Enhanced electron emission from tetrahedral amorphous carbon capped carbon nanotube core-shelled structure

Core-shelled composites have been shown to enhance material properties, notably for chemical sensing and biomolecular applications. In this comprehensive study, we show that a simple core–shell structure, made up of tetrahedral amorphous carbon (ta-C) tip-capped onto an aligned dense array of carbon nanotubes (CNT), exhibits superior electron emission properties, having a distinct enhancement in the turn-on field of < 1 V/μm without any lithography patterning. This is compared to ~ 2 V/μm for pristine CNT samples. A KrF pulsed laser deposition process was used to deposit high (> 70%) sp3 content non-hydrogenated ta-C films of varying thickness for the tip-capping process. Combining scanning electron microscopy images and electron emission testing results, our systematic study shows that first, the thickness of the ta-C can range from 20 to 100 nm and is sufficient to achieve the enhancement effect. However, thicker coatings > 200 nm will degrade the electron emission. Second, a simple tip-capping is sufficient to achieve the enhancement without the need to encapsulate the entire carbon nanotube.

► A core–shell structure was fabricated by tip-capping CNTs with ta-C.
► Field emission properties of CNTs with and without coatings were examined.
► A distinct enhancement on field emission was obtained with ta-C coatings.
► Ta-C thickness of 20–100 nm is sufficient to achieve the enhancement.
► Thicker ta-C coatings > 200 nm will degrade the electron emission.