Influence of Different Defects in Vertically Aligned Carbon Nanotubes on TiO₂ Nanoparticle Formation through Atomic Layer Deposition

Abstract

The chemical inertness of carbon nanotubes (CNT) requires some degree of "defect engineering" for controlled deposition of metal oxides through atomic layer deposition (ALD). The type, quantity, and distribution of such defects rules the deposition rate and defines the growth behavior. In this work, we employed ALD to grow titanium oxide (TiO2) on vertically aligned carbon nanotubes (VACNT). The effects of nitrogen doping and oxygen plasma pretreatment of the CNT on the morphology and total amount of TiO2 were systematically studied using transmission electron microscopy, Raman spectroscopy, and thermogravimetric analysis. The induced chemical changes for each functionalization route were identified by X-ray photoelectron and Raman spectroscopies. The TiO2 mass fraction deposited with the same number of cycles for the pristine CNT, nitrogen-doped CNT, and plasma-treated CNT were 8, 47, and 80%, respectively. We demonstrate that TiO2 nucleation is dependent mainly on surface incorporation of heteroatoms and their distribution rather than structural defects that govern the growth behavior. Therefore, selecting the best way to functionalize CNT will allow us to tailor TiO2 distribution and hence fabricate complex heterostructures.

Effects of Conformal Nanoscale Coatings on Thermal Performance of Vertically Aligned Carbon Nanotubes

“…The low penetration depth and the uneven uniformity of the ALD coating within the intricate CNT foam-like morphology has been the object of several studies. [23,28,29] The relatively low temperature of the ALD process represents the main limiting factor of the coating process itself. The initial diffusion of precursor molecules inside the foam is slow and it decreases with increasing the individual CNT diameters.…”

“…The resulting coating penetration depths are ≈700 nm for the ALD coated Al 2 O 3 /CNTs and around 66 µm for the LPCVD a‐SiC/CNTs, proving the superior ability of the LPCVD process to evenly coat complex high surface area nanostructures. The low penetration depth and the uneven uniformity of the ALD coating within the intricate CNT foam‐like morphology has been the object of several studies . The relatively low temperature of the ALD process represents the main limiting factor of the coating process itself.…”

Vertically aligned carbon nanotubes: production and applications for environmental sustainability

“…Compared with other large surface area supporting materials, the unique advantages of VACNT are their synergistic characteristics of high conductivity and well-ordered hierarchical structures. The metal oxides or metals can be deposited through electrodeposition, 103 nebulized spray, 104 wet chemistry coating, 105,106 and atomic layer deposition 107,108 (Fig. 4b).…”

Homogeneous Fe2O3 coatings on carbon nanotube structures for supercapacitors

“…Acid and oxidative plasma treatments and nitrogen doping can also generate functional groups to tailor the shape and distribution of the TMO coating. [31][32][33] The performance of these composites could be further improved by better understanding the role of the functional groups present in the CNT surface as anchoring sites for the ALD process and their effect on the electrochemical properties of the composites.…”