Au Thin Films Research Articles

Effect of Annealing and Ion Beam Irradiation on AC Electrical Properties for Gold Sputtered PM-355

Deposition of different gold thickness on PM-355 cleaned by ethanol forming thin films using magnetron sputtering. Gold layer with thickness 300, 400, 500, 700, 1000, 1300, and 1500 nm were deposited to prepare Au / PM-355 thin films. Then, ac electrical properties response of thin films for a wide frequency range 20Hz - 5MHz were measured at roomtemperature. Meanwhile, the measurements of ac conductivity, dielectric constant, and dielectric loss factor were plotted at different frequencies to determine the optimum thickness. Hence, the comparison was done between optimum Au thickness thin films cleaned by two organic solvents and ethanol before annealing at different frequencies. Also, study the effect of annealing and ion beam that extracted radially from conical anode and disc cathode ion source on optimum Au thickness thin film electrical properties. It is found that the annealing increases both dielectric constant, dielectric loss, and ac conductivity of optimum Au thin film at different frequencies. Despite, the nitrogen ion beam effected on these thin films by decreasing the dielectric constant and ac conductivity for all thin films except the chloroform one. Finally, study the comparison between the annealing and followed by ion irradiation thin films. It is noticed the decrease in ac electrical conductivity and dielectric constant at different frequencies.

Investigating the Secondary Electron Emission of Nanomaterials Induced by a High‐Resolution Proton Beam

Herein, the secondary electron emission (SEE) from 1D nanomaterials in the form of nanorods is investigated. The small beam of a 1.5 MeV +H2 hydrogen with a sub 70 nm in diameter allows studying the SEE with a very high resolution. A wide range of nanomaterials from various laboratories are studied, including thin ZnO and ZnO/GaN nanostructures grown on 1 μm thick Si3N4 membranes and thick InP, GaN and GaN/AlN nanorod structures grown on bulk Si substrates. By virtue of the small size of the exciting nanobeams, high‐resolution maps could be created presenting an SEE yield from various parts of the structures. This allows us to show that the top parts of nanorods in ZnO, ZnO/GaN, GaN, InP, and GaN/AlN nanostructures emit secondary electrons much more efficiently than the valley areas between nanorods. These results indicate that by a proper design and growth of 1D nanostructures, SEE properties could be improved over those of the traditionally used Au and CsI thin films. This work has been undertaken to find materials with the highest achievable SEE emission, which is a figure of merit for the detection efficiency relevant for the development and application of novel radiation detectors.

Effect of Au thin film thickness and surface nanoparticles morphologies on the optical band gap and photoluminescence of ZnO thin films deposited by pulsed electron deposition technique

Effect of Au thin film thickness and surface nanoparticles morphologies on the optical band gap and photoluminescence of ZnO thin films deposited by pulsed electron deposition technique

Effects of UV irradiation and thermal annealing on LiCl derivatives encapsulation in porous PET membranes coated with a thin Au film

Encapsulation of LiCl (LiCl derivatives) in porous Au-coated PET membranes after UV irradiation or thermal annealing was studied by ion and neutron beam analytical techniques. The shape of the pores in the PET membranes before and after LiCl doping were characterized by Ion Transmission Spectroscopy that enabled to describe their 3D geometry and filling after exposing to a LiCl aqueous solution. The content and depth distribution of Li (and Cl) in pores was examined by Neutron Depth Profiling (NDP). Using the ITS and NDP complementary methods, it was possible to determine the amount of lithium incorporated in the pores and assess the ability of the PET membranes (modified by UV irradiation or thermal annealing) to encapsulate lithium atoms (LiCl derivatives). The present study could be relevant to technology of porous separators for thin lithium ion batteries.

Surface Plasmon Resonance of Two-Dimensional Gold Colloidal Crystals Formed on Gold Plates.

The free electrons inside precious metals such as Au vibrate when the surface of the metal is irradiated with an electromagnetic wave of an appropriate frequency. This oscillation is referred to as surface plasmon resonance (SPR), and the resonance frequency varies with permittivity of the medium around the metal. SPR sensors are widely applied in the fields of bioscience and pharmaceutical sciences, including biosensing for drug discovery, biomarker screening, virus detection, and testing for food safety. Here, we fabricated a metal-insulator-metal (MIM) SPR sensor by constructing two-dimensional (2D) regular array of Au colloidal particles (2D colloidal crystals) on an insulator layer over a thin Au film coated on a glass substrate surface. The 2D crystals were fabricated by electrostatically adsorbing negatively charged three-dimensional crystals onto a positively charged thin insulator formed on Au film. The plasmon peaks/dips from the MIM structure were measured in aqueous solutions of ethylene glycol (EG) at various concentrations. Multiple plasmon peaks/dips were observed due to the localized SPR (LSPR) of the Au particles and the Fano resonance between the Au particles and thin film. The plasmon peaks/dips shifted to higher wavelengths on increasing EG concentrations due to an increase in the refractive index of the media. The observed peak/dip shift was approximately twice that of LSPR from an isolated Au particle. We expect the present MIM substrate will be useful as a highly sensitive sensor in the pharmaceutical field.

Plasmon resonance-induced photoluminescence enhancement of CdS quantum dots thin films on fabricated Au/Ag/Cu metallic thin films

Multi-metallic nanoparticles (NPs) offer tunable Localized Surface Plasmon Resonance properties which depend on their elemental and configurational variations, which have been used in optical sensing and biomedical imaging. In the present study, the composition and optical properties of hybrid nano-structured thin films of CdS quantum dots (QDs) incorporated on Au-, Ag- and Cu-NPs for photonic applications are investigated. Initially, CdS QDs were prepared by chemical reduction method and characterized by Transmission electron microscopy, UV–Visible absorption spectroscopy and Fourier transform infrared spectroscopy techniques. Then nanometer thin films of Au, Ag and Cu were fabricated by thermal evaporator and insitu heating along with uniform rotation of substrate was used to convert these into respective uniform spherical NPs on ITO substrate. Further, CdS QDs were deposited over these metallic NPs and we observed enhanced photoluminescence (PL) of CdS QDs due to Surface Plasmon Resonance effect by these metallic NPs. The time resolved spectroscopy of these films was carried out to correlate the enhanced PL emission from CdS–Au–Ag–Cu-ITO thin film. The results of the present study of these plasmonic nanostructures will be further utilized in metal enhanced fluorescence sensors.

Spectral Phase Measurements of Heterodyne Detection in Interfacial Broadband Electronic Spectroscopy

A spectral phase is vital to retrieve both the real and imaginary parts of both second-order vibrational and electronic sum frequency generation spectra. Despite recent efforts, phase measurements in electronic spectra at interfaces are lacking. In particular, references are not well established for frequency-dependent spectral phases in interfacial electronic spectroscopy. In this work, we present broadband heterodyne detection (HD) of interfacial electronic spectroscopy for spectral phases of references. Such a broadband HD method was based upon a broadband short-wave IR laser source from 1100 to 2200 nm. A collinear geometry method was adopted for passive phase stability. We further compared often-used reference samples, including gold (Au) thin films, silver (Ag) thin films, p-type GaP (100), p-type GaAs (100), as well as left-handed and right-handed z-cut α-quartz crystals. The phases of the second-order susceptibilities for Ag thin films, the GaP crystal, the GaAs crystal, and the quartz crystals are independent of frequency from 630 to 730 nm. More importantly, it was found that the often-used Au thin film in the literature is not a good phase reference for frequency-dependent phases.

Electron glass signatures up to room temperature in disordered insulators

This paper describes the observation of non-equilibrium field effects at room temperature in four disordered insulating systems: granular Al, discontinuous Au, amorphous NbSi and amorphous indium oxide thin films. The use of wide enough gate voltage ranges and a cautious analysis of the data allow us to uncover memory dips (MDs), the advocated hallmark of the electron glass, in the four systems. These MDs are found to relax slowly over days of measurements under gate voltage changes, reflecting the impossibility for the systems to reach an equilibrium state within experimentally accessible times. Our findings demonstrate that these electrical glassy effects, so far essentially reported at cryogenic temperatures, actually extend up to room temperature.

Improvement in Strain Sensor Stability by Adapting the Metal Contact Layer.

Research on stretchable strain sensors is actively conducted due to increasing interest in wearable devices. However, typical studies have focused on improving the elasticity of the electrode. Therefore, methods of directly connecting wire or attaching conductive tape to materials to detect deformation have been used to evaluate the performance of strain sensors. Polyaniline (PANI), a p-type semiconductive polymer, has been widely used for stretchable electrodes. However, conventional procedures have limitations in determining an appropriate metal for ohmic contact with PANI. Materials that are generally used for connection with PANI form an undesirable metal-semiconductor junction and have significant contact resistance. Hence, they degrade sensor performance. This study secured ohmic contact by adapting Au thin film as the metal contact layer (the MCL), with lower contact resistance and a larger work function than PANI. Additionally, we presented a buffer layer using hard polydimethylsiloxane (PDMS) and structured it into a dumbbell shape to protect the metal from deformation. As a result, we enhanced steadiness and repeatability up to 50% strain by comparing the gauge factors and the relative resistance changes. Consequently, adapting structural methods (the MCL and the dumbbell shape) to a device can result in strain sensors with promising stability, as well as high stretchability.

Au(001) Thin Films: Impact of Structure and Mosaicity on the Oxygen Reduction Reaction in Alkaline Medium

Au(001) thin films with thickness varying from ca. 25 to 83 nm were deposited on MgO(001) substrates using pulsed laser deposition. Epitaxial growth of (001) Au on the (001) MgO single-crystal substrate was observed with a Au(001)[010]//[010](001)MgO cube-on-cube epitaxial relationship for substrate temperature ≤200 °C. Detailed X-ray reciprocal space mapping (RSM) analysis and atomic force microscopy (AFM) imaging of films with different thicknesses were conducted. There is a nonmonotonic dependence of both the in-plane and out-of-plane lattice parameters with the films’ thickness, while the lateral coherence length increases with the thickness. The maximum tensile strain measured was 0.3% for 65 nm thick Au(001) film. Cyclic voltammetry (CV) in acidic and alkaline media and Pb underpotential deposition (Pb UPD) measurements were used as fingerprints to assess the structure of the surface. All films exhibited the characteristic response of Au(001) single-crystal surfaces, although with some differences in the potential region between 0.7 and 1.2 V vs reversible hydrogen electrode (RHE), which corresponds to the adsorption and partial discharge of OH– anions at the electrode surface. Since epitaxial Au(001) thin films do not lend themselves to steady-state voltammetry with rotating disks or microelectrodes due to their square shape and the insulating nature of MgO substrates, the electrocatalytic activity of the films for the oxygen reduction reaction (ORR) in the alkaline electrolyte was assessed by sampled current voltammetry. It was shown that both the onset potential (Eonset) and the half-wave potential (E1/2) for the ORR do not show any dependence on strain but rather become less negative (more active) with an increase of the lateral coherence length. These data are rationalized in the context of recent density functional theory (DFT) calculations and the mechanisms governing the ORR in alkaline electrolytes.

Photon spin angular momentum driven magnetization dynamics in ferromagnet/heavy metal bilayers

Thin-film magnetization controlled by optical helicity has been recently reported. Although circularly polarized light has spin angular momentum, helicity-dependent all-optical magnetization switching is mediated by the stochastic thermal process, such as magnetic circular dichroism, and the effect of photon spin angular momentum is considered to be a secondary role. Conversely, the inverse Faraday effect in ferromagnetic thin films and photon spin angular momentum injection into heavy metal thin films have been observed, which can induce torque on metallic thin-film magnets. In this study, we show photon spin angular momentum driven magnetization dynamics in bilayers of Co/(Pt, Au) thin films with various thicknesses. The heavy metal Pt, Au, and ferromagnetic Co layer thickness dependencies of photon spin angular momentum driven torques are discussed in terms of field-like torque owing to the inverse Faraday effect and spin-transfer torque caused by photon spin angular momentum injection into the heavy metal layer with details of optical and magnetic properties. This study provides a better understanding of photon spin angular momentum induced magnetization dynamics in metallic thin-film heterostructures for efficient photon-driven magnetization manipulation.

TiO2 nanoflowers@Au@MnO2 core-shell composite based on modified Ti foil for flexible supercapacitor electrode

Flexible supercapacitors have received increasing attention due to its portable, flexibility, lightweight and stability. Herein, the flexible supercapacitor electrode with core-shell structure is prepared by in-situ growth of 3D TiO2 nanoflowers on activated Ti foil and uniform coating of Au film and MnO2 nanowires. The porous Ti conductive substrate is achieved by adjusting HCl-KOH corrosion time, thereby providing more channels for charge transport. Free-standing 3D structure of TiO2 NFs provides more surface area to facilitate ions intercalation/deintercalation. Au thin film plays a pivotal role in enhancing conductivity of Ti/TiO2 substrate and adhesion of MnO2 nanowires. The TiO2 NFs@Au@MnO2 composite electrode performs an excellent specific capacitance (1322.5 F g−1 at 1 A g−1) and satisfying cycling stability (86.3% capacity retention after 2000 cycles). Additionally, the assembled solid-state symmetric supercapacitor also displays superior electrochemical performance (223.75 F g−1 at 0.5 A g−1), favourable rate capability (85.8% capacity retention after 2000 cycles) and remarkable flexibility. The combination of 3D architecture nanocomposite electrode with other carbon-based materials will open up a prospect for developing flexible asymmetric supercapacitors.

Multilayer Crossbar Array of Amorphous Metal-Oxide Semiconductor Thin Films for Neuromorphic Systems

A multilayer crossbar array has been developed using amorphous metal-oxide semiconductor (AOS) thin films and implemented into a neuromorphic system. The multilayer structure can be realized, because the AOS thin films can be deposited by a simple sputtering method without heat treatment, which does not damage the underlying structures. First, Au thin films are deposited by vapor evaporation as electrodes, an amorphous In-Ga-Zn-O (α-IGZO) thin film is deposited by a sputtering method as a conductance change layer, these processes are repeated, and a multilayer crossbar array is completed, where each of the three conductance change layers is sandwiched between the electrodes. Next, the multilayer crossbar array is implemented into a neuromorphic system with modified Hebbian learning, which enables autonomous learning without control circuitry, and an associative memory function is confirmed, which guarantees the possibility of further advanced functions. These results lead to astronomical large-scale integration (LSI) of synaptic elements in neuromorphic systems in the future.

Determination of thickness-dependent damping constant and plasma frequency for ultrathin Ag and Au films: nanoscale dielectric function.

This paper is devoted to determine an analytical expression for the thickness dependent complex dielectric function for the case of Ag and Au thin films. Free and bound electron contributions are dealt with independently. Using Drude model for the former and taking experimental refractive index values for Ag and Au thin films, we apply a previously developed method to determine for the first time damping constant and plasma frequency parameters for specific film thicknesses. Fitting separately each one of these parameters allowed us to find an analytical expression for their dependence on arbitrary film thickness and consequently for the free electron contribution. Concerning bound electrons, its contribution for small wavelengths is the same for all analyzed thicknesses and may be set equal to the bulk bound contribution. Taking these facts into account, the complex dielectric function is rewritten analytically, in terms of bulk dielectric function plus corrective film thickness dependent terms. From the fitting process for the damping constant we determine that electron scattering at the film boundary is mainly inelastic for both silver and gold thin films. It is also shown that, in accordance with theoretical studies, plasma frequency shows a red shift as the film thickness decreases.

Measurements of K-shell ionization cross sections and L-shell X-ray production cross sections of Al, Ti, Cu, Ag, and Au thin films by low-energy electron impact

The K-shell ionization cross sections of Al, Ti, Cu and L-shell characteristic X-ray production cross sections of Cu, Ag and Au (Lα, Lβ and Lγ subshells for Au) by electron impact at incident energy of 5–27 keV are determined experimentally. Thin films of the studied elements, deposited on thin carbon substrates, are employed as targets in the experiments. The thickness of the thin carbon substrate is 7 μg/cm<sup>2</sup>, the targets are Al, Ti, Cu, Ag and Au and their thickness values are 5.5 μg/cm<sup>2</sup>, 28 μg/cm<sup>2</sup>, Cu 35.5 μg/cm<sup>2</sup>, 44 μg/cm<sup>2</sup> and 44 μg/cm<sup>2</sup>, respectively. The target thickness values are checked by using Rutherford Backscattering Spectrometry (RBS). The electron beam is provided by a scanning electron microscope (KYKY-2800B). The characteristic X-rays produced are recorded by a silicon drifted detector (XR-100SDD, Amptek), which has a C2 ultrathin window and can detect the low-energy X-rays down to boron Kα line (0.183 keV). The detector efficiency is calibrated by using the standard sources (<sup>55</sup>Fe, <sup>57</sup>Co, <sup>137</sup>Cs and <sup>241</sup>Am) for X-ray energy larger than 3.3 keV while using the characteristic peak method (i.e. by measuring characteristic X-ray spectra produced by 20 keV electron impacting various thick solid targets) for X-ray energy less than 3.3 keV. The experimental results are corrected by the Monte Carlo code PENELOPE for the effects of target structure and Faraday cup. Meanwhile, the electron escape rates obtained from the Faraday cup and the signal pile-up effect are also considered. The results show that when the incident electron energy is low, the influences of electron energy loss and target thickness are significant. The thinner the target , the smaller the correction is. Experimental uncertainties for K-shell ionization cross sections of Al, Ti and Cu are about 5.0%, 5.6% and 5.1%, respectively; experimental uncertainties for L-shell X-ray production cross sections for Cu and Ag are about 5.3% and 4.0%, and for Lα,Lβ,and Lγ of Au are about 6.1%, 8.9% and 11.0%, respectively. The experimental L-shell characteristic X-ray production cross sections of Cu are given for the first time. Compared with the theoretical values of the semi-relativistic distorted-wave Born approximation (DWBA), most of the experimental values in this work are in good agreement within 7% deviation. The best agreement between the experimental results and the theoretical values is obtained for the K shell ionization cross section of Al, and the deviation is less than 1.7% for the data where the incident energy is above 10 keV. The least consistency with the theoretical values is the experimental L shell characteristic X-ray production cross sections of Cu, with a deviation being about 5–22%. The comparison of the experimental L shell characteristic X-ray production cross sections of Cu (including Ga and As elements) with those from the DWBA theory indicates that the theoretical calculations of L shell ionization cross sections of medium heavy elements and the corresponding atomic parameters (such as fluorescence yields and Coster-Kronig transition probabilities) need to be more accurately determined. According to the present results, the ionization cross sections or characteristic X-ray production cross sections measured by the thin target thin substrate, the thin target thick substrate and the thick target methods are equivalent to each other within the uncertainties.

Structure, Characteristics and Corrosion Behaviour of Gold Nanocoating Thin Film for Biomedical Applications

Nanocoatings thin films are layers deposited to improve required properties and corrosion resistance as a major objective for materials that are used for various biomedical applications such as biosensors. In this study, Gold (Au) thin films with 50 nm and 100 nm have been synthesized on Ni-Cr-Mo alloys by magnetron sputtering deposition technique. X-Ray diffraction (XRD), Atomic Force Microscopy (AFM), and Energy-dispersive X-Ray spectroscopy /Scanning Electron Microscopy (EDS/SEM ) have been used to distinguish the surfaces morphology. The results showed that there is no defects or micro-cracks with a uniform and homogenous film. It has spherical nanoparticles diameter morphology with 200-400 nm shaped to fine aggregation. The roughness average (Ra) decreased from 3.91 nm for 50 nm films to 3.70 nm for 100nm films with FCC crystal structure (111) for gold thin films. In vivo, after 50 nm and 100 nm nanocoated thin film by gold, a significant improvement in the localized corrosion resistance has been obtained in artificial saliva corrosive media at 37 °C compared with the uncoated surface.

Metal-Molecule-Metal Junctions on Self-Assembled Monolayers Made with Selective Electroless Deposition.

Electronic transport through molecular-scale devices has been studied extensively for its extraordinary dimension superiority. Assembling such devices into large-scale functional circuits is crucial since the molecular tunnel junctions must be reliable, stable and reproducible during technological applications. In ideal circumstances, the device architecture should be designed such that the metal-molecule-metal (MMM) junctions can be analyzed by the more sensitive four point probe system. In this paper, we expound a delicate method to manufacture molecular junctions, which show excellent stability and reproducibility with high yields (>91 per cent). We form self-assembled monolayers (SAMs) on conductive Au thin film by microcontact printing and then generate robust covalently bound metal thin film electrodes on top of the SAMs by selective electroless deposition. Following MMM junction formation, a photoresist is coated and wells are opened on each feature by lithography. Then, Au thin film, as a permanent top electrode, is deposited into the photolithographically defined well. Conductivity analyzations were carried out on the 50 μm square junctions by the four point probe measurement, and the results showed reproducible tunneling I-V characteristics. This method reveals an approach not only offering a unique vehicle to investigate the electrical properties of molecule ensembles in MMMs, but also making a significant step toward MMM applications at the device level.

Plasmon-enhanced photoemission from Au nanoparticles covered with cesiated film

The quantum efficiency (QE) and thermal emittance are two main parameters for photocathode, especially for the emission source of free electron laser (FEL) accelerator. It is in challenge how to reduce the rigorous fabrication of cathode and how to enhance the quantum efficiency for photocathode. Facing to the issues in our case, we have investigated plasmon-enhanced photoemission from Au nanoparticles (NPs) covered with Cs film in the microwave electron gun of free electron laser. The large-area preparation and low-cost photocathode are formed by rapid thermal annealing of thin Au films. Cs film covered is found to effectively excite photoelectrons from Au NPs under the visible light (at the 532 nm). The quantum efficiency (QE) of the Au NPs-Cs increases to 2.3 × 10−4 with the pico-second pulsed laser irradiation, and the normalized root mean square (RMS) thermal emittance of the electron beam is about 1.89 mm mrad. It confirms the feasibility for the proposed metallic nanoparticles to be applied to the high brightness electron sources.

Theoretical and Experimental Analysis of Surface Roughness and Adhesion Forces of MEMS Surfaces Using a Novel Method for Making a Compound Sputtering Target

Achieving a compound thin film with uniform thickness and high purity has always been a challenge in the applications concerning micro electro mechanical systems (MEMS). Controlling the adhesion force in micro/nanoscale is also critical. In the present study, a novel method for making a sputtering compound target is proposed for coating Ag–Au thin films with thicknesses of 120 and 500 nm on silicon substrates. The surface topography and adhesion forces of the samples were obtained using atomic force microscope (AFM). Rabinovich and Rumpf models were utilized to measure the adhesion force and compare the results with the obtained experimental values. It was found that the layer with a thickness of 500 nm has a lower adhesion force than the one with 120 nm thickness. The results further indicated that due to surface asperity radius, the adhesion achieved from the Rabinovich model was closer to the experimental values. This novel method for making a compound sputtering target has led to a lower adhesion force which can be useful for coating microgripper surfaces.

Optothermal characterization on thermal diffusivity, carrier diffusion and recombination properties of annealed thin Au film deposited on Si substrate

In this work, an optothermal wave characterization based on the photoacoustic (PA) technique was first implemented to investigate the thermal and carrier transport properties of Au thin film layer deposited on Si wafers (Au/Si) annealed at different temperatures. The XRD pattern showed that a metastable gold (Au) silicide of Au81Si19 phase formation was traced at annealing temperature of 330 oC and this structure disappeared when the temperature was further elevated up to 370 oC. The result showed that the PA signal obtained for Au/Si structure was lower than the pure Si wafer. The thermal and carrier transport properties of Si and Au/Si were elucidated from the fitting of PA signalphase relation. From the result, the thermal diffusivity and surface recombination velocity of Au/Si increased with shorter recombination lifetime as the raise of annealing temperature. Nonetheless, as the temperature approaches 370 oC, the surface recombination and thermal transport process diminishes, which may be ascribed to the rupture of silicide clusters.