Silver Thin Films Research Articles

Tamm-plasmon resonance based temperature sensor in a Ta2O5/SiO2 based distributed Bragg reflector

We demonstrate a Tamm-plasmon-polariton (TPP) based sensor for accurate determination of temperature. The sensing architecture is comprised of thin silver (Ag) film on a distributed-Bragg-reflector (DBR) structure made of periodically stratified multilayers of Ta2O5 and SiO2. TPP mode is excited using direct incidence of white-light-source at normal incidence as well as oblique incidence. The mode excitation is characterized by a sharp reflectivity minimum within the photonic bandgap (PBG) of DBR. It was observed that the depth of TPP resonance reduces uniformly as a function of temperature without affecting its sharpness. Defining temperature sensitivity in terms of change in reflectivity from the composite structure, a sensitivity of 7.8×10−4/°C is estimated for the sensing geometry. Also, the metallo-dielectric geometry supporting TPP modes is modeled using transfer-matrix-method for ascertaining the salient features of TPP modes which have a direct impact on sensing properties.

Effects of high temperature and film thicknesses on the texture evolution in Ag thin films

In situ high-temperature X-ray diffraction techniques were used to study the effect of high temperatures (up to $ 600 {}^{\circ}{\rm C}$ on the texture evolution in silver thin films. Ag thin films with different thicknesses of 40, 80, 120 and 160nm were sputtered on the Si(100) substrates at room temperature. Then, microstructure of thin films was determined using X-ray diffraction. To investigate the influence of temperature on the texture development in the Ag thin films with different thicknesses, (111), (200) and (220) pole figures were evaluated and orientation distribution functions were calculated. Minimizing the total energy of the system which is affected by competition between surface and elastic strain energy was a key factor in the as-deposited and post annealed thin films. Since sputtering depositions was performed at room temperature and at the same thermodynamic conditions, the competition growth caused the formation of the $ \{122\} \langle uvw \rangle$ weak fiber texture in as-deposited Ag thin films. It was significantly observed that the post annealed Ag thin films showed $ \{111\} \langle uvw \rangle$ orientations as their preferred orientations, but their preferred fiber texture varied with the thickness of thin films. Increasing thin film thickness from 40nm to 160nm led to decreasing the intensity of the $ \{111\} \langle uvw \rangle$ fiber texture.

IRRADIATION AND SILVER DEPOSITION FOR IMPROVEMENT OF NASOPHARYNGEAL AIRWAY MEDICAL DEVICE PROPERTIES

The thermal and mechanical properties of nasopharyngeal airway (NPA) samples are improved by irradiation using 4[Formula: see text]keV oxygen and nitrogen ion beams with different ion fluences varying from [Formula: see text] ions/cm2to [Formula: see text] ions/cm2. The thermal stability of NPA medical device increases with increasing nitrogen and oxygen ion fluences. The tensile strength increased from 48[Formula: see text]MPa for unirradiated sample to 74[Formula: see text]MPa for samples irradiated with nitrogen and to 58[Formula: see text]MPa for samples irradiated with oxygen ion, while the elongation at break decreases for irradiated samples. Silver thin films are deposited on NPA medical device samples using 4[Formula: see text]keV argon ion beam. The XRD spectra demonstrated that silver nanoparticles are deposited on NPA medical device substrate. The effects of Ag thin film on gram-positive and gram-negative bacteria are studied.

Spatial Confinement of Light onto a Flat Metallic Surface Using Hybridization between Two Cavities

Controlling the optical field down to the nanometer scale is a key step in optoelectronic applications and light–matter interaction at the nanoscale. Bowtie structures, rods, and sharp tapers are commonly used to realize such optical properties, but their fabrication is challenging. In this context, the complementary structures, namely, holes and cavities, are less explored. Herein, a simple system of two metallic nanocavities milled in thin silver film is used to confine the electromagnetic field to an area of ≈60 nm2. The field is confined onto a flat surface area and is either enhanced or suppressed by the polarization state of incident light. The energy of this spatially confined mode is determined by the distance between the two cavities and thus any color (wavelength) at the optical regime can be achieved. As a consequence, a dynamically controlled color is generated on an optical pixel size smaller than 1 µm2. Those results are supported by both transmission spectra and a cathodoluminescence study.

A novel U-bent plastic optical fibre local surface plasmon resonance sensor based on a graphene and silver nanoparticle hybrid structure

In this work, we have presented a novel local surface plasmon resonance (LSPR) sensor based on the U-bent plastic optical fibre (U-POF). Firstly, a layer of discontinuous silver (Ag) thin film was deposited on the U-POF and then the Ag film was covered by a layer of cladding synthesized by polyvinyl alcohol (PVA), graphene and silver nanoparticles forming the PVA/G/AgNPs@Ag film. The normalized transmittance spectrum of the LSPR sensor have been collected in a range of the refractive index (RI) from 1.330 to 1.3657 in ethanol solution, and 700.3 nm/RIU sensitivity of the developed LSPR sensor has been demonstrated. By experiments, we demonstrated that the graphene could improve the sensitivity of the LSPR sensor and delay the oxidation process of the AgNPs effectively to keep the stability of the LSPR sensor. The LSPR sensor also exhibited good sensitivity and linearity in the detection of glucose solutions. This work shows that the developed LSPR sensor may have promising applications in biosensing.

Metal oxide surfaces for enhanced colorimetric response in bioassays

Physical stability of metal nanoparticle films on planar surfaces can be increased by employing surface modification techniques and/or type of metal nanoparticles. Subsequently, the enzymatic response of colorimetric bioassays can be increased for improved dynamic range for the detection of biomolecules. Using a model bioassay b-BSA, three planar platforms (1) poly (methyl methacrylate) (PMMA) with silver thin films (STFs), (2) silver nanowires (Ag NWs) on paper and (3) indium tin oxide (ITO) on polyethylene terephthalate (PET) were evaluated to investigate the extent of increase in the colorimetric signal. Bioassays for b-BSA and Ki-67 antigen (a real-life bioassay) in buffer were performed using microwave heating (total assay time is 25–30min) and at room temperature (a control experiment, total assay time is 3h). Model bioassays showed that STFs were removed from the surface during washing steps and the extent of ITO remained unchanged. The lowest level of detection (LLOD) for b-BSA bioassays were: 10−10M for 10nm STFs on PMMA and Ag NWs on paper and 10−11M for ITO. Bioassays for Ki-67 antigen yielded a LLOD of <10−9M on ITO platforms, while STFs platforms were deemed unusable due to significant loss of STFs from the surfaces.

High quality transparent conductive Ag-based barium stannate multilayer flexible thin films

Transparent conductive multilayer thin films of silver (Ag)-embedded barium stannate (BaSnO3) structures have been deposited onto flexible polycarbonate substrates by magnetron sputtering at room temperature to develop an indium free transparent flexible electrode. The effect of thicknesses of Ag mid-layer and barium stannate layers on optical and electrical properties were investigated, and the mechanisms of conduction and transmittance were discussed. The highest value of figure of merit is 25.5 × 10−3 Ω−1 for the BaSnO3/Ag/BaSnO3 multilayer flexible thin films with 9 nm thick silver mid-layer and 50 nm thick barium stannate layers, while the average optical transmittance in the visible range from 380 to 780 nm is above 87%, the resistivity is 9.66 × 10−5 Ω · cm, and the sheet resistance is 9.89 Ω/sq. The change rate of resistivity is under 10% after repeated bending of the multilayer flexible thin films. These results indicate that Ag-based barium stannate multilayer flexible thin films can be used as transparent flexible electrodes in various flexible optoelectronic devices.

Microstructure and ellipsometric modelling of the optical properties of very thin silver films for application in plasmonics

Excitation of surface plasmons in silver nanoparticles is a promising method for enhancing light trapping. The present paper reports results for the optical properties of the nanocrystalline silver thin films in attempt to understand the effects of the particle size. The microstructure of the films was probed by scanning electron-microscopy, Atomic Force microscopy (AFM) and X-ray diffraction (XRD). The size of the crystallites/grains calculated from the XRD measurements by the Debye-Scherrer formula is in a good agreement with the AFM results. The optical properties were determined from spectral ellipsometric measurements. It was shown that the Drude-Lorentz model is suitable for characterization of porous films, while an island structure required the extended Drude model with frequency dependent damping parameter, Γ. It was demonstrated that the maximum of the imaginary part of the complex permittivity,ε^ω=ε′ω+iε′′ω, that is due to the transverse oscillations of the polarization of the silver grains, can be positioned in the energy range of 1.5–2.8eV in dependence of the deposition rate; it's been shifted to higher energies when reducing the grains size. Contemporary, the resulting changes in the surface/volume ratio lead to shifts the maximum in the loss function Im−1ε^ω from 3.8 to 3.5eV.

Room-Temperature Curing and Grain Growth at High Humidity in Conductive Adhesives with Ultra-Low Silver Content

Isotropic conductive adhesives (ICAs) are alternatives to metallic solders as interconnects in solar modules and electronic devices, but normally require silver contents >25 vol.% and elevated curing temperatures to achieve reasonable conductivity. In this work, ICAs are prepared with a silver content of 1.0 vol.% by using polymer spheres coated with nanograined silver thin films as filler particles. In contrast to conventional ICAs, there are no organic lubricants on the silver surfaces to obstruct the formation of metallic contacts, and conductivity is achieved even when the adhesive is cured at room temperature. When exposed to long-term storage at 85°C and 85% relative humidity, the silver films undergo significant grain growth, evidenced by field-emission scanning electron microscopy observation of ion-milled cross-sections and x-ray diffraction. This has a positive effect on the electrical conductivity of the ICA through the widening of metallic contacts and decreased scattering of electrons at grain boundaries, and is explained by an electrochemical Ostwald ripening process. The effects of decoupling heat and humidity is investigated by storage at either 85°C or immersion in water. It is shown that the level of grain growth during the various post-curing treatments is dependent on the initial curing temperature.

Enhanced intrinsic fluorescence from carboxidized nano-sculptured thin films of silver and their application for label free dual detection of glycated hemoglobin.

Enhanced intrinsic fluorescence (~x103) from novel carboxidized nanosculptured thin films (CO-nSTFs) of silver is reported. The sources of intrinsic fluorescence, confirmed by X-ray photoelectron spectroscopy, are Ag2O grains and residual carbon formed on the outer layer of silver nSTFs when exposed to air, while the localized surface plasmons on silver nSTFs enhance this intrinsic fluorescence. The CO-nSTFs are optimized with respect to porosity for the maximum enhancement. A sensor developed by using the self-assembled monolayer technique on optimized CO-nSTF is used for the label free detection of glycated hemoglobin, performed by simultaneously using fluorescence imaging and spectroscopy. The specificity of the sensor is established from control experiments on hemoglobin. These novel nanorod like intrinsically fluorescent CO-nSTFs pose huge potential in label free biosensing, light sources, imaging and many more applications.

Controlling the optical parameters of self-assembled silver films with wetting layers and annealing

We investigated the influence of presence of Ni and Ge wetting layers as well as annealing on the permittivity of Ag films with thicknesses of 20, 35 and 65nm. Most of the research on thin silver films deals with very small (<20nm) or relatively large (≥50nm) thicknesses. We studied the transition region (around 30nm) from charge percolation pathways to fully continuous films and compared the values of optical parameters among silver layers with at least one fixed attribute (thickness, wetting and capping material, post-process annealing). Our study, based on atomic force microscopy, ellipsometric and X-ray photoelectron spectroscopy measurements, shows that utilizing a wetting layer is comparable to increasing the thickness of the silver film. Both operations decrease the roughness-to-thickness ratio, thus decreasing the scattering losses and both narrow the Lorentz-shaped interband transition peak. However, while increasing silver thickness increases absorption on the free carriers, the use of wetting layers influences the self-assembled internal structure of silver films in such a way, that the free carrier absorption decreases. Wetting layers also introduce additional contributions from effects like segregation or diffusion, which evolve in time and due to annealing.

FABRICATION OF PERIODIC ARRAYS OF MICROHOLES IN THIN Ag-FILMS BY FEMTOSECOND LASER PULSES

Arrays of microholes with different diameters of micro-holes 2, 3, 4 μm and period 6 μm were produced in thin silver films with thicknesses 30, 50, 100, 150 nm by single femtosecond laser pulses with variable pulse energies, focused by different strong focusing optics. The microarray format is used for surface plasmon resonance (SPR) imaging, surface-enhanced IR adsorption (SEIRA) and its potential for applications in multiplex sensing.

Cu and Ag Nanoparticles Films Deposited on Glass Substrate Using Cold Cathode Ion Source

Structural, electrical and optical properties of Cu and Ag nanoparticles thin films deposited on glass substrates prepared by sputtering were investigated. Cold cathode ion source used for sputtered of copper and silver targets to deposit nanoparticles thin films on glass substrate using argon gas. X-ray diffraction was used to study the structure and the grain size of thin film which reveals that average grain size is in nano region. Copper nanoparticles was in rang 14 nm and silver nanoparticles size was 20 nm in first peak using Scherrer’s method. The electrical resistivities of copper and silver thin films were also investigated. The thin film resistance Rs of Cu and Ag equals 1.33 and 6.35 Ω respectively. I-V characteristics of thin films were recorded at room temperature and are found to be linear. Optical properties of the synthesized materials are studied by UV–Vis in the wavelength range 200–800 nm. The calculated band gap for the Cu thin film on glass are estimated to be EgCu = 2.18 eV.

Fabrication of 25 μm-filter microfluidic chip on silicon substrate**Invited talk at 8th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2016), 8-12 November 2016, Ha Long City, Vietnam.

This paper presents the entire fabrication process including photolithography, sputtering, deep reactive ion etching (Bosch DRIE process) on silicon substrate and bonding process between the lid and silicon substrate to create a designed filtration microfluidic chip with dimension of 28 mm × 7 mm, one inlet port and one outlet port. A pattered silver thin film was deposited on a silicon sample by the lift-off method. Subsequently the newly fabricated sample was anisotropically etched by Bosch DRIE process. Some parameters of Bosch DRIE process such as bias power, duration of etching step and passivation step, oxygen presence were studied to explore the dependence of silicon channel depth and etched shape profile on these parameters. An optimized process was utilized to fabricate a featured silicon channel with vertical, smooth sidewalls and an overall good uniformity. The silicon channel has four arrays of microposts with various distances between microposts from 25 μm to 100 μm. The depth of the silicon channel was about 150 μm. After that, silicon substrate was bonded with mica lid by adhesive bonding method to form the completed filtration microfluidic chip. The samples were characterized by scanning electron microscopy (SEM), mechanical profilometer (DEKTAK 6 M), optical microscopy (Olympus MX51). In this paper a test was performed to demonstrate how the microfluidic chip works by pumping solution with many various sizes of particles through the inlet port of the microfluidic chip and obtaining a solution with desired particles sizes (smaller than 25 μm) through another port. Moreover, the chip could be pumped de-ionized water through outlet port for backwash in order to make this microfluidic chip reusable. Finally, a few applications of microfluidic chips are presented to illustrate the advantages of this technology and the potential for future development.

Microscopic surface plasmon enhanced raman spectral imaging

A tightly focused radially polarized beam is employed to excite surface plasmon polaritons (SPPs) on a thin silver film, to form a sharp and strong plasmonic virtual probe at the center. The virtual probe provides a highly enhanced localized electric field with smaller full width at half maximum (~185nm), demonstrating great potential for Raman spectral detection and high spatial-resolution imaging. Here, an enhanced Raman signal of single-layer graphene is achieved, and its Raman intensity distributions at 2D Raman shifts are obtained by scanning the plasmonic virtual probe, which agrees well with the bright-field image. The system provides a stable Raman detection and imaging technique that can be widely used in fields of Raman spectral analysis.

Ultrathin plasmonic quarter waveplate using broken rectangular annular metasurface

We propose an ultrathin plasmonic metasurface-enabled quarter waveplate using a subwavelength broken rectangular annulus (BRA) arrays. The BRA structure is formed by two pairs of slits with perpendicular orientation embedded in a silver thin film. The elimination of the overlapping parts at four corners of a regular rectangular annulus increases significantly the phase anisotropy induced by localized surface plasmons, and thus decreases significantly the thickness of the metal film in order to achieve the required phase difference for a designed waveplate. Simulations show that an ultrathin quarter waveplate can be obtained with a as thin as 10nm thickness of a silver BRA arrays at wavelength band of 1.55µm which provides great potential in advancing manufacture of nanophotonic devices.

Tensile and fatigue behavior of polymer supported silver thin films at elevated temperatures

Tensile and fatigue tests were conducted at 50 and 70°C for evaluating the mechanical behavior of polyethylene-terephthalate (PET) supported silver (Ag) thin films. The strain amplitude-number of cycles (S-N) curves of Ag/PET at elevated temperatures were acquired for determining the failure life under in-situ heating condition. The stretchability at elevated temperature was found to be better than the tensile behavior at room temperature, whereas the fatigue behavior is worse at elevated temperature. The adhesion between silver and PET is better at elevated temperature. However, the tensile and fatigue characteristics were different results because the adhesion of silver and PET is not homogeneous at elevated temperatures. The good adhesion between thin metal films and flexible substrates is not always beneficial effect of the mechanical behavior. Therefore, we suggest a new fatigue failure mechanism for Ag/PET at elevated temperature.

Emission waveguiding in organic thin films supported by metal.

On silver thin film, an organic semiconductor rubrene layer consisting of a planar waveguide exhibits spectrally narrowing photoluminescence (PL) spectra with an increasing emission angle, which are compared with those of rubrene thin films on glass. The PL spectra of rubrene on Ag have a polarization characteristic. In the side direction of the multilayer structure, spectrally very sharp PL was observed. The PL characteristics are discussed from the viewpoint of waveguided modes allowed only for a phase-matching condition. The narrowed PL spectra are attributable to generation of a leaked waveguided mode in the rubrene layer, which is supported by the underlying Ag thin film.

Evolution of thin silver films under exposure to laser pulses in the air

The process of formation and the characteristics of silver nanostructures created by pulsed laser annealing in the air are studied. Nanoparticles were obtained by way of irradiating thin silver films (62 and 175 nm) on the dielectric (glass) base with an excimer laser emission (λ = 193 nm). Created nanostructures were studied using the methods of scanning electron microscopy and optical spectrometry, the dependencies of the mean size of obtained nanoparticles and the position of their plasmonic resonance on the number of laser pulses (ranging from 270 to 30,000) were drawn out. Based on the shift of the plasmonic resonance, the use of given nanostructures as optical components with narrow-band extinction (for example, notch filter), the magnitude and center frequency of which can be specified in advance, is suggested.

Investigation of thermal transport in polymer composites with percolating networks of silver thin films by the flash diffusivity method

The flash diffusivity method, also known as laser flash analysis (LFA), is commonly used to obtain the thermal diffusivity (α) and thermal conductivity (κ) of materials, due to its relative simplicity, rapid measurements, small sample size requirement, and standardized commercially available instruments. In this work, an epoxy adhesive was filled with a large fraction of homogeneous micron-sized polymethylmethacrylate spheres coated with thin silver films, such that a percolating metallic network that dominated the electric and thermal transport formed through the polymer at &amp;lt;3 vol. % silver. Specific heat capacity (Cp) was measured from the LFA measurements by a comparative method and from the total and reversible heat flow signals of modulated differential scanning calorimetry (MDSC). κ was estimated as the product of α, Cp, and density (ρ) and was found to vary significantly with the method to find Cp. The electron contribution was found from the electrical conductivity by the Wiedemann–Franz law and was used to elucidate the thermal transport mechanisms in the composite. A theoretical background for the various methods is included.