The Mirror Image Symmetry in the Optical Absorption/Luminescence Spectra of Silver Nanoparticles in Ag/Ag2O Composites Synthesized by Oxygen Plasma Treatment of Silver Thin Films

The aim of this paper is to compare the spectral features of the response plasmon peak in both the optical absorption and photoluminescence spectra of the Ag/Ag₂O composites synthesized by treating silver thin films manufactured by thermal evaporation method with oxygen plasma afterglow. Results show that close values of the relative area and spectral width of the plasmon response peaks in the optical absorption/photoluminescence spectra were obtained in the case of samples with high oxygen content. In addition, the intensity ratio (I_absorption/I_luminescence) of these samples decreases linearly with increasing silver oxide grain size.

     

Wide Band Gap Al and In Co-doped ZnO Films for Near-Infrared Plasmonic Application

In transparent conducting oxide films, tuning of plasmonic resonance is directly controlled by free electron concentration and thus by activated dopants. In this study, large area Al_xIn_yZn_1-x-yO thin films at various concentrations were prepared by spray coating using water as a solvent. The effect of Al/In dopant ratio on the structural, electrical, optical, and plasmonic properties was investigated. Tuning of optical response to a well-defined plasmon resonance is correlated to the above properties of Al_xIn_yZn_1-x-yO films. Theoretical fitting based on the Drude-Lorentz (D-L) theory was utilized for extracting the dielectric spectra and cross-over wavelength (ω_c). The studies revealed plasmonic properties in NIR for the films with Al/In ratios of A₅I₅, A_2.5I_7.5, and A₀I₁₀, indicating In as the most activated dopant. Surface plasmon mode simulated using the extracted permittivity values showed the influence of mobility of these films on the broadening of the dip. The minimum plasmonic loss suggests the suitability as an alternative plasmonic material in the near infrared.

     

Novel Covellite CuS Single-Crystal Thin Films for Optoelectronic Applications

Copper sulfide (CuS) thin films have been used in many applications such as solar cells, photo-thermal, electro-conductive, and microwave shielding. In this work, copper sulfide thin films were deposited on glass and silicon substrates by thermal evaporation of in situ synthesized CuS powder. XRD analysis of these films revealed a single-crystal structure, AFM measurements indicated the films have a surface roughness (14.1 nm) and agglomerates of multiple monocrystalline particles with average size (66 nm), and the optical properties were investigated by UV-Vis spectrophotometer showing the films have high transmission (>80%) in the visible region and low absorbance with wide energy gap (3.813 eV). This novel structure with outstanding optical properties makes it very promising optical materials in optoelectronics.

     

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto silicon (Si) substrates via different synthesized temperatures by using plasma enhanced chemical vapor deposition (PECVD) system. The effects of different synthesized temperatures on the crystal structure, surface morphologies and optical properties have been investigated. The X-ray diffraction (XRD) patterns indicated that the intensity of (0002) diffraction peak became stronger with increasing synthesized temperature until 400 ^oC. The diffraction intensity of (0002) peak gradually became weaker accompanying with appearance of (10-10) diffraction peak as the synthesized temperature up to excess of 400 ^oC. The RT photoluminescence (PL) spectra exhibited a strong near-band-edge (NBE) emission observed at around 375 nm and a negligible deep-level (DL) emission located at around 575 nm under high c-axis ZnO thin films. Field emission scanning electron microscopy (FE-SEM) images revealed the homogeneous surface and with small grain size distribution. The ZnO thin films have also been synthesized onto glass substrates under the same parameters for measuring the transmittance.For the purpose of ultraviolet (UV) photodetector application, the interdigitated platinum (Pt) thin film (thickness ~100 nm) fabricated via conventional optical lithography process and radio frequency (RF) magnetron sputtering. In order to reach Ohmic contact, the device was annealed in argon circumstances at 450 ^oC by rapid thermal annealing (RTA) system for 10 min. After the systematic measurements, the current-voltage (I-V) curve of photo and dark current and time-dependent photocurrent response results exhibited a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector application.     

Structural,Morphological, and Optical Properties of Nanocrystalline (Bi2O3)1−x:(TiO2)x Thin Films for Transparent Electronics

The fabrication of low cost and eco-friendly transparent electronics using metal oxide semiconductors is still a challenging task. In this work, transparent nanocrystalline (Bi₂O₃)_1−x:(TiO₂)_x thin films were synthesized using a pulsed laser deposition technique (PLD); XRD analysis shows the films have polycrystalline structure of monoclinic Bi₂O₃; morphological and topographical properties were analyzed by SEM and AFM showing the films have smooth surfaces with RMS roughness (4.26–7.37 nm) with micro-and nano-spheres (2 μm to 23 nm); the optical properties were analyzed by Uv-Vis spectrometer and revealed high transmittance in the visible range; the best results were obtained at x = 0.05 where the highest crystallinity, highest transmittance (> 82%), and highest band gap (3.769 eV) were achieved; and empirical models have been proposed to estimate the band gap and Bi–O bond lengths as a function of TiO₂ concentration with excellent coincidence with the experimental data.

     

Improved picoliter-sized micro-reactors for high-throughput biological analysis

High-throughput pyrosequencing, carried out in millions of picoliter-sized reactors on a fiber-optic slide, is known for its longer read length. However, both optical crosstalk (which reduces the signal-to-noise ratio of CCD images) and chemical retention adversely affect the accuracy of chemiluminescence determination, and ultimately decrease the read length and the accuracy of pyrosequencing results. In this study, both titanium and oxidized aluminum films were deposited on the side walls and upper faces of micro-reactor slides to enhance optical isolation; the films reduced the inter-well crosstalk by one order of magnitude. Subsequently, chemical retention was shown to be caused by the lower diffusion coefficient of the side walls of the picoliter-sized reactors because of surface roughness and random pores. Optically isolated fiber-optic slides over-coated with silicon oxide showed smoother surface morphology, resulting in little chemical retention; this was further confirmed with theoretical calculations. Picoliter-sized micro-reactors coated with titanium-silicon oxide films showed the least inter-well optical crosstalk and chemical retention; these properties are expected to greatly improve the high-throughput pyrosequencing performance.     

High Performance Infrared Plasmonic Metamaterial Absorbers and Their Applications to Thin-film Sensing

Plasmonic metamaterial absorbers (PMAs) have attracted considerable attention for developing various sensing devices. In this work, we design, fabricate and characterize PMAs of different geometrical shapes operating in mid-infrared frequencies, and explore the applications of the PMAs as sensor for thin films. The PMAs, consisting of metal-insulator-metal stacks with patterned gold nanostructured surfaces (resonators), demonstrated high absorption efficiency (87 to 98 %) of electromagnetic waves in the infrared regime. The position and efficiency of resonance absorption are dependent on the shape of the resonators. Furthermore, the resonance wavelength of PMAs was sensitive to the thin film coated on the surface of the PMAs, which was tested using aluminum oxide (Al₂O₃) as the film. With increase of the Al₂O₃ thickness, the position of resonance absorption shifted to longer wavelengths. The dependence of the resonant wavelength on thin film thickness makes PMAs a suitable candidate as a sensor for thin films. Using this sensing strategy, PMAs have potential as a new method for thin film detection and in situ monitoring of surface reactions.     

Anodization of aluminum and silicon in plasma of a non-self-sustained glow discharge

The results of anodization of aluminum and silicon in an oxygen plasma are presented. The plasma was generated by a non-self-sustained glow discharge with a hollow cathode excited by an electron beam at the oxygen pressure of 20 Pa. The density of the current flowing through the anodized specimen did not exceed 1.5 mA/cm², and its temperature was 200–250°C. Continuous Al₂O₃ and SiO₂ films were formed on the aluminum and silicon surfaces. The growth rate of the oxide layers was 150–200 nm/h for Al₂O₃ and 400–800 nm/h for SiO₂.     

Glucose sensor based on nano-baskets of tin oxide templated in porous alumina by plasma enhanced CVD

A feasibility study of glucose oxidase (GOx) immobilized tin oxide thin films, consisting of nano-baskets, for glucose sensing is presented. The nano-baskets of SnO(2) were grown on in-house fabricated anodized aluminum oxide pores of approximately 80-nm diameter using plasma enhanced chemical vapor deposition (PECVD) at an RF power of 60W. Hydrated stannic chloride was used as a precursor and O(2) (20 sccm) as a reactant gas. The deposition was carried out from 350 to 450 degrees C at a pressure of 0.2 Torr for 15 min each. Deposition at 450 degrees C resulted in crystalline film with basket-like (nano-sized) structure. GOx was immobilized by physical adsorption (soaking films in GOx solution containing 1000 units for 3h). Increase in film conductivity was noticed after GOx immobilization. The immobilized films were found sensitive to glucose (C(2)H(12)O(6), dextrose) concentration from 10 to 360 mg/dl. Sensitivity increases linearly with glucose concentration. Nano-baskets resulted in higher sensitivity in comparison with other structures. From the elemental analyses of the films after GOx immobilization, GOx was found covalently attached with tin oxide, as evident by N 1s peak in the photoelectron spectra. A possible sensing mechanism is presented and discussed.     

A theoretical investigation of single-molecule fluorescence detection on thin metallic layers

In the present paper, the excitation and detection of single-molecule fluorescence over thin metallic films is studied theoretically within the framework of classical electrodynamics. The model takes into account the specific conditions of surface plasmon-assisted optical excitation, fluorescence quenching by the metal film, and detection geometry. Extensive numerical results are presented for gold, silver, and aluminum films, showing the detectable fluorescence intensities and their dependence on film thickness and the fluorescent molecule's position under optimal excitation conditions.     

Dielectric Dispersion in Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> Thin Films

In this work, the structural, compositional, optical, and dielectric properties of Ga₂S₃ thin films are investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, and ultraviolet—visible light spectrophotometry. The Ga₂S₃ thin films which exhibited amorphous nature in its as grown form are observed to be generally composed of 40.7 % Ga and 59.3 % S atomic content. The direct allowed transitions optical energy bandgap is found to be 2.96 eV. On the other hand, the modeling of the dielectric spectra in the frequency range of 270–1,000 THz, using the modified Drude-Lorentz model for electron-plasmon interactions revealed the electrons scattering time as 1.8 (fs), the electron bounded plasma frequency as ~0.76–0.94 (GHz) and the reduced resonant frequency as 2.20–4.60 ×10¹⁵ (Hz) in the range of 270–753 THz. The corresponding drift mobility of electrons to the terahertz oscillating incident electric field is found to be 7.91 (cm ²/Vs). The values are promising as they nominate the Ga₂S₃ thin films as effective candidates in thin-film transistor and gas sensing technologies.     

Optical Absorption in Overcoats of Nanoparticle Arrays on a Metallic Substrate

Surface plasma oscillations in metallic particles as well as in thin metallic films have been studied extensively in the past decades. New features regarding surface plasma excitations are, however, constantly discovered, leading, for example, to surface-enhanced Raman scattering studies and enhanced optical transmission though metal films with nanohole arrays. In the present work, the role of a metallic substrate is examined in two cases, one involving an overcoat of dielectric nanoparticles and the other an overcoat of metallic nanoparticles. Theoretical results are obtained by modeling the nanoparticles as forming a two-dimensional, hexagonal lattice of spheres. The scattered electromagnetic field is then calculated using a variant of the Green function method. Comparison with experimental results is made for nanoparticles of tungsten oxide and tin oxide deposited on either gold or silver substrates, giving qualitative agreement on the extra absorption observed when the dielectric nanoparticles are added to the metallic surfaces. Such absorption would be attributed to the mirror image effects between the particles and the substrate. On the other hand, calculations of the optical properties of silver or gold nanoparticle arrays on a gold or a silver substrate demonstrate very interesting features in the spectral region from 400 to 1,000 nm. Interactions between the nanoparticle arrays surface plasmons and their images in the metallic substrate would be responsible for the red shift observed in the absorption resonance. Moreover, effects of particle size and ambient index of refraction are studied, showing a great potential for applications in biosensing with structures consisting of metallic nanoparticle arrays on metallic substrates.     

Study on the Effect of Poly(Styrene 4-Sulfonic Acid-co-Maleic Acid) Toward Metallization and Plasmonic Tuning of Silver Nanoparticle Thin Films

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces.

     

Mechanical,Optical, Thermal,and Barrier Properties of Poly (Lactic Acid)/Curcumin Composite Films Prepared Using Twin-Screw Extruder

In this present work, we synthesized poly (lactic acid) (PLA)/curcumin composite films using a twin-screw extruder and evaluated their mechanical, optical, thermal, and barrier properties. The composite films were characterized using Fourier transform infrared spectroscopy (FTIR), Universal testing machine (UTM), thermogravimetric analysis (TGA), ultraviolet-visible spectrometry (UV-visible), colorimetry, goniometry, and oxygen permeation analysis. The results confirmed that, the composite films exhibited better ultraviolet radiation-blocking properties and hydrophobicities than did the reference PLA film. The oxygen and water vapor permeabilities of the composite films were also lower than those of the reference PLA film.

     

Effects of Extraction Parameters on Particle Size of Titanium Dioxide Nanopowders Prepared by Physical Vapor Deposition Technique

In this work, the effects of different extraction parameters on the particle size of the nanopowders extracted from titanium dioxide thin film samples were studied. These nanopowders were obtained by the conjunctional freezing-assisted ultrasonic extraction method. Titanium dioxide thin films were different in their structures (anatase-only, rutile-only, and mixed phase), and their structural characteristics were determined. Results showed that extraction parameters such as freezing temperature, ultrasonic frequency, and application time are very effective in determining the nanoparticle size, which is very important for many applications and uses of highly pure nanomaterials and nanostructures.

     

Tuning Plasmonic Properties of Truncated Gold Nanospheres by Coating

The influence of TiO₂ coating on resonant properties of gold nanoisland films deposited on silica substrates was studied numerically and in experiments. The model describing plasmonic properties of a metal truncated nanosphere placed on a substrate and covered by a thin dielectric layer has been developed. The model allows calculating a particle polarizability spectrum and, respectively, its surface plasmon resonance (SPR) wavelength for any given cover thickness, particle radius and truncation parameter, and dielectric functions of the particle, the substrate, the coating layer, and the surrounding medium. Dependence of the SPR position calculated for truncated gold nanospheres has coincided with the measured one for the gold nanoisland films covered with titania of different thicknesses. In the experiments, gold films with thickness of 5 nm were deposited on a silica glass substrate, annealed at 500 °C to form nanoislands of 20 nm in diameter, and covered with amorphous titania layers using atomic layer deposition technique. The resulting structures were characterized with scanning electron microscopy and optical absorption spectroscopy. The measured dependence of the SPR position on titania film thickness corresponded to the one calculated for truncated sphere-shaped nanoparticles with the truncation angle of ~50°. We demonstrated the possibility of tuning the SPR position within ~100 nm range by depositing to 30 nm thick titania layer.

     

Plasmonic, Low-Frequency Raman, and Nonlinear Optical-Limiting Studies in Copper–Silica Nanocomposites

Nanocomposite thin films consisting of Cu nanoparticles embedded in silica matrix were synthesized by atom beam co-sputtering technique. Plasmonic, optical, and structural properties of the nanocomposite films were investigated by using ultraviolet (UV)–visible absorption spectroscopy, nonlinear optical transmission, X-ray diffraction (XRD), and low-frequency Raman scattering. UV–visible absorption studies revealed the surface plasmon resonance absorption at 564 nm which showed a red shift with increase in Cu fraction. XRD results together with surface plasmon resonance absorption confirmed the presence of Cu nanoparticles of different size. Low-frequency Raman studies of nanocomposite films revealed breathing modes in Cu nanoparticles. Nanocomposites with lower metal fractions were found to behave like optical limiters. The possibility of controllably tuning the optical nonlinearity of these nanocomposites could enable them to be the potential candidates for applications in nanophotonics.     

Strontium Diffusion in Magnetron Sputtered Gadolinia‐Doped Ceria Thin Film Barrier Coatings for Solid Oxide Fuel Cells

Strontium (Sr) diffusion in magnetron sputtered gadolinia‐doped ceria (CGO) thin films is investigated. For this purpose, a model system consisting of a screen printed (La,Sr)(Co,Fe)O_3?δ (LSCF) layer, and thin films of CGO and yttria‐stabilized zirconia (YSZ) is prepared to simulate a solid oxide fuel cell. This setup allows observation of Sr diffusion by observing SrZrO₃ formation using X‐ray diffraction while annealing. Subsequent electron microscopy confirms the results. This approach presents a simple method for assessing the quality of CGO barriers without the need for a complete fuel cell test setup. CGO films with thicknesses ranging from 250 nm to 1.2 μm are tested at temperatures from 850 °C to 1000 °C which yields an in‐depth understanding of Sr diffusion through CGO thin films that may be of high scientific and technical interest for implementation of novel fuel cell materials. Sr is found to diffuse along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier can be increased.     

Plasmonic and Nonlinear Optical Absorption Properties of Ag:ZrO2 Nanocomposite Thin Films

Ag nanoparticles (NPs) embedded in a zirconium oxide matrix in the form of Ag:ZrO₂ nanocomposite (NC) thin films were synthesized by using the sol–gel technique followed by thermal annealing. With the varying of the concentration of Ag precursor and annealing conditions, average sizes (diameters) of Ag nanoparticles (NPs) in the nanocomposite film have been varied from 7 to 20 nm. UV–VIS absorption studies reveal the surface plasmon resonance (SPR)-induced absorption in the visible region, and the SPR peak intensity increases with the increasing of the Ag precursor as well as with the annealing duration. A red shift in SPR peak position with the increase in the Ag precursor concentration confirms the growth of Ag NPs. Surface topographies of these NC films showed that deposited films are dense, uniform, and intact during the variation in annealing conditions. The magnitude and sign of absorptive nonlinearities were measured near the SPR of the Ag NPs with an open-aperture z-scan technique using a nanosecond-pulsed laser. Saturable optical absorption in NC films was identified having saturation intensities in the order of 10¹² W/m². Such values of saturation intensities with the possibility of size-dependent tuning could enable these NC films to be used in nanophotonic applications.