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

Contribution of photocatalysis and Fenton-based processes for the degradation of aqueous organic pollutants.

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.

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.

A novel self-textured nanofilament technique based on the resistive-switching effect in nano-scale transition-metal oxide films has been developed. While traditional tunneling and point-contact approaches to the electron–boson interaction spectroscopy in a strong-coupled superconductor are realized on different samples, the novel method allows one to get related data on the same device. Conductance traces of S/I/Pt junctions with two superconductors of interest (S = Nb and MgB2), a platinum counter-electrode and a double-oxide interlayer (I = Al2O3/TiO2) with a controllable interface transparency reveal superconducting-gap and phonon-induced features which disappear above the superconducting-to-normal state transition. In both cases, we have observed BCS gap features with comparatively strong broadening. In MgB2-based samples, nonlinearities in differential conductance-vs-voltage characteristics far above the energy gap were detected in two modes, a point-contact regime without any significant barrier at the superconductor/Pt interface and the tunneling one. In Nb-based junctions we have succeeded to realize only the first regime. The observed features arise at energies corresponding to maximums in the phonon density of states of niobium and magnesium diboride. Their amplitude and general shape agree with theoretical predictions of the electron–phonon coupling effect in the superconductors studied. We argue that the proposed nanoscale methodology provides a simple and promising way for studying an interaction responsible for Cooper pairing in superconducting materials.

The potential use of TiO2 nanotube layers as a self-sterilizing and self-cleaning material for environmental application is presented. Antimicrobial, antibiofilm and photocatalytic performance of anodic TiO2 nanotube layers under UV irradiation was investigated on titanium mesh and on Ti sputtered on silicon substrates. The nanotubes were prepared in fluoride containing ethylene glycol-based electrolyte to obtain ~ 4 µm thick nanotube layers, which were subsequently annealed at 450 °C. Structural and morphological properties of prepared TiO2 layers were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy. In addition, their surface wettability, before and after UV irradiation, was investigated. Their photoactivity was compared to TiO2 sol–gel films of similar thickness. The highest efficiency in photocatalytic degradation of organic dye and removal of free-floating bacteria of Gram-positive Staphylococcus epidermidis was observed for TiO2 nanotube layers on titanium mesh. The highest antibiofilm performance in impairments of biofilms was reached using the TiO2 nanotubes on silicon. The obtained results on silicon substrate are promising for the development of medical devices covered by TiO2 nanotubes that would decrease the risk of infection. On the other hand, the mesh substrate covered by TiO2 nanotubes could find environmental applications such as filters in flowing photocatalytic reactors.

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.

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)

Slow kinetics of oxygen evolution reaction (OER), combined with harsh conditions of acidic media, significantly limits the progress of large-scale hydrogen production by water splitting. Efficient, stable and less-expensive catalysts are required to overcome such restrictions. Herein, we report preparation of IrRe-IrOx based catalysts with record high mass activity. The electrocatalyst was prepared by magnetron sputtering deposition of metallic Ir-Re thin film with subsequent electrooxidation. The optimal composition of as-deposited Ir-Re catalyst was defined as Ir39Re61. During electrooxidation process Re atoms are dissolved promoting metallic Ir oxidation to highly active amorphous IrOx phase with high surface area. The IrRe-IrOx catalyst exhibits low OER overpotential of 248 mV at 10 mA•cm-2 current density and mass activity of 4400 mA•mg−1. High mass OER activity of the IrRe-IrOx catalyst is result of combination of high surface area, low catalyst loading and presence of amorphous IrOx on catalyst surface.

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.

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

High Target Utilization Sputtering (HiTUS) is a novel technique with an independent plasma source, which offers higher plasma densities, possibilities for the increase of the level of ionization of the sputtered material and significant reduction of negative effects accompanying reactive sputtering related to target poisoning. The aim of the work was to investigate some details of the reactive sputtering behavior during HiTUS and the possibilities of this technology in the increase of the hardness of W-C coatings. It was found out that HiTUS plasma is similar to that in DCMS and hysteresis behavior of sputtering rates during reactive sputtering after modification of acetylene flow was suppressed. The reason seems to be related to higher sputtering rates due to high plasma density from the independent plasma source compared to target poisoning rates within limited acetylene addition range. The reactive HiTUS resulted in substoichiometric amorphous or nanocrystalline WC 1− x /amorphous carbon coating containing at least 20% of free disordered carbon. The amount of carbon was proportional to the acetylene flow. Slight shifts of G peak of Raman spectra toward higher values at higher RF bias power were attributed to ordering of carbon structure. Moreover, hardness increased approximately linearly with biasing power within limited acetylene flow range. The highest nanohardness values of HiTUS W-C coatings of around 33 GPa–35 GPa were comparable to those obtained in the best magnetron sputtered coatings which emphasized the applicability of HiTUS technology in hard coatings.

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.

Arrays of micron-sized domains of modified surface potential were created on hydroxyapatite films by mid-energy (20 keV) electron beam irradiation available in a laboratory scanning electron microscope. The dosage of electron beam was varied between 10−3 and 103 μC/cm2 to inject charge into the film surface. Contrary to the conventional electrowetting theory, the dosage of injected charge used in creating such microdomains caused a gradual increase of the water contact angle from 57° to 93° due to the elimination of the polar component of the surface free energy. Surface contamination by carbonaceous species can be held only partially responsible for such behavior at lower dosage of electron beam. A transfer of free surface charge to water and an electron beam induced disruption of polar orientation of OH ions have been attributed to be influencial factors in the overall dewetting behavior.

Despite being one of the mostly studied biomaterials for orthopedic, dental, protein purification and stem cell applications, electrical properties of hydroxyapatite has received only limited attention. Since the prediction in 2005 of the possibility of piezo and pyroelectricity in hydroxyapatite several theoretical and experimental works in this field may lead to new understandings of electrical behaviors of calcified tissues in vertebrates. Also, the ability of creating discrete electrostatic domains on nanocrystalline films of hydroxyapatite will open the possibility of understanding how surface charge influences biological interactions. The outlook for future endeavours in this field will be discussed.

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.

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.

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.

Surface sulfation and Eu3+ doping of 0.2–2 µm anatase aggregates prepared by precipitation significantly increased their porosity, specific surface, crystallinity and photocatalytic activity in phenol photo-mineralization. Such large, porous clusters of photocatalysts containing nanocrystals with well developed crystallinity which sediment more quickly than nanopowder suspensions are advantageous in water treatment applications. Sulfated anatase co-doped with Eu3+ exhibited the highest photoactivity. This is composed of well developed crystallites in the 31–55 nm size-range, with evident faceting. Although the investigated powders showed very weak photo-disinfectant activity against Gram-negative Escherichia coli rods, they exhibit moderate efficacy against Gram-positive bacterial strains of methicillin resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis. The investigated powders, especially the Eu3+ doped ones, are highly active in elimination of the eukaryotic Candida albicans.

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.

Vanadium oxide thin films are promising materials for various applications. Much attention has been devoted to thermotropic VO2(M/R) films which exhibit semiconductor-conductor phase transition at 67 °C making them excellent materials for switching applications. Non-thermotropic VO2(B) films are semiconducting and have layered structure which makes them interesting for gas sensing applications. Vanadium pentoxide films are also of great interest for photocatalytic production of H2by H2O decomposition as well as for gas sensing. In this paper the preparation of vanadium oxide thin films by using the spin coating of V2O5·nH2O aqueous gel on Si/SiO2and lime-glass substrates is reported. The as-deposited films were annealed in either air or H2/Ar atmosphere at normal or low pressure in order to prepare V2O5and VO2thin films. The obtained samples were characterized by XRD and SEM.

The surface properties of hydroxyapatite, including electric charge, can influence the biological response, tissue compatibility, and adhesion of biological cells and biomolecules. Results reported here help in understanding this influence by creating charged domains on hydroxyapatite thin films deposited on silicon using electron beam irradiation and investigating their shape, properties, and carbon contamination for different doses of incident injected charge by two methods. Photoluminescence laser scanning microscopy was used to image electrostatic charge trapped at pre-existing and irradiation-induced defects within these domains, while phase imaging in atomic force microscopy was used to image the carbon contamination. Scanning Auger electron spectroscopy and Kelvin probe force microscopy were used as a reference for the atomic force microscopy phase contrast and photoluminescence laser scanning microscopy measurements. Our experiment shows that by combining the two imaging techniques the effects of trapped charge and carbon contamination can be separated. Such separation yields new possibilities for advancing the current understanding of how surface charge influences mediation of cellular and protein interactions in biomaterials.

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.

Point contact spectroscopy is commonly used to investigate electronic properties of superconductors. Here we show that nanometer scale point contacts, which enable to study the superconductor properties locally, can be created by means of the resistive switching phenomenon. Our experiments were performed on sandwiched MgB2/Al/TiO2/Pt structures, where multiple bipolar resistive switching cycles were conducted. The differential conductance as a function of voltage was measured at temperatures below the critical temperature of the MgB2 superconductor. In the low-resistance state the MgB2 and Pt electrodes are connected by an ultrathin metallic filament which creates at the MgB2 electrode the Sharvin point contact with diameter below 10 nm. In this case the differential conductance data demonstrate the Andreev reflections due to the carrier transport between the superconducting MgB2 electrode and filament. From these data the two-gap superconductivity of MgB2 is clearly visible which also confirms the fit by the Blonder-Tinkham-Klapwijk model. If the bottom electrode is made of a superconductor with known gap, our approach allows us to estimate from the Andreev reflection spectrum the resistance of both the filament and point contact. We can then determine from the Sharvin formula the cross-section size of the point contact and thus also the filament cross-section size. In the high resistance state when the filament is ruptured, the differential conductance data demonstrate the spectrum typical for tunneling between two normal metals, with a zero-bias anomaly due to the Altshuler-Aronov effect. This suggests that the filament is not ruptured at the superconducting MgB2 electrode but elsewhere.

Si–Cr–N coatings are promising candidates for protective coatings for materials with a poor resistance to oxidation at elevated temperatures. In this article, we examine and present the thermal stability and high temperature oxidation behavior of reactively magnetron sputtered Si x Cr y N z coatings with high content of silicon (> 30 at.%) and N/metal ratios of 0.48 and 1.1. These coatings are investigated under isothermal and dynamic conditions using differential scanning calorimetry and thermal gravimetric analysis for temperatures of up to 1400 °C. The structure and morphology of the oxidized coatings are studied by X-ray diffraction, and electron microscopy. As-deposited Si x Cr y N z coatings represent a composite system consisting of two chemically separated amorphous phases: a-SiN x phase and a-SiCrN phase. The decomposition process connected with N 2 release occurs in Si x Cr y N z coatings at an annealing temperature T a ≥ 1000 °C in an Ar atmosphere and involves a formation of nanocrystalline hcp-Cr 2 N, Cr 5 Si 3 , hcp-Si 3 N 4 and hcp-CrSi 2 phases. These structural changes are reflected in an increase in hardness from 13.2 GPa and 19.3 GPa to 34 GPa and 25.6 GPa for Si 0.66 Cr 0.34 N 0.48 and Si 0.66 Cr 0.34 N 1.1 coatings, respectively. Si x Cr y N z coatings exhibit considerable oxidation resistance due to the formation of stable and dense Cr 2 O 3 scales. The rapid oxidation of Si x Cr y N z coatings starts as temperature T a reaches ~ 1090 °C. The dense oxide scale of ~ 0.4 μm is formed during isothermal oxidation of Si 0.66 Cr 0.34 N 1.1 coatings at the temperature of 1100 °C for 48 h.

TiO2thin films with a thickness of about 150 nm were deposited by spin coating method on sapphire substrate from a sol-gel system. The hydrogen sensing properties of TiO2films annealed at various temperatures were studied and correlated with their structure, optical and electrical properties. The annealing temperatures in the range of 600 800 °C lead to anatase films with a roughness in the range of 0.6 0.9 nm. Their sensitivity towards hydrogen is low. The thin films annealed at temperatures in the range 900 1000 °C consist of rutile phase and their roughness increased to 11.7 13.5 nm. They showed good hydrogen sensitivity with optimal operating temperature 200 250 °C. The structure and sensing properties of the prepared films are compared with those synthesized with magnetron sputtering. The maximum of sensitivity was measured on the thin films with diameter of the grains about 100 nm in both cases, i.e. on thin films prepared by sol-gel method as well as on thin films prepared by magnetron sputtering. The maximum sensitivity correlates with the diameter of the grains and dont depend on the allotropy of the titanium dioxide anatase or rutile.

Surface potential (SP) of biomaterials surfaces is known to significantly influence adsorption of biological cells and biomolecules. Its modifications thus play an important role in biological and medical applications. In this work, focused electron beam typically available in scanning electron microscopes has been used to create micro-domains with modified SP on nano-crystalline hydroxyapatite thin films. The resulting SP distribution has been studied by the Kelvin probe force microscopy technique as a function of the incident electron energy in the range from 3 to 30 keV for varying beam current, i.e. speed of the charge injection. Factors limiting minimal size of such SP patterns are discusses.

Local surface conductivity properties and surface degradation of c-axis oriented YBa2Cu3O6+x (YBCO) thin films were studied by Scanning Spreading Resistance Microscopy (SSRM). For the surface degradation studies, the YBCO surface was cleaned by ion beam etching and the SSRM surface conductivity map has been subsequently repeatedly measured over several hours in air and pure nitrogen. Average surface conductivity of the scanned area was gradually decreasing over time in both cases, faster in air. This was explained by oxygen out-diffusion in both cases and chemical reactions with water vapor in air. The obtained surface conductivity images also revealed its high inhomogenity on micrometer and nanometer scale with numerous regions of highly enhanced conductivity compared to the surroundings. Furthermore, it has been shown that the size of these conductive regions considerably depends on the applied voltage. We propose that such inhomogeneous surface conductivity is most likely caused by varying thickness of degraded YBCO surface layer as well as varying oxygen concentration (x parameter) within this layer, what was confirmed by scanning Auger electron microscopy (SAM). In our opinion the presented findings might be important for analysis of current-voltage and differential characteristics measured on classical planar junctions on YBCO as well as other perovskites., 8 pages, 5 figures

The understanding and the precise control of protein adsorption is extremely important for the development and optimization of biomaterials. The challenge resides in controlling the different surface properties, such as surface chemistry, roughness, wettability, or surface charge, independently, as modification of one property generally affects the other. We demonstrate the creation of electrically modified patterns on hydroxyapatite by using scanning electron beam to tailor the spatial regulation of protein adsorption via electrostatic interactions without affecting other surface properties of the material. We show that domains, presenting modulated surface potential, can be created to precisely promote or reduce protein adsorption.

In this work, the optimal characteristics of etching TiO2 films in an inductively coupled plasma system with CF4/Ar plasma were investigated. The maximum etch rate of TiO2 was 93 nm/min at fixed 200 W of inductively coupled plasma power and the highest investigated value of RF chuck power of 150 W. Using the X-ray photoelectron spectroscopy the chemical reactions between TiO2 and F were analysed. It was found that the etching mechanism included ion-stimulated desorption of reaction products on the TiO2 surface and formation of a solid solution and non-volatile TiF3.

Design of hard ceramic material coatings with enhanced toughness, which prevents crack formation/propagation leading to brittle failure during application, is a primary industrial requirement. In this work, experimental methods supported by ab initio density functional theory (DFT) calculations and electronic structure analyses are used to investigate the mechanical behavior of magnetron sputtered Ti-Al-Ta-N hard coatings. The as-deposited Ti1-x-yAlxTayN (y = 0–0.60) films exhibit a single phase cubic sodium chloride (B1) structure identified as TiAl(Ta)N solid solutions. While the hardness H of Ti0.46Al0.54N (32.5 ± 2 GPa) is not significantly affected by alloying with TaN (H of the quaternary nitrides varies between 26 ± 2 and 35 ± 4 GPa), the elastic stiffness monotonically decreases from 442 to 354 GPa with increasing Ta contents, which indicates improved toughness in TiAlTaN. Consistent with the experimental findings, the DFT results show that Ta substitutions in TiAlN reduce the shear resistance due...

In this paper we focus our attention on preparation of superconducting MgB2 thin films and variable-thickness MgB2 thin film bridges using the Atomic Force Microscope nanolithographic technique. Microstructures and their following variable-thickness bridges were prepared on nonsuperconducting MgB thin films. Final structures were annealed in argon atmosphere at temperature 680 � C and exhibit transition to the superconducting state Tcon = 33 K and zero critical temperature Tc0 = 30.5 K. Critical current density jc (4.2 K) measured on the bridge was higher than 10 6 A/cm 2 .

Low cost, low power and highly sensitive gas sensors operating at room temperature are very important devices for controlled hydrogen gas production and storage. One of the disadvantages of chemosensors is their high operating temperature (usually 200 – 400 °C), which excludes such type of sensors from usage in explosive environment. In this report, a new concept of gas chemosensors operating at room temperature based on TiO 2 thin films is discussed. Integration of such sensor is fully compatible with sub-100 nm semiconductor technology and could be transferred directly from labor to commercial sphere.

Surface properties of Co-doped BaFe2As2 epitaxial superconducting thin films were inspected by X-ray photoelectron spectroscopy, scanning spreading resistance microscopy (SSRM), and point contact spectroscopy (PCS). It has been shown that surface of Fe-based superconductors degrades rapidly if being exposed to air, what results in suppression of gap-like structure on PCS spectra. Moreover, SSRM measurements revealed inhomogeneous surface conductivity, what is consistent with strong dependence of PCS spectra on contact position. Presented results suggest that fresh surface and small probing area should be assured for surface sensitive measurements like PCS to obtain intrinsic properties of Fe-based superconductors., Comment: 4 pages, 4 figures

Hydroxyapatite nanocrystals in natural form are a major component of bone- a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone- density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.

Resistance switching effects in metal/perovskite contacts based on epitaxial c-axis oriented Y-Ba-Cu-O (YBCO) thin films with different crystallographic orientations have been studied. Three types of Ag/YBCO junctions with the contact restricted to (i) c-axis direction, (ii) ab-plane direction, and (iii) both were designed and fabricated, and their current-voltage characteristics have been measured. The type (i) junctions exhibited conventional bipolar resistance switching behavior, whereas in other two types the low-resistance state was unsteady and their resistance quickly relaxed to the initial high-resistance state. Physical mechanism based on the oxygen diffusion scenario, explaining such behavior, is discussed., The final version was published in Journal of Applied Physics (2012)

Titanium dioxide thin films were deposited on sapphire substrates by reactive dc magnetron sputtering method. The prepared thin films were then annealed in air at various temperatures (600 – 800 °C) to achieve crystalline thin films having anatase phase. The comb-like Pt electrodes, with a distance of 10 μm, were prepared on the top of the films to measure the electrical and gas sensing properties. The films prepared in this work showed high electrical response for various concentrations of H2/air, ranging from 20 to 10 000 ppm. The response was tested in the working/operating temperature range 150 – 350 °C and it was observed that these thin films are the most sensitive at temperatures below 200°C.