Atomic layer deposition (ALD) offers excellent controllability
of spatial uniformity, film thickness at the Angstrom level, and film
composition even for high-aspect-ratio nanostructured surfaces, which
are rarely attainable by other conventional deposition methodologies.
Although ALD has been successfully applied to various substrates under
open-top circumstances, the applicability of ALD to confined spaces
has been limited because of the inherent difficulty of supplying precursors
into confined spaces. Here, we propose a rational methodology to apply
ALD growths to confined spaces (meter-long microtubes with an aspect
ratio of up to 10 000). The ALD system, which can generate
differential pressures to confined spaces, was newly developed. By
using this ALD system, it is possible to deposit TiO
x
layers onto the inner surface of capillary tubes with a length
of 1000 mm and an inner diameter of 100 μm with spatial deposition
uniformity. Furthermore, we show the superior thermal and chemical
robustness of TiO
x
-coated capillary microtubes
for molecular separations when compared to conventional molecule-coated
capillary microtubes. Thus, the present rational strategy of space-confined
ALD offers a useful approach to design the chemical and physical properties
of the inner surfaces of various confined spaces.