Evaporated Gold Films Research Articles

Study on the reflectivity of electron beam evaporated gold films on aluminum alloy substrates treated at 60, −20, and 25°C

Aluminum alloys are widely applied in optical turrets after coating and super-finishing. Gold films prepared on aluminum alloy substrates via electron beam (e-beam) evaporation are considered to be effective way to realize close to total reflection of incident light. Here, we investigated the optimization of the reflectivity parameters of e-beam evaporated gold films; then, the influence of different deposition parameters on the surface quality, adhesive force and reflectivity (incident light in the 650–1700 nm range) of the film at −20, 25 and 60°C were systematically studied. The results demonstrated that the reflectivity and adhesion of the gold films both increased after high temperature holding and decreased slightly after low temperature holding. However, the surface morphology of the gold film did not change substantially. After holding at 60 and −20°C, the adhesive force decreased, which indicated that the adhesion strength between the reflective membrane and the substrate decreased.

Verifying electromagnetic first layer effect on surface enhanced infrared absorption with evaporated gold nano island film

Infrared absorption enhancement is reported for a polyacrylic acid film deposited on evaporated gold film in normal transmission geometry. Comparison between absorption intensities measured with and without the self-assembled monolayer of p-nitrothiophenol demonstrates that the absorption intensities of polyacrylic acid are independent of the presence of a self-assembled monolayer. Results suggest that the first layer effect in the physical enhancement mechanism does not exist in this thermally evaporated island film.

Dielectric barrier layers by low-temperature plasma-enhanced atomic layer deposition of silicon dioxide

Electrothermal measurement techniques often require thin dielectric barriers to isolate active electrical test structures from samples of interest. The combined need for electrical passivation but thermal proximity necessitates the use of an electrically thick but thermally thin barrier layer. Here, we demonstrate a hybrid approach toward constructing sub-300 nm SiO2 multilayer barriers based upon low-temperature plasma-enhanced atomic layer deposition and high density plasma chemical vapor deposition. Using pairs of buried metal test structures, we quantify changes in device resistance and cross-talk after covering the dielectric barrier with thin evaporated gold films and thick electroplated copper films. We show that a hybrid approach to passivating electrothermal measurement devices outperforms individual homogenous barriers formed by either deposition technique.

Fabrication of well-ordered porous array mounted with gold nanoparticles and enhanced sensing properties for mixed potential-type zirconia-based NH3 sensor

The nano-bowl shaped structure and gold nanoparticle array were successfully fabricated on the YSZ substrate and examined to improve the sensitivity of mixed potential type NH3 gas sensor. The nano-bowl shaped structure was constructed by solution-dipping template (polystyrene spheres) strategy and gold nanoparticle inlaid in the nanostructure was fabricated by vacuum evaporation plating technology. The present study mainly explored the influence of gold layer’s thickness on the nanostructure. The perfect ordered gold nanoparticle array inlaid in nano-bowl shaped structure was obtained when the evaporated gold film thickness was about 50nm. The mixed potential type gas sensor which based on processed YSZ substrate displayed the improved sensitivity and selectivity to NH3 at elevated temperature. All the enhanced sensing properties might due to the enlarged three phase boundary (TPB) and inlaid gold nanoparticle array.

Electrical Characterization of Traditional and Aerosol Jet Printed Conductors Under Tensile Strain

ABSTRACTIn this work, we propose a model to quantify strain induced conductor discontinuities based on measuring electrical resistance while applying tensile strain to metal-polymer systems. Under strain, changing conductor geometry and induced conductor discontinuity increase electrical resistance. On Kapton substrates strained to ε = .07, evaporated gold films did not deform and resistance increase was only caused by geometry change. Conversely, discontinuity caused 31% and 72% of the resistance increase in evaporated and printed silver films at the same strain. On PDMS substrates, the same magnitude of discontinuity, causing 31% of the resistance increase, occurred at only ε = .024 in evaporated silver films. At the same strain, discontinuity caused 86% of the resistance increase in evaporated gold films. Printed silver films were inelastic. The results suggest that traditional fabrication techniques may be more suitable to flexible hybrid electronics applications than additively manufactured conductors.

Functional and Selective Bacterial Interfaces Using Cross-Scaffold Gold Binding Peptides

We investigated the functional and selective activity of three phage-derived gold-binding peptides on the Escherichia coli (E. coli) bacterial cell surface display scaffold (eCPX) for the first time. Gold-binding peptides, p3-Au12 (LKAHLPPSRLPS), p8#9 (VSGSSPDS), and Midas-2 (TGTSVLIATPYV), were compared side-by-side through experiment and simulation. All exhibited strong binding to an evaporated gold film, with approximately a 4-log difference in binding between each peptide and the control sample. The increased affinity for gold was also confirmed by direct visualization of samples using Scanning Electron Microscopy (SEM). Peptide dynamics in solution were performed to analyze innate structure, and all three were found to have a high degree of flexibility. Preferential binding to gold over silicon for all three peptides was demonstrated, with up to four orders of magnitude selectivity exhibited by p3-Au12. The selectivity was also clearly evident through SEM analysis of the boundary between the gold film and silicon substrate. Functional activity of bound E. coli cells was further demonstrated by stimulating filamentation and all three peptides were characterized as prolific relative to control samples. This work shows great promise towards functional and active bacterial–hybrid gold surfaces and the potential to enable the next generation living material interfaces.

Infrared Dielectric Function of Gold Films in Relation to Their Morphology

Though data concerning gold’s optical properties differ substantially in the literature, the causes for these discrepancies are poorly understood. Surface quality affects the optical response considerably, not only through crystal defects but also through the existing morphology. If optical data analysis is done under the assumption of ideally flat surfaces, the obtained dielectric function or dynamic conductivity and any model parameters represent an effective description that may differ from bulk values according to various preparation conditions. To show this finding in detail, we performed spectroscopic ellipsometry measurements of evaporated gold films in the mid-infrared range, below the onset of the interband transitions, and investigated the sample morphology by means of atomic force microscopy. This study yields effective Drude-model parameters that vary with film morphology over a range that includes most of the published values. Introducing a Bruggeman effective medium to model rough films as a mixture of bulk metal and empty volume makes it possible to find a relation between metal volume fraction and effective plasma frequency. In such a model, the plasma frequency and also the dielectric background resulting from interband transitions decrease as the fraction of empty volume inclusions increases. In contrast, while metal volume fraction is much less influential to relaxation time, the density of the gold crystallites’ grain boundaries yields a strong effect. We thus found a plasma frequency, relaxation rate, and dielectric background for the most ideal gold films at room temperature of 7.37(40) × 104 cm–1, 221(1) cm–1, and 9.6(3), respectively.

Exploiting the Facile Oxidation of Evaporated Gold Films to Drive Electroless Silver Deposition for the Creation of Bimetallic Au/Ag Surfaces

The golden road: The facile synthesis of gold-silver bimetallic surfaces was investigated through the spontaneous decoration of silver on evaporated gold films. This spontaneous reaction was found to be driven by the oxidation of the gold surfaces at potentials lower than that expected for bulk gold, providing a simple method of metal decoration to create bimetallic surfaces.

Thermally Activated Wetting Dynamics in the Presence of Surface Roughness

From simple models of thermally activated contact line dynamics far below the depinning transition, one expects the velocity to depend exponentially on the applied force and the activation area to be the size of the defects on the surface. We study contact line motion on evaporated gold films and find that the dynamics are activated, but the activation area is not straightforwardly linked to the surface roughness. Surprisingly, the activation area can be significantly smaller than any features on the surface. Furthermore, it depends strongly on the liquid. We show that this indicates that the line is close to the depinning threshold at experimentally accessible velocities. A model based on independent defects is developed and used to show deviations from the purely exponential law. The dynamics are written entirely in terms of properties of the surface and partially wetting liquid. In addition, we are able to show that the region of validity of models of thermal activation on mesoscopically rough surfaces typically corresponds to velocities of less than 1 mm/s.

Ten-Nanometer Dense Hole Arrays Generated by Nanoparticle Lithography

Large area dense hole arrays with a feature size of ~10 nm were generated using self-assembled monolayers of nanoparticles as etch masks. To fabricate the hole arrays, monolayers of nanoparticles were irradiated by electron beam to turn surfactants into amorphous carbon, treated by acid to remove the nanoparticle cores, and then etched by CF(4) to deepen the holes. Evaporated gold films preferentially diffuse into the holes to generate gold nanoparticle arrays. However no obvious diffusion into holes was observed for a sputtered iron platinum film.

Large Scale Fabrication of Gold Nano-Structured Substrates Via High Temperature Annealing and Their Direct Use for the LSPR Detection of Atrazine

The present work is reporting on the fabrication of localized surface plasmonic resonant (LSPR) gold nano-structures on glass substrate by using different high annealing temperatures (500 °C, 550 °C, 600 °C) of initially created semi-continue gold films (2 nm and 5 nm) by the electron beam evaporation technique. Interestingly, well-defined gold nano-structures were also obtained from continuous 8 nm evaporated gold film - known as the value above gold percolated thickness - once exposed to high temperatures. The surface morphology and plasmonic spectroscopy of “annealed” nano-structures were controlled by key experimental parameters such as evaporated film thickness and annealing temperature. By using scanning electron microscopy (SEM) characterization of annealed surface it was noticed that the size and inter-particle distance between nano-structures were highly dependent on the evaporated thin film thickness, while the nanoparticle shape evolution was mainly affected by the employed annealing temperature. Due to the well-controlled morphology of gold nano-particles, prominent and stable LSPR spectra were observed with good plasmon resonance tunability from 546 nm to 780 nm that recommend the developed protocol as a robust alternative to fabricate large scale LSPR surface. An example of a LSPR-immunosensor is reported. Thus, the monoclonal anti-atrazine antibodies immobilizion on the “annealed” gold nano-structures, as well as the specific antigen (atrazine) recognition were monitored as variations of the resonance wavelength shifts and optical density changes in the extinction measurements.

Sensitive Localized Surface Plasmon Resonance Multiplexing Protocols

Herein are reported two new protocols to obtain different zones of localized surface plasmon resonance (LSPR) gold nanostructures on single glass substrate by using a vacuum evaporation technique followed by a high-temperature annealing (550 °C). The thickness of the gold film, considered as the essential parameter to determine specific LSPR properties, is successfully modulated. In the first protocol, a metal mask is integrated onto the glass substrate during vacuum evaporation to vary the gold film thickness by a "shadowing effect", while in the second protocol several evaporation cycles (up to four cycles) at predefined areas onto the single substrate are performed. The resulting gold-modified samples are characterized using a transmission UV-vis extinction optical setup and scanning electron microscopy (SEM). The size distribution histograms of nanoparticles are also acquired. By employing the first protocol, thanks to the presence of different zones of gold nanoparticles on a single substrate, optimized LSPR responses to different (bio)functionalization zones are rapidly screened. Independently, the second protocol exhibited an excellent correlation between the nominative evaporated gold film thickness, gold nanoparticle sizes, and plasmonic properties (resonant wavelength and peak amplitude). Such substrates are further used in the construction of LSPR immunosensors for the detection of atrazine herbicide.

Robust plasmonic sensors based on hybrid nanostructures with facile tunability

Here, we demonstrate the preparation of a hybrid nanoplasmonic probe array, a nanoforest, which consists of gold nanostructures coated on top of silica nanospheres and evaporated gold film structure onto bottom through masks. Optically tunable plasmonic surfaces could be achieved by varying the nanoforest fabrication conditions, which acted as a selective nanoantenna. Plasmon coupling effects were effectively controlled by adjusting the vertical distance (nanogap) between the gold nanostructures on the silica bead and the bottom. Such control is critical to highly sensitive molecular detection applications. As a proof of concept, nanoforests were used as colorimetric sensors of refractive index changes. The sensors were highly sensitive and displayed distinct colors for small refractive index (RI) changes. The flexible and sensitive near/far-field optical properties render these nanoforests excellent plasmonic substrates for quantitative, sensitive and label-free sensing with nanoscale spatial resolution.

Influence of Diffusion-Annealing Temperature on the Physico-Mechanical Properties of Au-doped Bi-2223 Superconductors

In order to investigate the influence of Au doping and diffusion-annealing temperature on the mechanical and superconducting properties of Bi-2223, Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of gold diffusion during sintering from an evaporated gold film on pellets. The investigation consisted of scanning electron microscopy, dc resistivity and hardness measurements. Electrical-resistivity measurements indicated that the room-temperature resistivity value decreased with decreasing diffusion-annealing temperature from 830 to 500 °C and these samples (G830, G800, G750, G700, G600 and G500) show the resistive behavior above the onset critical transition temperature with the zero-resistivity transition temperatures of 104 K, 80 K, 98 K, 95 K, 102 K and 103 K, respectively. To investigate mechanical properties of the samples, we have measured the diagonal length as a function of test load in the range of 0.245–2.940 N. Mechanical properties (microhardness, Young’s modulus, yield strength and fracture toughness) of the samples are found to be load and diffusion-annealing temperature dependent. In addition, we have calculated the load independent hardness, Young’s modulus, yield strength, and fracture toughness of the samples. The possible reasons for the observed changes in superconducting and mechanical properties due to Au diffusion and diffusion-annealing temperature were discussed.

Excitation power dependence of lifetime of photoluminescence from gold film in the Kretschmann geometry

We have investigated picosecond-laser-pulse-excited photoluminescence (PL) from an evaporated gold film in the Kretschmann geometry. The total intensity of PL was proportional to the square of continuous wave equivalent laser power for excitation, showing that PL is excited via two-photon optical processes. The lifetime of PL was directly determined as a function of excitation laser power by use of a streak camera. We found that the lifetime is inversely proportional to excitation laser power, indicating that the lifetime of d-band holes created by the two-photon optical processes is inversely proportional to their density.

Revisiting the physical processes of vapodeposited thin gold films on chemically modified glass by atomic force and surface plasmon microscopies

The preparation of very thin (at the scale of a few tens of nanometers) gold films by thermal evaporation and deposition on a solid substrate (glass) remains a key step for the elaboration of transparent and sensitive optical biosensors. We study the influence of the glass surface treatment and its thermal conductivity on the structure and composition of evaporated gold films. Using a combination of atomic force microscopy (AFM), high resolution surface plasmon resonance (SPR) imaging, and X-ray photoelectron spectroscopy (XPS), we demonstrate that the grafting of a layer of long chain mercaptant, using 11-mercaptoundecyltrimethoxysilane ( S ξ Si ) , prior to gold deposition produces a drastic modification of gold inner and surface textures. A thorough investigation of AFM image topography by 2D wavelet-based segmentation method reveals the flat conical shape of the gold surface grains and their shape invariance with the glass surface chemical treatment. However, this treatment leads to a drastic decrease of the mean size and polydispersity of these grains by a factor of 2, thereby lowering the gold surface roughness. The rationale is that the combination of surface forces and thermal transfer drives the formation of homogeneous and flatter gold films.

Floating-gate memory based on an organic metal-insulator-semiconductor capacitor

A floating gate memory element is described which incorporates an evaporated gold film embedded in the gate dielectric of a metal-insulator-semiconductor capacitor based on poly(3-hexylthiophene). On exceeding a critical amplitude in the voltage sweep, hysteresis is observed in the capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the device. The anticlockwise hysteresis in C-V is consistent with strong electron trapping during the positive cycle but little hole trapping during the negative cycle. We argue that the clockwise hysteresis observed in the negative cycle of the I-V plot, arises from leakage of trapped holes through the underlying insulator to the control gate.

Influence of gold diffusion-doped on phase formation, superconducting and microstructure properties of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconductors

We report on low-field magnetic properties of gold diffusion-doped Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy superconducting bulk samples by performing ac susceptibility measurements. The undoped samples were prepared by the standard solid-state reaction method. Doping of Bi1.8Pb0.35Sr1.9Ca2.1Cu3Oy was carried out by means of Au-diffusion during sintering from an evaporated gold film on pellets. To investigate the effect of gold-diffusion and diffusion-annealing duration on transport, magnetic and microstructure properties of the superconducting samples we performed magnetoresistivity, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. The ac susceptibility as a function of temperature measurements were carried out at different values of the ac magnetic field amplitudes (Hac) in the range between 20A/m and 320 A/m for 211 Hz. The imaginary part of ac susceptibility measurements is used to calculate intergranular critical current density Jc(Tp) using the Bean Model. Jc(Tp) is seen to increase from 60 A cm-2 to 90 A cm-2 with increasing diffusion-annealing time from 10 h to 50 h. The peak temperature, Tp, in the imaginary part of the ac susceptibility is shifted to a lower temperature with decreasing diffusion-annealing duration as well as increasing ac magnetic fields. The force pinning density (αjj (0)) increased with increasing diffusion annealing time. The value of Tc in gold-diffused samples, in comparison with the undoped samples, increased from 100 ± 0.2 K to 104 ± 0.2 K. It was observed that the value of Tc-offset of the gold-doped samples enhanced with further increasing diffusion-annealing duration. XRD patterns and SEM micrographs are used to obtain information about Bi-2223 phase ratio, lattice parameters and grain size of the samples. Gold doping enhanced the formation high-Tc phase and increased the grain size. The possible reasons for the observed improvements in transport, microstructure and magnetic properties due to Au diffusion and diffusion-annealing time were discussed.

Characterization of gold films by surface plasmon spectroscopy: Large errors and small consequences

Evaporated gold films have a smooth interface with their substrate and a rougher top surface. We investigate the optical response of such a film by excitation of surface plasmons both on the rough and on the smooth side. The smooth side, although polycrystalline, has an optical response that is very similar to a monocrystalline surface. The film can be modeled as two-layers with significantly different optical constants. For investigations on thin dielectric films though, this heterogeneity introduces only a negligible error.

Growth and characterization of ZnO nanostructures on sapphire substrates

We used the metalorganic vapor-phase epitaxy for the growth of ZnO nanostructures on sapphire substrate. We studied the mechanism of epitaxial nanoneedle growth and the formation of quantum dots (QDs) into amorphous ZnO. The precursor combination diethylzinc (DEZn) and N 2 O was used for needle growth via the vapor liquid solid mechanism with evaporated gold films and for “initiator free” needle growth without catalyst. The needle orientations, the epitaxial relationships between ZnO and Al 2 O 3 substrate and the dependences on growth parameters were investigated using scanning electron microscopy and X-ray diffraction measurements. For the growth of ZnO QDs iso-propanol (i-PrOH) was used as oxygen source. The QDs with radius of only few nanometers were embedded into amorphous ZnO. They show blue-shifted cathodoluminescence spectra and their mean diameter depends on the supersaturation in the gas phase.