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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.

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.

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.

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.

Owing to its high energy density and environmentally friendly nature, hydrogen has already been regarded as the ultimate energy of the 21st century and gained significant attention from the worldwide researchers. Meanwhile, there are increasing concerns about its safe use, storage and transport as, despite being colorless and odorless, after certain concentration level it becomes flammable and explosive in air. Therefore, it is imperative to develop H2 sensors for real-time monitoring of the H2 leakage for an early warning. This paper firstly introduces the general hydrogen gas sensing mechanism of TiO2-based hydrogen sensors. Then we summarize and comment on the current hydrogen gas sensor based on various TiO2 materials, which include pristine TiO2, metal-assisted TiO2, organic-TiO2 composites, carbon-TiO2 composites, MOX-TiO2 composites and novel sensor concept with effective top-bottom electrode configuration. Finally, we briefly discuss the obstacles that TiO2-based H2 sensors have to overcome in the progress of the systematically practical application, possible solutions, and future research perspectives that can be focused in this area.

In this report, we demonstrate a simple and cost-effective strategy to prepare polycrystalline rutile TiO2 based gas sensors with tunable n/p type response inversion depending on gas concentration, operating temperature, and applied voltage. The effect of surface modification by Ag and Ni thin film on structural, morphological, and gas sensor characteristics is studied in detail. The sensors show excellent sensing performance in terms of sensitivity (sensor response∼25 for 0.1 vol. % H2 diluted in technical air), selectivity (selectivity factor for 0.1 vol. % H2 is about ∼24 against NH3, CH4, and NO2 and ∼8 for CO in the same concentration range), stability (both long-term and short-term), and reaction times (∼0.7 min for 0.1 vol. % H2). The aforementioned performance is recorded at 300 °C with applied voltage of 0.1 V. Excluding the power consumption of sensor heater (typically ∼5 × 10−5 watt), this applied voltage 0.1 V can reduce the power consumption to 3 × 10−10 watt. For the first time, we found a critical point, defined with critical-concentration (Cc), critical-temperature (Tc) and critical-voltage (VC), at which the response inverses from one kind to another, something intriguing to novel sensing phenomena that can be exploited to tailor the selectivity of the sensors. A physical-chemical sensing model is presented to understand the aforesaid peculiar occurrence.

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.

Owing to their excellent hydrogen surface susceptibility, TiO

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.

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.

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.

The asymmetric nano-channel diode (ANCD) is the 2-dimensional electron gas (2DEG) semiconductor nanodevice that, unlike a conventional diode, relies on the device nanostructure and field-controlled transport in a ballistic nanometerwidth channel instead of barriers to develop its asymmetric, diode-like current-voltage (I-V) characteristics. We focus on ANCD optoelectronic properties, and demonstrate that the devices can act as very sensitive, single-photon-level, visiblelight photodetectors. Our test structures consist of 2-μm-long and ~230-nm-wide channels and were fabricated using electron-beam lithography on a GaAs/AlGaAs heterostructure with a 2DEG layer, followed by reactive ion etching. The I-V curves were collected by measuring the transport current under the voltage-source biasing condition, both in the dark and under light illumination. The experiments were conducted inside a cryostat, in a temperature range from 300 K to 78 K. As an optical excitation, we used a 800-nm-wavelength, generated by a commercial Ti:sapphire laser operated either at a quasi-continuous–wave mode or as a source of 100-fs-wide pulses. The impact of the light illumination was very clear, and at low temperatures we observed a significant photocurrent Iph ~ 0.25 μA at temperature 78 K for the incident optical power as low as 1 nW, with a limited dark-current background. The magnitude of the device optical responsivity increased linearly with the decrease of the optical power, reaching for 1-nW optical excitation the value as high as ~400 A/W at room temperature and >800 A/W at 78K. The physics of the photoresponse gain mechanism in the ANCD arises from a vast disparity between the sub-picosecond transit time of photo-excited electrons travelling in the 2DEG nanochannel and the up to microsecond lifetime of photo-excited holes pushed towards the device substrate.

This article reports on how an additional interfacial nickel oxide (NiO) influenced the hydrogen sensory performance of a Pt/AlGaN/GaN Schottky gate diode of a circular HEMT device. The oxide was formed by the oxidation of a thin Ni layer on top of the Pt/AlGaN gate interface at a high temperature. We propose that the oxide should provide a thermally stable interface, and its nanocrystalline surface morphology should be a favourable platform for the subsequent deposition of a catalytic Pt absorption layer on top. We analyzed the electrical properties of this interface and studied the sensory performance of such Schottky gate diode sensors to hydrogen versus the varied thickness of the NiO layer. It is shown that the parameters of the gate interface (barrier height, ideality factor) and the hydrogen sensory performance (sensitivity, time response) can be tuned with the thickness of the NiO interfacial layer. The diode exhibited a 60-fold increase in sensitivity for an optimized 20 nm thick oxide interlayer compared with that of a conventional Pt/AlGaN/GaN gate diode sensor. This can be explained considering that hydrogen dissociated more efficiently at the nanocrystalline surface of the Pt/NiO stack. However, the transient characteristics of the sensors with NiO showed a longer response time due to a longer diffusion path for hydrogen. We show that the optimal operation temperature of the sensor shifted considerably from 250 °C (reference Pt/AlGaN/GaN sensor) to as low as 50 °C (sensor with the NiO layer). This temperature shift is desirable for battery-powered hydrogen sensors.

In this paper we demonstrate the superconducting properties of MgB2 coplanar waveguide resonator patterned from 300 nm thin film fabricated by vapor deposition. We measured the temperature dependence of the quality factor and the resonant frequency of the resonator. Surprisingly, we also observed hysteretic periodic response of resonance frequency to external magnetic field, which is characteristic of bistable systems with double-well potential, such as superconducting RF SQUID or phase-slip flux qubits. This property seems to be peculiar for granular and disordered superconductors where a superconducting loop of large effective diameter with weak links can be formed.

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.

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.

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.

Surface properties of Co-doped BaFe 2 As 2 (Ba-122) thin films prepared by pulsed laser deposition on MgO with Fe buffer layer and CaF 2 substrates were inspected by atomic force microscopy, scanning spreading resistance microscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy, auger electron spectroscopy/microscopy and point contact spectroscopy (PCS). Selected PCS spectra were fitted by extended 1D BTK model. The measurements were done on as-received as well as ion beam etched surfaces. Our results show that the substrate is considerably influencing the surface properties of the films, particularly the topography and surface conductivity distribution, what can affect results obtained by surface-sensitive techniques like PCS.

Capacitorlike metal/metal oxide/metal structures are widely used as resistive switching cells and are utilized in resistive random access memories. Recently, it has been demonstrated that they also perform well as gas sensors. In this work, we have merged the gas sensing and resistive switching capabilities of the capacitorlike Pt/TiO2/Pt structures to constitute a simple device which works as a gas-triggered thyristorlike switch and as a gas sensor with a built-in memory.

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.

Thin films of titanium dioxide with thickness of about 150 nm were deposited by spin coating method on a sapphire substrate from a sol–gel and annealed at various temperatures (from 600 °C to 1000 °C). Structural, optical and hydrogen gas sensing properties of the films were investigated. The annealing temperatures from 600 to 800 °C led to anatase phase with grain size in the range of 14–28 nm. Further increase of the annealing temperature resulted in transformation to rutile phase with larger grain size of about 100–120 nm. The optical band gap tended to decrease with increasing annealing temperature. The estimated values of activation energy for charge transport were in the range of 0.6–1.0 eV for films annealed at temperatures from 600 °C to 800 °C and 0.37–0.38 eV for films annealed at 900 °C and 1000 °C. The films annealed at 900 °C and 1000 °C showed better hydrogen sensitivity, what can be at least partially caused by their higher surface roughness.

One of the potential applications of TiO2 is its use in gas sensor technology. The aim of this work was to study the gas sensing properties of TiO2 thin films in combination with the effect of post-deposition annealing treatment. Titanium dioxide thin films with thickness 100 nm were prepared by the reactive dc magnetron sputtering. The thin films were deposited on sapphire substrate from a titanium target in an oxygen atmosphere. The samples were then post-annealed in air in the temperature range 600 °C 1000 °C. Crystal structure, surface topography and absorption edge of the thin films have been studied by X-ray Diffraction technique, Atomic Force Microscopy and UV-VIS Spectroscopy. It was found that the phase gradually changed from anatase to rutile, the grain size and roughness tended to increase with increasing post-annealing temperature. The effect of these factors on gas sensing properties was discussed. For electrical measurements comb-like Pt electrodes were prepared by standard photolithography and the films were exposed to different concentrations of H2 gas up to 10000 ppm in synthetic air at various operating temperatures from 200 °C to 350 °C.

We present a new approach in design of high temperature stable AlGaN/GaN HEMT gate absorption layers for hydrogen sensing at elevated temperature. To suppress undesirable chemical interaction of Pt on the gate interface, a thin conductive IrO2 oxide layer (t ∼ 10 nm) is formed by high temperature oxidation (T= 800 ̊C for 1min in O2 ambience) before Pt catalytic metal deposition. The comparative study of the hydrogen detection on AlGaN/GaN HEMT device with the Pt and Pt-IrO2 based gate absorption layers is shown. The sensitivity of the Pt gate Schottky diode is significantly enhanced with the insertion of IrO2 gate interfacial layer. The proposed Pt-IrO2 gate based diode exhibits a maximum sensing response value of 70%/ppm at 100 ̊C under a 0.1% H2/N2 gas. As comparing with the conventional Pt diode it is increased by more than 12 times. Additionally, the operating temperature for the maximum sensing response is decreased from 150 ̊C to 100 ̊C with the insertion of IrO2 interfacial layer. Moreover, the Schottky gate barrier height lowering at is found to be 254 meV and 100 meV for the IrO2 and Pt gate based diodes, respectively.

Many applications based on TiO 2 thin films are strongly influenced by the film crystalline quality, microstructure and surface morphology. We have utilized x-ray scattering methods for crystal structure study of TiO 2 films, grown by DC reactive magnetron sputtering without heating. We have observed the formation of ordered phases after post-deposition ex-situ annealing in air at 600 °C. The distinct biaxial texture with respect to the c -plane (0001) Al 2 O 3 substrate surface, which developed during heating, shows remarkable patterns in pole figures. We have identified epitaxial relationships of anatase A(001)[110]‖sub(001)[1100] and rutile R(100)[001]‖sub(0001)[100] within single TiO 2 layer. In addition, within the same sample, we have observed the anatase in (112) orientation with two in-plane relationship options A(112)[110]‖sub(0001)[2110] and A(112)[110]‖sub(0001)[1100].

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.

The influence of the deposition parameters on the growth, structure and mechanical properties of the TiBx coatings is studied. The TiBx coatings represent a nanocomposite system, in which random or oriented TiB2 nanocrystallites are embedded in an amorphous matrix as is revealed by cross-sectional transmission electron microscopy. We show that low-energy ion bombardment (Ei ) of growing TiBx coating, influences the preferred orientation of TiB2 crystallites. The increase of ion current density (is) by means of negative substrate bias voltage (Us) leads to change from random to the (0001) preferred crystal orientation whereby the electrical biasing promotes crystal growth in the coating and the (0001) texture appears gradually during the film growth. Together with the (0001) preferred orientation selection the composition B/Ti ratio was changed from 2.9 (floating potential, Ei = 8 eV) to 2.4 (Ei = 94 eV). The highest amount of oriented (0001) crystallites and highest hardness H = 53 GPa exhibit TiBx coatings deposited at Ei = 94 eV and is = 2.69 mA.cm−2.

Current-voltage characteristics of planar junctions formed by an epitaxial c-axis oriented YBa2Cu3O7-x thin film micro-bridge and Ag counter-electrode were measured in the temperature range from 4.2 K to 300 K. A hysteretic behavior related to switching of the junction resistance from a high-resistive to a low-resistive state and vice-versa was observed and analyzed in terms of the maximal current bias and temperature dependence. The same effects were observed on a sub-micrometer scale YBa2Cu3O7-x thin film - PtIr point contact junctions using Scanning Tunneling Microscope. These phenomena are discussed within a diffusion model, describing an oxygen vacancy drift in YBa2Cu3O7-x films in the nano-scale vicinity of the junction interface under applied electrical fields., Comment: To be published in Applied Surface Science.

Smooth MgB 2 superconducting thin films with roughness below 10 nm, critical temperature T c = 31 K and critical current density j c (4.2 K) ≈ 5 × 10 6 A/cm 2 were prepared by magnetron sputtering and ex-situ annealing in vacuum. On these films, weak links and radio frequency superconducting interference devices were prepared by combination of optical lithography and AFM scratching as well as by focused ion beam milling. Phase and current-phase characteristics have been investigated on our superconducting quantum interference devices.