Browsing by Author "Brinzari, Vladimir"

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Conductometric gas sensors based on metal oxides modified with gold nanoparticles : a review [Articol]
(Springer, 2016) Korotcenkov, Ghenadii; Brinzari, Vladimir; Cho, Beong K.
This review (with 170 refs.) discusses approaches towards surface functionalizaton of metal oxides by gold nanoparticles, and the application of the resulting nanomaterials in resistive gas sensors. The articles is subdivided into sections on (a) methods for modification of metal oxides with gold nanoparticles; (b) the response of gold nanoparticle-modified metal oxide sensors to gaseous species, (c) a discussion of the limitations of such sensors, and (d) a discussion on future tasks and trends along with an outlook. It is shown that, in order to achieve significant improvements in sensor parameters, it is necessary to warrant a good control the size and density of gold nanoparticles on the surface of metal oxide crystallites, the state of gold in the cluster, and the properties of the metal oxide support. Current challenges include an improved reproducibility of sensor preparation, better long-term stabilities, and a better resistance to sintering and poisoning of gold clusters during operation. Additional research focused on better understanding the role of gold clusters and nanoparticles in gas-sensing effects is also required.
Electronic structure and structural defects in 3d-metal doped In2O3 [Articol]
(Springer, 2019) Ho, J.; Becker, J.; Leedahl, B.; Boukhvalov, D. W.; Zhidkov, I. S.; Kukharenko, A. I.; Kurmaev, E. Z.; Cholakh, S. O.; Gavrilov, N. V.; Brinzari, Vladimir; Moewes, A.
Dilute magnetic semiconductors (DMSs) are a highly attractive field of research due to their potential to open new technological functionality. Here, we perform a systematic study of In2O3 thin films with dopant ions of Mn, Co, Ni, and Fe to investigate the unique interaction of each of these ions and their incorporation into the semiconductor lattice. We report substitutional positioning of Fe atoms into the In3+ site and a mixture of interstitial, metallic clustering, and substitutional positioning for Co, Mn, and Ni, discriminating between oxidation states for all dopant atoms.
Energetic, structural and electronic features of Sn-, Ga-, O-based defect complexes in cubic In2O3 [Articol]
(IOP Publishing Ltd, 2020) Cocemasov, Alexandr; Brinzari, Vladimir; Nika, Denis
Defect energy formation, lattice distortions and electronic structure of cubic In2O3 with Sn, Ga and O impurities were theoretically investigated using density functional theory. Different types of point defects, consisting of 1–4 atoms of Sn, Ga and O in both substitutional and interstitial (structural vacancy) positions, were examined. It was demonstrated, that formation of substitutional Ga and Sn defects are spontaneous, while formation of interstitial defects requires an activation energy. The donor-like behavior of interstitial Ga defects with splitting of conduction band into two subbands with light and heavy electrons, respectively, was revealed. Contrarily, interstitial O defects demonstrate acceptor-like behavior with the formation of acceptor levels or subbands inside the band gap. The obtained results are important for an accurate description of transport phenomena in In2O3 with substitutional and interstitial defects.
Fundamental crystal field excitations in magnetic semiconductor SnO2: Mn, Fe, Co, Ni [Articol]
(Royal Society of Chemistry, 2019) Brinzari, Vladimir; Leedahl, B.; McCloskey, D. J.; Boukhvalov, D. W.
Directly measuring elementary electronic excitations in dopant 3d metals is essential to understanding how they function as part of their host material. Through calculated crystal field splittings of the 3d electron band it is shown how transition metals Mn, Fe, Co, and Ni are incorporated into SnO2. The crystal field splittings are compared to resonant inelastic X-ray scattering (RIXS) experiments, which measure precisely these elementary dd excitations. The origin of spectral features can be determined and identified via this comparison, leading to an increased understanding of how such dopant metals situate themselves in, and modify the host's electronic and magnetic properties; and also how each element differs when incorporated into other semiconducting materials. We found that oxygen vacancy formation must not occur at nearest neighbour sites to metal atoms, but instead must reside at least two coordination spheres beyond. The coordination of the dopants within the host can then be explicitly related to the d-electron configurations and energies. This approach facilitates an understanding of the essential link between local crystal coordination and electronic/magnetic properties.
In2O3- and SnO2-based ozone sensors: Design and characterization [Articol]
(Taylor & Francis Ltd, 2018) Korotcenkov, Ghenadii; Brinzari, Vladimir; Cho, B.K.
This article describes in detail the SnO2 and In2O3 metal oxides as materials for designing solid state conductometric ozone sensors. The main focus of this article is on the description of the SnO2 and In2O3 films' structural parameters important for gas sensor design and on the establishment of the main regularities of the film parameters influence on the sensor characteristics. Advantages and disadvantages of approaches used for optimization of ozone sensor parameters are also analyzed. In particular, surface modification, bulk doping of SnO2 and In2O3, and the use of 1D structures and hybrid materials are considered. The main factors, controlling parameters of SnO2- and In2O3-based ozone sensors, are determined, and recommendations for the process of the SnO2 and In2O3 films deposition, facilitating the search of the film parameters and the fabrication technologies that optimize the ozone sensor performance, are formulated.
In2O3-based thermoelectric materials: the state of the art and the role of surface state in the improvement of the efficiency of thermoelectric conversion [Articol]
(MDPI, 2018) Korotcenkov, Ghenadii; Brinzari, Vladimir; Ham, Moon-Ho
In this paper, the thermoelectric properties of In2 O3 -based materials in comparison with other thermoelectric materials are considered. It is shown that nanostructured In2 O3 Sn-based oxides are promising for thermoelectric applications at moderate temperatures. Due to the nanostructure, specific surface properties of In2 O3 and filtering effects, it is possible to significantly reduce the thermal conductivity and achieve an efficiency of thermoelectric conversion inaccessible to bulk materials. It is also shown that a specific surface state at the intergrain boundary, optimal for maximizing the filtering effect, can be achieved through (1) the engineering of grain boundary parameters, (2) controlling the composition of the surrounding atmosphere, and (3) selecting the appropriate operating temperature.
The influence of gold nanoparticles on the conductivity response of SnO2-based thin film gas sensors [Articol]
(Elsevier, 2015) Korotcenkov, Ghenadii; Brinzari, Vladimir; Gulina, L.B.; Cho, B. K.
The results presented in this study demonstrate that the successive ionic layer deposition (SILD) method for gold nanoparticle formation can be used for surface functionalization of SnO2 films to improve their gas sensing properties. As a result of successive treatments in HAuCl4•nH2O and NaBH4 solutions, gold nanoparticles can be formed on the surface of SnO2 crystallites. The size of the gold particles varies over the range of 1–50 nm depending on the number of SILD cycles. Gas sensing characteristics of the Au-modified SnO2 films are discussed as well. Unlike most studies focused on the development of CO sensors, the present research focuses on the specifics of the response of the SnO2:Au-based sensors to other gases, such as hydrogen and ozone. It is established that gold nanoparticles deposited on the SnO2 surface are active toward both reducing and oxidizing gases, and the effect of the SnO2 surface decoration by the gold nanoparticles on the gas sensing characteristics depends on the number of deposition cycles (i.e., the size of the gold particles). The sensitization to ozone and hydrogen suggests that the application of the surface modification by gold in the field of gas sensor design should not be limited by optimization of the CO sensor's parameters. Models showing the promotional role of Au additives are discussed, and a mechanism of sensitization in the SnO2:Au-based gas sensor is proposed.
Kinetic approach to receptor function in chemiresistive gas sensor modeling of tin dioxide. Steady state consideration [Articol]
(Elsevier, 2018) Brinzari, Vladimir; Korotcenkov, Ghenadii
Kinetic approach in phenomenological modeling of SnO2 chemiresistive gas sensor is proposed. It is based on a new perception of chemisorbed oxygen forms and consistent account of main reaction rates into a balance equation of particles on (110) surface. So-called receptor function was considered for dry and humid atmosphere and in the presence of CO. Transducer function was calculated within an electron filtering model. Numerical simulation of the surface coverage by oxygen and major gas sensing characteristics of SnO2 within 150–600 °C temperature range showed sufficient agreement with experimental behavior of nanocrystalline SnO2-based sensors. Model allows interpretation of some of the important features in these characteristics.
Thermal transport evolution due to nanostructural transformations in Ga-doped indium-tin-oxide thin films [Articol]
(MDPI, 2021) Brinzari, Vladimir; Jeong, Do-Gyeom; Korotcenkov, Ghenadii; Vatavu, Sergiu; Lee, Jong S.; Nika, Denis; Cocemasov, Alexandr
We report on a comprehensive theoretical and experimental investigation of thermal conductivity in indium-tin-oxide (ITO) thin films with various Ga concentrations (0–30 at. %) deposited by spray pyrolysis technique. X-ray diffraction (XRD) and scanning electron microscopy have shown a structural transformation in the range 15–20 at. % Ga from the nanocrystalline to the amorphous phase. Room temperature femtosecond time domain thermoreflectance measurements showed nonlinear decrease of thermal conductivity in the range 2.0–0.5 Wm−1 K−1 depending on Ga doping level. It was found from a comparison between density functional theory calculations and XRD data that Ga atoms substitute In atoms in the ITO nanocrystals retaining Ia-3 space group symmetry. The calculated phonon dispersion relations revealed that Ga doping leads to the appearance of hybridized metal atom vibrations with avoided-crossing behavior. These hybridized vibrations possess shortened mean free paths and are the main reason behind the thermal conductivity drop in nanocrystalline phase. An evolution from propagative to diffusive phonon thermal transport in ITO:Ga with 15–20 at. % of Ga was established. The suppressed thermal conductivity of ITO:Ga thin films deposited by spray pyrolysis may be crucial for their thermoelectric applications.
Thermal transport evolution due to nanostructural transformations in ga-doped indium-tin-oxide thin films [Articol]
(2021) Cocemasov, Alexandr; Brinzari, Vladimir; Jeong, Do-Gyeom; Korotcenkov, Ghenadii; Lee, Jong S.; Nika, Denis L.
We report on a comprehensive theoretical and experimental investigation of thermal con- ductivity in indium-tin-oxide (ITO) thin films with various Ga concentrations (0–30 at. %) deposited by spray pyrolysis technique. X-ray diffraction (XRD) and scanning electron microscopy have shown a structural transformation in the range 15–20 at. % Ga from the nanocrystalline to the amorphous phase. Room temperature femtosecond time domain thermoreflectance measurements showed nonlinear decrease of thermal conductivity in the range 2.0–0.5 Wm−1 K−1 depending on Ga doping level. It was found from a comparison between density functional theory calculations and XRD data that Ga atoms substitute In atoms in the ITO nanocrystals retaining Ia-3 space group symmetry. The calculated phonon dispersion relations revealed that Ga doping leads to the appearance of hybridized metal atom vibrations with avoided-crossing behavior. These hybridized vibrations possess shortened mean free paths and are the main reason behind the thermal conductivity drop in nanocrystalline phase. An evolution from propagative to diffusive phonon thermal transport in ITO:Ga with 15–20 at. % of Ga was established. The suppressed thermal conductivity of ITO:Ga thin films deposited by spray pyrolysis may be crucial for their thermoelectric applications.
XPS study of Rh/In2O3 system [Articol]
(Elsevier, 2021) Korotcenkov, Ghenadii; Brinzari, Vladimir; Nehasil, Vaclav
The effect of surface modification of In2O3 films by rhodium atoms deposited by electron beam sputtering on the XP spectra is considered. The surface coverage with rhodium ranged from 0 to 0.1 ML. It was shown that the main changes in the XP spectra occur in the Rh3d region and are caused by the dimensional effect of rhodium particles. With an increase in the surface coverage with rhodium, Rh particles grow from an atomically dispersed state to relatively large clusters. As the particle size increases, its electronic structure tends to approach the state corresponding to the bulk Rh. Such a process is accompanied by a decrease in BE Rh3d5/2 by 0.3–0.6 eV, which behaviour depends on the surface structure of the used In2O3 films.
XPS study of the SnO2 films modified with Rh [Articol]
(John Wiley and Sons, 2018) Korotcenkov, Ghenadii; Brinzari, Vladimir; Hanyš, P.; Nehasil, V.
In this paper, we have analyzed the effect of the rhodium surface modification on the surface state of SnO2 films. SnO2 films, subjected for the surface modification, were deposited by spray pyrolysis, while Rh was deposited by using a microelectron beam evaporation. The thickness of the Rh coating varied in the range 0 to 0.1 monolayer. An explanation of the observed effects was proposed. Basing on the results of X‐ray photoelectron spectroscopy, it was assumed that at a small thickness of the rhodium covering, Rh was in a the well‐dispersed state, close to atomically dispersed state. The growth in the size of the nanoparticles began mainly when the thickness of the Rh covering exceeeded 0.01 monolayer. The size of clusters did not exceed 0.5 to 1.0 nm.