Morphological\nEvolution of Atomic Layer Deposited\nHafnium Oxide on Aligned Carbon Nanotube Arrays

Microscopic study of the nucleation and growth of atomic\nlayer\ndeposition (ALD) dielectrics onto carbon nanotubes (CNTs) is an essential\nwhile challenging task toward high-performance devices. Here, we capture\nthe morphological evolution and growth behaviors of ALD-HfO<sub>2</sub> onto SiO<sub>2</sub>/Si-supported aligned CNT arrays (A-CNTs) under\nthree ALD recipes via cross-sectional high-resolution scanning transmission\nelectron microscopy. The HfO<sub>2</sub> in ALD I (200 °C) preferentially\nnucleates on the SiO<sub>2</sub> substrate in heterogeneous growth\nmode, resulting in films with considerable pinholes, while ALD II\n(90 °C) and III (90 °C and extra H<sub>2</sub>O presoak)\nexhibit homogeneous growth with nucleation on both SiO<sub>2</sub> and CNTs, yielding uniform films. Arrangement defects in A-CNTs\nexacerbate nonuniformity of HfO<sub>2</sub> and tube–tube separation\nplays deterministic roles affecting the HfO<sub>2</sub>-CNT interfacial\nmorphology. Electrical measurements from A-CNTs metaloxide-semiconductor\ndevices validate these findings. Our investigation contributes valuable\ninsights for optimizing ALD processes for enhanced dielectric integration\non A-CNTs in next-generation electronics.