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Atomic layer deposited (ALD) transparent thermoelectric materials enable the introduction of energy harvesting and sensing devices onto surfaces of various shapes and sizes in imperceptible manner. Amongst these materials, ZnO has shown promising results in terms of both thermoelectric and optical characteristics. The thermoelectric performance of ZnO can be further optimized by introducing extrinsic doping, to the realization of which ALD provides excellent control. Here, we explore the effects of sandwiching of ZrO2 layers with ZnO on glass substrates. The room-temperature thermoelectric power factor is maximised at 116ÎĽW mâˆ'1 Kâˆ'2 with samples containing a 2% nominal percentage of ZrO2. The addition of ZrO2 layers is further shown to reduce the thermal conductivity, resulting in a 20.2% decrease from the undoped ZnO at 2% doping. Our results contribute to increasing the understanding of the effects of Zr inclusion in structural properties and growth of ALD ZnO, as well as the thermal and thermoelectric properties of Zr-doped ZnO films in general. [ABSTRACT FROM AUTHOR]

Semiconductor heterostructure junctions are known to improve the water oxidation performance in photoelectrochemical (PEC) cells. Depending on the semiconductor materials involved, different kinds of junctions can appear, for instance, type II band alignment where the conduction and valence bands of the semiconductor materials are staggered with respect to each other. This band alignment allows for a charge separation of the photogenerated electron-hole pairs, where the holes will go from low-to-high valance band levels and vice versa for the electrons. For this reason, interface engineering has attracted intensive attention in recent years. In this work, a simplified model of the Fe 2 O 3 -TiO 2 heterostructure was investigated via first-principles calculations. The results show that Fe 2 O 3 -TiO 2 produces a type I band alignment in the heterojunction, which is detrimental to the water oxidation reaction. However, the results also show that interstitial hydrogens are energetically allowed in TiO 2 and that they introduce states above the valance band, which can assist in the transfer of holes through the TiO 2 layer. In response, well-defined planar Fe 2 O 3 -TiO 2 heterostructures were manufactured, and measurements confirm the formation of a type I band alignment in the case of Fe 2 O 3 -TiO 2 , with very low photocurrent density as a result. However, once TiO 2 was subjected to hydrogen treatment, there was a nine times higher photocurrent density at 1.50 V vs. the reversible hydrogen electrode under 1 sun illumination as compared to the original heterostructured photoanode. Via optical absorption, XPS analysis, and (photo)electrochemical measurements, it is clear that hydrogen treated TiO 2 results in a type II band alignment in the Fe 2 O 3 -H:TiO 2 heterostructure. This work is an example of how hydrogen doping in TiO 2 can tailor the band alignment in TiO 2 -Fe 2 O 3 heterostructures. As such, it provides valuable insights for the further development of similar material combinations., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Herein, enhancements in thermoelectric (TE) performance, both the power factor (PF) and thermal stability, are exhibited by sandwiching HfO 2 and TiO 2 layers onto atomic layer deposited-ZnO thin films. High-temperature TE measurements from 300 to 450 K revealed an almost two-fold improvement in electrical conductivity for TiO 2 /ZnO (TZO) samples, primarily owing to an increase in carrier concentration by Ti doping. On the other hand, HfO 2 /ZnO (HZO) achieved the highest PF values owing to maintaining Seebeck coefficients comparable to pure ZnO. HZO also exhibited excellent stability after multiple thermal cycles, which has not been previously observed for pure or doped ZnO thin films. Such improvement in both TE properties and thermal stability of HZO can be attributed to a shift in crystalline orientation from the a axis to c axis, as well as the high bond dissociation energy of Hf-O, stabilizing the ZnO structure. These unique properties exhibited by HZO and TZO thin films synthesized by atomic layer deposition pave the way for next-generation transparent TE devices.

RuO 2 /TiO 2 catalysts have shown broad use in promoting a variety of photocatalytic phenomena, such as water splitting and the photodecomposition of organic dyes and pollutants. Most current methods of photodepositing ruthenium oxide species (RuO x ) onto titanium dioxide (TiO 2 ) films involve precursors that are either difficult to produce and prone to decomposition, such as RuO 4 , or require high-temperature oxidations, which can reduce the quality of the resulting catalyst and increase the risks and toxicity of the procedure. The present work demonstrates the photodeposition of RuO x onto TiO 2 films, using potassium perruthenate (KRuO 4 ) as a precursor, by improving substantially a procedure known to work on TiO 2 nanopowders. In addition to demonstrating the applicability of this method of photodeposition to TiO 2 films, this work also explores the importance of the material phase of the TiO 2 substrate, outlines viable concentrations and photodeposition times at a given optical intensity, and demonstrates that the morphology of the photodeposited nanostructures changes from cauliflower-like spheroids to a matted, porous sponge-like structure with the addition of methanol to the precursor solution. This morphology change has not been documented previously. By providing an explanation for this difference in the morphology, this work provides both newer insights into the photodeposition process and provides an excellent foundation for future procedures, allowing a more targeted and controlled deposition based on the desired morphology., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)