficiency is very close to that achievable using a conventional indium-tin oxide glass electrode; 9.6 % ± 0.2 % vs 10.0 % ± 0.3 %, with the advantage that the silver electrode has a sheet resistance one third that of the ITO glass (4 Ohms sq-1). The mercaptosilane monolayer is also shown to retard silver diffusion into the ZnO layer whilst imparting a favorable 400 meV reduction in electrode work function. In addition to its utility inside the device, this molecular layer is shown to be useful for improving the stability of the silver film electrodes in top-illuminated semi-transparent photovoltaics, since it can be deposited directly onto a completed device from the vapor phase.

Significant texture improvement in single-crystalline-like materials on low-cost flexible metal foils through growth of silver thin films

Low texture spreads of single-crystalline-like materials are critical for high performance of low-cost flexible semiconductors and second-generation high-temperature superconductors based on metal foils. For texture improvement, a single-crystalline-like Ag film is epitaxially grown on an ion-beam-assisted deposition TiN substrate using magnetron sputtering. Ultra-low texture spreads are found in the thin Ag film (∼330 nm), with an out-of-plane texture spread (Δω) of ∼1.03° and an in-plane texture spread (Δϕ) of ∼1.34°. Compared with the texture spreads of the TiN substrate, Δω and Δϕ of the Ag film are reduced by ∼42 and ∼79%, respectively. Applying this Ag buffer, the texture spreads of a single-crystalline-like Ge film are reduced by ∼37% (Δω) and ∼36% (Δϕ). Factors contributing to the texture improvement by Ag are studied using single-crystalline-like Ag films with various thicknesses.

Effect of the Magnetic field and duration time on Thickness and Structure of Silver Thin films Deposition by Magnetron Sputtering

In this paper, the effect of magnetic field on thickness of silver (Ag) thin films were deposition on glass substrates by DC magnetron sputtering method of silver target were studied, with permanent and variable magnetic field. Ag thin films with (84,89,94,269,290) nm, thickness were prepared at different deposition times (10,30,60) sec. The crystalline structure of thin films was evaluated by X-ray diffraction (XRD) and the atomic force microscopy (AFM) were employed for surface morphological studies of the films. The results show that the thickness of the films increases with increases magnetic field to 250 Gauss, and when are greater than (250Gauss) the effect of magnetic field starts to decrease and be ineffective, and also the results indicate an increase of the grain size from (144.9 -276.7) nm and films surface roughness from (0.431-22.7) nm.

Investigation on surface morphological and optical properties of black silicon fabricated by metal-assisted chemical etching with different etchant concentrations

In this study, the surface morphological and optical properties of black silicon (b-Si) fabricated by two-step metal-assisted chemical etching (MACE) process are investigated. The two-step MACE combines low-temperature annealing of silver (Ag) thin film to produce Ag nanoparticles (NPs) and short etching duration of crystalline silicon (c-Si) wafer. The etching is carried out in HF:H2O2:DI H2O solution for 70 s with different etchant concentrations (represented in the form of volume ratio). The MACE process produces b-Si nanopores on the wafer. Compared with planar c-Si reference, broadband reflection (in 300-1100 nm wavelength region) of the b-Si is significantly lower. B-Si wafer with volume ratio of 1:5:10 exhibits the lowest broadband reflection of 3% at wavelength of 600 nm, which is believed to be due to refractive index grading which leads to enhanced light coupling into the b-Si wafer. The best b-Si wafer (with lowest reflection) shows 50 nm average pillar width and 300 nm height. The increased broadband light absorption results in the highest maximum potential short-circuit current density (Jsc(max)) of 40.9 mA/cm2. This represents 55.4% enhancement, if compared with the planar c-Si reference wafer, assuming unity carrier collection.