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Improved Stability of Atomic Layer Deposited Amorphous TiO₂ Photoelectrode Coatings by Thermally Induced Oxygen Defects.

ABSTRACT: Amorphous titanium dioxide (a-TiO₂) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO₂ without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO₂ induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO₂ is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO₂. The surface analysis allows us to interpret the improved stability to the thermally induced formation of O^- species within a-TiO₂ that are essentially electronic defects in the anionic framework.

SUBMITTER: Hannula M

PROVIDER: S-EPMC6156093 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Atomic-layer-deposited alumina (ALD Al2O3) can be utilized for passivation, structural, and functional purposes in electronics. In all cases, the deposited film is usually expected to maintain chemical stability over the lifetime of the device or during processing. However, as-deposited ALD Al2O3 is typically amorphous with poor resistance to chemical attack by aggressive solutions employed in electronics manufacturing. Therefore, such films may not be suitable for further processing as solvent treatments could weaken the protective barrier properties of the film or dissolved material could contaminate the solvent baths, which can cause cross-contamination of a production line used to manufacture different products. On the contrary, heat-treated, crystalline ALD Al2O3 has shown resistance to deterioration in solutions, such as standard clean (SC) 1 and 2. In this study, ALD Al2O3 was deposited from four different precursor combinations and subsequently annealed either at 600, 800, or 1000 °C for 1 h. Crystalline Al2O3 was achieved after the 800 and 1000 °C heat treatments. The crystalline films showed apparent stability in SC-1 and HF solutions. However, ellipsometry and electron microscopy showed that a prolonged exposure (60 min) to SC-1 and HF had induced a decrease in the refractive index and nanocracks in the films annealed at 800 °C. The degradation mechanism of the unstable crystalline film and the microstructure of the film, fully stable in SC-1 and with minor reaction with HF, were studied with transmission electron microscopy. Although both crystallized films had the same alumina transition phase, the film annealed at 800 °C in N2, with a less developed microstructure such as embedded amorphous regions and an uneven interfacial reaction layer, deteriorates at the amorphous regions and at the substrate-film interface. On the contrary, the stable film annealed at 1000 °C in N2 had considerably less embedded amorphous regions and a uniform Al-O-Si interfacial layer.

Dataset Information

Improved Stability of Atomic Layer Deposited Amorphous TiO₂ Photoelectrode Coatings by Thermally Induced Oxygen Defects.

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Dataset Information

Improved Stability of Atomic Layer Deposited Amorphous TiO2 Photoelectrode Coatings by Thermally Induced Oxygen Defects.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Improved Stability of Atomic Layer Deposited Amorphous TiO₂ Photoelectrode Coatings by Thermally Induced Oxygen Defects.