Simultaneous growth of self-patterned carbon nanotube forests with dual height scales

Abstract

In this study, we report on a unique, one-step fabrication technique enabling the simultaneous synthesis of vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with dual height scales through alcohol catalyzed chemical vapor deposition (ACCVD). Regions of VA-MWCNTs with different heights were well separated from each other leading to a self-patterning on the surface. We devised a unique layer-by-layer process for application of catalyst and inhibitor precursors on oxidized Si (100) surfaces before the ACCVD step to achieve a hierarchical arrangement. Patterning could be controlled by adjusting the molarity and application sequence of precursors. Contact angle measurements on these self-patterned surfaces indicated that manipulation of these hierarchical arrays resulted in a wide range of hydrophobic behavior changing from that of a sticky rose petal to a lotus leaf.Inspired by the self-cleaning effect of lotus leaves, researchers have paid increasing attention to the generation of superhydrophobic surfaces having hierarchical structures with features ranging from micro-to nanoscale. The lotus leaf has a highly textured surface with protruding nubs (20-40 mm) which are further covered with nanometre sized wax crystals.1 Lotus leaf-like surfaces can be created either by covering a rough surface with a low surface energy material or by roughening/ etching/patterning the surface of a hydrophobic material. 10,11Functionalized vertically aligned multi-walled carbon nanotube (VA-MWCNT) arrays synthesized by CVD have also demonstrated superhydrophobic properties. 9,12Moreover, combining the CVD technique with photolithography for generating patterned carbon nanotube (CNT) arrays on surfaces has also been shown to improve and tailor superhydrophobicity of these surfaces.13 However, additional steps such as patterning with lithography for creating complex structures to improve hydrophobic behavior or imparting self-cleaning properties are not often cost efficient. Therefore, a simple, one-step production technique is required for the generation of artificial lotus leaf-like surfaces.Hence, the aim of this study is to imitate lotus leaf structures by creating dual-scale micro/nanostructures of aligned and patterned CNTs during the growth. For this purpose, we developed a unique technique based on the layer-by-layer application of catalyst and inhibitor precursors which is normally used to grow VA-MWCNTs by our group.14 By tuning the molarity, types, sequence and number of precursor and catalyst layers, we were able to not only generate hierarchical and patterned superhydrophobic VA-MWCNT arrays but also tailor the wettability properties. The resultant hierarchical structures were fully characterized (contact angle, surface topography, physical properties, and geometry) in order to identify the contribution of micro-and nano-structured aspects on water repellency. These hierarchical CNT arrays with micro-and nanoscales can be further developed to potentially find applications as self-cleaning dry-adhesives (gecko ...

Strain-engineered manufacturing of freeform carbon nanotube microstructures

“…This process leverages the influence of the catalyst-substrate interactions on the growth rate of CNTs 21 , creating strain gradients during synthesis that guide the CNTs into curved microscale geometries. Our method is analogous to the well-known use of thin-film stress to create curved and folded MEMS structures 22 .…”

A flexible and stackable 3D interconnect system using growth-engineered carbon nanotube scaffolds

“…Based on the one-step fabrication technique enabling the simultaneous synthesis of dual-height vertically aligned multi-walled carbon nanotubes proposed by Sam et al [16], and learning from the experience of de Volder et al [17], we show how dual-height vertically-aligned CNT scaffolds can be grown by chemical vapor deposition (CVD) in a one-step process by modifying the catalyst underlayer. Due to the different growth rates caused by the different catalyst underlayers, vertically aligned CNT scaffolds for the through-substrate-vias can be grown simultaneously with the much lower in height vertically aligned CNT scaffolds for the horizontal finwire interconnects in a one-step CVD process.…”