Corrosion and tribological performance of quasi-stoichiometric titanium containing carbo-nitride coatings

Zr, Nb and Si doped TiCN coatings, with (C+N)/(metal + Si) ratios of approximately 1, were deposited on stainless steel and Si wafer substrates using a cathodic arc technique in a mixture of N2 and CH4 gases. The coatings were comparatively analysed for elemental and phase composition, adhesion, anticorrosive properties and tribological performance at ambient and 250 °C. Zr, Nb and Si alloying contents in the coatings were in the range 2.9–9.6 at.%. All the coatings exhibited f.c.c. solid solution structures and had a 〈111〉 preferred orientation. In the adhesion tests conducted, critical loads ranged from 20 to 30 N, indicative of a good adhesion to substrate materials. The Ti based coatings with Nb or Si alloying elements proved to be resistant to corrosive attack in 3.5% NaCl and of these coatings the TiNbCN was found to have the best corrosion resistance. TiCN exhibited the best tribological performance at 250 °C, while at ambient temperatures it was TiNbCN. Abrasive and oxidative wear was found to be the main wear mechanism for all of the coatings. Of the tested coatings, TiNbCN coatings would be the most suitable candidate for severe service (high temperature, corrosive, etc.) applications

Chemiresistive/SERS dual sensor based on densely packed gold nanoparticles

Chemiresistors are a class of sensitive electrical devices capable of detecting (bio)chemicals by simply monitoring electrical resistance. Sensing based on surface enhanced Raman scattering (SERS) represents a radically different approach, in which molecules are optically detected according to their vibrational spectroscopic fingerprint. Despite different concepts are involved, one can find in the literature examples from both categories reporting sensors made of gold nanoparticles. The same building blocks appear because both sensor classes share a common principle: nanometric interparticle gaps are needed, for electron tunneling in chemiresistors, and for enhancing electromagnetic fields by plasmon coupling in SERS-based sensors. By exploiting such nano-gaps in self-assembled films of gold nanoparticles, we demonstrate the proof of concept of a dual electrical/optical sensor, with both chemiresistive and SERS capabilities. The proposed device is realized by self-assembling 15 nm gold nanoparticles into few micrometers-wide strips across commercially available interdigitated electrodes. The dual-mode operation of the device is demonstrated by the detection of a biologically relevant model analyte, 4-mercaptophenyl boronic acid

Flexible transparent sensors from reduced graphene oxide micro-stripes fabricated by convective self-assembly

International audienceReduced graphene oxide (rGO) currently represents an attractive alternative material for graphene and its already well-known electronics applications. Due to its liquid phase processing it can be produced inexpensively on large scale, but its deposition into films/patterns of defined geometry on solid substrates remains challenging. In this work, rGO micro-stripes with controlled morphology are prepared on polyethylene terephthalate substrates by Stop&Go Convective Self-Assembly. This method allows the deposition of regular arrays of rGO stripes by independently adjusting the stripe geometry and array period in an inexpensive, clean and fast way, and without any lithographic patterning. The as-obtained rGO stripes are highly transparent, flexible and good electrical conductors, properties which are of great value for future electronic devices. We exploit these properties for fabricating for the first time a bi-functional strain and humidity sensor which is optically transparent

Flexible transparent sensors from reduced graphene oxide micro-stripes fabricated by convective self-assembly

International audienceReduced graphene oxide (rGO) currently represents an attractive alternative material for graphene and its already well-known electronics applications. Due to its liquid phase processing it can be produced inexpensively on large scale, but its deposition into films/patterns of defined geometry on solid substrates remains challenging. In this work, rGO micro-stripes with controlled morphology are prepared on polyethylene terephthalate substrates by Stop&Go Convective Self-Assembly. This method allows the deposition of regular arrays of rGO stripes by independently adjusting the stripe geometry and array period in an inexpensive, clean and fast way, and without any lithographic patterning. The as-obtained rGO stripes are highly transparent, flexible and good electrical conductors, properties which are of great value for future electronic devices. We exploit these properties for fabricating for the first time a bi-functional strain and humidity sensor which is optically transparent

Gold Nanopost-Shell Arrays Fabricated by Nanoimprint Lithography as a Flexible Plasmonic Sensing Platform

Plasmonic noble metal nanostructured films have a huge potential for the development of efficient, tunable, miniaturized optical sensors. Herein, we report on the fabrication and characterization of gold-coated nanopost arrays, their use as refractometric sensors, and their optimization through photonics simulations. Monolithic square nanopost arrays having different period and nanopost size are fabricated by nanoimprint lithography on polymer foils, and sputter-coated by gold films. The reflectivity of these gold nanopost-shell arrays present dips in the visible range, which are efficient for refractometric sensing. By finite-difference time-domain (FDTD) simulations we reproduce the experimental spectra, describe the electric fields distribution around the nanopost-shells, and then explain their good sensitivity, around 450 nm/RIU. Furthermore, we determine by simulations the influence of several geometrical parameters, such as array period, nanopost width, gold film thickness, and nanopost side coverage on both reflectivity spectra and sensing capabilities. Fully coated nanoposts provide an extremely deep reflectivity minimum, approaching zero, which makes the relative reflectivity change extremely high, more than two orders of magnitude higher than for partially coated nanoposts. These results contribute to the understanding of the plasmonic properties of metal coated nanopost arrays, and to the development of efficient platforms for sensing and other surface plasmon based applications

Shaping light spectra and field profiles in metal-coated monolayers of etched microspheres

Hybrid colloidal plasmonic-photonic crystals (HPPCs) are known for their interesting optical properties, which are relevant both fundamentally and for their applicative potential. The optical response of HPPCs is easily tunable from the visible to the infraredspectral range, while their fabrication, based on colloidal self-assembly, keeps production costs rather low. Both arguments make HPPCs a class of attractive functional materials. Here, we explore the optical properties of HPPCs obtained by gradual etching of a hexagonal closepacked monolayer of polystyrene microspheres, subsequently covered by a thin metal layer. We analyze the optical transmission characteristics of these etched colloidal crystals and HPPCs as a function of the etching degree. Finite-difference time-domain simulations allowed us to explain the correlations between the observed optical response and morphology. The transmission gap in bare colloidal crystals can be blue-shifted up to at least 50 nm, and its depth increased by more than 20%. In HPPCs on the other hand, it is possible to tune not only the wavelength of the enhanced plasmonic fields, but also their locations within the nanostructure. Thus, both spectra and near-field profiles can be fine-tuned in a controlledmanner by plasma etching in these hybrid plasmonic-photonic structures, expanding the current understanding of the physical working principles of HPPCs and their applications

PDLC composites based on polyvinyl boric acid matrix – a promising pathway towards biomedical engineering

<p>Polymer dispersed liquid crystal (PDLC) systems based on a smectic liquid crystal embedded in polyvinylalcohol-boric acid (PVAB) as biocompatible carrying matrix were prepared and characterised. The smectic liquid crystal contains biologically friendly structural blocks and was designed to have a direct isotropic–smectic transition and a mesophase stability range at human body temperature. The resulted PDLCs were characterised from morphological and thermotropic aspects by polarised light microscopy (POM), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Raman microspectroscopy, and their surface properties were determined by contact angle measurements and surface energy calculations.</p> <p>It was concluded that the electron-deficient PVAB matrix constrains the ester liquid crystal to grow as spherical droplets with planar anchoring. The droplet diameter was comprised in the range 4–11 µm, with a predominant droplet population around 7 µm and a narrower polydispersity as the amount of the liquid crystal in the polymeric matrix increases. The resulted PDLC films exhibited versatile morphology and surface properties which allow targeting of their application.</p