Search

TiO2 nanotube (TNT) layers were prepared in fluoride-free nitrate-based electrolytes i.e., NaNO3, KNO3, Sr(NO3)2, and AgNO3via electrochemical anodization.

Metal oxide semiconductor gas sensors of hydrogen with a typical capacitor-like Pt/TiO2/Pt electrode arrangement exhibit excellent sensitivity to hydrogen even at room temperature. At the same time, very similar Pt/TiO2/Pt cells can also be used as memristive elements exhibiting resistive switching between two resistive states, which has been recently exploited to create a gas sensor with built-in memory. Merging of these two functionalities within a single device also opens new possibilities for smart gas sensor arrays. However, so far such sensors have been prepared only on rigid substrates. In this work, a flexible hydrogen gas sensor with such capacitor-like Pt/TiO2/Pt electrode arrangement fabricated on polyimide foil is presented and characterized in terms of hydrogen gas sensing properties and bending endurance. The sensor exhibits high response (Rair/RH2) of more than 105 to 10 000 ppm H2 at 150 °C with minor decline at elevated humidity and is capable of room temperature operation. The lowest detected concentration was 3 ppm at 150 °C and 300 ppm at room temperature in dry conditions. Bending the sensor 105 times over diameter of 10 mm led to slight improvement of the sensing performance.

Titanium dioxide aerogel (TiAP) powders were prepared by lyophilization of peroxo-polytitanic gels followed by annealing at 800 °C to obtain an anatase structure. The surface modification of TiAP was performed for the first time by low amounts of Ce ions (in the range of 0.0025 to 0.025 wt%) using a wet impregnation method. The photocatalytic activity of the aerogel samples was investigated for the removal of different organic pollutants (i.e., Rhodamine B, phenol and caffeine) and the results were compared with the reference P25. Both TiAP and Ce ion surface-modified TiAP (Ce/TiAP) have exhibited better degradation efficiencies for the removal of pollutants than P25, especially for Ce/TiAP with an enhancement in the degradation efficiencies of +18% and +37% for the removal of caffeine and Rhodamine B, respectively. These results have been partly explained by the high active surface area of Ce/TiAP compared to TiAP as well as its better photoelectrochemical properties which have shown, for instance, ∼10% increased incident photon-to-electron conversion efficiency at 360 nm. Interestingly, the energetic position of the valence band maximum of Ce/TiAP is shifted from 3.2 eV to 2.8 eV (compared to TiAP), thus improving the generation of reactive oxygen species (ROS), especially hydroxyl radicals. Indeed, the presence of HO˙ is confirmed by electron paramagnetic resonance, and fluorescence spectroscopy and their photoinduced generation are enhanced in the case of Ce/TiAP. Finally, the surface modification of TiAP by cerium ions led not only to better photoinduced properties, thus limiting the electron–hole pair recombination, but also to the improvement of ROS generation via different plausible mechanisms.

In this work, synthesis of Ag3PO4 and its composite with TiO2 (Ag3PO4/TiO2) toward study of two phenomena naturally occurring in Ag3PO4 is reported, specifically a visible light-driven (i.e., photocorrosion) and chloride ion-driven transformation of Ag3PO4 to AgCl in chloride-free and chloride-present aqueous solution. A deeper insight on this transformation via study of their structural and morphological changes using X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) is performed. Substantial amount of AgCl is detected in both Ag3PO4-based materials after visible light irradiation in chloride-present environment. This led to an increase in optical band gap of Ag3PO4 and Ag3PO4/TiO2 from 2.52 to 2.99 eV and 2.48 to 3.02 eV, respectively. Impact of these structural changes in Ag3PO4 and Ag3PO4/TiO2 on their photocatalytic activity is evaluated from the photoinduced catalytic, antibacterial, and antifungal performance under visible light irradiation. The photocatalytic activity of pristine and photocorroded Ag3PO4 is increased by similar to 10 times compared to that of pristine and photocorroded Ag3PO4/TiO2. Photocorroded Ag3PO4 and Ag3PO4/TiO2 possess minor antibacterial and antifungal activities (cell survival similar to 90%), whereas using pristine Ag3PO4 and Ag3PO4/TiO2 the cell survival is reduced by 100% after 60 and 120 min, respectively. Tato práce představuje syntézu Ag3PO4 a jeho kompozitu s TiO2 (Ag3PO4/TiO2) a studuje dva fenomény přirozené se vyskytujíci v Ag3PO4 materiálu. Konkrétně se jedná o viditelným světlem řízenou transformaci (tj. fotokorozi) a chloridovými ionty řízenou transformaci Ag3PO4 na AgCl v kapalných roztocích za přítomnosti a nepřítomnosti chloridových iontů Hlubší pohled této transformace byl sledován pomoci studia strukturních a morfologických změn za pomocí skenovací elektronové mikroskopie (SEM), rentgenové difrakce (XRD) a energiově-disperzní rentgenové spektroskopie (EDS). Značné množství AgCl bylo detekováno v obou Ag3PO4 materiálech po ozáření viditelným světlem a v přítomnosti chloridových iontú. To vedlo k zvýšení optického zakázaného pásu Ag3PO4 z 2.52 na 2.99 eV a Ag3PO4/TiO2 z 2.48 na 3.02 eV, respektive. Impakt těchto strukturálních změn v Ag3PO4 a Ag3PO4/TiO2 na jejich fotokatalytické, antibakteriální a antifungální vlastnosti byl studovan na základě ozáření viditelným světlem. Fotokatalytická aktivita čistého a fotokorodovaného Ag3PO4 byla zvýšens přibližně 10 krát v porovnání s čistým a fotokorodovaným Ag3PO4/TiO2. Fotokorodovaný Ag3PO4 a Ag3PO4/TiO2 měli slabé antibakteriální a antifungální aktivity (experiment přežilo 90% buněk), zatímco aktivita čistého Ag3PO4 a Ag3PO4/TiO2 byla 100% za 60 a 120 minut, respektive.

Owing to their excellent hydrogen surface susceptibility, TiO2 thin films have been proven worthy of sensing hydrogen. However, these sensors work best at temperatures of 150–400 °C, with poor sele...

Hydrogen gas sensors with capacitor-like Pt/Nb-TiO2/Pt structure and various amount of Nb doping were successfully prepared by magnetron sputtering and lift-off photolithography. The Nb incorporation in the TiO2 layer has been confirmed by XPS and GIXRD measurements. It has been shown that the Nb doping delays the anatase to rutile phase transformation during annealing and according to the AFM measurements it also improves the homogeneity of the sensing films. However, unexpectedly the response of the sensors with Nb doped TiO2 film is lower compare to the undoped Pt/TiO2/Pt sensors, which exhibit highest response ( 2.08 × 10 4 ) and shorter response time (49.4 s) to 1000 ppm hydrogen at 100 °C. This can be partially explained by the intrinsic characteristics (lower surface roughness and porosity) of Nb doped TiO2 films, which resulting in smaller active surface and lower diffusion of the oxygen and hydrogen gases into the films. Although the Nb doping did not improve the sensing performance, this study can be also useful for the future research on the capacitor-like metal oxide gas sensor.

In this work, we study the effect of the various substrates on the growth and superconducting properties of NbN thin films grown by using pulsed laser ablation in a N2 + 1%H2 atmosphere on MgO, Al2O3 and Si substrates. Structural and superconducting analyses of the films demonstrate that using MgO and Al2O3 substrates can significantly improve the film properties compared to Si substrate. The X-ray diffraction data indicate that MgO and Al2O3 substrates produce highly oriented superconducting NbN films with large coherent domain size in the out-of plane direction on the order of layer thickness and with a superconducting transition temperature of 13.1 K and 15.2 K, respectively. On the other hand, the NbN film grown on the Si substrate exhibits random polycrystalline orientation. Together with the smallest coherent domain size it leads to the lower critical temperature of 8.3 K. Finally, by using a passivation surface layer we are able to improve superconducting properties of NbN thin film and we observe superconducting transition temperature 16.6 K, the one of the highest value reported so far for 50 nm thick NbN film on sapphire.

Magnetron sputtering is widely used for deposition of silicon oxynitride (SiOxNy) coatings on glass in large-area applications. Since repeated deposition simulates the factory-scale in-line processing, amorphous aluminum-doped SiOxNy layers with thickness of about 250 nm were deposited by reactive pulsed DC sputtering in a multi-pass process with repeated linear movement of a glass substrate under an Al-alloyed Si target. Using specular X-ray reflectivity we show periodic fluctuations of the material density throughout the entire thickness of the resulting coating. The number of periods corresponds to the number of passes of the substrate through the plasma of the magnetron. Fitting results suggest a model consistent with a periodic alternation of the O/N ratio. These subtle stoichiometric fluctuations in the SiOxNy layer composition were confirmed by scanning transmission electron microscopy analysis with nanoscale resolution, and with detailed elemental maps of characteristic X-rays of the layered cross-section. Our study demonstrates the superior sensitivity of the relatively simple nondestructive X-ray reflectivity method for industrial line-process inspection compared to ellipsometry.

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

Combining experiments and density functional theory, we investigate the effect of yttrium alloying on thermally-induced structure evolution and mechanical properties of TiB2+Δ. Ti0.78Y0.22B2.2 films consisting of TiYB2 filaments embedded in excess boron exhibit lower hardness of 31 GPa and significant reduction in elastic stiffness of 398 GPa in comparison with 38 GPa and 485 GPa, respectively, of reference TiB3.1. Formation of the TiB2 and YB4 nano-sized grains as a result of spinodal decomposition of TiYB2 phase at 1200 °C is accompanied by a slight decrease in hardness to 28 GPa and further reduction of elastic stiffness to 383 GPa.

Superconducting MgB2 thin films were fabricated on c-cut sapphire substrates by vacuum co-evaporation of magnesium and boron followed by an ex situ post-annealing. We show that annealing in oxygen atmosphere can significantly improve the superconducting properties of the MgB2 thin films compared to the typical annealing in argon atmosphere. In this work, influence of the ex-situ annealing atmosphere on the structure, texture and morphology of the superconducting MgB2 thin films has been studied by transmission electron microscopy, X-ray diffraction and pole figure measurements. Samples annealed at 800 °C in Ar, at 800 °C in O2 and at 500 °C in O2 have been compared. The annealing in O2 at 800 °C produces MgB2 thin films with the highest superconducting transition temperature and critical current density. We show that this is thanks to the thickest MgO layer at the surface produced in this case, which acts as a protecting barrier against out-diffusion of Mg during the annealing and leads to better stoichiometry and larger MgB2 grains compared to the samples annealed in Ar. Our method can be alternative to the customary ex-situ post annealing of Mg-B precursor in sealed vapor cell. In all samples, the MgB2 phase showed single axis texture with the (0 0 0 1) planes slightly inclined by 0° to 15° with respect to the Al2O3(0 0 0 1) substrate surface incurred with the initial precursor evaporation geometry. During the annealing, the excess Mg also reacts with the Al2O3 substrate and minor MgAl2O4 and MgO phases are produced at the substrate-layer interface.

In this work, we show that significant enhancement of superconducting properties of MgB2 thin films prepared by vacuum evaporation and ex-situ annealing can be obtained when the annealing is performed in O2 atmosphere instead of the usually employed inert atmosphere (Ar in the current study). Rapid annealing in O2 significantly improves the critical transition temperature (Tc), critical current density (jc), and upper critical magnetic field (Hc2) compared to the control sample prepared in the same way, but annealed in Ar. Structural and composition analyses of the films demonstrate that the annealing in O2 atmosphere produces a sufficiently thick MgO layer on the surface of MgB2 thin films, which acts as a protective barrier preventing out-diffusion of Mg from the films during the high-temperature annealing. This consequently leads to better stoichiometry (B/Mg ratio), increased MgB2 grain size and enhanced intergrain connectivity. The higher residual resistivity of the films annealed in O2 atmosphere also indicates higher concentration of intragrain impurities, which causes a further increase of the jc and Hc.

Mo-Se-N films were prepared by pulsed direct current (DC) High Target Utilisation Sputtering (HiTUS) in reactive Ar + N2 atmosphere. Here, the effect of nitrogen doping was studied. MoSex film with Se/Mo atomic ratio ~ 2 exhibited polycrystalline structure and the lowest coefficients of friction (COFs) in humid air from 0.025 to 0.1 for loads in the range 2–45 N. Mo-Se-N coatings were deposited with N concentrations ranging from 1 to 40 at.%, whereas Se/Mo ratio varied from 0.6 to 2. Mo-Se-N coatings formed amorphous structures for the N contents above 7 at.% and increased hardness proportional with the N content up to 9 GPa. The addition of nitrogen also resulted in a general decrease in wear rate of two orders of magnitude when compared to pristine films while retaining a reasonably low coefficient of friction. Mo-Se-N films showed notable COF values in humid environment ranging from 0.22 to 0.015 when tested using loads from 2 to 45 N. The excellent friction properties of Mo-Se-N films were associated to the crystallisation of a MoSe2 tribofilm in the wear scar. Moreover, we showed that modern pulsed DC HiTUS technology represents a suitable way of producing thin films with a variety of elemental compositions and desired mechanical and tribological properties, even from sensitive, semi-conducting and extremely low thermally conductive MoSe2 targets.

Single-crystal rocksalt-structure (B1) (V,Mo)N alloys are inherently hard and tough ceramics [Kindlund et al., APL Mater. 1, 042104 (2013)]. However, the mechanical properties and thermal stability of (V,Mo)N solid solutions at temperatures (≈1000 K) of relevance for practical applications have not been previously investigated. In this work, we synthesize single-phase B1 polycrystalline V 0.57 Mo 0.43 N 0.95 coatings to investigate the effects induced by temperature on the nanostructural evolution and hardness (H) of the material. Nanoindentation measurements show that the as-deposited film (H = 23±3 GPa) becomes ≈30% harder (up to 31±2 GPa) upon annealing at 730 oC. Experimental characterization and analyses, based on dispersive X-ray spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM), reveal that the age-hardening effect originates from decomposition of the solid solution into coherent strained cubic VN-rich / MoN-rich domains. The experimental results are complemented by the composition/temperature (V,Mo)N phase diagram – constructed upon ab initio molecular dynamics free-energies – which indicates that the separation observed in V 0.57 Mo 0.43 N solid solutions is of spinodal nature. Films annealed at temperatures exceeding 850 oC undergo structural coarsening, with formation of hexagonal Mo x N y and cubic VN phases, which cause a decrease in hardness to ≈22 GPa. Our present findings, corroborated by the fact that V and Mo are known to enhance the resistance to corrosion and the lubricant properties of hard refractory nitrides, indicate that (V,Mo)N coatings may offer outstanding mechanical and tribological performances during operation at elevated temperatures.

Inorganic submicron fibers (ISF) are nowadays widely studied material. Usually, they are produced by 2-step process. First, the composite metal-organic fibers are produced from polymer matrix and metallic precursor, typically alkoxides or salts by standard spinning techniques. After this, prepared composite fibers are thermally calcinated to remove polymer and form ceramic fibers. In this study, we used low temperature plasma generated at atmospheric pressure using Diffuse Coplanar Surface Barrier Discharge (DCSBD) to eliminate organics from the composite fibers before thermal treatment to reduce the time required for thermal calcination of Al2O3 fibers. This plasma pre-treatment enables using significantly higher heating rates compared to standard calcination without damaging the fiber structure.

TiO2 nanotube (TiNT) arrays were grown on silicon substrate via electrochemical anodization of titanium films sputtered by magnetron. To improve the photocatalytic activity of arrays annealed in air (o-TiNT), doping of o-TiNT with vanadium was performed (o-V/TiNT). These non-doped and doped TiNT arrays were also hydrogenated in H2/Ar atmosphere to r-TiNT and r-V/TiNT samples, respectively. Investigation of composition and morphology by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and X-ray photoelectron spectroscopy (XPS) showed the presence of well-ordered arrays of anatase nanotubes with average diameter and length of 100 nm and 1.3 μm, respectively. In both oxidized and reduced V-doped samples, vanadium is partly dissolved in the structure of anatase and partly deposited in form of oxide on the nanotube surface. Vanadium-doped and reduced samples exhibited higher rates in the photodegradation of organic dyes (compared to non-modified o-TiNT sample) and this is caused by limitation of electron-hole recombination rates and by shift of the energy gap into visible region. The photocatalytic activity was measured under UV, sunlight and visible irradiation, and the corresponding efficiency increased in the order (o-TiNT)

WC/a-C:H tribological nanocomposite coatings were deposited by reactive magnetron sputtering of tungsten carbide targets in acetylene atmosphere on substrates of various materials – cemented carbide and three types of steel. All the substrates were pretreated by various magnetron plasma-based techniques to evaluate their efficiency in promotion of coating adhesion. All the studied processes took place at temperatures lower than 180 °C. The structure of the WC/a-C:H coatings and their mechanical properties did not depend on the pretreatment technique nor the type of substrate material. On the other hand, the surface roughness of the substrate and the deposited coating can be affected by the intensity and duration of the pretreatment process. The adhesion of the coatings is significantly dependent on the substrate material and the particular plasma pretreatment process, as well as their combination. HiPIMS pretreatment processes with lower duty cycle at higher substrate bias voltage result in excellent adhesion with scratch critical load values higher than 130 N. Further, the substrate-target distance influences the efficiency of the pretreatment process and also partly affects the performance of the coatings. It is concluded that magnetron plasma-based pretreatment and deposition processes might involve potential practical problems in industrial coating of various objects in the same process batch. This is particularly connected with their shape and their composition.

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 1–4 nm) in amorphous matrix a-(Ti)BSiN was formed. The prevailing B N, Si N and Ti N bonds remained also unchanged as observed by X-ray photoelectron spectroscopy. The gradual increase of hardness to maximum at 14 GPa 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.

In this work, we doped sputtered MoSe2 coatings with Ti to improve their mechanical and tribological properties. Mo-Se-Ti coatings were prepared onto steel discs by High Target Utilisation Sputtering (HiTUS). The Ti was in the range 7–31 at.%, which led to Se/Mo ratios of 1.7–2.7. The Mo-Se-Ti coatings possessed a polycrystalline structure for the lower Ti contents and became amorphous when Ti content was above approx. 18 at.%. The hardness of the initially soft (0.3 GPa) pure MoSe2 coatings was dramatically improved with Ti additions (up to 7.5 GPa). Sliding experiments confirmed excellent tribological properties: coefficient of friction values from 0.02 to 0.08 and very low wear rates ( 8 × 10 - 8 mm3N-1m−1) of the Ti-containing coatings tested in the humid air at the loads in the range of 2–45 N. The outstanding self-lubricant properties of Mo-Se-Ti coatings were attributed to the transformation of the topmost amorphous part of the coating into crystalline MoSe2 tribofilm while preserving inner parts of the coating in as-deposited state ensuring good load-bearing capacity. There is strong experimental evidence that Ti has a gettering effect in the tribological contact, which protects MoSe2 tribofilm against oxidation.

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 ( 10 1 ¯ 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

Few-layer films of transition metal dichalcogenides have emerged as promising candidates for applications in electronics. Within this group of 2D materials, platinum diselenide (PtSe2) was predicted to be a compound with one of the highest charge carrier mobility. Recently, the successful integration of group III–V nitride semiconductors with NbNx-based superconductors was reported with a semiconductor transistor grown directly on a crystalline superconductor. This opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic, and piezoelectric properties of the semiconducting material. Here, we report on the fabrication of a few-layer PtSe2 film on top of an NbN substrate layer by selenization of pre-deposited 3 nm thick Pt layers. We found the selenization parameters preserving the chemical and structural integrity of both the PtSe2 and NbN films. The PtSe2 film alignment can be tuned by varying the nitrogen flow rate through the reaction chamber. The superconducting critical temperature of NbN is only slightly reduced in the optimized samples compared to pristine NbN. The carrier mobility in PtSe2 layers determined from Hall measurements is below 1 cm2/V s.

Niobium nitride (NbN) has suitable mechanical properties for application as protective coatings in mechanical engineering, and also its superconductivity can be utilized in thin film devices for sensorics or in combination with ferromagnet in spintronics. Long-range superconducting proximity effect at the heterostructures with a weak ferromagnet can be used for generation of spin-polarized current. For any operational heterostructure application the high quality NbN thin films need to be prepared. In this work we have investigated impact of the substrates on the structure and preferential orientation of niobium nitride thin films fabricated by pulsed laser deposition at 600 °C on Si (0 0 1), MgO (0 0 1), C-plane and R-plane Al2O3 substrates. Growth parameters have been tuned in order to obtain single superconducting δ-NbN phase. Microstructure was analyzed by X-ray diffraction and transmission electron microscopy. Si substrate does not induce the film preferential orientation. Films on MgO are epitaxial (0 0 1) oriented. Films on R-Al2O3 show (1 3 5) orientation with twinned crystallites on the lower symmetry substrate surface. The (1 1 1) epitaxial growth with the largest crystallites and their smallest tilting was achieved on C-Al2O3 substrate leading to the best superconducting properties.

BiVO4/TiO2 layered photoanode was prepared by simple methods, such as sol-gel and metal organic decomposition processes. The photoanode was studied for hydrogen production by water splitting under simulated solar irradiation. Various multilayer configurations of the film were electrochemically tested. The optimal combined photocatalyst consisted of four bottom BiVO4 layers covered by four TiO2 layers on the top. This optimal layered film was characterized by XRD measurements, which showed the presence of the most photoactive phases of BiVO4 and TiO2. The energy band gap measured by diffuse reflectance spectroscopy demonstrated a small blue shift compared to pure BiVO4. Solar-to-hydrogen efficiency reached 1.1% at 1.08 V vs. RHE. The corresponding faradaic efficiency was 64%. The photocurrent at 2.08 V vs. RHE for the optimal BiVO4/TiO2 photoanode was approximately 5.5 mA/cm2. Hydrogen production rate was measured at different external bias from 1.08 to 2.08 V vs. RHE and the cumulative production reached 0.6 mmol after 10 hours of irradiation at 2.08 V, which was the highest reported for the BiVO4/TiO2 system.

There is currently a high demand for highly-sensitive semiconductor gas sensors operating at low temperature, which would be compatible with semiconductor technology and could be incorporated in one chip with other electronic circuits. Although some suitable sensors were already developed, recent trend of flexible electronics brings yet another challenge for researchers − to prepare such sensors on flexible substrates. In this work, we present a flexible semiconductor gas sensor of hydrogen prepared on 38 μm thick Kapton ® polyimide foil, based on a TiO 2 thin film with platinum interdigital electrodes on top. In dry conditions, the sensor is highly sensitive even at room temperature, with response (R 0 /R H2 ) reaching ∼10 4 for 10000 ppm H 2 in synthetic air and its capability of sensing H 2 concentrations as low as ∼30 ppm has been demonstrated. At elevated temperature of 150 °C, the response reached more than ∼10 6 for 10000 ppm H 2 . Humidity negatively affects the sensor performance particularly at room temperature, where at 32% relative humidity the sensor response to 10000 ppm H 2 decreased to ∼10 3 and the lowest detected H 2 concentration was ∼300 ppm H 2 . Bending the sensor 1000 times over diameter of 10 mm did not cause any significant damage of the device or decrease of sensitivity. On the contrary, the response of the sensor at close-to-room temperatures and at low concentrations of H 2 increased after the bending.

Bismuth vanadate is a promising visible-light driven photocatalyst due to its convenient band gap value and position. However, the efficiency of BiVO4 is very low due to high recombination rates. In this work, a comparative study between pristine and Nb-modified BiVO4 films was made. Modified BiVO4 has shown a hierarchical nanostructure, but its energy band gap remained equal to pristine BiVO4. The IPCE efficiency of Nb-BiVO4 increased importantly. The ideal nominal content of Nb(V) in BiVO4 was 10 at%. At such atomic rate, the quantity of photoelectrochemically produced hydrogen by water splitting significantly increased compared to pristine BiVO4. Photocatalytic degradation of organic compounds by Nb-modified bismuth vanadate films also exhibited higher oxidation rate.

Obtaining high hardness combined with enhanced toughness represents one of the current challenges in material design of hard ceramic protective coatings. In this work, we combine experimental and a ...

Owing to their excellent hydrogen surface susceptibility, TiO

Rocksalt-structure (B1) (V,Mo)N alloys are inherently hard and tough ceramics. However, the mechanical properties and thermal stability of (V,Mo)N solid solutions at temperatures ⪆ 700 °C of relevance for practical applications have not been previously investigated. In this work, we synthesize single-phase B1 polycrystalline V0.57Mo0.43N0.95 coatings to investigate the effects induced by temperature on the nanostructural evolution and hardness (H) of the material. Nanoindentation measurements show that the as-deposited film (H = 23 ± 3 GPa) becomes ≈30% harder (up to 31 ± 2 GPa) upon annealing at 730 °C. Experimental characterization and analyses, based on dispersive X-ray spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM), reveal that the age-hardening effect originates from decomposition of the solid solution into coherent strained cubic VN-rich/MoN-rich domains. The experimental results are complemented by the composition/temperature (V,Mo)N phase diagram – constructed upon ab initio molecular dynamics free-energies – which indicates that the separation observed in the solid solutions is of spinodal nature. Films annealed at temperatures exceeding 850 °C undergo structural coarsening, with formation of hexagonal MoxNy and cubic VN phases, which cause a decrease in hardness to ≈22 GPa. Our present findings indicate that (V,Mo)N coatings may offer outstanding mechanical performances during operation at elevated temperatures.

The study concerns different surface pretreatment procedures of the 100Cr6 bearing steel substrates using DC magnetron sputtering and high-power impulse magnetron sputtering. The influence of the pretreatment technique on structure, adhesion and overall performance of the deposited tungsten carbide tribological coatings is characterized. The substrate pretreatment and deposition processes are maintained at process temperatures lower than 180 °C in order not to affect the intrinsic structural and mechanical properties of the bearing steel substrates. It is shown that the pretreatment method does not influence the structure and composition of the coatings. On the other hand, it strongly affects the surface structure and more important the adhesion and the tribological properties of the coatings. It is shown that the high-power impulse magnetron sputtering technique in combination with a high bias voltage can be a valuable tool for substrate surface pretreatment to obtain a good adhesion even at low process temperature.

Cu6PS5I-based thin films were deposited onto silicate glass substrates by non-reactive radio-frequency magnetron sputtering. The chemical composition of thin films was determined using energy-dispersive X-ray spectroscopy. Electrical conductivity of Cu6PS5I-based thin films was studied as dependent on chemical composition. Optical transmission spectra of Cu5.46P1.68S5.06I0.80 thin film were investigated within the temperature interval 77…300 K; temperature behaviour of optical absorption spectra and dispersion of the refractive index were also studied. Temperature dependences of the energy position of absorption edge, Urbach energy and refractive index of Cu5.46P1.68S5.06I0.80 thin film have been analyzed.

Nanocrystalline bismuth vanadate was deposited by simple wet chemistry procedure on FTO electrodes in order to construct visible light responsive photoanodes, which were employed for photoelectrochemical hydrogen production by water splitting. The specific surface area of the films was controlled by the presence of a surfactant template (Triton X-100). It was, however, found that when the quantity of surfactant was relatively high, the stoichiometry of the photocatalyst as well as its activity was lost. The obtained materials were characterized by SEM, XRD, AFM, BET and UV–Vis spectroscopy. Optimized photoanodes were employed in photoelectrochemical cells for water splitting and hydrogen production under electric and chemical bias. Maximum hydrogen production rate was 0.15 mmol/h under electric bias of 1.4 V vs Ag/AgCl plus 0.37 V chemical bias.

Substitutions of metallic elements in Al-containing ternary transition metal nitrides are a promising method for improving the alloy thermal stability and oxidation resistance. In this work, combined experimental and ab initio analysis of thermal stability and structural evolution of CrAlYN alloyed to tantalum nitride is presented. As-deposited reactively-sputtered Cr 1 − x − y − z Al x Y y Ta z N coatings (z = 0 ÷ 0.21) exhibit single phase cubic sodium chloride (B1) structure identified as fcc-CrAlY(Ta)N solid solution. The presence of Ta in the solid solution shifts the decomposition process to higher temperatures (> 1000 °C for Ta content of z = 0.21) compared to CrAlYN (~ 900 °C), thus enhancing the alloy thermal stability. Improved thermal stability of tantalum-containing solid solutions may be attributed to their higher cohesive energies, as revealed from ab initio calculations. X-ray diffraction and transmission electron microscopy investigation of the N 2 -depleted structure after exposure at high temperature (1200 °C) in Ar + H 2 atmosphere revealed the presence of wurtzite AlN (w-AlN), cubic, hexagonal and tetragonal Cr- and Ta-containing binary or ternary nitrides (h-Cr 2 N, h-TaN, h-Ta 2 N, t-Cr 0.8 Ta 1.2 N) and metallic phases (bcc-Cr(AlTa), fcc-Cr 2 Ta). First-principle calculations show negative values of mixing free energies for fcc-Cr 1 − x Ta x N over the whole composition range at 1600 K indicating its enhanced thermodynamic stability compared to cubic Al 1 − x Ta x N and Al 1 − x Cr x N.

Tantalum diboride (TaB2) belonging to the ultrahigh temperature ceramics family is proving to be a promising material for hard protective films, thanks to its high thermal stability and excellent mechanical properties. However, growth of TaB2 ± x films prepared using physical vapor deposition techniques is strongly affected by Ar neutrals reflected from a stoichiometric TaB2 target due to a significant mass difference of heavy Ta and light B atoms leading to substantial changes in the final chemical composition and structure of films. In this work, TaB2 ± x films are experimentally prepared using high target utilization sputtering. Stopping and range of ions in matter simulations are used to investigate the behavior of Ar neutrals during deposition processes. A wide range of analytical methods is used to completely characterize the chemical composition, structure, and mechanical properties of TaB2 ± x films, and the explanation of the obtained results is supported by density functional theory calculations. TaB2 ± x films grow in a broad compositional range from TaB1.36 to TaB3.84 depending on the kinetic energy of Ar neutrals. The structure of overstoichiometric TaB2 + x films consists of 0001 preferentially oriented α-TaB2 nanocolumns surrounded by a boron-tissue phase. In the case of highly understoichiometric TaB2 − x films, the boron-tissue phase disappears and the structure consisting of 0001 and 10 1 ¯ 1 oriented α-TaB2 nanocolumns is formed. All TaB2 ± x films exhibit excellent mechanical properties with high hardness, ranging from 27 to 43 GPa and relatively low values of Young's modulus in the range of 304–488 GPa.

Due to the combustible and explosive nature of hydrogen, it is important to keep its safety during the production, storage, transportation and utilization. To this context, new type of sensors based on TiO2 nano-films with 100, 50 and 30 nm thickness and capacitor-like sandwiched Pt/TiO2/Pt structure were fabricated to monitor the hydrogen leakage. The gas sensing tests indicate that sensing performance improved with the decrease of TiO2 film thickness thus the sensors with 30 nm thick TiO2 film show higher performance in terms of response (6.16 × 104 to 1000 ppm H2) and response time (25.2 s). Moreover, tests also prove that humidity shows a negative effect on the performance. To investigate the sensing mechanism, temperature dependent resistance (R-T) and voltage dependent current (I-V) measurements was performed. The structure and surface topography of the TiO2 film is characterized by the GIXRD and AFM, respectively. In addition, the elemental depth profile of the sensor was studied by the XPS, about 0.9 at.% Pt element was clearly observed in the middle region of the annealed TiO2 layer. Based on the hydrogen diffusion, sensing mechanism of the presented structures is discussed.

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 (∼30 nm) nanocrystalline TiO2 layer with ∼10 nm grains, placed between the bottom Pt electrode layer and top Pt electrode shaped as a long narrow (width w down to 80 nm) stripe. If we decrease w to ∼100 nm and below, the sensor exposed to air with 1% H2 exhibits the increase of response ( R air / R H 2 ) 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 ∼ 100 nm. 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.

A way of preparation of VO2(B) thin films by reduction of V2O5 films synthesized from an aqueous sol–gel system has been developed and photocatalytic properties of the obtained films were studied. The reduction was performed by annealing of the V2O5 film in vacuum as well as in H2/Ar atmosphere, which was followed by temperature dependent XRD. It has been shown that the reduction is influenced by the layered-structure of the vanadium oxides. It is a two-step process, where the mixed-valence vanadium oxide V4O9 is first formed before reaching the VO2(B) phase. The film microstructure was characterized by SEM and AFM and the valence states of vanadium in VO2(B) films were evaluated by XPS. The VO2(B) polymorph shows an energy band-gap around 2.8 eV and it exhibits photocatalytic properties. It was measured by following the degradation of rhodamine B under UVA as well as metalhalogenide lamp irradiation, which has similar spectral distribution as natural sunlight. The VO2(B) films show distinct photoactivities under both lamps, although they were found to be more active under the UVA irradiation. The film annealed under reducing hydrogen atmosphere, which exhibits higher granularity and surface roughness, shows higher photoactivity than the vacuum-annealed film.

Cu6PS5I-based thin films were deposited onto silicate glass substrates by magnetron sputtering. Chemical composition of the thin films was determined by energy-dispersive X-ray spectroscopy. With increasing Cu content, a red shift of the exponential absorption edge energy position as well as a decrease of the Urbach energy are observed. Optical transmission spectra of Cu8.05P0.68S3.54I0.73 thin film were investigated in the temperature interval 77–300 K; the temperature behaviour of the optical absorption spectra and the refractive index dispersion was studied. Temperature dependences of the energy position of the absorption edge, the Urbach energy, and the refractive index of the Cu8.05P0.68S3.54I0.73 thin film were analysed. The influence of structural disorder on the optical properties of the Cu6PS5Ibased thin films is discussed.

Nanostructured hard coatings are becoming fundamental in many application areas due to their highly enhanced mechanical properties compared to conventional materials. Among others, novel quaternary systems are attracting increasing attention since they are expected to further improve endurance of such coatings. In this work, combined experimental and ab initio analysis of thermal stability and structural evolution of quaternary Ti–Ta–B‐N coatings with Ta content 0–40 at.% prepared by reactive magnetron co‐sputtering is presented. All prepared Ti 1–x–y Ta x B y N coatings in the as-deposited state exhibit amorphous structure, which is supported by ab initio calculations. Structural development of Ti–Ta–B–N coatings induced by vacuum annealing leads to the formation of a nanocomposite system consisting of fcc -TiN, possibly fcc -TaN phase and disordered a -BTi y (Ta z )N x phase. At further increase of annealing temperature above 1100 °C, other nitride, boride and diboride crystalline phases begin to form. This process is accompanied by release of nitrogen from all samples, phase transformations and grain coarsening. Calculations of formation and cohesive energies for various phases of possible Ti–Ta–B–N decomposition products as well as molecular dynamics simulations of the Ti 1–x–y Ta x B y N system at high temperatures were performed in order to give deeper insight into the structural evolution and thermal stability of the investigated alloy. Increased value of hardness at higher Ta content and low elastic modulus as well as high elastic recovery of the Ti–Ta–B–N coatings are also reported in this work and show a promising way to improve toughness of nitride coatings.

Influence of an ex situ annealing temperature and atmosphere on chemical composition and structural and superconducting properties of MgB 2 thin films deposited by vacuum evaporation has been investigated. The annealing has been done in Ar, N 2 and Ar + 5%H 2 atmospheres at pressure of 700 Pa and temperature varying from 700 to 800 °C. It has been shown that annealing in Ar and N 2 atmosphere at 700–800 °C produces relatively thick MgO layer on the surface of the films, while creation of such layer is highly reduced if the annealing is done in reducing Ar + 5%H 2 atmosphere. The XPS and XRD results suggest that the MgO layer prevents out-diffusion of Mg from the film during the annealing, what assures better stoichiometry of the films as well as creation of larger MgB 2 grains. The films with the highest amount of MgO on the surface, annealed in nitrogen atmosphere, thus paradoxically exhibited the highest critical temperature of T c 0 = 34.8 K with very sharp transition width of 0.1 K.

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 330 K (well above room temperature) and the highest resistivity of metal–insulator transition is at temperature (TP) above 400 K. Temperature coefficient of the resistance (TCR) has achieved values of 3.4% K−1 at 325 K 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.

Simple gas sensors based on resistivity change of TiO2 thin films using combined top and bottom metallic contacts are very promising. In this work influence of ex situ annealing in ambient air on structure of TiO2 thin film stacked between two platinum contact layers has been studied. The layers were deposited using DC magnetron sputtering on unheated c-cut sapphire substrates. For lowering of the Schottky barrier at the Pt–TiO2 interfaces and for improved crystalline stability, ex situ annealing at 600 °C in air was carried out. In order to study separately influence of top and bottom platinum layers on crystal structure, also reference samples Pt/TiO2/Al2O3 and TiO2/Pt/Al2O3 have been prepared. Non-ambient X-ray diffraction measurement during annealing process and X-ray pole figures after annealing has been measured. Near epitaxial relationship was observed for bottom Pt layer grown on c-cut sapphire substrate: Pt(1 1 1)[ 1 1 ¯ 0 ]||Al2O3(0 0 0 1)[ 1 1 ¯ 00 ]. Inner titania layer shows randomly oriented both TiO2-rutile (R) and anatase (A) phases with the volumetric ratio of R/A ∼ 2.7. If prepared without top Pt contact layer, the TiO2 transforms during annealing to random single anatase phase. The TiO2 layer overgrown with only single Pt top contact layer shows randomly oriented both rutile and anatase phases with volumetric ratio R/A ∼ 2.3. The top Pt layer on TiO2 shows filamentary uniaxial orientation Pt(1 1 1)||Al2O3(0 0 0 1). The interdiffusion at the Pt–TiO2 interfaces extends to several nm.

In this paper we describe a process of MoC superconducting thin films preparation by reactive magnetron sputtering in argon–acetylene atmosphere. The deposition process was optimized to achieve very smooth superconducting thin films with high sheet resistance. We present the results of four-point resistance measurements in cryostat cooled down to 300 mK. The roughness was measured by the atomic force microscope (AFM). The results are so far promising and enable us to pattern superconducting coplanar waveguide resonator with embedded nanostructures.

a b s t r a c t Double layer films based on TiO2 and NiOx for gas detection were studied. Two layouts with opposite position of functional films were deposited via DC magnetron sputtering method and annealed at 600 ◦ C. The compositional, structural, morphological, electrical and gas sensing parameters were investigated. The depth profiles and the chemical state of the thin films elements were explored by X-ray photoelectron spectroscopy (XPS). Differences between the surface and subsurface NiOx were confirmed. In this way the formation of surface oxides and subsurface metallic Ni were observed. The structural changes and polycrystalline character were noticed by X-ray diffraction (XRD). The atomic force microscopy (AFM) revealed nanocrystalline character of the examined surfaces (both layouts). Different position of TiO2 and NiOx functional films brought difference in the type of response to reducing gas. Moreover, inversion of response type due to different H2 concentrations was confirmed.

Titanium dioxide gas sensors are typically employing metastable anatase nanocrystalline phase. Operation at high temperature can thus negatively affect their long term stability. Employment of rutile phase with strong texture and larger grain size may ensure better reliability and longer lifetime. Therefore in this work we study the possibility to utilize stable rutile phase thin films prepared at relatively low temperature on c-cut sapphire substrates. Technological conditions have been chosen in order to obtain highly oriented titanium dioxide rutile thin films using reactive DC magnetron sputtering on unheated substrates. Subsequent ex-situ annealing in temperature range from 500°C to 800°C leads to increase of crystallite size and improvement of in-plane preferential orientation. Surface topography has been characterized by atomic force microscopy. Structure, texture and the strain evolution has been investigated using x-ray diffraction measurements. All investigated thin films showed epitaxial relationship with respect to the substrate: rutile-TiO2(100)[00 || Al2O3(0001)[10. Sensitivity of such rutile films to hydrogen has been measured and compared with our previous results on anatase thin films.

In this work, we investigate the influence of position of electrodes on the sensitivity of hydrogen gas sensors based on TiO2 thin films. We have prepared two types of sensors with platinum comb-like electrodes deposited on top and under the TiO2 layer. Response of these sensors to hydrogen gas in the concentration range of 0 10 000 ppm at temperature of 350 °C has been studied. The sensors with electrodes placed under the TiO2 layer showed two orders of magnitude lower sensitivity for 10 000 ppm compared to sensors with electrodes on top of the layer, but it was considerably increased when thickness of the TiO2 layer was lowered. This gives a possibility to improve the sensitivity of gas sensors in which the electrodes must be placed below the sensing layer for their protection from harsh environment.