[en] A nanocomposite material is presented that optimally combines the excellent gas sensitivity of SnO₂ and the selectivity of TiO₂. Nanostructured, rutile titanium-tin oxide solid solutions up to 81.5% Ti, as determined by x-ray diffraction, are made by scalable spray combustion (flame spray pyrolysis) of organometallic precursor solutions, directly deposited and in situ annealed onto sensing electrodes in one step. Above that content, segregation of anatase TiO₂ takes place. It was discovered that at low titanium contents (less than 5 Ti%), these materials exhibit higher sensitivity to ethanol vapor than pure SnO₂ and, in particular, limited cross-sensitivity to relative humidity, a long standing challenge for metal oxide gas sensors. These solid solutions are aggregated nanoparticles with an enhanced presence of Ti on their surface as indicated by Raman and IR-spectroscopy. The presence of such low Ti-content in the SnO₂ lattice drastically reduces the band gap of these solid solutions, as determined by UV-vis absorption, almost to that of pure TiO₂. Furthermore, titania reduces the number of rooted and terminal OH species (that are correlated to the cross-sensitivity of tin oxide to water) on the particle surface as determined by IR-spectroscopy. The present material represents a new class of sensors where detection of gases and organic vapors can be accomplished without pre-treatment of the gas mixture, avoiding other semiconducting components that require more heating power and that add bulkiness to a sensing device. This is attractive in developing miniaturized sensors especially for microelectronics and medical diagnostics.

[en] Silica nanowire arrays were grown directly onto plain glass substrates by scalable flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate). The silicon dioxide films consisted of a network of interwoven nanowires from a few to several hundred nanometres long (depending on the process conditions) and about 20 nm in diameter, as determined by scanning electron microscopy. These films were formed rapidly (within 10-20 s) at high growth rates (ca 11-30 nm s^-1) by chemical vapour deposition (surface growth) at ambient conditions on the glass substrate as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, on high purity quartz nearly no nanowires were grown while on steel substrates porous SiO₂ films were formed. Functionalization with perfluorooctyl triethoxysilane converted the nanowire surface from super-hydrophilic to hydrophobic. Additionally, their hermetic coating by thin carbon layers was demonstrated also revealing their potential as substrates for synthesis of other functional 1D composite structures. This approach is a significant step towards large scale synthesis of SiO₂ nanowires facilitating their utilization in several applications.

[en] Screens of Y₂O₃:Eu³⁺-nanophosphor (d_BET = 24 nm) with coating densities in the range 0.23-3.8 mg cm^-2 were obtained by flame aerosol deposition (FAD) from nitrate-based precursors. The average deposition rate was 0.22 mg cm^-2 min^-1. Porosity of the obtained deposits was 0.973 ± 0.004. Light scattering of the coatings in the visible range showed a Rayleigh-like dependence on wavelength and, in comparison to the screens made of the commercial micrometer-sized phosphor powder (d_SEM = 4 μm), was reduced by up to two orders of magnitude. As a result, the nanophosphor coatings maintained nearly constant brightness in a very wide range of coating densities. Furthermore, it should be expected that a substantially improved screen resolution can be achieved with such screens. For excitation at a wavelength of 254 nm, the maximum brightness of the FAD-deposited (Y_0.92Eu_0.08)₂O₃ phosphor screens in the transmission mode was nearly one third of that of the screens made of the commercial phosphor. It was demonstrated that light reflection from the supporting substrate and porosity of the coating significantly influence its photoluminescent performance.

[en] We report methyl ammonium lead iodide (MAPbI₃) solar cells with an ultra-porous TiO₂ electron transport layer fabricated using sequential flame aerosol and atomic layer depositions of porous and compact TiO₂ layers. Flame aerosol pyrolysis allows rapid deposition of nanostructured and ultra-porous TiO₂ layers that could be easily scaled-up for high-throughput low-cost industrial solar cell production. An efficiency of 13.7% was achieved with a flame-made nanostructured and ultra-porous TiO₂ electrode that was coated with a compact 2 nm TiO₂ layer. This demonstrates that MAPbI₃ solar cells with a flame-made porous TiO₂ layer can have a comparable efficiency to that of the control MAPbI₃ solar cell with the well-established spin-coated porous TiO₂ layer. The combination of flame aerosol and atomic layer deposition provides precise control of the TiO₂ porosity. Notably, the porosity of the as-deposited flame-made TiO₂ layers was 97% which was then fine-tuned down to 87%, 56% and 35% by varying the thickness of the subsequent compact TiO₂ coating step. The effects of the decrease in porosity on the device performance are discussed. It is also shown that MAPbI₃ easily infiltrates into the flame-made porous TiO₂ nanostructure thanks to their high porosity and large pore size. (paper)

[en] Highlights: ► Portable sensors were developed and tested for monitoring acetone in the human breath. ► Acetone concentrations down to 20 ppb were measured with short response times (<30 s). ► The present sensors were highly selective to acetone over ethanol and water. ► Sensors were applied to human breath: good agreement with highly sensitive PTR-MS. ► Tests with people at rest and during physical activity showed the sensor robustness. - Abstract: Breath analysis has the potential for early stage detection and monitoring of illnesses to drastically reduce the corresponding medical diagnostic costs and improve the quality of life of patients suffering from chronic illnesses. In particular, the detection of acetone in the human breath is promising for non-invasive diagnosis and painless monitoring of diabetes (no finger pricking). Here, a portable acetone sensor consisting of flame-deposited and in situ annealed, Si-doped epsilon-WO₃ nanostructured films was developed. The chamber volume was miniaturized while reaction-limited and transport-limited gas flow rates were identified and sensing temperatures were optimized resulting in a low detection limit of acetone (∼20 ppb) with short response (10–15 s) and recovery times (35–70 s). Furthermore, the sensor signal (response) was robust against variations of the exhaled breath flow rate facilitating application of these sensors at realistic relative humidities (80–90%) as in the human breath. The acetone content in the breath of test persons was monitored continuously and compared to that of state-of-the-art proton transfer reaction mass spectrometry (PTR-MS). Such portable devices can accurately track breath acetone concentration to become an alternative to more elaborate breath analysis techniques.

[en] Quantum dots (QDs) of lead chalcogenides (e.g. PbS, PbSe, and PbTe) are attractive near‐infrared (NIR) active materials that show great potential in a wide range of applications, such as, photovoltaics (PV), optoelectronics, sensors, and bio‐electronics. The surface ligand plays an essential role in the production of QDs, post‐synthesis modification, and their integration to practical applications. Therefore, it is critically important that the influence of surface ligands on the synthesis and properties of QDs is well understood for their applications in various devices. In this Review we elaborate the application of colloidal synthesis techniques for the preparation of lead chalcogenide based QDs. We specifically focus on the influence of surface ligands on the synthesis of QDs and their solution‐phase ligand exchange. Given the importance of lead chalcogenide QDs as potential light harvesters, we also pay particular attention to the current progress of these QDs in photovoltaic applications. (© 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

[en] Controlling the interaction between multiple ion fluxes is a major challenge that hampers the adoption of post-Li intercalation battery systems, which offer a multifold increase in energy density over existing technologies. Here, a dual-ion flux management strategy is introduced to simultaneously control the distribution of Li and polysulfide ions in high-energy Li-S batteries. This approach enables long-term use of high S-loading cathodes with 13.6 mg${}_{sulfur}$ cm${}^{-<!--\; ???\; -->2}$, achieving 9 mAh cm${}^{-<!--\; ???\; -->2}$ areal capacity with 73% capacity retention for 1000 charging/discharging cycles. The battery system relies on the use of a multiscale membrane, with comparable size to existing battery separators, which simultaneously acts as an atomic redisperser for Li ions, dielectric and mechanical separator, polysulfide barrier, and extended cathode. Combined characterization and modeling reveal that the membrane is stable down to <1.0 V versus Li${}^{+}$/Li and result in a uniform Li-ion flux to the anode and effective polysulfide confinement and reutilization. The potential of this approach for application is demonstrated by the fabrication of stable pouch cells with a horizontal surface of 40 cm${}^2$ and 6.8 mAh cm${}^{-<!--\; ???\; -->2}$ capacity. These findings provide an exemplification of the potential for effective multi-ion flux management for future energy storage and emerging electrochemical systems. (© 2022 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH)