Top-down fabrication of small carbon nanotubes
The control of diameter and chirality of carbon nanotubes (CNTs) has long been extremely challenging and critical for various CNT applications. Here, we report a top-down method that allows for reliable control of the diameter of individual few-walled carbon nanotubes (CNTs), thereby producing nanotubes with a desired diameter, including the smallest ones. This method involves the use of electron irradiation assisted by concurrent thermal annealing, which enables carbon removal from a CNT in a rather organized fashion, leading the nanotube to shrink uniformly and flawlessly. The smallest nanotubes can be routinely obtained by this self-contracting process of any few-walled nanotubes (1–4 shells) to reach their diameter limits, that is, 4.1 Å for single-walled CNTs (likely indexed as (5, 0) or (3, 3)), and 1.01, 1.66 and 2.41 nm for 2–4 walled CNTs, respectively (with their innermost tubes of ∼3.2 Å presumably indexed as (4, 0)). A new scenario based solely on the climb movements of 5|7 dislocations is proposed to well explain the observed nanotube shrinking processes, which are associated with the motions of atomic-scale kinks in different pathways. Due to the unique ability to dictate the exact CNT diameter, this facile method may open up a new avenue toward the ultimate strategy for bulk production of monosized and even chirality-specific small CNTs.