Multi-Walled Carbon Nanotube Growth on Fe/Al-Coated Thermally Stable Glass Substrates with Relevance to Field Emission

Abstract

The integration of vertically aligned carbon nanotubes (CNTs) onto glass substrates is a critical step toward realizing transparent and microfabrication-compatible electronic devices. The direct synthesis of patterned vertically aligned multi-walled CNTs (MWCNTs) on glass substrates using chemical vapor deposition (CVD) is demonstrated. Photolithographic patterning was employed prior to CNT growth to define the spatial geometry of the vertically aligned MWCNTs, enabling precise control over the emitter layout. A key factor influencing CNT morphology was found to be the thickness of the Al buffer layer. Among the tested thicknesses, an aluminum (Al) buffer layer with a thickness of 5 nm yielded optimal results. This configuration facilitates the growth of highly aligned MWCNTs with an average length of approximately 7 μm and a number density of about 10⁹ cm^-2. The patterned MWCNTs exhibit excellent vertical alignment and well-defined hexagonal geometries consistent with photolithographic designs. Field emission measurements further validate the material quality, with patterned vertically aligned MWCNTs demonstrating uniform emission and good temporal stability. These results establish a practical and scalable approach for growing patterned vertically aligned MWCNTs directly on thermally stable glass substrates, offering a promising platform for transparent field emission technologies and CNT-based microsystems.

Keywords: buffer layer; chemical vapor deposition; field emission; glass substrate; multi-walled carbon nanotube.

Figure 1

Cross-sectional SEM images of CNTs synthesized on glass substrates with a 3 nm Fe catalyst layer and Al buffer layers of different thicknesses: (a) 1 nm, (b) 3 nm, (c) 5 nm, (d) 7 nm, and (e) 9 nm. The images illustrate the influence of Al buffer layer thickness on CNT growth morphology.

Figure 2

(a) SEM image showing vertically aligned CNT bundles grown on a glass substrate. (b) High-magnification SEM image of an individual CNT bundle, highlighting its vertical alignment. (c) TEM image of MWCNTs synthesized on glass substrates; the inset presents the SAED pattern, confirming the crystalline nature of the CNT walls.

Figure 3

Raman spectrum of vertically aligned MWCNTs, showing characteristic D and G bands indicative of graphitic structure and defect levels.

Figure 4

Comparison of field emission characteristics between unpatterned vertically aligned MWCNTs and patterned arrays of vertically aligned MWCNT bundles.

Figure 5

Time dependence of the field emission current density at 3.5 mA/cm². The inset shows the fluorescent screen used to monitor the field emission, which is displaying a uniform emission pattern.