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Plasmonic nanostructures ensure the reception and harvesting of visible lights for novel photonic applications. In this area, plasmonic crystalline nanodomains decorated on the surface of two-dimensional (2D) semiconductor materials represent a new class of hybrid nanostructures. These plasmonic nanodomains activate supplementary mechanisms at material heterointerfaces, enabling the transfer of photogenerated charge carriers from plasmonic antennae into adjacent 2D semiconductors and therefore activate a wide range of visible-light assisted applications. Here, the controlled growth of crystalline plasmonic nanodomains on 2D Ga2O3 nanosheets was achieved by sonochemical-assisted synthesis. In this technique, Ag and Se nanodomains grew on 2D surface oxide films of gallium-based alloy. The multiple contribution of plasmonic nanodomains enabled the visible-light-assisted hot-electron generation at 2D plasmonic hybrid interfaces, and therefore considerably altered the photonic properties of the 2D Ga2O3 nanosheets. Specifically, the multiple contribution of semiconductor–plasmonic hybrid 2D heterointerfaces enabled efficient CO2 conversion through combined photocatalysis and triboelectric-activated catalysis. The solar-powered acoustic-activated conversion approach of the present study enabled us to achieve the CO2 conversion efficiency of more than 94% in the reaction chambers containing 2D Ga2O3-Ag nanosheets.

Gallium oxide (Ga2O3) has emerged as a fourth-generation semiconductor for futuristic device requirements. Integration of Ga2O3 with industry-viable gallium nitride (GaN) can provide a pathway to design efficient device technology. In this paper, we design Ga2O3/GaN heterointerface by using a simple thermal annealing method under an oxygen-rich environment. Thermal annealing at 850 °C for 5 h results in a good yield of Ga2O3 from surficial GaN which was grown on sapphire and Si substrates. Surface morphology revealed a nanorod structure-based Ga2O3 on the GaN surface grown on industrial compatible Si substrate. XPS measurements provide a quantitative understanding of the heterostructure, where 84.62% and 70.92% of surficial GaN is converted into Ga2O3. Besides, the valence band maximum is shifted to a higher energy side in comparison to bare GaN samples. This helps in understanding the device physics of the grown heterostructures. Current-Voltage (I–V) characteristics revealed Schottky behaviour where the Schottky barrier height is increased after thermal annealing of the GaN films. Temperature correlated I–V characteristics suggest that the thermally annealed GaN films are stable up to 300 °C. These material structures can potentially be used in the high-temperature applications for power devices, optoelectronics, and sensing applications.

Group 2, 3, and 13 element-doped zirconium oxide catalysts M-ZrO2 (M = Mg, Sr, Y, La, Ce, Sm, Er, Yb, B, Al, Ga, In, and Tl; 5 mol%) were prepared by impregnation of each metal salt aqueous solution on amorphous zirconium hydroxide, followed by calcination at 773 K. The M-ZrO2 samples were characterized by the catalytic performance of 2-butanol decomposition at 573 K, XRD, XANES and EXAFS spectroscopic techniques. Detailed analyses were performed herein for a series of Ga-ZrO2 with various doping amounts in the range of 1 - 60 mol%. The addition of Group 2 and 3 elements little influenced the catalytic performance of ZrO2 itself to promote dehydration to produce 1-butene with 90% selectivity. Ga-ZrO2 and In-ZrO2 gave methyl ethyl ketone as the main product via dehydrogenation. The doped Ga ion mainly existed inside the bulk of zirconia by forming the GaxZr1-xO2 solid solution up to 5 mol%. Highly doped species more than 10 mol% aggregated to form e-Ga2O3. Each fraction forming the solid solution and Ga2O3-like species was evaluated by XANES analysis.

A high-performance Schottky diode based on a 600- ${\mu }\text{m}$ -thick Cr-doped ${\beta }$ -Ga2O3 single crystal has been fabricated using SnOx as the Schottky contact. The SnOx film was deposited in argon/oxygen mixture gas to ensure an oxygen-rich stoichiometry in Ga2O3 near the Schottky interface, thus reducing oxygen deficiency-related interface state density. The SnOx film included three components: Sn, SnO, and SnO2, as revealed by X-ray photoelectron spectroscopy characterization. The high-quality Ga2O3 single crystal grown by an edge-defined film-fed method has a carrier concentration of $1.0 \times 10^{18}$ cm $^{-3}$ and an electron mobility of ~90 cm2/Vs. The current density–voltage characteristics of the Schottky diode demonstrated high performance with a large barrier height of 1.19 eV, a close-to-unity ideality factor of 1.02, and a high rectification ratio beyond $10^{10}$ . The frequency-dependent capacitance and conductance analysis revealed that the maximum active interface state density is $2.46 \times 10^{12}$ eV $^{-1}$ cm $^{-2}$ at a frequency of 500 kHz.

A simple and inexpensive thermal oxidation process was performed to synthesize gallium oxide (Ga2O3) nanowires using Ag thin film as a catalyst at 800 &deg, C and 1000 &deg, C to understand the effect of the silver catalyst on the nanowire growth. The effect of doping and orientation of the substrates on the growth of Ga2O3 nanowires on single-crystal gallium arsenide (GaAs) wafers in atmosphere were investigated. A comprehensive study of the oxide film and nanowire growth was performed using various characterization techniques including XRD, SEM, EDS, focused ion beam (FIB), XPS and STEM. Based on the characterization results, we believe that Ag thin film produces Ag nanoparticles at high temperatures and enhances the reaction between oxygen and gallium, contributing to denser and longer Ga2O3 nanowires compared to those grown without silver catalyst. This process can be optimized for large-scale production of high-quality, dense, and long nanowires.

Gallium oxide (Ga2O3) is a new wide bandgap semiconductor with remarkable properties that offers strong potential for applications in power electronics, optoelectronics, and devices for extreme conditions. In this work, we explore the morphology of Ga2O3 nanostructures on different substrates and temperatures. We used silver catalysts to enhance the growth of Ga2O3 nanowires on substrates such as p-Si substrate doped with boron, 250 nm SiO2 on n-Si, 250 nm Si3N4 on p-Si, quartz, and n-Si substrates by using a thermal oxidation technique at high temperatures (~1000 &deg, C) in the presence of liquid silver paste that served as a catalyst layer. We present the results of the morphological, structural, and elemental characterization of the Ga2O3 nanostructures. This work offers in-depth explanation of the dense, thin, and long Ga2O3 nanowire growth directly on the surfaces of various types of substrates using silver catalysts.

In this study, brazing AA6061 to Q235 steel using flame brazing was performed with 70.9 wt.% CsF-0.5 wt.% RbF-28.6 wt.% AlF3 fluxes doped with GaF3, ZnF2, Zn(BF4)2 and Ga2O3 nanoparticles, matched with a Zn-15Al filler metal, and the spreadability of the filler metal and the mechanical properties of brazed joints were investigated at the same time. The results showed suitable amounts of GaF3, ZnF2, Zn(BF4)2 and Ga2O3 doped into the base flux could strengthen the filler metal in wetting and spreading on the surface of aluminum alloy and steel to different degrees. The suitable ranges of GaF3, ZnF2, Zn(BF4)2 and Ga2O3, respectively, were 0.0075&ndash, 0.01 wt.%, 0.0075&ndash, 0.01 wt.% and 0.009&ndash, 0.01 wt.%, and the maximum spreading area was obtained via doping with GaF3. The shear strength of brazed joints reached the peak at 126 MPa when 0.075 wt.% GaF3 was added. Comparative tests proved that the activity of the CsF-RbF-AlF3 flux doped with GaF3 was the best. The reason was that the CsF-RbF-AlF3-GaF3 flux was competent in removing oxides of the base metal and decreasing the interfacial tension, in virtue of the activity of Ga3+ as well as F&minus

In this study, a Ga2O3 nano-particle was added into CsF-RbF-AlF3 flux to develop a highly active flux for brazing aluminum alloy to steel, and the spreadability and wettability of Zn-Al filler metal that matched the CsF-RbF-AlF3 flux-doped Ga2O3 nano-particle on the steel were investigated. The results showed that the spreadability and wettability of the CsF-RbF-AlF3 flux-doped Ga2O3 nano-particle could be remarkably improved when matching Zn-Al filler metals on both aluminum and low-carbon steel, for which the optimal content is in the range of 0.001&ndash, 0.003 wt.% of Ga2O3. An investigation and analysis on the mechanism of reactions among CsF-RbF-AlF3-doped Ga2O3 nano-particle flux and filler metal or base metals showed that the Ga2O3 nano-particle is selectively absorbed by the interface of molten Zn-2Al filler metal and base metal, which released the surface-active element Ga to enrich the molten Zn-2Al filler metal and decreased the interfacial tension, so as to promote the enlargement of its spreading area during the brazing process. It was concluded that adding a trace amount of Ga2O3 nano-particle into CsF-RbF-AlF3 flux is a meaningful way to improve the activity of flux for brazing aluminum to steel compared with adding ZnCl2, which poses the risk of corrosion on aluminum.

We report silicon delta-doped $\beta $ -Ga2O3 metal semiconductor field effect transistors (MESFETs) with source–drain ohmic contacts formed by patterned regrowth of n-type Ga2O3. We show that regrown n-type contacts can enable a lateral low-resistance contact to the two-dimensional electron gas channel, with contact resistance lower than $1.5~\Omega $ -mm. The fabricated MESFET has a peak drain current ( ${I} _{D,\text{MAX}}$ ) of 140 mA/mm, transconductance ( ${g} _{m}$ ) of 34 mS/mm, and 3-terminal off-state breakdown voltage of 170 V. The proposed device structure could provide a promising path towards vertically scaled $\beta $ -Ga2O3 field effect transistors.

Gallium oxide (Ga2O3) thin films were fabricated on glass substrates using a combination of chemical bath deposition and post-annealing process. From the field-emission scanning electron microscopy and x-ray diffraction results, the GaOOH nanorods precursors with better crystallinity can be achieved under higher concentrations (&ge, 0.05 M) of gallium nitrate (Ga(NO3)3). It was found that the GaOOH synthesized from lower Ga(NO3)3 concentration did not transform into &alpha, Ga2O3 among the annealing temperatures used (400&ndash, 600 &deg, C). Under higher Ga(NO3)3 concentrations (&ge, 0.05 M) with higher annealing temperatures (&ge, 500 &deg, C), the GaOOH can be transformed into the Ga2O3 film successfully. An &alpha, Ga2O3 sample synthesized in a mixed solution of 0.075 M Ga(NO3)3 and 0.5 M hexamethylenetetramine exhibited optimum crystallinity after annealing at 500 &deg, C, where the &alpha, Ga2O3 nanostructure film showed the highest aspect ratio of 5.23. As a result, the photodegeneration efficiencies of the &alpha, Ga2O3 film for the methylene blue aqueous solution can reach 90%.

In the last few years, interest in the use of gallium oxide (Ga2O3) as a semiconductor for high power/high temperature devices and UV nano-sensors has grown. Ga2O3 has an enormous band gap of 4.8 eV, which makes it well suited for applications in harsh environments. In this work, we explored the effect of Ag thin film as a catalyst to grow gallium oxide. The growth of gallium oxide thin film and nanowires can be achieved by heating and oxidizing pure gallium at high temperatures (~1000 &deg, C) in the presence of trace amounts of oxygen. We present the results of structural, morphological, and elemental characterization of the &beta, Ga2O3 thin film and nanowires. In addition, we explore and compare the sensing properties of the &beta, Ga2O3 thin film and nanowires for UV detection. The proposed process can be optimized to a high scale production Ga2O3 nanocrystalline thin film and nanowires. By using Ag thin film as a catalyst, we can control the growth parameters to obtain either nanocrystalline thin film or nanowires.

The development of sensors working in a large range of temperature is of crucial importance in areas such as monitoring of industrial processes or personal tracking using smart objects. Devices integrating GaN/Ga2O3 core/shell nanowires (NWs) are a promising solution for monitoring carbon monoxide (CO). Because the performances of sensors primarily depend on the material properties composing the active layer of the device, it is essential to control them and achieve material synthesis in the first time. In this work, we investigate the synthesis of GaN/Ga2O3 core-shell NWs with a special focus on the formation of the shell. The GaN NWs grown by plasma-assisted molecular beam epitaxy, are post-treated following thermal oxidation to form a Ga2O3-shell surrounding the GaN-core. We establish that the shell thickness can be modulated from 1 to 14 nm by changing the oxidation conditions and follows classical oxidation process: A first rapid oxide-shell growth, followed by a reduced but continuous oxide growth. We also discuss the impact of the atmosphere on the oxidation growth rate. By combining XRD-STEM and EDX analyses, we demonstrate that the oxide-shell is crystalline, presents the &beta, Ga2O3 phase, and is synthesized in an epitaxial relationship with the GaN-core.

In this work, the thermal synthesis and characterization of gallium oxide and indium oxide nanowires using vapour-liquid-solid mechanism at atmospheric pressure were described. Au nanoislands formed by the solid-state dewetting process of various thickness metal layer were applied as growth catalyst of nanowires while high-purity metal reactants (In, Ga) were applied as AIII precursors. The catalytic layer thickness influence on the morphology of investigated nanostructures was studied. Material composition and structural properties were used for crystallographic quality of AIII-oxide nanowires examination.

A four-step reaction mechanism is proposed for the H2 dissociation over pure ceria and Gallium promoted mixed oxide materials, in a combined experimental and computational investigation. Two samples of cerium-gallium mixed oxides with Ce/Ga atomic ratios equal to 90/10 and 80/20 were studied by time-resolved diffuse reflectance infrared spectroscopy under H2 (D2) flow at isothermal condition in the range of 523?623 K. X-ray photoelectron spectrometry allowed to conclude that only Ce4+ is reduced to Ce3+ (Ga3+ is not reduced), in agreement with density functional theory (DFT) results. The time evolution profiles of gallium hydride ðGaAHÞ species, hydroxyl groups (OH) and Ce3+ infrared signals were analyzed and kinetic rate parameters for each step were obtained by mathematical modeling. The values for activation energies were in agreement with those calculated by DFT, for the different elementary pathways. A small activation energy (4 kcal/mol) was found for H2 dissociation found on GaOCe sites assuming that the heterolytic cleavage of the HAH bond is the rate determining step. On pure ceria, the experimental activation energy is 23 kcal/mol, showing that the addition of Ga3+ cations boosts the splitting of H2. Interestingly, the reduction step of pure CeO2 surface domains seems to proceed via a CeH/OH pair intermediate, according to DFT calculations. Moreover, 71Ga NMR experiments indicatethe possible presence of gallia nanodomains. It is proposed that the generation of Ga OACe sites in the perimeter of such surface gallia nanodomains is responsible for the enhanced reactivity of the mixed materials. The key role of this new type of sites to improve the efficiency of relevant catalytic reactions such as selective alkyne hydrogenation and light alkane dehydrogenation is then analyzed. Fil: Vecchietti, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Baltanas, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Gervais, Christel. Universite de Paris VI; Francia Fil: Collins, Sebastián Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Blanco. Ginesa. Universidad de Cádiz; España Fil: Matz, Olivier. Universite de Paris VI; Francia Fil: Calatayud, Monica. Universite de Paris VI; Francia Fil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

Our laboratory has previously revealed the use of metal-semiconductor-metal (MSM) varactors against malicious pulses, as well as completed the related verification and measurements of such a circuit. To improve the reliability of this protection module further, in this study, we deposited a gallium oxide (Ga2O3) thin film in between the Schottky contact electrode to manufacture a metal-oxide-semiconductor-oxide-metal (MOSOM) varactor. However, the thin-film quality and heterojunction interfaces will affect these fabricated varactors in various ways, such as the asymmetry threshold voltage to the variable capacitance characteristics. This study aims to address the issues associated with the inserted oxide thin film, as well as to determine how improvements could be obtained by using an oxygen furnace annealing process. As a result, the breakdown voltage of the MOSOM varactor was further promoted and a more robust anti-surge module was thus realized.

The effect of trace amounts of GaF3 and Ga2O3 nanoparticles on the wettability and spreadability of CsF-AlF3 flux matched Zn-15Al filler metal were comparatively studied on 6061 aluminum alloy and Q235 low-carbon steel. The experimental results indicate that appropriate amounts of GaF3 and Ga2O3 added into the flux could significantly promote the Zn-15Al filler metal to wet and spread on the surface of 6061 aluminum alloy and Q235 low-carbon steel. The optimum ranges for GaF3 and Ga2O3 were 0.0075&ndash, 0.01wt.% and 0.009&ndash, 0.01 wt.%, respectively. Comparative analysis showed that the activity of CsF-AlF3 flux bearing GaF3 was higher than that bearing Ga2O3. The reason for this is that the former flux has a stronger ability to remove oxides of the base metal and reduce the interfacial tension of the molten filler metal and the base metal.

Due to their relevance for electronic and optoelectronic applications, transparent conductive oxides (TCO) have been extensively studied in the last decades. Among them, monoclinic β-Ga 2 O 3 is well known by its large direct bandgap of ∼4.9 eV being considered a deep UV TCO suitable for operation in short wavelength optoelectronic devices. The wide bandgap of β-Ga 2 O 3 is also appropriate for the incorporation of several electronic energy levels such as those associated with the intra-4 f n configuration of rare earth ions. Among these, Eu 3+ ions (4 f 6 ) are widely used as a red emitting probes both in organic and inorganic compounds. In this work, undoped and Eu 2 O 3 doped (0.1 and 3.0 mol%) Ga 2 O 3 crystalline fibres were grown by the laser floating zone approach. All fibres were found to stabilize in the monoclinic β-Ga 2 O 3 structure while for the heavily doped fibres the X-ray diffraction patterns show, in addition a cubic europium gallium garnet phase, Eu 3 Ga 5 O 12 . The spectroscopic properties of the undoped and Eu doped fibres were analysed by Raman spectroscopy, low temperature photoluminescence (PL) and photoluminescence excitation (PLE). The Eu 3+ luminescence is mainly originated in the garnet, from where different europium site locations can be inferred. The spectral analysis indicates that at least one of the centres corresponds to Eu 3+ ions in dodecahedral site symmetry. For the lightly doped samples, the spectral shape and intensity ratio of the 5 D 0 → 7 F J transitions is totally different from those on Eu 3 Ga 5 O 12 , suggesting that the emitting ions are placed in low symmetry sites in the β-Ga 2 O 3 host.

Solvothermal oxidation of gallium metal in various organic solvents at 300 °C under the autogenous vapor pressure of the solvents was examined. The reaction of gallium metal in 1-butanol or 2-methoxy-ethanol at 300 °C did not proceed and unreacted gallium metal was recovered even with prolonged reaction time. On the other hand, gallium metal reacted in aminoalcohols such as 2-aminoethanol, 2-methylaminoethanol, 2,2′-iminodiethanol and 2,2′,2″-nitrilotriethanol yielding γ-Ga 2 O 3 . The product obtained by this reaction has a relatively large crystallite size as compared with γ-Ga 2 O 3 prepared by the conventional method.

In this study, the dehydrogenation component of Ga2O3 was introduced into ZSM-5 nanocrystals to prepare Ga2O3/ZSM-5 hollow fiber-based bifunctional catalysts. The physicochemical features of as-prepared catalysts were characterized by means of XRD, BET, SEM, STEM, NH3-TPD, etc., and their performances for the catalytic conversion of n-butane to produce light olefins and aromatics were investigated. The results indicated that a very small amount of gallium can cause a marked enhancement in the catalytic activity of ZSM-5 because of the synergistic effect of the dehydrogenation and aromatization properties of Ga2O3 and the cracking function of ZSM-5. Compared with Ga2O3/ZSM-5 nanoparticles, the unique hierarchical macro-meso-microporosity of the as-prepared hollow fibers can effectively enlarge the bifunctionality by enhancing the accessibility of active sites and the diffusion. Consequently, Ga2O3/ZSM-5 hollow fibers show excellent catalytic conversion of n-butane, with the highest yield of light olefins plus aromatics at 600 °C by 87.6%, which is 56.3%, 24.6%, and 13.3% higher than that of ZSM-5, ZSM-5 zeolite fibers, and Ga2O3/ZSM-5, respectively.

This contribution describes the effect of HMS-Ti substrate decoration with variable amounts of Ga2O3 on the catalytic response of bifunctional Ga2O3/HMS-Ti catalysts in the hydroisomerization of ortho-xylene carried out in a batch reactor at 300 °C. The effect of hydrogen pressure (5, 10 and 40 bar) was investigated. The synthetized Ga2O3/HMS-Ti samples were characterized by variety of techniques: HRTEM, XRD, N2 adsorption–desorption isotherms, FTIR in the –OH region, TPR and XPS. The catalyst activity showed a volcano-type curve being the catalyst with Ga loading of 1.1 wt.% the most active among the catalysts studied. Both FT-IR spectra of adsorbed pyridine and HRTEM images indicated that this behavior is linked to its high Brønsted and Lewis acidities and presence of small Ga2O3 particles homogeneously dispersed on the support surface. All catalysts exhibited larger isomerization than hydrogenation of ortho-xylene. At equilibrium, the products detected were meta- and para-xylenes, and dimethylcyclohexane (DMCH); meta-xylene being the main reaction product. An increase of hydrogen pressure from 5 to 10 bar led to an increase of isomerization and hydrogenation of ortho-xylene. Further increase of the hydrogen pressure from 10 to 40 bar had a very small effect on the catalyst activity., This study is partially supported by The Spanish Ministry of Science and Innovation (ENE2007-67533-C02-01 project) and The Community of Madrid (P2013/MAE-2882 project) with financial aid from the Scientific Cooperation FONCICYT Program (FONCICYT-96194 project).

In this research, monocrystalline gallium oxide (Ga2O3) nanobelts were synthesized through oxidation of metal gallium at high temperature. An electronic device, based on an individual Ga2O3 nanobelt on Pt interdigital electrodes (IDEs), was fabricated to investigate the electrical characteristics of the Ga2O3 nanobelt in a dry atmosphere at room temperature. The current-voltage (I-V) and I/V-t characteristics show the capacitive behavior of the Ga2O3 nanobelt, indicating the existence of capacitive elements in the Pt/Ga2O3/Pt structure.

Gallia (gallium oxide) has been proved to enhance the performance of metal catalysts in a variety of catalytic reactions involving methanol, CO and H2. The presence of formate species as key intermediates in some of these reactions has been reported, although their role is still a matter of debate. In this work, a combined theoretical and experimental approach has been carried out in order to characterize the formation of such formate species over the gallium oxide surface. Infrared spectroscopy experiments of CO adsorption over H2 (or D2) pretreated b-Ga2O3 revealed the formation of several formate species. The b-Ga2O3 (100) surface was modelled by means of periodic DFT calculations. The stability of said species and their vibrational mode assignments are discussed together with the formate interconversion barriers. A possible mechanism is proposed based on the experimental and theoretical results: first CO inserts into surface (monocoordinate) hydroxyl groups leading to monocoordinate formate; this species might evolve to the thermodynamically most stable dicoordinate formate, or might transfer hydrogen to the surface oxidizing to CO2 creating an oxygen vacancy and a hydride group. The barrier for the first step, CO insertion, is calculated to be significantly higher than that of the monocoordinate formate conversion steps. Monocoordinate formates are thus short-lived intermediates playing a key role in the CO oxidation reaction, while bidentate formates are mainly spectators. Fil: Calatayud, M.. Universite Pierre et Marie Curie; Francia Fil: Collins, Sebastián Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Baltanas, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Bonivardi, Adrian Lionel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

This status report overviews activities of the German gas sensor research community. It highlights recent progress in the field of potentiometric, amperometric, conductometric, impedimetric, and field effect-based gas sensors. It is shown that besides step-by-step improvements of conventional principles, e.g. by the application of novel materials, novel principles turned out to enable new markets. In the field of mixed potential gas sensors, novel materials allow for selective detection of combustion exhaust components. The same goal can be reached by using zeolites for impedimetric gas sensors. Operando spectroscopy is a powerful tool to learn about the mechanisms in n-type and in p-type conductometric sensors and to design knowledge-based improved sensor devices. Novel deposition methods are applied to gain direct access to the material morphology as well as to obtain dense thick metal oxide films without high temperature steps. Since conductometric and impedimetric sensors have the disadvantage that a current has to pass the gas sensitive film, film morphology, electrode materials, and geometrical issues affect the sensor signal. Therefore, one tries to measure directly the Fermi level position either by measuring the gas-dependent Seebeck coefficient at high temperatures or at room temperature by applying a modified miniaturized Kelvin probe method, where surface adsorption-based work function changes drive the drain-source current of a field effect transistor.

The authors have applied positron annihilation spectroscopy to study the vacancy defects in undoped and Si-doped Ga2O3 thin films. The results show that Ga vacancies are formed efficiently during metal-organic vapor phase epitaxy growth of Ga2O3 thin films. Their concentrations are high enough to fully account for the electrical compensation of Si doping. This is in clear contrast to another n-type transparent semiconducting oxide In2O3, where recent results show that n-type conductivity is not limited by cation vacancies but by other intrinsic defects such as Oi.