Atomic Layer Deposition for Coating of High Aspect Ratio TiO₂ Nanotube Layers

Abstract

We present an optimized approach for the deposition of Al2O3 (as a model secondary material) coating into high aspect ratio (≈180) anodic TiO2 nanotube layers using the atomic layer deposition (ALD) process. In order to study the influence of the diffusion of the Al2O3 precursors on the resulting coating thickness, ALD processes with different exposure times (i.e., 0.5, 2, 5, and 10 s) of the trimethylaluminum (TMA) precursor were performed. Uniform coating of the nanotube interiors was achieved with longer exposure times (5 and 10 s), as verified by detailed scanning electron microscopy analysis. Quartz crystal microbalance measurements were used to monitor the deposition process and its particular features due to the tube diameter gradient. Finally, theoretical calculations were performed to calculate the minimum precursor exposure time to attain uniform coating. Theoretical values on the diffusion regime matched with the experimental results and helped to obtain valuable information for further optimization of ALD coating processes. The presented approach provides a straightforward solution toward the development of many novel devices, based on a high surface area interface between TiO2 nanotubes and a secondary material (such as Al2O3).

Atomic Layer Deposition Al2O3 Coatings Significantly Improve Thermal, Chemical, and Mechanical Stability of Anodic TiO2 Nanotube Layers

“…This technique based on sequential and self-limiting gas–surface reactions allows conformal deposition of various coatings within TiO 2 nanotube layers with a nanometer scale accurate thickness, as shown previously. 36,38 Trimethylaluminum (TMA, Strem, elec. grade, 99.999+%) and deionized water (18 MΩ) were used as aluminum and oxygen precursors, respectively.…”

Spaced TiO2 Nanotubes Enable Optimized Pt Atomic Layer Deposition for Efficient Photocatalytic H2 Generation

“…photo‐deposition, vapor deposition, electrochemical deposition, or sputter deposition). In contrast, atomic layer deposition (ALD) can yield the uniform deposition of complex nanostructures and allows for a controlled loading amount by varying the number of ALD cycles . Also, it provides precise thickness control conformability on high‐aspect‐ratio nanostructures …”

“…In contrast, atomicl ayer deposition (ALD)c an yield the uniform deposition of complex nanostructures and allows for ac ontrolled loading amount by varying the number of ALD cycles. [17,18] Also, it providesp recise thickness control conformability on high-aspect-ratio nanostructures. [19,20] In the presentw ork, we evaluate the deposition of Pt by using ALD into SP and CP TiO 2 NTsu sing different numberso f ALD cycles, which influences the size and density of Pt nanoparticles.…”

ALD Al2O3-Coated TiO2Nanotube Layers as Anodes for Lithium-Ion Batteries

“…24−26 However, although several reports can be found on utilization of the ALD coatings of different materials to modify the electrodes for lithium-ion battery application, 27−33 only one publication reports on the use of ALD to coat an anode prepared from an anodic TiO 2 nanotube layer with ZnO. 23 …”