Multitarget Reactive Magnetron Sputtering towards the Production of Strontium Molybdate Thin Films.

X-ray photoelectron spectroscopy was used to study the direct synthesis of strontium and molybdenum oxide thin films deposited by multitarget reactive magnetron sputtering (MT-RMS). Sr and Mo targets with a purity of 99.9% and 99.5%, respectively, were co-sputtered in an argon-oxygen gas mixture. The chamber was provided with an oxygen background flow plus an additional controlled oxygen supply to each of the targets. We demonstrate that variation in the power applied to the Mo target during MT-RMS enables the production of strontium and molybdenum oxide films with variable concentrations of Mo atoms. Both molybdenum and strontium were found in the oxidized state, and no metallic peaks were detected. The deconvoluted high-resolution XPS spectra of molybdenum revealed the presence of several Mo 3d peaks, which indicates molybdenum bonds in a lower valence state. Contrary to the Mo spectra, the high-resolution strontium Sr 3d spectra for the same samples were very similar, and no additional peaks were detected.

Shape influence on the ultrafast plasmonic properties of gold nanoparticles.

The aim of shape-controlled colloidal synthesis of gold (Au) is to produce Au nanoparticles (NPs) with fine control of shapes, sizes, and dispersities. We show how transient absorption spectroscopy (TAS) can be used to rapidly and accurately quantify the vast ensemble of shapes of Au NPs in solution within minutes, including the synthesized nanorods, decahedra, and nanospheres. Colloidal solutions containing Au NPs were measured in TAS and their localized surface plasmon resonance (LSPR) modes were classified according to the shape, wavelength and number of peaks. Then their excited-state relaxation dynamics were used to ascertain their electron-phonon (e-ph) coupling time constant and frequency of optomechanical modes. TAS can quickly show that an Au nanosphere sample contains a tiny fraction of Au nanorods, whereas steady-state absorbance is totally blind to the presence of nanorods. Additionally, the TAS experiments indicate that the characteristic e-ph coupling time constants in Au nanorods depend on the NPs dimensions at high excitation intensity (> 6 µJ/cm2) which can help identify if there are any elongated Au NPs in Au spheres samples. Finally, optomechanical oscillations formed by NPs breathing modes were observed, providing information related to the average size and monodispersity of Au nanospheres and nanorods.

Practical Approaches to Apply Ultra-Thick Graphite Anode to High-Energy Lithium-Ion Battery: Carbonization and 3-Dimensionalization.

Lithium-ion batteries with ultra-thick electrodes have high energy density and low manufacturing costs because of the reduction of the inactive materials in the same battery volume. However, the partial usage of the full capacity and the low rate capability are caused by poor ionic and electronic conduction. In this work, the effects of two approaches, such as electrode binder carbonization by heat treatment and 3-dimensionalization by the laser structuring of ultra-thick graphite anodes to lithium-ion batteries for high energy density, are investigated. During the heat treatment, the polyvinylidene fluoride (PVDF) binder is carbonized to form fluorinated graphitic carbons, thereby increasing the number of lithium-ion storage sites and the improvement of the electrode capacity by 14% (420 mAh g-1 and 20 mAh cm-2). Further, the carbonization improves the rate capability by 31% at 0.1 C by simultaneously reducing the ionic and electronic resistances. Furthermore, after the laser structuring of the carbonized electrode, the areal discharge capacity increases to 50% at the increasing current rates, resulting from drastically improved ionic conduction. In addition to the electrochemical characteristics, these two approaches contribute considerably to the fast wetting of the electrolyte into the ultra-thick electrode. The carbonization and laser structuring of the ultra-thick graphite anodes are practical approaches for high-energy batteries to overcome the thickness limitation.

Fabrication of an Extremely Cheap Poly(3,4-ethylenedioxythiophene) Modified Pencil Lead Electrode for Effective Hydroquinone Sensing.

Hydroquinone (HQ) is one of the major deleterious metabolites of benzene in the human body, which has been implicated to cause various human diseases. In order to fabricate a feasible sensor for the accurate detection of HQ, we attempted to electrochemically modify a piece of common 2B pencil lead (PL) with the conductive poly(3,4-ethylenedioxythiophene) or PEDOT film to construct a PEDOT/PL electrode. We then examined the performance of PEDOT/PL in the detection of hydroquinone with different voltammetry methods. Our results have demonstrated that PEDOT film was able to dramatically enhance the electrochemical response of pencil lead electrode to hydroquinone and exhibited a good linear correlation between anodic peak current and the concentration of hydroquinone by either cyclic voltammetry or linear sweep voltammetry. The influences of PEDOT film thickness, sample pH, voltammetry scan rate, and possible chemical interferences on the measurement of hydroquinone have been discussed. The PEDOT film was further characterized by SEM with EDS and FTIR spectrum, as well as for stability with multiple measurements. Our results have demonstrated that the PEDOT modified PL electrode could be an attractive option to easily fabricate an economical sensor and provide an accurate and stable approach to monitoring various chemicals and biomolecules.

Preclinical Study of a Multi-Layered Antimicrobial Patch Based on Thin Nanocomposite Amorphous Diamond Like Carbon Films with Embedded Silver Nanoparticles.

A growing number of severe infections are related to antibiotic-resistant bacteria, therefore, in recent years, alternative antimicrobial materials based on silver nanoparticles (NPs) attracted a lot of attention. In the current research, we present a medical patch prototype containing diamond-like carbon nanocomposite thin films doped with silver nanoparticles (DLC:Ag), as a source of silver ions, and an aqueous mass of the gelatin/agar mixture as a silver ion accumulation layer. The DLC:Ag thin films with 3.4 at.% of silver were deposited on synthetic silk employing reactive unbalanced DC magnetron sputtering of the silver target with argon ions performed in the acetylene gas atmosphere. The average size of the silver nanoparticles as defined by scanning electron microscope was 24 nm. After the film deposition, the samples were etched with RF oxygen plasma, aiming at efficient silver ion release in aqueous media from the nanocomposite film. In the patch prototype, a mixture of agar and gelatin was applied in silicone carrier with cavities, acting as a silver ion accumulation layer that further enhanced the antimicrobial efficiency. It was found that the DLC:Ag thin film on the silk after soaking in water for 24 h was able to release up to 4 ppm of Ag. The microbiological experiments using S. aureus bacteria were performed with the patch prototype and the silver ion saturated water, demonstrated the inactivation of 99% and 79% of bacteria, respectively. Scanning electron microscopy analysis showed that silver NPs destroyed the bacteria cell and the bacteria affected by Ag ions had spots and perforated cell wall areas with cytoplasm leakage out was obtained. A preliminary preclinical study using the laboratory animals demonstrated that using the patch prototype, the methicillin-resistant S. aureus (MRSA)-infected wound on skin surface healed faster compared with control and was able to kill all MRSA bacteria strains in the wound's bed after 72 h of treatment.

Diamond Like Carbon Films Containing Si: Structure and Nonlinear Optical Properties.

In the present research diamond-like carbon (DLC) films containing 4-29 at.% of silicon were deposited by reactive magnetron sputtering of carbon target. Study by X-ray photoelectron spectroscopy revealed the presence of Si-C bonds in the films. Nevertheless, a significant amount of Si-O-C and Si-Ox bonds was present too. The shape of the Raman scattering spectra of all studied diamond-like carbon containing silicon (DLC:Si) films was typical for diamond-like carbon. However, some peculiarities related to silicon doping were found. Studies on the dependence of DLC:Si of the optical transmittance spectra on the Si atomic concentration have shown that doping by silicon affects linear, as well as nonlinear, optical properties of the films. It is shown that the normalized reflectance of DLC:Si films decreased with the increased exciting light fluence. No clear relation between the normalized reflectance and photoexcited charge carrier relaxation time was found. It was suggested that that the normalized reflectance decrease with fluence can be related to nonlinear optical properties of the hydrogenated diamond-like carbon phase in DLC:Si film.

Hydrogen-Free Diamond Like Carbon Films with Embedded Cu Nanoparticles: Structure, Composition and Reverse Saturable Absorption Effect.

In the present research, hydrogen-free diamond like carbon films with embedded copper nanoparticles (DLC:Cu) were grown by simultaneous DC magnetron sputtering of the graphite and copper targets. X-ray photoelectron spectroscopy was used to define the composition of the samples. Atomic force microscopy studies of diamond, like carbon films containing different amount of copper, revealed wide range of the surface morphologies as well as sizes and shapes of the embedded copper nanoclusters. Raman scattering spectra of all the DLC:Cu films investigated were typical for diamond-like carbon (including samples containing more than 60 at.% of copper). sp3/sp2 carbon bond ratio in the films decreased with the increase of the Cu amount in the films. According to the optical absorbance measurements, the surface plasmon resonance related absorption peak of DLC:Cu films was only detected in the films containing 28.45 at.% Cu. For the diamond like carbon films containing more than 40 at.% Cu, a further increase of Cu amount in the nanocomposite resulted in minor changes of the absorbance spectra. Some correlation between the changes of the samples surface morphology as well as phase structure and optical absorbance spectra of the films was found. In all cases, reverse-saturable absorption of the DLC:Cu films was observed. For some DLC:Cu films damage of the sample occurred at higher light fluences that can be related to the heating that is caused by the surface plasmon resonance effect.

Surface Lattice Resonances in Self-Assembled Arrays of Monodisperse Ag Cuboctahedra.

Plasmonic metal nanoparticles arranged in periodic arrays can generate surface lattice plasmon resonances (SLRs) with high Q-factors. These collective resonances are interesting because the associated electromagnetic field is delocalized throughout the plane of the array, enabling applications such as biosensing and nanolasing. In most cases such periodic nanostructures are created via top-down nanofabrication processes. Here we describe a capillary-force-assisted particle assembly method (CAPA) to assemble monodisperse single-crystal colloidal Ag cuboctahedra into nearly defect-free >1 cm2 hexagonal lattices. These arrays are large enough to be measured with conventional ultraviolet-visible spectroscopy, which revealed an extinction peak with a Q-factor of 30 at orthogonal illumination and up to 80 at oblique illumination angles. We explain how the experimental extinction changes with different light polarizations and angles of incidence, and compare the evolution of the peaks with computational models based on the coupled dipole approximation and the finite element method. These arrays can support high Q-factors even when exposed to air, because of the high aspect ratio of the single-crystal nanoparticles. The observation of SLRs in a self-assembled system demonstrates that a high level of long-range positional control can be achieved at the single-particle level.

High-Density Plasmonic Nanoparticle Arrays Deposited on Nanoporous Anodic Alumina Templates for Optical Sensor Applications.

This study demonstrates a new, robust, and accessible deposition technique of metal nanoparticle arrays (NPAs), which uses nanoporous anodic alumina (NAA) as a template for capillary force-assisted convective colloid (40, 60, and 80 nm diameter Au) assembly. The NPA density and nanoparticle size can be independently tuned by the anodization conditions and colloid synthesis protocols. This enables production of non-touching variable-density NPAs with controllable gaps in the 20-60 nm range. The NPA nearest neighbor center distance in the present study was fixed to 100 nm by the choice of anodization protocol. The obtained Au NPAs have the resonant scattering maxima in the visible spectral range, with a refractometric sensitivity, which can be tuned by the variation of the array density. The thickness of the NAA layer in an Aluminum-NAA-NPA multilayer system enables further tuning of the resonance frequency and optimization for use with specific molecules, e.g., to avoid absorption bands. Applicability of the mentioned multilayers for colorimetric refractive index (RI) sensing is demonstrated. Their use as Surface-Enhanced Raman Scattering (SERS) substrates is tested using hemoglobin as a biological probe molecule.

Dot-Matrix Hologram Rendering Algorithm and its Validation through Direct Laser Interference Patterning.

The fight against forgery of valuable items demands efficient and reasonably priced solutions. A security tag featuring holographic elements for anti-counterfeiting is one of them. However, the content and colours of a diffraction image that would be seen by an observer are often counterintuitive in the design stage. Here, we propose an original algorithm based on the conical diffraction formalism, which can be used to describe the variations of a diffraction image with respect to all aspects of observation. We validate the output of the algorithm by comparing it to test holograms, which we have produced by employing direct laser interference patterning (DLIP) in electrochemically grown nickel foil. We have employed a motorized femtosecond laser system to micro-machine arrays of 65 µm × 65 µm sized diffraction gratings with a defined orientation and pitch on the order of 1 µm. Based on completed diffraction efficiency measurements, we determined optimal ablation parameters, i.e. 57.4 mJ/cm2 fluence per pulse and 1100 pulses/pixel. Furthermore, we show how accurate the proposed algorithm is through measured diffraction spectra as well as captured diffraction images of test holograms produced using the obtained parameters. Finally, we showcase anti-counterfeiting tag prototypes with complex holographic effects, i.e. colour reconstruction, animation effects, and image multiplexing. The proposed algorithm can severely shorten the time between design and production of a holographic tag, especially when realizing it via a competitive origination technology-DLIP.

Giant Negative Piezoresistive Effect in Diamond-like Carbon and Diamond-like Carbon-Based Nickel Nanocomposite Films Deposited by Reactive Magnetron Sputtering of Ni Target.

Piezoresistive properties of hydrogenated diamond-like carbon (DLC) and DLC-based nickel nanocomposite (DLC:Ni) films were studied in the range of low concentration of nickel nanoparticles. The films were deposited by reactive high power pulsed magnetron sputtering (HIPIMS) of Ni target, and some samples were deposited by direct current (dc) reactive magnetron sputtering for comparison purposes. Raman scattering spectroscopy, energy-dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) were used to study the structure and chemical composition of the films. A four-point bending test was applied to study piezoresistive properties of the films. For some samples containing less than 4 at. % Ni and for the samples containing no Ni (as defined by both EDS and XPS), a giant negative piezoresistive effect was observed. The giant negative piezoresistive effect in DLC films deposited by either reactive HIPIMS or dc magnetron sputtering of Ni target was explained by possible clustering of the sp2-bonded carbon and/or formation of areas with the decreased hydrogen content. It was suggested that the tensile stress-induced rearrangements of these conglomerations have resulted in the increased conductivity paths.

Twisted Intramolecular Charge Transfer States in Trinary Star-Shaped Triphenylamine-Based Compounds.

Excited state dynamics of trinary star-shaped dendritic compounds with triphenylamine arms and different cores were studied by means of time-resolved fluorescence and transient absorption. Under optical excitation, nonpolar C3 symmetry molecules form polar excited states localized on one of the molecular substituents. Conformational excited state stabilization of molecules with an electron-accepting core causes a formation of twisted internal charge transfer (TICT) states in polar solvents. A low transition dipole moment from TICT state to the ground state causes very weak fluorescence of those compounds and strong dependence on the solvent polarity. The compound formed from the triphenylamine central core and identical arms also experiences excited state twisting, however, weakly sensitive to the solvent polarity.

Femtosecond laser micro-machined polyimide films for cell scaffold applications.

Engineering of sophisticated synthetic 3D scaffolds that allow controlling behaviour and location of the cells requires advanced micro/nano-fabrication techniques. Ultrafast laser micro-machining employing a 1030-nm wavelength Yb:KGW femtosecond laser and a micro-fabrication workstation for micro-machining of commercially available 12.7 and 25.4 µm thickness polyimide (PI) film was applied. Mechanical properties of the fabricated scaffolds, i.e. arrays of differently spaced holes, were examined via custom-built uniaxial micro-tensile testing and finite element method simulations. We demonstrate that experimental micro-tensile testing results could be numerically simulated and explained by two-material model, assuming that 2-6 µm width rings around the holes possessed up to five times higher Young's modulus and yield stress compared with the rest of the laser intacted PI film areas of 'dog-bone'-shaped specimens. That was attributed to material modification around the micro-machined holes in the vicinity of the position of the focused laser beam track during trepanning drilling. We demonstrate that virgin PI films provide a suitable environment for the mobility, proliferation and intercellular communication of human bone marrow mesenchymal stem cells, and discuss how cell behaviour varies on the micro-machined PI films with holes of different diameters (3.1, 8.4 and 16.7 µm) and hole spacing (30, 35, 40 and 45 µm). We conclude that the holes of 3.1 µm diameter were sufficient for metabolic and genetic communication through membranous tunneling tubes between cells residing on the opposite sides of PI film, but prevented the trans-migration of cells through the holes. Copyright © 2016 John Wiley & Sons, Ltd.

Diamond like carbon nanocomposites with embedded metallic nanoparticles.

In this work we present an overview on structure formation, optical and electrical properties of diamond like carbon (DLC) based metal nanocomposites deposited by reactive magnetron sputtering and treated by plasma and laser ablation methods. The influence of deposition mode and other technological conditions on the properties of the nanosized filler, matrix components and composition were studied systematically in relation to the final properties of the nanocomposites. Applications of the nanocomposites in the development of novel biosensors combining resonance response of wave guiding structures in DLC based nanocomposites as well as plasmonic effects are also presented.

Photovoltaic Properties and Ultrafast Plasmon Relaxation Dynamics of Diamond-Like Carbon Nanocomposite Films with Embedded Ag Nanoparticles.

Ultrafast relaxation dynamics of diamond-like carbon (DLC) films with embedded Ag nanoparticles (DLC:Ag) and photovoltaic properties of heterojunctions consisting of DLC:Ag and crystalline silicon (DLC:Ag/Si) were investigated by means of transient absorption (TAS) spectroscopy and photovoltaic measurements. The heterojunctions using both p type and n type silicon were studied. It was found that TAS spectra of DLC:Ag films were dependent on the used excitation wavelength. At wavelengths where Ag nanoparticles absorbed light most intensively, only DLC signal was registered. This result is in good accordance with an increase of the DLC:Ag/Si heterojunction short circuit current and open circuit voltage with the excitation wavelength in the photovoltaic measurements. The dependence of the TAS spectra of DLC:Ag films and photovoltaic properties of DLC:Ag/Si heterostructures on the excitation wavelength was explained as a result of trapping of the photoexcited hot charge carriers in DLC matrix. The negative photovoltaic effect was observed for DLC:Ag/p-Si heterostructures and positive ("conventional") for DLC:Ag/n-Si ones. It was explained by the excitation of hot plasmonic holes in the Ag nanoparticles embedded into DLC matrix. Some decrease of DLC:Ag/Si heterostructures photovoltage as well as photocurrent with DLC:Ag film thickness was observed, indicating role of the interface in the charge transfer process of photocarriers excited in Ag nanoparticles.

Nitrogen-doped twisted graphene grown on copper by atmospheric pressure CVD from a decane precursor.

We present Raman studies of graphene films grown on copper foil by atmospheric pressure CVD with n-decane as a precursor, a mixture of nitrogen and hydrogen as the carrier gas, under different hydrogen flow rates. A novel approach for the processing of the Raman spectroscopy data was employed. It was found that in particular cases, the various parameters of the Raman spectra can be assigned to fractions of the films with different thicknesses. In particular, such quantities as the full width at half maximum of the 2D peak and the position of the 2D graphene band were successfully applied for the elaborated approach. Both the G- and 2D-band positions of single layer fractions were blue-shifted, which could be associated with the nitrogen doping of studied films. The XPS study revealed the characteristics of incorporated nitrogen, which was found to have a binding energy around 402 eV. Moreover, based on the statistical analysis of spectral parameters and the observation of a G-resonance, the twisted nature of the double-layer fraction of graphene grown with a lower hydrogen feeding rate was demonstrated. The impact of the varied hydrogen flow rate on the structural properties of graphene and the nitrogen concentration is also discussed.

Micromachining and validation of the scanning acoustic microscope spatial resolution and sensitivity calibration block for 20-230 MHz frequency range.

Scanning acoustic microscopy (SAM) is used as a routine non-destructive test tool for different diagnostic examinations: detection of defects such as microcracks, delamination, disbonding, inclusions, subsurface features in materials such as pores and cracks. SAM can be operated in a wide frequency range from Megahertz to Gigahertz. SAM measurement spatial resolution is diffraction limited by the wavelength of the acoustic wave in particular medium and also depends on individual transducers geometry. Actual SAM spatial resolution can be determined by measuring calibrated lithographically formed microstructures in high acoustic impedance materials. Numerical acoustic signal simulation method, based on the diffraction approach, was employed for the selection of the calibration block pattern geometry and linear dimensions of the elements. Universal calibration block for SAM operating in a 20-230 MHz frequency range was micromachined in high acoustic impedance ceramic substrates. Differently spaced (from 18 to 185 µm) lines of the same width and different widths (from 17 to 113 µm) but similar spacing lines were imposed in alumina ceramics employing one step lithography process, i.e. femtosecond laser ablation. Proposed SAM calibration pattern linear dimensions were characterized employing optical and scanning electron microscopy. Finally the samples were measured with SAM employing different frequency transducers and results were compared with the numerical simulations. It was obtained that resolution of SAM operating with 230 MHz transducer is not worse than 40 µm.

Annealing Effects on Structure and Optical Properties of Diamond-Like Carbon Films Containing Silver.

In the present study, diamond-like carbon films with embedded Ag nanoparticles (DLC:Ag) were deposited by reactive magnetron sputtering. Structure of the films was investigated by Raman scattering spectroscopy. Atomic force microscopy was used to define thickness of DLC:Ag films as well as to study the surface morphology and size distribution of Ag nanoparticles. Optical absorbance and reflectance spectra of the films were studied in the 180-1100-nm range. Air annealing effects on structure and optical properties of the DLC:Ag were investigated. Annealing temperatures were varied in the 180-400 °C range. Changes of size and shape of the Ag nanoclusters took place due to agglomeration. It was found that air annealing of DLC:Ag films can result in graphitization following destruction of the DLC matrix. Additional activation of surface-enhanced Raman scattering (SERS) effect in DLC:Ag films can be achieved by properly selecting annealing conditions. Annealing resulted in blueshift as well as significant narrowing of the plasmonic absorbance and reflectance peaks. Moreover, quadrupole surface plasmon resonance peaks appeared. Modeling of absorption spectra of the nanoclusters depending on the shape and surrounding media has been carried out.

Antimicrobial Properties of Diamond-Like Carbon/Silver Nanocomposite Thin Films Deposited on Textiles: Towards Smart Bandages.

In the current work, a new antibacterial bandage was proposed where diamond-like carbon with silver nanoparticle (DLC:Ag)-coated synthetic silk tissue was used as a building block. The DLC:Ag structure, the dimensions of nanoparticles, the silver concentration and the silver ion release were studied systematically employing scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic absorption spectroscopy, respectively. Antimicrobial properties were investigated using microbiological tests (disk diffusion method and spread-plate technique). The DLC:Ag layer was stabilized on the surface of the bandage using a thin layer of medical grade gelatin and cellulose. Four different strains of Staphylococcus aureus extracted from humans' and animals' infected wounds were used. It is demonstrated that the efficiency of the Ag⁺ ion release to the aqueous media can be increased by further RF oxygen plasma etching of the nanocomposite. It was obtained that the best antibacterial properties were demonstrated by the plasma-processed DLC:Ag layer having a 3.12 at % Ag surface concentration with the dominating linear dimensions of nanoparticles being 23.7 nm. An extra protective layer made from cellulose and gelatin with agar contributed to the accumulation and efficient release of silver ions to the aqueous media, increasing bandage antimicrobial efficiency up to 50% as compared to the single DLC:Ag layer on textile.

Spectroellipsometric characterization and modeling of plasmonic diamond-like carbon nanocomposite films with embedded Ag nanoparticles.

Diamond-like carbon nanocomposite films with embedded silver nanoparticles are considered experimentally (spectroellipsometric characterization) and theoretically (modeling of optical properties). Metallic nanocomposite films were synthesized by reactive magnetron sputtering and were studied by transmission electron microscope (TEM) and atomic force microscope (AFM). The optical constants of the films were determined from spectroscopic ellipsometry measurements and were modeled using the Maxwell-Garnett approximations. Comparison between the extended and renormalized Maxwell-Garnett theory was conducted. Surface plasmon resonance peak have been found to be strongly dependent on the shape of nanoparticles and interaction between them.