•Hydrogen gas sensor based on the nanoscale Pt–TiO2–Pt sandwich is presented.•The sensor exhibits high sensitivity and fast reaction time at room temperature.•The high sensitivity is due to the high ...applied field and small top electrode width.•The hot-electron-transport theory of the sensor response is developed.
Development of fast highly-sensitive semiconductor gas sensors operating at room temperature, which would be compatible with semiconductor technology, remains a challenge for researchers. Here we present such sensor based on a nanoscale Pt–TiO2–Pt sandwich. The sensor consists of a thin (∼30nm) nanocrystalline TiO2 layer with ∼10nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80nm) stripe. If we decrease w to ∼100nm and below, the sensor exposed to air with 1% H2 exhibits the increase of response (Rair/RH2) up to ∼107 and decrease of the reaction time to only a few seconds even at room temperature. The sensitivity increase is due to a nontrivial non-ohmic effect, a sudden decrease (by three orders of magnitude) of the electrical resistance with decreasing w for w∼100nm. This non-ohmic effect is explained as a consequence of two nanoscale-related effects: the hydrogen-diffusion-controlled spatially-inhomogeneous resistivity of the TiO2 layer, combined with onset of the hot-electron-temperature instability when the tiny grains are subjected to high electric field.
The magnetron sputtered tantalum diboride (TaBy) coatings from stoichiometric TaB2 target are often reported to be deposited in broad B/Ta interval with diverse structure and mechanical properties. ...In this article, the effect of Ar neutrals reflected from TaB2 target on the B/Ta ratio is examined. Two targets with different thickness are used to influence the current-voltage characteristic of the discharge and the energy of reflected Ar neutrals. In addition, external magnetic field from Helmholtz coils is applied to influence the plasma density in the substrate region. It is demonstrated that the reflected Ar neutrals have a significant effect on B/Ta ratio reduction from 1.9 to 1.4. While decreasing the B/Ta ratio, preferred TaBy crystal orientation changes from (0001) to (101¯1). Intense Ar bombardment results in loss of crystallinity exemplified by diffraction maxima broadening. The variation of B/Ta ratio is accompanied by change of hardness and Young's modulus in range from 48 GPa to 32 GPa and from 532 GPa to 390 GPa, respectively. The coatings with B/Ta ratio < 1.6 show material pile-up around cube-corner indents, an indication for improved ductility.
•The TaB2 target thickness variation affects the energy of reflected Ar neutrals.•The reflected Ar neutrals have a significant effect on B/Ta ratio reduction.•Intense Ar bombardment results in loss of crystallinity.•The B/Ta reduction is accompanied by change in preferred crystallite orientation.•Indication for improved ductility is observed in the coatings with B/Ta < 1.6.
Bragg scattering effects in bottom-emitting organic light-emitting diodes (OLEDs) grown on corrugated aluminum-doped zinc oxide electrodes are analyzed. Periodic corrugation is introduced by ...structuring the oxide electrode via UV laser ablation, a process that enables flexible adjustment of the period and height of corrugation. We demonstrate that fabrication of stable and electrically efficient OLEDs on these rough substrates is feasible. Sharp spectral features are superimposed onto the broad emission spectra of the OLEDs, providing clear evidence for Bragg scattering of light from guided modes into the air cone. Theoretical analysis based on an emissive dipole model and conservation of momentum considerations allows a quantitative description of scattering and the associated dispersion relations.
Immunocompatibility and non-thrombogenicity are important requirements for biomedical applications such as vascular grafts. Here, gelatin-based hydrogels formed by reaction of porcine gelatin with ...increasing amounts of lysine diisocyanate ethyl ester were investigated in vitro in this regard. In addition, potential adverse effects of the hydrogels were determined using the "Hen's egg test on chorioallantoic membrane" (HET-CAM) test and a mouse model.The study revealed that the hydrogels were immunocompatible, since complement activation was absent and a substantial induction of reactive oxygen species generating monocytes and neutrophils could not be observed in whole human blood. The density as well as the activation state of adherent thrombocytes was comparable to medical grade polydimethylsiloxane, which was used as reference material. The HET-CAM test confirmed the compatibility of the hydrogels with vessel functionality since no bleedings, thrombotic events, or vessel destructions were observed. Only for the samples synthesized with the highest LDI amount the number of growing blood vessels in the CAM was comparable to controls and significantly higher than for the softer materials. Implantation into mice showed the absence of adverse or toxic effects in spleen, liver, or kidney, and only a mild lymphocytic activation in the form of a follicular hyperplasia in draining lymph nodes (slightly increased after the implantation of the material prepared with the lowest LDI content). These results imply that candidate materials prepared with mid to high amounts of LDI are suitable for the coating of the blood contacting surface of cardiovascular implants.
La0.67Sr0.33MnO3 (LSMO) thin films have been grown by a pulsed laser deposition (PLD) on Bi4Ti3O12(BTO)/CeO2/YSZ buffered silicon-on-insulator (SOI) substrates. We compare the properties of these ...films with results of other authors. We analyse structural properties of LSMO/BTO/CeO2/YSZ/SOI multilayer structure prepared using PLD. Electrical measurements have shown that the temperature corresponding to maximum of resistance derivative (operating temperature of a microbolometer) is about 330K (well above room temperature) and the highest resistivity of metal-insulator transition is at temperature (T P) above 400K. Temperature coefficient of the resistance (TCR) has achieved values of 3.4%K-1 at 325K for some LSMO films. Transmission electron microscopy analysis has confirmed epitaxial growth of all the layers and showed a mosaic character of the LSMO films due to strain relaxation.
Magnetron co-sputtering from TiB2 and TaB2 stoichiometric targets is used to prepare AlB2-prototype ternary Ti1-xTaxB2±Δ solid solution, with x in the range from 0 to 1. Using this technique, the ...boron-to-metal ratio (B/Me) varies with the actual Ti and Ta content. The boron-to‑tantalum ratio can be increased by decreasing the TaB2 target voltage, which has a considerable effect on the coating structure. Coatings with B/Me > 2 reveal highly textured nanocolumnar structure, while the coatings with B/Me < 2 tend to be nanocrystalline (without any preferred crystallite orientation) or amorphous. All the deposited coatings have a hardness higher than 32 GPa. The under-stoichiometric (B/Me < 2) coatings show material pile-up around the cube-corner indent edges, an indication for plastic flow and increased ductility.
•The boron-to-metal ratio was not constant while varying the Ti and Ta content.•By decreasing the TaB2 target voltage the B concentration can be increased.•The boron-to-metal ratio has a considerable effect on the coatings structure.•Hardness of all coatings was higher than 32 GPa.•The under-stoichiometric (B/Me<2) coatings show improved toughness.
Due to their homogenous structure without grain boundaries, amorphous nitride-based coatings represent a potentially attractive material for high-temperature applications in aggressive environment. ...In this article, we report on the thermal stability and mechanical properties of amorphous quaternary Ti-B-Si-N coatings with variable Si/B concentration ratio prepared by reactive magnetron co-sputtering. Biaxial stress temperature measurement was used to evaluate thermal stability of amorphous as-deposited coatings in the region up to 600°C. The chemical composition of the coatings was stable up to 1100°C. During the annealing small amount of nanocrystalline fcc-TiN phase (with grain size of 1–4nm) in amorphous matrix a-(Ti)BSiN was formed. The prevailing BN, SiN and TiN bonds remained also unchanged as observed by X-ray photoelectron spectroscopy. The gradual increase of hardness to maximum at 14GPa and the overall positive effect on thermal stability was observed with increasing Si/B concentration ratio. The dominating volume of the amorphous phase after annealing had a significant influence on maintaining constant hardness values up to 1100°C.
•The as-deposited Ti-B-Si-N coatings were amorphous.•During the annealing fcc-TiN nanograins were formed in the amorphous matrix.•The chemical composition of the coatings was stable up to 1100°C.•The increasing Si/B ratio had a positive effect on the thermal stability.
In this work the effect of Si addition on the mechanical properties and the high temperature oxidation resistance of TiB2 coatings is investigated. Nanocrystalline Ti–B–Si coatings were prepared by ...magnetron sputtering using co-deposition from TiB2 and Si targets. Si addition causes decrease of hardness and effective Young's elastic modulus of the coating. Annealing in high vacuum increases the content of crystalline TiB2 phase that in turn leads to enhanced hardness. High resolution thermogravimetry together with x-ray diffraction (XRD), electron probe microanalysis (EPMA), x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) is used to investigate the processes associated with exposure to air at elevated temperatures. The formation of nanocrystalline Ti–Si–O oxide scale after exposure to air at 500°C is related to B2O3 release. Increased Si content suppresses the growth of crystal phase and contributes to the high temperature oxidation resistance. At 800°C the oxidized scale formed the layered structure of globular TiO2, columnar TiO2 and amorphous borosilicate.
•Si addition in Ti–B–Si coatings improves their oxidation resistance.•Dense Ti–Si–O oxide scale is formed after annealing in air at ~500°C.•After annealing in air at 800°C the oxide scale has layered cross-sectional morphology.•Si addition in Ti–B–Si decreases the coating hardness and elastic modulus.•Annealing in high vacuum increases hardness of Ti–B–Si coating.
Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption ...shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.
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