Atomic Layer Deposition of CeOx Nanoclusters on TiO2

Titanium dioxide has a band-gap in the ultra violet region and there have been many efforts to shift light absorption to the visible region. In this regard, surface modification with metal oxide clusters has been used to promote band-gap reduction. CeOx-modified TiO2 materials have exhibited enhanced catalytic activity in water gas shift, but the deposition process used is not well-understood or suitable for powder materials. Atomic layer deposition (ALD) has been used for deposition of cerium oxide on TiO2. The experimentally reported growth rates using typical Ce metal precursors such as β-diketonates and cyclopentadienyls are low, with reported growth rates of ca. 0.2-0.4 Å/cycle. In this paper, we have performed density functional theory calculations to reveal the reaction mechanism of the metal precursor pulse together with experimental studies of ALD of CeOx using two Ce precursors, Ce(TMHD)4 and Ce(MeCp)3. The nature and stability of hydroxyl groups on anatase and rutile TiO2 surfaces are determined and used as starting substrates. Adsorption of the cerium precursors on the hydroxylated TiO2 surfaces reduces the coverage of surface hydroxyls. Computed activation barriers for ligand elimination in Ce(MeCp)3 indicate that ligand elimination is not possible on anatase (101) and rutile (100) surface, but it is possible on anatase (001) and rutile (110). The ligand elimination in Ce(TMHD)4 is via breaking the Ce-O bond and hydrogen transfer from hydroxyl groups. For this precursor, the ligand elimination on the majority surface facets of anatase and rutile TiO2 are endothermic and not favourable. It is difficult to deposit Ce atom onto hydroxylated TiO2 surface using Ce(TMHD)4 as precursor. Attempts for deposit cerium oxide on TiO2 nanoparticles that expose the anatase (101) surface show at best a low deposition rate and this can be explained by the non-favorable ligand elimination reactions at this surface.

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First Principles Mechanistic Study of Self-Limiting Oxidative Adsorption of Remote Oxygen Plasma During the Atomic Layer Deposition of Alumina

10.26434/chemrxiv.6377372 ◽

2018 ◽

Author(s):

Glen N. Fomengia ◽

Michael Nolan ◽

Simon D. Elliott

Keyword(s):

Atomic Layer Deposition ◽

First Principles ◽

Density Functional ◽

Atomic Layer ◽

Molecular Water ◽

Mechanistic Study ◽

Hydroxyl Groups ◽

Layer Deposition ◽

Surface Intermediates ◽

By Products

Plasma-enhanced atomic layer deposition (ALD) of metal oxides is a rapidly gaining interest especially in the electronics industry because of its numerous advantages over the thermal process. However, the underlying reaction mechanism is not sufficiently understood, particularly regarding saturation of the reaction and densification of the film. In this work, we employ first principles density functional theory (DFT) to determine the predominant reaction pathways, surface intermediates and by-products formed when constituents of O2-plasma or O3 adsorb onto a methylated surface typical of TMA-based alumina ALD. The main outcomes are that a wide variety of barrierless and highly exothermic reactions can take place. This leads to the spontaneous production of various by-products with low desorption energies and also of surface intermediates from the incomplete combustion of –CH3 ligands. Surface hydroxyl groups are the most frequently observed intermediate and are formed as a consequence of the conservation of atoms and charge when methyl ligands are initially oxidized (rather than from subsequent re-adsorption of molecular water). Anionic intermediates such as formates are also commonly observed at the surface in the simulations. Formaldehyde, CH2O, is the most frequently observed gaseous by-product. Desorption of this by-product leads to saturation of the redox reaction at the level of two singlet oxygen atoms per CH3 group, where the oxidation state of C is zero, rather than further reaction with oxygen to higher oxidation states. We conclude that the self-limiting chemistry that defines ALD comes about in this case through the desorption by-products with partially-oxidised carbon. The simulations also show that densification occurs when ligands are removed or oxidised to intermediates, indicating that there may be an inverse relationship between Al/O coordination numbers in the final film and the concentration of chemically-bound ligands or intermediate fragments covering the surface during each ALD pulse. Therefore reactions that generate a bare surface Al will produce denser films in metal oxide ALD.

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First Principles Mechanistic Study of Self-Limiting Oxidative Adsorption of Remote Oxygen Plasma During the Atomic Layer Deposition of Alumina

10.26434/chemrxiv.6377372.v1 ◽

2018 ◽

Author(s):

Glen N. Fomengia ◽

Michael Nolan ◽

Simon D. Elliott

Keyword(s):

Atomic Layer Deposition ◽

First Principles ◽

Density Functional ◽

Atomic Layer ◽

Molecular Water ◽

Mechanistic Study ◽

Hydroxyl Groups ◽

Layer Deposition ◽

Surface Intermediates ◽

By Products

Plasma-enhanced atomic layer deposition (ALD) of metal oxides is a rapidly gaining interest especially in the electronics industry because of its numerous advantages over the thermal process. However, the underlying reaction mechanism is not sufficiently understood, particularly regarding saturation of the reaction and densification of the film. In this work, we employ first principles density functional theory (DFT) to determine the predominant reaction pathways, surface intermediates and by-products formed when constituents of O2-plasma or O3 adsorb onto a methylated surface typical of TMA-based alumina ALD. The main outcomes are that a wide variety of barrierless and highly exothermic reactions can take place. This leads to the spontaneous production of various by-products with low desorption energies and also of surface intermediates from the incomplete combustion of –CH3 ligands. Surface hydroxyl groups are the most frequently observed intermediate and are formed as a consequence of the conservation of atoms and charge when methyl ligands are initially oxidized (rather than from subsequent re-adsorption of molecular water). Anionic intermediates such as formates are also commonly observed at the surface in the simulations. Formaldehyde, CH2O, is the most frequently observed gaseous by-product. Desorption of this by-product leads to saturation of the redox reaction at the level of two singlet oxygen atoms per CH3 group, where the oxidation state of C is zero, rather than further reaction with oxygen to higher oxidation states. We conclude that the self-limiting chemistry that defines ALD comes about in this case through the desorption by-products with partially-oxidised carbon. The simulations also show that densification occurs when ligands are removed or oxidised to intermediates, indicating that there may be an inverse relationship between Al/O coordination numbers in the final film and the concentration of chemically-bound ligands or intermediate fragments covering the surface during each ALD pulse. Therefore reactions that generate a bare surface Al will produce denser films in metal oxide ALD.

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One-Dimensional TiO2@GaON Core-Shell Nanowires with Controlled Shell Thickness from Atomic Layer Deposition for Stable and Efficient Photoelectrochemical Water Splitting

10.26434/chemrxiv.9199796 ◽

2019 ◽

Author(s):

Jiajia Tao ◽

Hong-Ping Ma ◽

Kaiping Yuan ◽

Yang Gu ◽

Jianwei Lian ◽

...

Keyword(s):

Atomic Layer Deposition ◽

Band Gap ◽

Water Splitting ◽

Atomic Layer ◽

Photoelectrochemical Water Splitting ◽

Core Shell ◽

Photoelectrochemical Performance ◽

Highly Efficient ◽

Layer Deposition ◽

Shell Nanowires

<div>As a promising oxygen evolution reaction semiconductor, TiO2 has been extensively investigated for solar photoelectrochemical water splitting. Here, a highly efficient and stable strategy for rationally preparing GaON cocatalysts on TiO2 by atomic layer deposition is demonstrated, which we show significantly enhances the</div><div>photoelectrochemical performance compared to TiO2-based photoanodes. For TiO2@20 nm-GaON core-shell nanowires a photocurrent density up to 1.10 mA cm-2 (1.23 V vs RHE) under AM 1.5 G irradiation (100 mW cm-2) has been achieved, which is 14 times higher than that of TiO2 NWs. Furthermore, the oxygen vacancy formation on GaON as well as the band gap matching with TiO2 not only provides more active sites for water oxidation but also enhances light absorption to promote interfacial charge separation and migration. Density functional theory studies of model systems of GaON-modified TiO2 confirm the band gap reduction, high reducibility and ability to activate water. The highly efficient and stable systems of TiO2@GaON core-shell nanowires provide a deeper understanding and universal strategy for enhancing photoelectrochemical performance of photoanodes now available. </div>

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Synthesis of Cerium-Oxide Coated Platinum Core-Shell Structure Catalysts with Enhanced Stability and Activity via Atomic Layer Deposition

ECS Transactions ◽

10.1149/07506.0187ecst ◽

2016 ◽

Vol 75 (6) ◽

pp. 187-193

Author(s):

K. Cao ◽

L. Shi ◽

J. Cai ◽

B. Shan ◽

R. Chen

Keyword(s):

Atomic Layer Deposition ◽

Cerium Oxide ◽

Shell Structure ◽

Atomic Layer ◽

Core Shell ◽

Layer Deposition ◽

Core Shell Structure ◽

Enhanced Stability

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Composite Nanostructures of TiO2and ZnO for Water Splitting Application: Atomic Layer Deposition Growth and Density Functional Theory Investigation

Advanced Functional Materials ◽

10.1002/adfm.201505524 ◽

2016 ◽

Vol 26 (27) ◽

pp. 4882-4889 ◽

Cited By ~ 30

Author(s):

Marina Kulmas ◽

Leanne Paterson ◽

Katja Höflich ◽

Muhammad Y. Bashouti ◽

Yanlin Wu ◽

...

Keyword(s):

Density Functional Theory ◽

Atomic Layer Deposition ◽

Water Splitting ◽

Density Functional ◽

Atomic Layer ◽

Functional Theory ◽

Composite Nanostructures ◽

Layer Deposition

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A Study on the Structure and the Photoelectrical Properties of the Al-Doped ZnO Thin Films by Atomic Layer Deposition in Low Temperatures

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2018.16378 ◽

2018 ◽

Vol 18 (12) ◽

pp. 8333-8336 ◽

Cited By ~ 3

Author(s):

Guangde Wang ◽

Xinyu Zhang ◽

Wenlong Jiang ◽

Lizhong Wang

Keyword(s):

Thin Films ◽

Atomic Layer Deposition ◽

Visible Region ◽

Atomic Layer ◽

Transparent Electrode ◽

Low Resistivity ◽

Photoelectrical Properties ◽

Photoelectric Properties ◽

Layer Deposition ◽

Doping Ratio

The AZO transparent conductive films are prepared by the atomic layer deposition (ALD) at a low temperature of 150 °C. The different Al–Zn doping ratios were designed during the deposition. The phase structure of the films was characterized by XRD, the electrical properties of thin films were analyzed by the Holzer test, and the optical properties of thin films were analyzed by the UV-3600 (UV-VIS-NIR) spectrophotometer. The results showed that all the films preferred the orientation of the C axis during the growth process, the AZO films have a very low resistivity of 6.955×10−4 Ω·cm with the Al doping ratio by 2%, the deposition temperature is 150 °C and the thickness of the film is 200 nm. The transmission of AZO films with the different doping ratios in the visible region is 85%. The proper doping ratio can be selected to get the excellent photoelectric properties of AZO thin films. Such low resistivity AZO transparent conductive film is expected to replace the ITO as the transparent electrode for the organic light-emitting devices and the other new generation of the optoelectronic devices.

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Air Annealing Effect on Oxygen Vacancy Defects in Al-doped ZnO Films Grown by High-Speed Atmospheric Atomic Layer Deposition

Molecules ◽

10.3390/molecules25215043 ◽

2020 ◽

Vol 25 (21) ◽

pp. 5043

Author(s):

Chia-Hsun Hsu ◽

Xin-Peng Geng ◽

Wan-Yu Wu ◽

Ming-Jie Zhao ◽

Xiao-Ying Zhang ◽

...

Keyword(s):

Atomic Layer Deposition ◽

Band Gap ◽

Photoelectron Spectroscopy ◽

High Speed ◽

Oxygen Vacancies ◽

Annealing Temperature ◽

Atomic Layer ◽

Zno Films ◽

X Ray ◽

Layer Deposition

In this study, aluminum-doped zinc oxide (Al:ZnO) thin films were grown by high-speed atmospheric atomic layer deposition (AALD), and the effects of air annealing on film properties are investigated. The experimental results show that the thermal annealing can significantly reduce the amount of oxygen vacancies defects as evidenced by X-ray photoelectron spectroscopy spectra due to the in-diffusion of oxygen from air to the films. As shown by X-ray diffraction, the annealing repairs the crystalline structure and releases the stress. The absorption coefficient of the films increases with the annealing temperature due to the increased density. The annealing temperature reaching 600 °C leads to relatively significant changes in grain size and band gap. From the results of band gap and Hall-effect measurements, the annealing temperature lower than 600 °C reduces the oxygen vacancies defects acting as shallow donors, while it is suspected that the annealing temperature higher than 600 °C can further remove the oxygen defects introduced mid-gap states.

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