Thickness-, alignment- and defect-tunable growth of carbon nanotube arrays using designed mechanical loads

We demonstrate the thickness-, morphology-, and defect-tunable growth and simultaneous integration of aligned carbon nanotube (CNT) arrays using a novel microscale platform. This platform consists of a micromechanical spring of desired stiffness, which applies a precise vertical load to a vertically aligned CNT array during its growth by chemical vapor deposition (CVD). The micromechanical spring is strained by the extrusive growth force output from the aligned CNT array during its growth and, at the same time, exerts a mechanical restoring force against the buckling resistance of the CNTs. This application of a designed vertical load on the CNTs allows modulation of the thickness and degree of alignment of the CNT array, as well as the structural quality of the individual CNTs. Consequently, the electrical resistance between two opposing CNT arrays can be tuned by adjusting the vertical load. In addition, their sensing responsiveness toward chemical species can also be enhanced by applying larger vertical load on the CNTs. In contrast to conventional growth methods for producing aligned CNT arrays, our approach offers an efficient way for the growth engineering and on-chip integration of aligned CNT arrays in a single step of the CVD.