Noble Metal Films Research Articles

Achieving a comparable transverse magneto-optical Kerr effect by spin–orbit field driven magnetoplasmonic

In this study, we propose and simulate a magnetoplasmonics heterostructure that utilizes spin–orbit fields to generate an internal magnetic field and create a significant magneto-optical effect. Our approach offers a new way to overcome the challenges of using permanent magnets or magnetic coils in conventional magnetoplasmonics, such as high-power consumption and non-scalability. We demonstrate that it is possible to create an appropriate amount of magnetic field using spin–orbit fields induced by the spin-Hall effect, such that the consumption power becomes reasonable and the dimensions could be miniaturized. This approach will be an important development in the field of magneto-optics, as it can lead to enhanced transverse magneto-optical Kerr effect in the present of surface plasmon polaritons. The proposed nanostructure consists of a ferromagnetic film adjacent to a heavy metal layer, both sandwiched between two noble metal films, and deposited on a dielectric prism. The strength of the Kerr signal strongly depends on the thickness of the ferromagnetic layer, with the maximum effect observed at a thickness of 5nm. This concept has potential for various nanophotonic and spintronic applications, particularly for developing high-speed active plasmonic devices for ultrafast light modulation.

Fluorophore-Induced Plasmonic Current Generation from Copper Nanoparticle Films.

We describe the process of generating a fluorophore-induced plasmonic current (FIPC) from copper nanoparticle films. Previous work and the literature have shown that excited near-field fluorophores are able to plasmonically couple with metal nanoparticle films (MNFs), inducing surface plasmons in the films. These induced surface plasmons are then in turn able to generate a directly measurable electrical current across the film. These generated currents have been quantified and detected in noble metal films, such as those made from Ag and Au, but due to the cost of such films, there has been a push to use lower cost materials for FIPC. Previous work has detailed the use of gold, silver, and aluminum films for these purposes, and in this paper, we will subsequently examine the ability of thermally deposited copper films to generate FIPC when in close proximity to excited near-field fluorophores. We report the effects of copper film thickness, the effects of light polarization and solution conductance, and the effects of metal-enhanced fluorescence (MEF) emission on the generation of plasmonic current.

In vacuo studies on reaction mechanisms in ALD processes of ruthenium and platinum films

Noble metal ALD processes with organometallic precursors together with oxygen have been developed extensively. Reaction mechanisms in this family of processes involve combustion of the ligands of the metal precursor by the O2 counter reactant. The ligands are oxidized and form gaseous CO2 and H2O as byproducts. Simultaneously the metallic center is reduced and a noble metal film is deposited. The overall reaction mechanism is fairly well-known, however details regarding the carbonaceous intermediates on the surface at different states of an ALD cycle and the nature of the active surface oxygen are still lacking. In this work, these details are studied mainly with in vacuo X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) for platinum and ruthenium processes. Trimethyl(methylcyclopentadienyl) platinum(IV) (MeCpPtMe3) and bis(cyclopentadienyl) ruthenium(II) RuCp2 are used as precursors together with O2.

Heterostructures Based on Noble Metal Films with Ag and Au Nanoparticles: Fabrication, Study of In Vivo Biocompatibility and Antibacterial Activity

In this work, approaches to the formation of multifunctional film heterostructures based on noble metals for the modification of the surface of implant materials (titanium alloy TiAl6V4 and carbon-fiber-reinforced polyetheretherketone CFR-PEEK) are developed. Such heterostructures consist of continuous layers of platinum (Pt) or iridium (Ir) and antibacterial components on their surface, namely silver (nanoparticles or discontinuous films) and gold (nanoparticles). Chemical or physical gas-phase deposition methods were used for their preparation. The influence of the concentration and form of the antibacterial component on the antibacterial activity and in vivo biocompatibility of the film structures was evaluated for the first time. Differences in the dynamics of silver dissolution depending on Ag concentration in the sample and the type of bottom surface (the noble metal layer = Ir, Pt or TiAl6V4) surfaces allowed us to better understand the nature of the antibacterial action against Staphylococcus aureus and Pseudomonas aeruginosa (S. aureus and P. aeruginosa) of Ag/M heterostructures. From in vivo histological studies using rats, the best biocompatibility was shown by the Ag/M heterostructure with a prolonged release of the low fraction of antibacterial component (Ag).

In English

Zinc oxide nanostructures (NS) were grown on thin discontinuous films of noble metals of silver and gold in order to study their structure, optical properties as well as photocatalytic and antiviral activity. The paper presents the results of X-ray diffraction study, scanning electron microscopy study, photoluminescence and Raman measurements. X-ray diffraction experiments demonstrate similar patterns for all grown ZnO nanostructures. The SEM images of ZnO NS grown on Ag/Si and Au/Si wafers demonstrate more dense surface microstructure compared to ZnO NS grown on bare Si wafers. The most intensive ultraviolet and deep level emissions are observed for ZnO NS grown on Ag/Si wafers. Increase in thicknesses of Ag island film from 5 nm to 10 nm gives significant increase in intensity of ultraviolet and deep level emissions. Photocatalysis of grown ZnO nanostructures was studied by methyl orange dye degradation. Superior photocatalytic results are demonstrated by ZnO nanostructures grown on Ag/Si wafers, for which constants of dye degradation were twice higher than for ZnO nanostructures grown on Si and Au/Si substrates. The photocatalytic results correlates with photoluminescence spectra: more intensive photoluminescence in ultraviolet and visible ranges of optical spectrum leads to better photocatalytic performance. The cytotoxic effect of ZnO nanostructures was studied without photoactivation by the help of cell cultures MDCK and Hep-2 while the virucidal effect of ZnO nanostructures was studied by the help of Influenza A virus (H1N1) (strain FM / 1/47) and human adenovirus serotype 2 (HAdV2). ZnO nanostructures in a 1:10 dilution were not toxic to Hep-2 and MDCK cells. Most of the tested ZnO nanostructures exhibited no virucidal activity against human adenovirus serotype 2 (HAdV2) and influenza A virus (H1N1) (strain FM / 1/47) in the absence of photoexcitation.

Nanoscale ITO Films for Plasmon Resonance-Based Optical Sensors

The developing field of plasmonics has led to the possibility of creating a new type of high-speed, highly sensitive optical sensors for the analysis of chemical and biological media. The functional conducting layers of surface plasmon resonance (SPR) optical sensors are almost always nanoscale thin films of noble metals. To enhance the plasmon resonance, nanostructured films of transparent conductive oxides are introduced into the optical sensors. However, such modified optical sensors operate in the infrared region of the spectrum. In this work, we demonstrate that the use of indium tin oxide (ITO) films with a high concentration of charge carriers makes it possible to shift the surface plasmon resonance into the visible radiation region. The work presents the results of the development of magnetron deposition technology for ITO thin films, with optimal parameters for optical sensors based on surface plasmon resonance operating in the visible range of the spectrum. Their optical and electrical characteristics are investigated. Excitation of the surface and volume plasmon resonance at the dielectric-ITO film interface, using the Kretschman configuration, is studied. It is shown that SPR is excited in the investigated ITO films with a concentration of free charge carriers of the order of 1021–1022 cm−3, when irradiated with a beam of light with TM polarization in the wavelength range of 350–950 nm. At the same time, the addition of various analytes to the surface of an ITO film changes the excitation wavelength of the SPR.

Controlled Surface Morphology and Electrical Properties of Sputtered Titanium Nitride Thin Film for Metal–Insulator–Metal Structures

Titanium nitride (TiN) is a material of interest for electrodes owing to its high-temperature stability, robustness, low-cost, and suitable electrical properties. Herein, we studied the surface morphology and electrical properties of TiN thin film deposited onto an Si/SiO2 <100> substrate through direct current (DC) sputtering with a high-purity TiN target in an argon-gas environment. The electrical properties and surface morphology of TiN thin film significantly improved with increased source power and decreased working pressure. The improved electrical properties could be attributed to the suppressed secondary phase (Ti2N) formation and the reduced electron scattering on smoother surface. Consequently, high-quality TiN thin film with the lowest resistivity (ρ = 0.1 mΩ·cm) and the smallest surface roughness (RMS roughness, Rq = 0.3 nm) was obtained under the optimized condition. The TiN film was further used as the bottom electrode for a metal–insulator–metal (MIM) capacitor. Results demonstrated that the electrical properties of TiN film were comparable to those of noble-metal thin films. Therefore, the TiN thin film fabricated by DC sputtering method had excellent electrical properties and good Rq, indicating its potential applications in MIM capacitors and Si technology.

Biological Studies of New Implant Materials Based on Carbon and Polymer Carriers with Film Heterostructures Containing Noble Metals.

This paper presents pioneering results on the evaluation of noble metal film hetero-structures to improve some functional characteristics of carbon-based implant materials: carbon-composite material (CCM) and carbon-fiber-reinforced polyetheretherketone (CFR-PEEK). Metal-organic chemical vapor deposition (MOCVD) was successfully applied to the deposition of Ir, Pt, and PtIr films on these carriers. A noble metal layer as thin as 1 µm provided clear X-ray imaging of 1–2.5 mm thick CFR-PEEK samples. The coated and pristine CCM and CFR-PEEK samples were further surface-modified with Au and Ag nanoparticles (NPs) through MOCVD and physical vapor deposition (PVD) processes, respectively. The composition and microstructural features, the NPs sizes, and surface concentrations were determined. In vitro biological studies included tests for cytotoxicity and antibacterial properties. A series of samples were selected for subcutaneous implantation in rats (up to 3 months) and histological studies. The bimetallic PtIr-based heterostructures showed no cytotoxicity in vitro, but were less biocompatible due to a dense two-layered fibrous capsule. AuNP heterostructures on CFR-PEEK promoted cell proliferation in vitro and exhibited a strong inhibition of bacterial growth (p < 0.05) and high in vitro biocompatibility, especially Au/Ir structures. AgNP heterostructures showed a more pronounced antibacterial effect, while their in vivo biocompatibility was better than that of the pristine CFR-PEEK, but worse than that of AuNP heterostructures.

Hot Electron Extraction Enabled By Single-Crystal Metal Films and Nanostructures

In contrast to conventional photovoltaic devices which rely on bulk semiconductor material absorption and separation of electron-hole pairs, surface plasmon-based solar energy harvesting employs rectifying metal/dielectric interfaces to capture light and separate charges. Here, we describe the requirements for efficient hot electron extraction in plasmonic photovoltaic devices and demonstrate a new scalable and environmentally friendly electroless deposition method for single-crystal epitaxial noble metals films and nanostructures. The method produces ultra-smooth, low loss, single-crystal noble metal films ideal for subtractive patterning of nanostructures through ion beam milling, and high definition, sub-wavelength single crystal nanostructures through lithographic patterning methods. We describe the nucleation and growth of these metal films and nanostructures in the absence and presence of anionic shape-control agents and examine the role of specific anions in determining the resulting film and nanostructure morphologies via scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). These effects have been exploited to yield large area patterned, and shape-controlled nanoarrays of single crystal metal nanostructures for plasmonic and metamaterial applications. These approaches offer new and cost effective routes to achieve crystalline, shape-controlled surface nanostructure to enable efficient hot electron extraction for energy harvesting and catalysis applications and new noble metal alloys for improved electrocatalysis.

Manipulation of thin metal film morphology on weakly interacting substrates via selective deployment of alloying species

We demonstrate a versatile concept for manipulating morphology of thin (≤25 nm) noble-metal films on weakly interacting substrates using growth of Ag on SiO2 as a model system. The concept entails deployment of minority metallic (Cu, Au, Al, Ti, Cr, and Mo) alloying species at the Ag-layer growth front. Data from in situ and real-time monitoring of the deposition process show that all alloying agents—when deployed together with Ag vapor throughout the entire film deposition—favor two-dimensional (2D) growth morphology as compared to pure Ag film growth. This is manifested by an increase in the substrate area coverage for a given amount of deposited material in discontinuous layers and a decrease of the thickness at which a continuous layer is formed, though at the expense of a larger electrical resistivity. Based on ex situ microstructural analyses, we conclude that 2D morphological evolution under the presence of alloying species is predominantly caused by a decrease of the rate of island coalescence completion during the initial film-formation stages. Guided by this realization, alloying species are released with high temporal precision to selectively target growth stages before and after coalescence completion. Pre-coalescence deployment of all alloying agents yields a more pronounced 2D growth morphology, which for the case of Cu, Al, and Au is achieved without compromising the Ag-layer electrical conductivity. A more complex behavior is observed when alloying atoms are deposited during the post-coalescence growth stages: Cu, Au, Al, and Cr favor 2D morphology, while Ti and Mo yield a more pronounced three-dimensional morphological evolution. The overall results presented herein show that targeted deployment of alloying agents constitutes a generic platform for designing bespoken heterostructures between metal layers and technologically relevant weakly interacting substrates.

Printing noble metal alloy films with compositional gradient

Additive manufacturing has offered great promise in fabricating materials and devices with complex structures and unique properties. In addition to fabricating complex structures, additive manufacturing also allows for local changes to material compositions and structure, ideal for combinatorial material investigations. However, the on-demand control of compositional distributions in low dimensional materials remains challenging. In this work, we demonstrate a combinatorial aerosol jet printing technique to create noble metal films with gradient compositions. Nanoparticle sizes and ink chemistry are critical for aerosol jet printing and sintering process in order to achieve defect free thin films. Ruthenium (Ru) and platinum (Pt) nanoparticles with size <5 nm were synthesized and formulated into printable inks. After thermal sintering at temperature as low as 400 °C, printed nanoparticles formed highly reflective films free from microstructural defect. Alloy films of gradient compositions were realized via in-situ mixing Ru and Pt ink streams and varying the mixing ratio during the printing process. This combinatorial printing method provides great potential to rapidly transform nanoparticle inks into new materials compositions and structures unobtainable via conventional methods.

The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High-Quality Ru Films by Zero-Oxidation State Ru(DMBD)(CO)3.

Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η4 -2,3-dimethylbutadiene ruthenium(0) tricarbonyl (Ru(DMBD)(CO)3 ), a zero-valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. The authors study the growth mechanism of this precursor by in situ quartz-crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO)3 produces high-quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical chemical vapor deposition processes, with a strong dependence on both temperature and reaction timescale. The non-self-limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, it is suggested that the findings can be generalized to the broader class of zero-oxidation state carbonyl-based precursors used in thermal ALD, with insight into the design of effective saturation studies.

Spatial aspects of spin polarization of structurally split surface states in thin films with magnetic exchange and spin–orbit interaction

A theoretical study is presented of the effect of an in-plane magnetic exchange field on the band structure of centrosymmetric films of noble metals and topological insulators. Based on an ab initio relativistic k ⋅ p theory, a minimal effective model is developed that describes two coupled copies of a Rashba or Dirac electronic system residing at the opposite surfaces of the film. The coupling leads to a structural gap at and causes an exotic redistribution of the spin density in the film when the exchange field is introduced. We apply the model to a nineteen-layer Au(111) film and to a five-quintuple-layer Sb2Te3 film. We demonstrate that at each film surface the exchange field induces spectrum distortions similar to those known for Rashba or Dirac surface states with an important difference due to the coupling: at some energies, one branch of the state loses its counterpart with the oppositely directed group velocity. This suggests that a large-angle electron scattering between the film surfaces through the interior of the film is dominant or even the only possible for such energies. The spin-density redistribution accompanying the loss of the counterpart favors this scattering channel.

Nonlinear plasmonic response in atomically thin metal films.

Nanoscale nonlinear optics is limited by the inherently weak nonlinear response of conventional materials and the small light-matter interaction volumes available in nanostructures. Plasmonic excitations can alleviate these limitations through subwavelength light focusing, boosting optical near fields that drive the nonlinear response, but also suffering from large inelastic losses that are further aggravated by fabrication imperfections. Here, we theoretically explore the enhanced nonlinear response arising from extremely confined plasmon polaritons in few-atom-thick crystalline noble metal films. Our results are based on quantum-mechanical simulations of the nonlinear optical response in atomically thin metal films that incorporate crucial electronic band structure features associated with vertical quantum confinement, electron spill-out, and surface states. We predict an overall enhancement in plasmon-mediated nonlinear optical phenomena with decreasing film thickness, underscoring the importance of surface and electronic structure in the response of ultrathin metal films.

Heat flow dynamics in planar multilayer antennas excited by far-infrared picosecond laser pulses

Thin metallic buffer layers are commonly used between semiconductor substrates and noble metal films or nanostructures. We propose an extended two-temperature heat transfer model that can be used to investigate the heat flow in multilayer antennas and includes metallic layers, a dielectric substrate, and their respective interfaces. It is demonstrated how the heat flow dynamics in a layered material, excited by short laser pulses, can be controlled by the thermal properties of the buffer layer. A large buffer layer electron-phonon coupling was found to induce a non-intuitive reverse internal heat flow in the layered material and transient energy retention on time scales of a few tens of picoseconds, while the buffer layer-substrate Kapitza conductance was found to be the limiting parameter for the heat dissipation on nanosecond time scales.

Study of Pt growth on Si, Al2O3, Au, and Ni surfaces by plasma enhanced atomic layer deposition

Atomic layer deposition is a powerful technique for achieving atomic-level control in the deposition of thin films and nanoparticles. The ultrathin noble metal films can be applied in many functional devices, but it is a challenge to obtain such films since the island growth mode generally happens instead of the layer growth mode. In this work, the nucleation and growth of platinum on Si, Al2O3, Au, and Ni substrates were studied using (MeCp)PtMe3 and O2 plasma as a precursor and a co-reactant, respectively. The evolution of Pt coverage on different surfaces was observed and discussed based on the experimental results by x-ray photoelectron spectra. The chemical adsorption of the precursor and the following processes like metal atom diffusion on substrate surfaces and up-stepping onto the existing metal islands were considered to dominate the growth before continuous films formed. The chemisorption determined the metal coverage on bare substrate surfaces, and the total coverage was influenced by metal atom diffusion and up-stepping behaviors that are determined by surface energy relationships between the deposited metal and substrate surfaces. Pt films were easier to form on Al2O3 and Ni surfaces compared with on Si and Au surfaces, respectively. A model was proposed to help to understand the mechanisms in the nucleation and growth processes, involving the chemisorption, diffusion, and up-stepping, which contributed to prepare ultrathin continuous Pt films on different substrates.

Noble Metallic Pyramidal Substrate for Surface-Enhanced Raman Scattering Detection of Plasmid DNA Based on Template Stripping Method.

In this paper, a new method for manufacturing flexible and repeatable sensors made of silicon solar cells is reported. The method involves depositing the noble metal film directly onto the Si template and stripping out the substrate with a pyramid morphology by using an adhesive polymer. In order to evaluate the enhancement ability of the substrate, Rhodamine 6G (R6G) were used as surface-enhanced Raman scattering (SERS) probe molecules, and the results showed a high sensitivity and stability. The limit of detection was down to M for R6G. The finite-difference time domain (FDTD) was used to reflect the distribution of the electromagnetic field, and the electric field was greatly enhanced on the surface of the inverted pyramidal substrate, especially in pits. The mechanism of Raman enhancement of two types of pyramidal SERS substrate, before and after stripping of the noble metal film, is discussed. By detecting low concentrations of plasmid DNA, the identification of seven characteristic peaks was successfully realized using a noble metallic pyramidal substrate.

MOCVD of Noble Metal Film Materials for Medical Implants: Microstructure and Biocompatibility of Ir and Au/Ir Coatings on TiNi

Noble metals such as Ir, Pt, Au are promising as coatings for metal medical implants to improve biocompatibility and corrosion resistance. Moreover, these coatings can be used as a basis for the further formation of bimetallic hetero-structures with enhanced antibacterial properties. In this work, we develop an approach to obtain such coatings by metal-organic chemical vapor deposition (MOCVD). We have been focused on the formation of Ir coating with developed morphology and subsequent discrete Au coating onto the titanium nickelide (TiNi) implant material. Iridium was deposited in an oxidizing atmosphere from the volatile precursor [Ir(cod)(acac)] (cod = cyclooctadiene-1,5, acac = acetylacetonate-anion). The effects of the deposition temperature (290–350 °C) and amount of introduced oxygen on the composition (Ir, Ir + IrO2) and microstructure of the samples were studied. Hetero-metallic Au/Ir coatings were obtained using [(CH3)2Au(thd)] precursor (thd = dpm = dipivaloylmethanate-anion) at a deposition temperature of 240 °C in the presence of oxygen. To assess the biocompatibility, the toxicity of Ir/TiNi, Au/Ir/TiNi, and uncoated TiNi in relation to human embryonic stem cell line Man-1 was examined after 1, 3, and 5 days of incubation. The results obtained were explained based on the coating microstructures.

Role of pH on Nanostructured SERS Active Substrates for Detection of Organic Dyes.

Surface Enhanced Raman Spectroscopy is commonly used as analytical improvement to conventional Raman spectroscopy, able to respond to qualitative diagnostic enquiries, which involve low-concentrated molecular species in complex matrix. In this paper, we described fabrication, characterization and testing of a type of SERS-active substrates realized specifically to detect pigments in work of art. In particular, we detailed the SERS activity of nanostructured noble metal films deposited by pulsed laser ablation onto glass and polishing sheets substrates. The SERS response of the substrates was tested against the presence of some organic dyes in aqueous solutions. Measurements were performed at different pH values, in acidic or basic range, in order to investigate its role in the adsorption mechanism, thus fostering the SERS amplification. In addition, we checked the possible deterioration of the structural properties of the substrates that could occur in presence of alkaline or acidic environment. SERS activity of the substrates was tested against a commonly dye used as a SERS standard (Blue Methylene). Thereafter, substrates have been tested on two organic dyes (Alizarine red-S and Brazilwood), which had proven to be Raman active but present also either a weak Raman scattering cross section and/or a high fluorescence emission. The substrates have proven effective in amplifying Raman scattering of all dyes, quenching troubling fluorescence effects. Furthermore, they have proven to be stable in the pH range between 3 and 11. Furthermore, we carry out of vibrational DFT-calculation of dyes that provide a complete description of the observed SERS spectra.

Strong Coupling, Hyperbolic Metamaterials and Optical Tamm States in Layered Dielectric-Plasmonic Media

Thin films of noble metals with thickness smaller than the wavelength of light constitute one of the most investigated structures in plasmonics. The fact that surface plasmon modes can be excited in these films by different ways and the simplicity of fabrication offer ideal conditions for applications in nanophotonics. The generation of optical modes in coupled Fabry-Pérot planar cavities and their migration to hyperbolic metamaterials is investigated. Coupled Fabry-Pérot cavities behave as simple coupled resonators. When the intra-cavity media have different refractive indices in two or more coupled cavities resonance anti-crossings arise. The application of this kind of strong coupling in sensing is foreseen. Beyond the cavity modes excited by propagating waves, also long range plasmonic guided modes can be excited using emitters or evanescent waves. A periodic structure made by multiple plasmonic films and dielectrica supports bulk plasmons, of large propagation constant and increasing field amplitude. The optical response of these structures approaches that of the hyperbolic metamaterial predicted by the effective medium theory. Light can propagate with full transmission in a structure made of a photonic crystal based on quarter wavelength layers and a second photonic crystal with an overlapping forbidden band, but presenting a non-trivial topological phase achieved by band inversion. This is due to excitation of optical Tamm states at the boundary between both crystals. The extension to multiple optical Tamm states using dielectric and plasmonic materials and the symmetries of the edge states is investigated.