Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1 at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 degrees C, proper laser annealing (fluence 50 mJ/cm2, 5-15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under-and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.

Chemiresistive gas sensors were produced by functionalizing graphene with a ~3 nm layer of mixed oxide xCu2O⸱yMnO using pulsed laser deposition (PLD) from a hopcalite CuMn2O4 target. Sensor response time traces were recorded for strongly oxidizing (NO2, O3) and reducing (NH3, H2S) poisonous gases at ppb and ppm levels, respectively. The morphology of the MOX layer was modified by growth temperature during PLD, resulting in the optimization of the sensor response. Differences in decomposition or oxidation rates on catalytically active metal oxide (MOX) were utilized to achieve partial selectivity for pairs of gases that have similar adsorption and redox properties. The predominant selectivity towards ozone in most samples at different measuring conditions remained difficult to suppress. A distinct selectivity for H2S emerged at higher measurement temperatures (100–150 °C), which was assigned to catalytic oxidation with O2. Several gas–MOX interaction mechanisms were advanced to tentatively explain the sensor behavior, including reversible electron transfer in the simplest case of NO2, decomposition via ionic transients for O3, and complex catalytic oxidative transformations for NH3 and H2S.

Samarium-doped CdWO4 thin films were prepared by pulsed laser deposition; their morphological, structural and photoluminescent properties were studied. In the luminescence spectra of the films with thicknesses ranging from 100 nm down to 2 nm, strong Sm3+-related emission dominated and efficient host-to-guest energy transfer was observed. Also for the same series of films, both Sm3+-related and intrinsic (excitonic) emissions became increasingly sensitive to ambient oxygen as the layer thickness was decreased. Time-resolved measurements indicated that the luminescence became partly quenched as ambient oxygen concentration was decreased. Implications of the results, in relation to previously studied TiO2:Sm nanomaterials and CdWO4:Sm single crystals, are discussed.

Miniature and low-power gas sensing elements are urgently needed for a portable electronic nose, especially for outdoor pollution monitoring. Hereby we prepared chemiresistive sensors based on wide-area graphene (grown by chemical vapor deposition) placed on Si/Si3N4 substrates with interdigitated electrodes and built-in microheaters. Graphene of each sensor was individually functionalized with ultrathin oxide coating (CuO-MnO2, In2O3 or Sc2O3) by pulsed laser deposition. Over the course of 72 h, the heated sensors were exposed to randomly generated concentration cycles of 30 ppb NO2, 30 ppb O3, 60 ppb NO2, 60 ppb O3 and 30 ppb NO2 + 30 ppb O3 in synthetic air (21% O2, 50% relative humidity). While O3 completely dominated the response of sensors with CuO-MnO2 coating, the other sensors had comparable sensitivity to NO2 as well. Various response features (amplitude, response rate, and recovery rate) were considered as machine learning inputs. Using just the response amplitudes of two complementary sensors allowed us to distinguish these five gas environments with an accuracy of ~ 85%. Misclassification was mostly due to an overlap in the case of the 30 ppb O3, and 30 ppb O3 + 30 ppb NO2 responses, and was largely caused by the temporal drift of these responses. The addition of recovery rates to machine learning input variables enabled us to very clearly distinguish different gases and increase the overall accuracy to ~94%.

Graphene in its pristine form has demonstrated a gas detection ability in an inert carrier gas. For practical use in ambient atmosphere, its sensor properties should be enhanced with functionalisation by defects and dopants, or by decoration with nanophases of metals or/and metal oxides. Excellent sensor behaviour was found for two types of single layer graphenes: grown by chemical vapour deposition (CVD) and transferred onto oxidized silicon (Si/SiO2/CVDG), and the epitaxial graphene grown on SiC (SiC/EG). Both graphene samples were functionalised using a pulsed laser deposited (PLD) thin V2O5 layer of average thickness ≈ 0.6 nm. According to the Raman spectra, the SiC/EG has a remarkable resistance against structural damage under the laser deposition conditions. By contrast, the PLD process readily induces defects in CVD graphene. Both sensors showed remarkable and selective sensing of NH3 gas in terms of response amplitude and speed, as well as recovery rate. SiC/EG showed a response that was an order of magnitude larger as compared to similarly functionalised CVDG sensor (295% vs. 31% for 100 ppm NH3). The adsorption site properties are assigned to deposited V2O5 nanophase, being similar for both sensors, rather than (defect) graphene itself. The substantially larger response of SiC/EG sensor is probably the result of the smaller initial free charge carrier doping in EG.

Some nanocrystalline TiO2 materials are notorious for their photoluminescence (PL), which exhibits a pronounced sensitivity to ambient oxygen and has a potential for optical gas sensing. Here, we utilized pulsed laser deposition to obtain thin (70 nm) anatase TiO2 films containing 1-2 atom % of either samarium (Sm) or neodymium (Nd) impurity ions. The highly porous nanostructure consisted of quite regular, interconnected nanopillars with a wall thickness of 15-20 nm, fully exposing the material to ambient environment. The PL intensity. of both ions (induced by 355 nm pulsed laser) responded in a reversible manner to changes of oxygen volume fraction in dry O-2/N-2 flow. Sm3+:TiO2 worked effectively at room temperature, whereas Nd3+:TiO2 showed an improved relative response at 100-150 degrees C. Switching between pure nitrogen and oxygen atmospheres affected the PL intensities up to 6 times, with response time of 1 min to 02 and recovery time of 10 min in N-2. The PL decay kinetics of Sm3+:TiO2 showed unambiguously that both decreasing 02 concentration and increasing temperature reduced the fluorescence quantum yield of excited Sm3+ ions. Such behavior is compatible with the proposed model of energy acceptors created by (reversible) electron transfer from desorbed charged 02 species to certain lattice defects. In contrast, decreasing O-2 concentration increased the PL intensity of Nd3+:TiO2. In this case, PL decay kinetics showed an increased excitation efficiency of Nd3+ ions, suggesting that O-2 adsorption favors a concurrent relaxation path for the photoexcited charge carriers.

Exceptionally sensitive and selective graphene-based chemiresistive gas sensors were produced as a result of graphene functionalisation with a sub-nanometer V2O5 layer by using the method of pulsed laser deposition. Two different types of graphene were used—epitaxial graphene on SiC and CVD graphene on Si/SiO2—and both showed remarkable enhancement of sensing properties in terms of response and recovery speed, response magnitude and selectiveness towards NH3 gas. The epitaxial graphene-based sensor was demonstrating the highest relative response towards ammonia amounting to 80% for 0.1 ppm NH3.

Graphene has been recognized as a promising gas sensing material. The response of graphene-based sensors can be radically improved by introducing defects in graphene using, e. g., metal or metal oxide nanoparticles. We have functionalised CVD grown, single layer graphene by applying pulsed laser deposition (PLD) of V2O5 which resulted in a thin V2O5 layer on graphene with average thickness of ~0.6 nm. According to Raman analysis, PLD process also induced defects in graphene. Compared to unmodified graphene, the obtained chemiresistive sensor showed considerable improvement of sensing ammonia at room temperature. In addition, also the response time, sensitivity and reversibility were essentially enhanced due to graphene functionalisation by laser deposited V2O5. This can be explained by increased surface density of gas adsorption sites introduced by high energy atoms in laser ablation plasma and formation of nanophase boundaries between deposited

Graphene has been recognized as a promising gas sensing material. The response of graphene-based sensors can be radically improved by introducing defects in graphene using, for example, metal or metal oxide nanoparticles. We have functionalised CVD grown, single-layer graphene by applying pulsed laser deposition (PLD) of V2O5 which resulted in a thin V2O5 layer on graphene with average thickness of ≈0.6 nm. From Raman spectroscopy, it was concluded that the PLD process also induced defects in graphene. Compared to unmodified graphene, the obtained chemiresistive sensor showed considerable improvement of sensing ammonia at room temperature. In addition, the response time, sensitivity and reversibility were essentially enhanced due to graphene functionalisation by laser deposited V2O5. This can be explained by an increased surface density of gas adsorption sites introduced by high energy atoms in laser ablation plasma and formation of nanophase boundaries between deposited V2O5 and graphene.

Rare earth oxycarbonates are potential candidate materials for constructing simple and low-cost chemiresistive sensors for monitoring carbon dioxide (CO 2 ) gas in the living and working environment for personal comfort and health reasons. Also, measurement of CO 2 concentrations is needed in many industrial processes. Specifically, sol-gel made nanoparticles of Nd and La oxycarbonates have been studied previously as novel CO 2 gas sensor materials. In this paper, pulsed laser deposition of La oxycarbonate (La 2 O 2 CO 3 ) thin films was studied and structural properties of obtained thin films were characterized. Also, CO 2 gas sensing ability of synthesized films was evaluated. The films deposited under CO 2 partial pressure in various conditions were all Raman amorphous. In situ or ex situ annealing procedure at high CO 2 partial pressure was needed for obtaining crystalline La 2 O 2 CO 3 films, whereby hexagonal and monoclinic polymorphs were obtained in ex situ and in situ processes, respectively. Sensor structure, made using in situ process, was sensitive to CO 2 gas and showed relatively fast response and recovery characteristics.

Rare earth oxycarbonates are potential candidate materials for constructing simple and low-cost chemiresistive sensors for monitoring carbon dioxide (CO 2 ) gas in the living and working environment for personal comfort and health reasons. Also, measurement of CO 2 concentrations is needed in many industrial processes. Specifically, sol-gel made nanoparticles of Nd and La oxycarbonates have been studied previously as novel CO 2 gas sensor materials. In this paper, pulsed laser deposition of La oxycarbonate (La 2 O 2 CO 3 ) thin films was studied and structural properties of obtained thin films were characterized. Also, CO 2 gas sensing ability of synthesized films was evaluated. The films deposited under CO 2 partial pressure in various conditions were all Raman amorphous. In situ or ex situ annealing procedure at high CO 2 partial pressure was needed for obtaining crystalline La 2 O 2 CO 3 films, whereby hexagonal and monoclinic polymorphs were obtained in ex situ and in situ processes, respectively. Sensor structure, made using in situ process, was sensitive to CO 2 gas and showed relatively fast response and recovery characteristics.

In this study we investigated the interaction of atmospheric-pressure helium (He) and He/H2 pulsed-discharge plasma with different water solutions. We developed a synthetic path to obtain fairly uniform, small (~2 nm), surfactant-free silver (Ag) nanoparticles (NPs) with the treatment of an AgNO3 solution with He/H2 bipolar pulsed discharge. The colloidal solutions containing Ag NPs are stable for months and do not show any agglomeration (the measured zeta potential is −41 mV at pH ~8). The adsorption of negatively charged hydroxide (OH−) ions on the surface of Ag NPs could be responsible for the electrostatic stabilization. The treatment of the air-saturated water by pure He plasma with a negative polarity leads to the creation of HNO3 and hydrogen peroxide (H2O2) as stable species. Contrary to the acidification of the solution by He plasma treatment, He/H2 discharge with negative and, in particular, with bipolar pulses produces only traces of HNO3 and no H2O2. We demonstrate here that He/H2 discharge with bipolar pulses is remarkably efficient in near-complete nitrate decomposition and slight alkalization of dilute HN03 and KNO3 solutions.

Thin CdWO4 films were produced on various substrates by pulsed laser deposition. A method of producing transparent films of high structural and optical quality on MgO substrate was developed. It is based on deposition of an amorphous film from a non-stoichiometric CdWO4 CdO target and a consequent crystallization of the film in oxygen atmosphere at 750 degrees C. The quality of the films produced was verified by x-ray diffraction, electron probe microanalysis, scanning electron microscopy, Raman and optical spectroscopy. (C) 2016 Elsevier Ltd. All rights reserved.

Graphene as a single-atomic-layer material is fully exposed to environmental factors and has therefore a great potential for the creation of sensitive gas sensors. However, in order to realize this potential for different polluting gases, graphene has to be functionalized—adsorption centers of different types and with high affinity to target gases have to be created at its surface. In the present work, the modification of graphene by small amounts of laser-ablated materials is introduced for this purpose as a versatile and precise tool. The approach has been demonstrated with two very different materials chosen for pulsed laser deposition (PLD)—a metal (Ag) and a dielectric oxide (ZrO2). It was shown that the gas response and its recovery rate can be significantly enhanced by choosing the PLD target material and deposition conditions. The response to NO2 gas in air was amplified up to 40 times in the case of PLD-modified graphene, in comparison with pristine graphene, and it reached 7%–8% at 40 ppb of NO2 and 20%–30% at 1 ppm of NO2. The PLD process was conducted in a background gas (5 × 10−2 mbar oxygen or nitrogen) and resulted in the atomic areal densities of the deposited materials of about 1015 cm−2. The ultimate level of NO2 detection in air, as extrapolated from the experimental data obtained at room temperature under mild ultraviolet excitation, was below 1 ppb.

Al doped ZnO is used as a material for transparent conductive electrodes in solar energy and display screen applications, as well as semiconducting material in electronic and photonic devices. For effective use it is essential to control the electrical and optical properties of ZnO:Al thin films. In order to investigate the influence of oxygen environment on effective Al solubility and intrinsic defects introduced at high doping levels during the film growth, ZnO:Al thin films were deposited in vacuum and oxygen background by pulsed laser deposition method. Films were doped with varying Al concentrations by using targets with Al doping levels of 1-10 at%. In vacuum, substantially increased free electron concentrations were observed for all Al doping levels, which indicates that the formation of acceptor-type defects, acting as electron killer centers, was largely suppressed during the growth in oxygen-poor conditions. The dependence of carrier mobility from Al concentration was also greatly influenced by oxygen conditions during the film growth, suggesting that ionized impurity concentrations in the films deposited in vacuum and oxygen background were significantly different. The results were interpreted in the context of intrinsic acceptortype defects Vzn (zinc vacancy), which concentration is strongly modified by the presence of oxygen during the film deposition. These vacancies are assumed to influence free electron concentration and electron mobility by acting as deep electron acceptors and charged electron scattering centers (V-zn(2-)). (C) 2014 Elsevier B.V. All rights reserved.

Responses of enzymatic bio-optrodes in flow regime were studied and an original model was proposed with the aim of establishing a reliable method for a quick determination of biosensor signal parameters, applicable for biosensor calibration. A dual-optrode glucose biosensor, comprising of a glucose bio-optrode and a reference oxygen optrode, both placed into identical flow channels, was developed and used as a model system. The signal parameters of this biosensor at different substrate concentrations were not dependent on the speed of the probe flow and could be determined from the initial part of the biosensor transient phase signal, providing a valuable tool for rapid analysis. In addition, the model helped to design the biosensor system with reduced impact of enzyme inactivation to the system stability (20% decrease of the enzyme activity lead to only a 1% decrease of the slope of the calibration curve) and hence significantly prolong the effective lifetime of bio-optrodes.

Gas sensor material was prepared by encapsulation of functionalized single-walled carbon nanotubes (SWCNT) into a gas-permeable polymer poly(1-trimethylsilyl-1-propyne) (PTMSP). A phenylhydrazino group was used for the functionalization of SWCNTs to improve their solubility and compatibility with polymers. Syntheses were carried out in aqueous surfactant solutions and in pure phenylhydrazine without surfactant. Two different temperatures (24 and 50°C) and two surfactants (sodium dodecyl sulfate and tricaprylmethylammonium chloride — Aliquat®336) were compared. Functionalized SWCNTs were characterized by X-ray photoelectron (XPS), Raman and Fourier transform infrared (FTIR) spectroscopy. Analyses showed that the synthesis at higher temperature in pure phenylhydrazine resulted in the highest functionalization yield. Phenylhydrazine itself proved to be a good solvent for SWCNTs. The functionalized nanotubes were soluble in organic solvents that under the same conditions were appropriate solvents for polymers. The sensitivity of functionalized SWCNT-PTMSP thin film composite to NO 2 gas at room temperature was significantly higher than that of the similar sensor material containing the pristine SWCNTs.

Amorphous granular SnO2 thin films were investigated from a standpoint of an NO2 gas sensor working at room temperature. The films were deposited using pulsed laser deposition method with substrate at room temperature and ∼90nm thick SnO2 films with amorphous structure were obtained as a result. SnO2 films deposited on Pt electrode substrates formed a sensor structure that showed response Iair/Igas to 4ppm NO2 up to ∼8000. I–V characteristics of the sensor structure were described by the power law dependence, whereas the power indexes were different for measurements in pure air and in the presence of NO2. As a result, the sensor response was highly dependent on bias voltage between the sensor electrodes. It was demonstrated that the nonlinear electrical characteristics and bias dependent gas sensitivity were the inherent properties of thin films and the contacts were ohmic.

Tuning of band gaps in materials by changing the ionic content of nanopores (in the case of 12CaO·7Al2O3) and nanochannels (in Ca-phosphate apatite) was demonstrated using low-temperature luminescence spectroscopy methods under vacuum ultraviolet excitation. Luminescence excitation spectra enabled us to conclude that the replacement of O2− ions with F− in the cages of 12CaO·7Al2O3 shifts the absorption edge from ≈ 5.1 to ≈ 5.8 eV. Non-homogeneously broadened 2p states of O2− ions inside cages of 12CaO·7Al2O3 form the dominating trapping levels for valence band holes and their replacement with F− ions facilitates efficient self-trapping of holes at the framework oxygen ions. In the case of Ca-phosphate apatite, the replacement of OH− groups with F− ions shifts the onset of host absorption from ≈ 7.8 to ≈ 8.4 eV. The intrinsic emissions of Ca-phosphate apatites revealed in the UV region were tentatively interpreted as radiative decay of Frenkel-type self-trapped excitons, where the hole component is localized on oxygen ions of PO4 tetrahedra.

Hydrogen doped MgO films were grown by pulsed laser deposition method. Gaseous hydrogen stored in cavities of milky MgO single crystal targets provided doping in film deposition process. Clear MgO targets without hydrogen were used in the preparation of reference films. The influence of hydrogen doping on firing voltage (FV) of gas discharge and its AC frequency dependence was investigated. According to thermoluminescence experiments, the films grown from milky targets contained two kinds of electron traps with the activation energies of 0.051 and 0.31eV, while latter traps were absent in reference samples. The 0.31eV trap was assigned to the hydride ion H− occupying an oxygen vacancy site in MgO crystal structure. Using standard gas mixture (Ne–10% Xe), FVs of hydrogen doped sample showed considerable frequency dependence and were up to 55V lower in comparison to the reference sample. The FVs of reference sample were shifted 14–28V to higher values when N2 gas was added to the mixture. The N2 addition lowered the FVs of hydrogen doped sample up to 38V and almost eliminated the FV frequency dependence.