Control of Curvature in Highly Compliant Probe Cantilevers during Carbon Nanotube Growth

Abstract

Direct growth of a sharp carbon nanotube (CNT) probe on a very thin and highly flexible cantilever by plasma-enhanced chemical vapor deposition (PECVD) is desirable for atomic force microscopy (AFM) of nanoscale features on soft or fragile materials. Plasma-induced surface stresses in such fabrication processes, however, tend to cause serious bending of these cantilevers, which makes the CNT probe unsuitable for AFM measurements. Here, we report a new tunable CNT growth technique that controls cantilever bending during deposition, thereby enabling the creation of either flat or deliberately curved AFM cantilevers containing a CNT probe. By introducing hydrogen gas to the (acetylene + ammonia) feed gas during CNT growth and adjusting the ammonia to hydrogen flow ratio, the cantilever surface stress can be altered from compressive to tensile stress, and in doing so controlling the degree of cantilever bending. The CNT probes grown under these conditions have high aspect ratios and are robust. Contact-mode imaging has been demonstrated using these probe tips. Such CNT probes can be useful for bio-imaging involving DNA and other delicate biological features in a liquid environment.