Gallium oxide thin films, containing either α-Ga2O3 or κ-Ga2O3 crystalline phases, were grown by atomic layer deposition (ALD) by using GaI3 and O3 as precursors. The κ-Ga2O3 phase was observed in ...the films grown on Si(1 0 0) at substrate temperatures ≥450 °C, while α-Ga2O3 was obtained at temperatures ≥275 °C on α-Cr2O3 seed layers deposited on Si(1 0 0). The seed layers with thicknesses down to 0.7 nm appeared to be sufficient to initiate the α-Ga2O3 growth. The densities of 5.2–5.3 g/cm3 for amorphous films deposited at the substrate temperatures 150–234 °C, 5.9−6.1 g/cm3 for the films deposited on uncoated Si substrates at 450–550 °C, and 6.3−6.4 g/cm3 for the films deposited on α-Cr2O3 seed layers at 350–550 °C were determined from X-ray reflectometry measurements. The growth per cycle decreased from 0.17 to 0.05–0.09 nm with the growth temperature increase from 150 to 550 °C. Notably, the growth rates of α-Ga2O3 films on α-Cr2O3 seed layers were significantly higher at 350–450 °C than those of the films deposited on uncoated Si at the same temperatures, indicating that crystal structure influenced the growth per cycle in this ALD process. The concentration of iodine impurities did not exceed 3.2 at. % in the films deposited at 150 °C. With the growth-temperature increase to 350 °C, the concentration of impurities decreased to ≤0.04 at. % in the films grown on bare Si and ≤0.01 at. % in the films grown on α-Cr2O3 seed layers.
Atomic layer deposition was applied to grow TiO2 thin films containing anatase, rutile and mixture of TiO2-II and rutile phases with the aim to investigate the dependence of optical parameters on the ...formation of metastable TiO2-II phase. The films were grown at a substrate temperature of 450 °C using TiCl4 and O3 as the precursors. The crystal structure obtained depended on the substrates used. The films deposited on amorphous SiO2 substrates contained only the anatase phase when the film thicknesses did not exceed 88 nm while in thicker films, anatase with inclusions of rutile was formed. The films deposited on α-Al2O3 substrates contained epitaxial rutile without traces of other crystalline phases on α-Al2O3(0 1 1̄ 2) (r-sapphire) and epitaxial TiO2-II with inclusions of rutile phase on α-Al2O3(0 0 0 1) (c-sapphire) substrates. The films that contained TiO2-II had refractive indices of 2.8 at a wavelength of 500 nm and 2.61–2.67 at 633 nm. These values were higher than those of anatase films (2.6 and 2.48–2.49, respectively) and rutile films (2.74 and 2.57–2.62, respectively). Optical band gaps of 3.28–3.36 eV obtained for the films containing TiO2-II were by 0.20 ± 0.08 eV wider than the band gaps of rutile films and by 0.06 ± 0.05 eV narrower than the band gaps of anatase films. A band gap value of 3.00 ± 0.08 eV was measured for a non-epitaxial film that was deposited on amorphous SiO2 and contained anatase with inclusions of rutile.
•Optical properties of TiO2 films containing anatase, rutile and TiO2-II were studied.•Refractive indices, absorption spectra and band gaps of the films were determined.•Refractive index values of films that contained TiO2-II exceeded those of other films.•Band gap energies of films containing TiO2-II were determined to be 3.28–3.36 eV.
Orange carotenoid proteins (OCPs) are photoswitchable macromolecules playing an important role in nonphotochemical quenching of excess energy in cyanobacterial light harvesting. Upon absorption of a ...blue photon (450–500 nm), OCPs undergo a structural change from the ground state OCPO to the active state OCPR, but high-resolution structures of the active state OCPR are not yet available. Here, we use small-angle scattering methods combined with simulation tools to determine low-resolution structures of the active state at low protein concentrations via two approaches: first, directly by in situ illumination of wild-type OCP achieving a turnover to the active state of >90% and second, by using the mutant OCPW288A anticipated to mimic the active state structure. Data fits assuming the shape of an ellipsoid yield three ellipsoidal radii of about 9, 29, and 51 ± 1 Å, in the case of the ground state OCPO. In the active state, however, the molecule becomes somewhat narrower with the two smaller radii being 9 and only 19 ± 3 Å, while the third dimension of the ellipsoid is significantly elongated to 85–92 ± 5 Å. Reconstitutions of the active state structure corroborate that OCPR is significantly elongated compared to the ground state OCPO and characterized by a separation of the N-terminal and C-terminal domains with unfolded N-terminal extension. By direct comparison of small-angle scattering data, we directly show that the mutant OCPW288A can be used as a structural analogue of the active state OCPR. The small-angle experiments are repeated for OCPO and the mutant OCPW288A at high protein concentrations of 50–65 mg/mL required for neutron spectroscopy investigating the molecular dynamics of OCP (see accompanying paper). The results reveal that the OCPO and OCPW288A samples for dynamics experiments are preferentially dimeric and widely resemble the structures of the ground and active states of OCP, respectively. This enables us to properly characterize the molecular dynamics of both states of OCP in the accompanying paper.
Atomic layer deposition of hafnium–titanium-oxide (Hf x Ti1–x O y ) films on silicon substrates and Ru, RuO2, and Pt seed layers was investigated. The films were grown using HfCl4 and TiCl4 as the ...metal precursors and H2O and O3 as the oxygen precursors. At a temperature of 350 °C and x ≤ 0.12, tetragonal phases isomorphous with anatase- and rutile-phase TiO2 grew on silicon and on Ru and RuO2, respectively. The films with 0.3 ≤ x ≤ 0.65 grown on silicon and Pt were amorphous, while those deposited on Ru and RuO2 contained the crystal structure isomorphous with orthorhombic HfTiO4. Independently of substrates, the phase isomorphous with monoclinic HfO2 was formed in the films with 0.73 ≤ x ≤ 1.0. The crystal structure influenced the concentration of chlorine impurities that was lower in crystalline films grown on Ru and RuO2 at 350–400 °C than that in amorphous films simultaneously deposited on Si. No significant effect of substrates on the chlorine concentrations was revealed for amorphous films deposited on Si, Ru, and RuO2 at 250 °C. The relative permittivity measured at 10 kHz for Hf x Ti1–x O y grown on RuO2 ranged from 21 to 90 and monotonically increased with decreasing Hf content.
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 O2/N2 flow. Sm3+:TiO2 worked effectively at room temperature, whereas Nd3+:TiO2 showed an improved relative response at 100–150 °C. Switching between pure nitrogen and oxygen atmospheres affected the PL intensities up to 6 times, with response time of 1 min to O2 and recovery time of 10 min in N2. The PL decay kinetics of Sm3+:TiO2 showed unambiguously that both decreasing O2 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 O2 species to certain lattice defects. In contrast, decreasing O2 concentration increased the PL intensity of Nd3+:TiO2. In this case, PL decay kinetics showed an increased excitation efficiency of Nd3+ ions, suggesting that O2 adsorption favors a concurrent relaxation path for the photoexcited charge carriers.
The atomic layer deposition of Al2O3 films on Si(100) and α-Cr2O3 was studied. The films were grown via AlCl3-H2O, AlCl3-O3, Al(CH3)3-H2O, and Al(CH3)3-O3 processes at 300–750 °C. The films ...deposited from AlCl3 and H2O at temperatures ≥ 400 °C on α-Cr2O3 contained the corundum phase of alumina (α-Al2O3). The densities and refractive indices of the α-Al2O3 films were close to the corresponding values of single-crystal α-Al2O3 and exceeded markedly those of amorphous Al2O3. The α-Al2O3 phase was also obtained in the films deposited at 450 °C on α-Cr2O3 from AlCl3 and O3 and from Al(CH3)3 and H2O. However, the crystallinity, densities, and refractive indices of the latter films were lower than those of the films deposited at 450 °C on α-Cr2O3 from AlCl3 and H2O. Etching in hot (110 °C) 80% H2SO4 was used to characterize the chemical resistance of the films in aggressive environments. The etching rate of α-Al2O3 deposited at 450–750 °C was more than 1000 times lower than that of predominantly amorphous Al2O3, and also lower than those of the films that were grown on Si(100) at 750 °C and contained γ-Al2O3, δ-Al2O3, and/or θ-Al2O3.
To minimize greenhouse gas emissions, efficient carbon dioxide capture and utilization need to be addressed. In this study, to determine the structure–activity interplay, three different promising ...catalytic systems for the CO
2
hydrogenation process were synthesized using mesoporous silica SBA-15 as a support material: copper-based catalyst with zinc, indium-based catalyst with palladium and iron-based catalyst with potassium. The role of metal–metal oxide interaction has been showed. The use of Cu/Zn catalytic system and SBA-15 allowed to obtain very small crystallite size of tenorite and zinc oxide, good dispersion of active phases with strong basic sites. In order to find the most effective catalyst providing the maximal methanol yield and selectivity, these catalytic systems were compared under the same reaction conditions (250 °C, 20 bar, H
2
to CO
2
molar ratio 4 to 1) using fixed-bed tubular micro-activity reactor. Results showed that the highest methanol yield can be obtained with Cu/Zn/SBA-15 catalyst as might be expected according to obtained characterization.
Atomic layer deposited alumina doped zirconia films can exhibit advanced mechanical properties with potential to increase the suitability of ZrO2 films for mechanically resilient coatings. In the ...present study, Al2O3-doped ZrO2 films were deposited on a TiN substrate to thicknesses around 100 nm at 300 °C. A zirconia film containing 4.6 mol. % Al2O3 was crystallized in its tetragonal polymorph. Increasing the Al2O3 content up to 5.8 and 8.2 mol. % stabilized the cubic polymorph in the ZrO2-based films. The films with even higher Al2O3 contents remained amorphous. All the crystalline films possessed a preferential grain orientation to extents differing beneath the surface and in the vicinity of the substrate. The most rigid films with hardness up to 15 GPa and elastic modulus above 170 GPa could be obtained when crystallized in the form of cubic ZrO2 stabilized upon doping with Al2O3. For all the crystalline films, the hardness and elastic modulus increased near the substrate.
The capture and utilization of carbon dioxide (CO2) has been attracting increasing interest. Producing methanol from captured CO2 and renewable hydrogen is one promising route for CO2 utilization ...because it would introduce recycled carbon to a vast global fuels and chemicals market. It is known that the Cu or Pd based catalysts are highly active for methanol synthesis. In this study, Cu/ZnO/SBA-15/kaolinite catalysts were prepared with Zn loading varying – 2.4, 1.6 and 0.5 wt% – to find the optimum amount of Zn in this catalytic system. The catalysts have been characterized using XRD analysis, N2 adsorption–desorption analysis and SEM-EDX analysis. The performance of catalysts was evaluated in a fixed-bed tubular micro-activity reactor at 20 bar 250 °C with H2 to CO2 molar ratio 3 to 1. The activity tests showed that the amount of Zn loaded has a significant impact on methanol yield-catalysts with Zn loading 2.4 and 1.6 have approximately 1.7 times higher space–time yield of methanol than catalyst with Zn loading of 0.5 wt%.
Cr2O3 thin films were grown on a Si (1 0 0) substrate using Cr(thd)3 and O3 by atomic layer deposition (ALD) at substrate temperatures (TG) from 200 to 300 °C. X-ray amorphous films were deposited at ...a TG ≤ 225 °C, whereas at higher temperatures (TG ≥ 250 °C), the eskolaite phase was observed in the films. The growth rate of the films increased from 0.003 to 0.01 nm/cycle by increasing TG from 200 to 275 °C. The relatively low growth rate of Cr(thd)3—O3 makes it appropriate for the ALD of precisely controllable solid solution-type ternary-component thin films. The Ti-doped Cr2O3 film showed higher hardness (16.7 GPa) compared with that of the undoped film (12.8 GPa) with similar thickness. The band gap values of the pure Cr2O3 corresponding to the indirect transition model showed no dependence on TG; however, doping the Cr2O3 with Ti decreased its band gap energy value from 3.1 to 2.2 eV.
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