Basics of Atomic Layer Deposition: Growth Characteristics and Conformality

Dendooven, Jolien; Detavernier, Christophe

doi:10.1002/9783527694822.ch1

Cited by 18 publications

(22 citation statements)

References 143 publications

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“…Atomic layer deposition (ALD) is known for providing thin films with excellent controllability, uniformity, and conformality, and provides a potential method to modify the TiO 2 defect composition in a controlled manner via surface chemical reactions. − Particularly, the ALD growth temperature is an essential factor affecting surface reaction pathways during the growth process. , For example, an alkylamido organometallic ALD precursor, tetrakis(dimethylamido)titanium (TDMAT), has been shown to leave nitrogen residues into as-grown TiO 2 thin films, especially at lower growth temperatures. ,, Use of a higher growth temperature (200 °C) has been found to decrease the amount of nitrogen but simultaneously result in the formation of Ti 3+ species. ,, These Ti 3+ defects can increase electrical conductivity and induce visible-light absorption in am.-TiO 2 . The mechanism is different from the visible absorption induced by substitutional nitrogen doping of crystalline TiO 2 but similar to the hydrogenated “black” TiO 2 that can be also categorized as reduced TiO 2 with a disordered structure. ,,− The commonly accepted view is that an oxygen vacancy within TiO 2 is surrounded by three pentacoordinated Ti 5c ions and initially two of them are Ti 3+ ions. , These Ti 3+ defects carry unpaired excess electrons that can couple with phonons from vibrations of surrounding ions and form quasiparticles called electron polarons. , These polarons can hop from Ti 3+ ion to an adjacent Ti 4+ ion converting it to a Ti 3+ ion, which is known as polaron hopping , Based on molecular dynamics simulations, Deskins et al proposed that electron transport in amorphous TiO 2 depends on the distances between adjacent Ti 4+ ions, whereas hole transport is related to the distances between Ti 3+ ions .…”

Section: Introductionmentioning

confidence: 99%

Tunable Ti³⁺-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO₂

et al. 2022

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Amorphous titania (am.-TiO2) has gained wide interest in the field of photocatalysis, thanks to exceptional disorder-mediated optical and electrical properties compared to crystalline TiO2. Here, we study the effects of intrinsic Ti3+ and nitrogen defects in am.-TiO2 thin films via the atomic layer deposition (ALD) chemistry of tetrakis(dimethylamido)titanium(IV) (TDMAT) and H2O precursors at growth temperatures of 100–200 °C. X-ray photoelectron spectroscopy (XPS) and computational analysis allow us to identify structural disorder-induced penta- and heptacoordinated Ti4+ ions (Ti5/7c 4+), which are related to the formation of Ti3+ defects in am.-TiO2. The Ti3+-rich ALD-grown am.-TiO2 has stoichiometric composition, which is explained by the formation of interstitial peroxo species with oxygen vacancies. The occupation of Ti3+ 3d in-gap states increases with the ALD growth temperature, inducing both visible-light absorption and electrical conductivity via the polaron hopping mechanism. At 200 °C, the in-gap states become fully occupied extending the lifetime of photoexcited charge carriers from the picosecond to the nanosecond time domain. Nitrogen traces from the TDMAT precursor had no effect on optical properties and only little on charge transfer properties. These results provide insights into the charge transfer properties of ALD-grown am.-TiO2 that are essential to the performance of protective photoelectrode coatings in photoelectrochemical solar fuel reactors.

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Section: Introductionmentioning

confidence: 99%

Tunable Ti³⁺-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO₂

et al. 2022

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“…Atomic layer deposition providing good controllability, uniformity, and conformality can be used to fabricate high-quality and pinhole-free TiO 2 photoelectrode protection layers. ,, The choices of precursors and process conditions affect the TiO 2 phase structure. ALD of crystalline TiO 2 has been reported using TiCl 4 (at 200 °C) or TTIP (at 250 °C) as titanium precursors and H 2 O or O 3 as oxygen sources, respectively. , The growth of TiO 2 using more volatile TDMAT and H 2 O allows ALD at growth temperatures as low as 50 °C, which enables growth on sensitive materials .…”

Section: Introductionmentioning

confidence: 99%

Interface Engineering of TiO₂ Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon

et al. 2021

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Titanium dioxide (TiO2) can protect photoelectrochemical (PEC) devices from corrosion, but the fabrication of high-quality TiO2 coatings providing long-term stability has remained challenging. Here, we compare the influence of Si wafer cleaning and postdeposition annealing temperature on the performance of TiO2/n+-Si photoanodes grown by atomic layer deposition (ALD) using tetrakis(dimethylamido)titanium (TDMAT) and H2O as precursors at a growth temperature of 100 °C. We show that removal of native Si oxide before ALD does not improve the TiO2 coating performance under alkaline PEC water splitting conditions if excessive postdeposition annealing is needed to induce crystallization. The as-deposited TiO2 coatings were amorphous and subject to photocorrosion. However, the TiO2 coatings were found to be stable over a time period of 10 h after heat treatment at 400 °C that induced crystallization of amorphous TiO2 into anatase TiO2. No interfacial Si oxide formed during the ALD growth, but during the heat treatment, the thickness of interfacial Si oxide increased to 1.8 nm for all of the samples. Increasing the ALD growth temperature to 150 °C enabled crystallization at 300 °C, which resulted in reduced growth of interfacial Si oxide followed by a 70 mV improvement in the photocurrent onset potential.

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“…One possible approach to modify the defect structure of titania is atomic layer deposition, known for its controllable, uniform, and conformal thin film growth via self-limiting surface reactions. ,,, Previously, we have shown that intrinsic precursor traces and oxide defects are highly sensitive to ALD growth temperature when using tetrakis(dimethylamido)titanium(IV) and water as precursors . Interestingly, the growth temperature is also shown to steer the crystallization process toward anatase or rutile TiO 2 phases, but understanding of this phenomenon in more detail has remained without comprehensive investigation. , …”

Section: Introductionmentioning

confidence: 99%

Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO₂ Thin Films Grown by Atomic Layer Deposition

et al. 2022

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The physicochemical properties of titanium dioxide (TiO2) depend strongly on the crystal structure. Compared to anatase, rutile TiO2 has a smaller bandgap, a higher dielectric constant, and a higher refractive index, which are desired properties for TiO2 thin films in many photonic applications. Unfortunately, the fabrication of rutile thin films usually requires temperatures that are too high (>400 °C, often even 600–800 °C) for applications involving, e.g., temperature-sensitive substrate materials. Here, we demonstrate atomic layer deposition (ALD)-based fabrication of anatase and rutile TiO2 thin films mediated by precursor traces and oxide defects, which are controlled by the ALD growth temperature when using tetrakis(dimethylamido)titanium(IV) (TDMAT) and water as precursors. Nitrogen traces within amorphous titania grown at 100 °C inhibit the crystal nucleation until 375 °C and stabilize the anatase phase. In contrast, a higher growth temperature (200 °C) leads to a low nitrogen concentration, a high degree of oxide defects, and high mass density facilitating direct amorphous to rutile crystal nucleation at an exceptionally low post deposition annealing (PDA) temperature of 250 °C. The mixed-phase (rutile–brookite) TiO2 thin film with rutile as the primary phase forms upon the PDA at 250–500 °C that allows utilization in broad range of TiO2 thin film applications.

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Basics of Atomic Layer Deposition: Growth Characteristics and Conformality

Cited by 18 publications

References 143 publications

Tunable Ti³⁺-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO₂

Tunable Ti³⁺-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO₂

Interface Engineering of TiO₂ Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon

Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO₂ Thin Films Grown by Atomic Layer Deposition

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Basics of Atomic Layer Deposition: Growth Characteristics and Conformality

Cited by 18 publications

References 143 publications

Tunable Ti3+-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO2

Tunable Ti3+-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO2

Interface Engineering of TiO2 Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon

Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO2 Thin Films Grown by Atomic Layer Deposition

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Resources

About

Tunable Ti³⁺-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO₂

Tunable Ti³⁺-Mediated Charge Carrier Dynamics of Atomic Layer Deposition-Grown Amorphous TiO₂

Interface Engineering of TiO₂ Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon

Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO₂ Thin Films Grown by Atomic Layer Deposition