Nanoscale Gold Film Research Articles

THE INFLUENCE OF THE STRUCTURAL PARAMETERS OF THE MATERIALS OF THE SENSITIVE ELEMENT OF THE OPTICAL SENSOR ON ITS SENSORY PROPERTIES

The sensor element of an optical sensor based on surface plasmon resonance is investigated in the paper. In particular, the influence of the components of the sensor element on its sensor properties by modeling design options. The Kretschmann configuration was chosen as the model, which is a glass prism with a multilayer nanoscale structure applied to one face. It was established that the material of the prism affects only the resonance angle of the structure. The thickness of nanoscale gold and silver films varied from 1 to 100 nm. The minimum value of the coefficient was obtained when the thickness of the gold and silver nanoscale films was 50 nm and 45 nm, respectively. The thickness of the silicon dioxide film varied from 10 to 150 nm. In the Au – SiO2 structure, the addition of silicon dioxide improved the optical properties of the multilayer structure. The minimum value of the reflection coefficient has decreased, but the thickness of the silicon dioxide is 3 nm. When the thickness of the dielectric layer increases, the optical properties of the structure deteriorate. The structure of the sensitive element, which uses a nanosized silver film, almost does not change its optical properties when adding a layer of SiO2, its thickness can reach 50 nm.

Comparative study of lab-on-fiber vector magnetic field sensor based on multimode and few-mode fiber

A kind of reflective vector magnetic field sensor with wedge-shaped fiber tip based on surface plasmon resonance (SPR) and magnetic fluid (MF) has been fabricated and investigated. Multimode fiber (MMF) and few-mode fiber (FMF) were grinded and polished to get the wedge-shaped fiber tip, which was then plated with nanoscale gold film for exciting SPR. The as-fabricated tip was immersed in MF, which was used as the magnetic field sensitive material. Experimental results show that the magnetic field intensity and direction sensitivities of the magnetic field sensors based on MMF and FMF are 2317 pm/mT, 497 pm/° and 6776 pm/mT, 2313 pm/° respectively, which proves that the proposed sensor based on wedge-shaped fiber tip has great potential for realizing lab-on-fiber devices and applications.

Highly sensitive PCF based plasmonic biosensor for hemoglobin concentration detection

The present study reports on the investigation carried out on a newly designed photonic crystal fiber (PCF) based plasmonic biosensor for label-free hemoglobin concentration detection. In the first part, a new approach is proposed to avail external sensing mechanism by introducing the solid core at fiber periphery and nanoscale gold film coating outside the fiber. By analyzing modal characteristics using finite element method (FEM), the wavelength sensitivity is found to be varied nonlinearly up to 34,800 nm/RIU within the analyte detection range of 1.34 − 1.41 RIU (refractive index unit). In later study, the proposed fiber is investigated as hemoglobin concentration sensor (HbCS) to detect unknown hemoglobin concentration. From the detail study, to calculate sensitivity of HbCS, a nonlinear equation as a function of hemoglobin concentration has been proposed to detect unknown concentration and a maximum sensitivity of 31.2 nm/g/dL is achieved. Moreover, the minimum measurable deviation of the sensor is found to be lies of the order of 10−6 with a high figure of merit (FOM) up to 229 RIU−1 representing an overall good sensing performance. The proposed plasmonic sensor provides high sensitivity, good specificity, environmental stability along with high resolution compare to other existing technologies. Therefore, this study opens an easy and reliable window for hemoglobin concentration detection in biomedical applications.

Neural network method for solving nonlocal two-temperature nanoscale heat conduction in gold films exposed to ultrashort-pulsed lasers

Recently, we have presented an artificial neural network (ANN) method for solving the parabolic two-temperature heat conduction equations (PTTM) in double-layered thin films exposed to ultrashort-pulsed lasers. In this article, we extend this study and develop an ANN method for the nonlocal (or weakly nonlocal) two-temperature model (NTTM), which takes into account both time and space nonlocal effects when the relaxation time becomes more effective such as in low temperature and when the characteristic length scale becomes comparable with the mean free path of heat carriers such as in nano systems under femtosecond laser irradiation where the PTTM may not be suitable. We analyze the well-posedness of the NTTM and the convergence of the ANN solution to the analytical solution. The ANN method is finally used to predict the electron and lattice temperatures in nanoscale gold films when exposed to ultrashort-pulsed lasers. As compared with the experimental data, the NTTM-based ANN method gives more accurate solutions than the PTTM-based ANN method.

Investigating the effects of metallic submicron and nanofilms on fiber-reinforced composites for lightning strike protection and EMI shielding

Lightning strike protection (LSP) and electromagnetic interference (EMI) shielding topics have been extensively investigated, since composite material was first introduced to an aircraft a few decades ago. Generally, electrically and thermally conductive materials, such as metallic foils, metal mesh, ply-integrated interwoven wires, a continuous conductive path of low-resistance materials, and highly conductive nanoparticles and nanoflakes are used to dissipate the high-density current, shockwaves, electromagnetic forces/charges, and heat generated during lightning strikes. This study deals with the fabrication of pre-impregnated (prepreg) composite structures of carbon and glass fibers incorporated with submicron and nanoscale gold (Ag), silver (Au), aluminum (Al), and copper (Cu) films on top of composite surfaces during the curing process, and determining the effectiveness of LSP and EMI shielding. Initially, electrical conductivity experiments were conducted on composite test coupons and the electrical properties investigated under tensile loadings within the elastic regions of the composites. Test results indicated that the surface resistivity did not change much under the tensile loads. EMI shielding tests confirmed that noise was not audible on an AM radio because of the metallic submicron and nanoscale film surfaces on the composites. During lightning strike tests, a high current of 200-k amps was applied on the surface of the composite structures. The LSP test indicated that after the lightning strike, the resulting damage on both sides of the fiber composite was considerably low due to the metallic films co-cured on the fiber-reinforced composites. An increase in current with the metallic films certainly helped to reduce damage to the composites and avionics systems after lightning strike tests.

Analysis of a highly sensitive side polished hollow fiber plasmonic sensor and its application as a magnetometer.

A highly sensitive hollow fiber (HF) sensor based on surface plasmon resonance is proposed and analyzed numerically. The sensor design involves a side polished HF with a nanoscale gold film deposited over the polished surface and an analyte filled core. The hollow portion of the fiber serves simultaneously as an analyte channel and core, when filled with high refractive index liquid. By analyzing the modal characteristics of the sensor using the finite element method, it is found that the wavelength sensitivity of the HF sensor varies from 25,642 nm/RIU (refractive index unit) to 60,000 nm/RIU in the range 1.45 to 1.47 RIU along with highest amplitude sensitivity of ${4231.7}\,\,{{\rm RIU}^{-1}}$4231.7RIU-1. The minimum measurable alteration by the sensor lies in the order of ${{10}^{-6}}\,\,{\rm RIU}$10-6RIU. The sensor also exhibits a high value of figure of merit (FOM) up to ${976}\,\,{{\rm RIU}^{-1}}$976RIU-1 representing a very good overall performance. Moreover, due to the feasibility of design, the specific application of the sensor to magnetic field sensing is also demonstrated and achieved maximum sensitivity of 1361 pm/Oe.

Electrochemical Plasmonic Fiber-optic Sensors for Ultra-Sensitive Heavy Metal Detection

Real-time and high-sensitivity monitoring of heavy metal ions in solution is of great significance in environmental monitoring. The traditional electrochemical methods suffer from electrochemical noise and environmental interferences for heavy metal trace detection. To address these issues, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor. The sensor comprises a tilted fiber Bragg grating imprinted in a commercial single-mode fiber and coated with a nanoscale gold film for high-efficiency SPR excitation. The gold-coated optical fiber serves as a working electrode, performing the dual functions of anodic stripping voltammetry and SPR optical sensing. We demonstrate detection of Pb2+ as an example of a typical heavy metal ion. We show a stable and reproducible correlation between the real-time ion deposition–stripping cycles and the optical transmission of the optical fiber, with a limit of detection of 10−10 M and a dynamic range of nearly five orders of magnitude. Moreover, by taking derivative of the SPR amplitude change, we can clearly identify the peak stripping potential of the detected ions, and therefore, realize specific ion identification. The method proposed is inherently immune to temperature cross-talk because the core mode is temperature dependent but insensitive to the surrounding media. The proposed EC-SPR fiber-optic sensor has the advantages of compact size, flexible shape, and remote operation capability, thereby, opening the way for other opportunities for electrochemical monitoring in various hard-to-reach locations and remote environments.

Reflex optical fiber probe for simultaneous determination of seawater salinity and temperature by surface plasmon resonance

A new high-sensitivity optical reflective probe is reported for the simultaneous measurement of seawater salinity and temperature. A concise interference structure was used for exciting the cladding mode. A nanoscale gold film served as the sensitive detection area to induce surface plasmon resonance (SPR). A photosensitive material (polydimethylsiloxane) was partially coated on the sensitive layer to produce double SPR peaks. The SPR effect model of the optical fiber structure was modified and a complete detection system was constructed. The preparation and structural parameters were optimized to obtain high-quality spectral properties. Through the calibration experiments, the response to salinity at its characteristic wavelength had a sensitivity of 0.0558 nm/%, while the temperature response at its characteristic wavelength was −4.418 nm/°C. The reflective probe was shown to have low crossover sensitivity. Compared with standard instrumentation, this device was shown to be stable and precise and is expected to have significant practical applications.

Dual communication windows polarization filter based on photonic crystal fiber with nano-scale gold film

Abstract A photonic crystal fiber (PCF) polarization filter with dual communication bands is proposed in this paper. The polarization characteristics of the double-hole gold-coated PCF are numerically analyzed by utilizing the finite element method (FEM). As we know, the filter can achieve polarization filtering effect on input signals at 1310 nm (y-polarized mode) and 1550 nm (x-polarized mode) bands simultaneously in two orthogonal polarization states. In the above two communication bands, the confinement losses of the unwanted polarization mode can reach 192.7 dB/cm (y-polarized mode) and 427.5 dB/cm (x-polarized mode), whereas other polarization mode losses are very low. Furthermore, when the transmission length of the PCF is 800 μm, x and y polarization mode crosstalk can reach −275.4 and 126.9 dB in the 1550 and 1310 nm bands, respectively. Meanwhile, the crosstalk is less than −20 dB or better than 20 dB, the optical bandwidth can reach 220 and 150 nm, respectively.

Plasmonic Optical Fibre Sensors for Electrochemical Activities Monitoring in Energy Storage Devices

Surface Plasmon resonance (SPR) optical fibre sensors can be used as a cost-effective and relatively simple-to-implement configurations for in situ high sensitivity electrochemical measurements. The flexible configuration, miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces. The nano-scale plasmonic metal-coating over optical fibre offers the sensor the ability to monitor the electronical and optical information simultaneously, with unprecedented sensitivities and limits of detection. Meanwhile, such sensor provides a multi-resonant mechanism of optical modes (cladding modes and core mode) for high accuracy plasmonic interrogation and inherent elimination of environmental cross talk. In this paper, we briefly introduce the principle and implementation of electrochemical plasmonic optical fibre sensors based on a tilted fibre Bragg grating imprinted in a commercial single-mode fibre and coated with a nanoscale gold film, and our recent studies of in situ and continuous monitoring the electrochemical activities (the potential and the stored charge) of supercapacitors for energy storage devices.

Highly sensitive plasmonics temperature sensor based on photonic crystal fiber with a liquid core

An ultra-high sensitivity temperature sensor based on photonic crystal fiber (PCF) is proposed and demonstrated. The central hole and the two holes coated with nanoscale gold film are assumed to be filled with temperature sensitive liquid. The refractive index of the liquid decreases as the temperature increases with the temperature sensitive coefficient of -3.9 × 10−4/oC. The liquid of the central hole with high refractive index supports liquid-core mode. As the phase matching condition is satisfied, the liquid-core mode couples to the surface plasmon polariton mode and presents energy loss. The influences of the PCF structural parameters and the thickness of the gold film on the resonance wavelength, loss value and sensitivity are studied. The resonance wavelength and confinement loss increase as the temperature increases. The average sensitivity can reach to 9.89 nm/oC (∼25359 nm/RIU) as the temperature changes from 35 °C to 45 °C and the R-square is 0.99992. By replacing the liquid core by silica core, we find the sensitivity is very low. We also compare the PCF without liquid in the holes coated with gold film by our structure and find that the sensitivity is nearly unchanged and the confinement loss is slightly decreased.

In situ plasmonic optical fiber detection of the state of charge of supercapacitors for renewable energy storage.

In situ and continuous monitoring of electrochemical activity is key to understanding and evaluating the operation mechanism and efficiency of energy storage devices. However, this task remains challenging. For example, the present methods are not capable of providing the real-time information about the state of charge (SOC) of the energy storage devices while in operation. To address this, a novel approach based on an electrochemical surface plasmon resonance (SPR) optical fiber sensor is proposed here. This approach offers the capability of in situ comprehensive monitoring of the electrochemical activity (the electrode potential and the SOC) of supercapacitors (used as an example). The sensor adopted is a tilted fiber Bragg grating imprinted in a commercial single-mode fiber and coated with a nanoscale gold film for high-efficiency SPR excitation. Unlike conventional “bulk” detection methods for electrode activity, our approach targets the “localized” (sub-μm-scale) charge state of the ions adjacent to the electrode interface of supercapacitors by monitoring the properties of the SPR wave on the fiber sensor surface located adjacent to the electrode. A stable and reproducible correlation between the real-time charge–discharge cycles of the supercapacitors and the optical transmission of the optical fiber has been found. Moreover, the method proposed is inherently immune to temperature cross-talk because of the presence of environmentally insensitive reference features in the optical transmission spectrum of the devices. Finally, this particular application is ideally suited to the fundamental qualities of optical fiber sensors, such as their compact size, flexible shape, and remote operation capability, thereby opening the way for other opportunities for electrochemical monitoring in various hard-to-reach spaces and remote environments.

Groove micro-structure optical fiber refractive index sensor with nanoscale gold film based on surface plasmon resonance

Abstract A groove micro-structure optical fiber refractive index sensor with nanoscale gold film based on surface plasmon resonance (SPR) is proposed and analyzed by the finite element method (FEM). Numerical results show that the average sensitivity is 15,933 nm/refractive index unit (RIU) with the refractive index of analyte ranging from 1.40 to 1.43 and the maximum sensitivity is 28,600 nm/RIU and the resolution of the sensor is 3.50 × 10−8 RIU. The groove micro-structure optical fiber refractive index sensor do some changes on the D-shaped fiber sensor, compared with conventional D-shaped fiber sensor, it has a higher sensitivity and it is easier to produce than the traditional SPR sensor.

Grain boundary instability dependent fatigue damage behavior in nanoscale gold films on flexible substrates

Quantitative investigation was performed to understand effects of length scales (film thickness) on grain growth and corresponding fatigue damage behaviors in the nanocrystalline Au thin films on flexible substrates with a film thickness ranging from 930nm to 20nm. In thicker films (h ≥ 90nm), abnormal grain growth happened due to the local high stress, while in thinner films uniform grain growth occurred. Such length–dependent grain growth mechanisms was found to be associated with the film strength and the film thickness. Consequently, the main damages in thicker films exhibited the applied load range-related competition between the intergranular cracks and the intragranular cracks along the localized slip. In the thinner film, fatigue damage is associated with GB-related behaviors, such as intergranular cracking and deformation twinning.

Design of a polarization filtering photonic crystal fiber with a big gold-coated air hole

The polarization characteristics of photonic crystal fiber (PCF) with nanoscale gold film is evaluated by using the finite element method. The cross-section structure of the PCF is composed of a hexagonal lattice of air holes in which an air hole is gold coated. The resonance strength and the impact of structural parameters of the PCF on the polarization filter characteristics are studied. By our structure, the loss of y-polarized mode is further larger than the loss of x-polarized mode at the wavelength 1.31 and 1.55 μm. The corresponding loss in y-polarized can reach a value of 136,253 and 167607 dB/m at the resonance wavelengths of 1.31 and 1.55 μm respectively. It can be used for carrying data/voice at the communication windows of 1.31 and 1.55 μm. Meanwhile, we can realize the filtering effect with a very short fiber.

Acid-Free Electrochemical Chromium Etch and Release of Nanoscale Gold Films

We describe a method for releasing coated and uncoated 100-nm gold films from a 5-nm chromium-coated glass substrate. The method is rapid at room temperature within a non-toxic solution of sodium phosphate or sodium hydroxide. Etching processes using hydroxide successfully etch the chromium layer without affecting a ZnO coating layer deposited on the gold film. Etching using sodium phosphate at neutral pH causes some surface damage to the ZnO surface while leaving the bulk of the film intact. Other anions tested include nitrates and chlorides, both demonstrating poor etching selectivity, damaging the gold as well as the chromium layers. A copper counter electrode is used to collect the chromium from the solution, minimizing chromium persistence in the etching solution and any contamination of the ZnO surface. This single step acid-free process can be applied to a variety of materials and structures formed on gold, where insulating materials and many oxides do not require any special protection from the etching solution. An uncoated or polyimide coated $2~\text {cm}\times 1.5$ cm film can be released in under 1 h, while ZnO-coated films require up to 7 h to to release films 1 cm $\times $ 1 cm in size. [2015-0331]

Electrochemical Surface Plasmon Resonance Fiber-Optic Sensor: In Situ Detection of Electroactive Biofilms.

Spectroelectrochemistry has been found to be an efficient technique for revealing extracellular electron transfer (EET) mechanism of electroactive biofilms (EABs). Herein, we propose a novel electrochemical surface plasmon resonance (EC-SPR) optical fiber sensor for monitoring EABs in situ. The sensor uses a tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber and coated with nanoscale gold film for high-efficiency SPR excitation. The wavelength shift of the surface plasmon resonance (SPR) over the fiber surface clearly identifies the electrochemical activity of the surface localized (adjacent to the electrode interface) bacterial cells in EABs, which differs from the "bulk" detections of the conventional electrochemical measurements. A close relationship between the variations of redox state of the EABs and the changes of the SPR under potentiostatic conditions has been achieved, pointing to a new way to study the EET mechanism of the EABs. Benefiting from its compact size, high sensitivity, and ease of use, together with remote operation ability, the proposed sensor opens up a multitude of opportunities for monitoring EABs in various hard-to-reach environments.

A Kind of Broadband Polarization Filter Based on Photonic Crystal Fiber with Nanoscale Gold Film

A kind of polarized filtering photonic crystal fiber (PCF) with nanoscale gold film is studied by using the finite element method. The cross-section structure of the PCF is composed of a hexagonal lattice of air holes in which an air hole is gold coated, and the air-hole layout is modified. By our structure, the loss of x-polarized mode is further larger than the loss of y-polarized mode and the loss peak appears at the wavelength 1.31 μm. The corresponding loss in x-polarized can reach a value of 85,780 dB/m at the resonance wavelength. It can be used for the communication windows of 1.31 μm which can be used for carrying data/voice. When the length of fiber is longer than 30 μm, the extinction ratio is better than 20 dB at the wavelength 1.31 μm. When the length of fiber is longer than 210 μm, the extinction ratio is better than 20 dB with the wavelength ranging from 1.26 to 2 μm. The broadband polarized filtering PCF covering 740 nm is achieved.

Reduced Photoconductivity Observed by Time-Resolved Terahertz Spectroscopy in Metal Nanofilms with and without Adhesion Layers.

Non-contact, optical time-resolved terahertz spectroscopy (TRTS) has been used to study the transient photoconductivity of nanometer-scale metallic films deposited on fused quartz substrates. Samples of 8 nm thick gold or titanium show an instrument-limited (ca. 0.5 ps) decrease in conductivity following photoexcitation due to electron-phonon coupling and subsequent increased lattice temperatures which increases charge carrier scattering. In contrast, for samples of 8 nm gold with a 4 nm adhesion layer of titanium or chromium, a ca. 70 ps rise time for the lattice temperature increase is observed. These results establish the increased transient terahertz transmission sign change of metallic compared to semiconductor materials. The results also suggest nanoscale gold films that utilize an adhesion material do not consist of distinct layers.

SPR Detection and Discrimination of the Oligonucleotides Related to the Normal and the Hybrid bcr-abl Genes by Two Stringency Control Strategies.

In this study, we applied two stringency control strategies for surface plasmon resonance (SPR) detection of DNA hybridization and discrimination of completely and partially complementary 24-mer sequences. These sequences are specific to the human normal bcr and the hybrid bcr-abl genes, protein products of which are responsible for some leukemia. SPR sensors based on resonance phenomena in nanoscale gold films are well suited for label-free, real-time investigations of the macromolecule interactions. Thermodynamic parameters obtained using the web server DINAMelt allowed supposing the possibility for realization (a) stringency control based on the ionic strength of the hybridization buffer and (b) stringency control based on the temperature elevation. The first one resulted in that the discrimination index of completely complementary and partially complementary oligonucleotides depending on the target concentration varied from 1.3 to 1.8 in 2 × SSC and from 2.0 to 2.9 in 0.5 × SSC. For implementation of the second stringency control strategy, SPR spectrometer measuring flow cell with built-in high-precision temperature control and regulation as well as corresponding software was created. It is shown that the duplexes formed by the immobilized probes mod-Ph and completely complementary oligonucleotides P1 remained without significant changes until ~50 °C, while the duplexes formed with partially complementary oligonucleotide Bcrex14 almost entirely disrupted at 40 °C. Thus, the absolutely effective thermodiscrimination of this pair of oligonucleotides was achieved in this temperature range (40–50 °C).