Highly ordered carbon nanotubes based on porous aluminum oxide: fabrication and mechanism

Tunable Low Crystallinity Carbon Nanotubes/Silicon Schottky Junction Arrays and Their Potential Application for Gas Sensing

Highly ordered nanostructure arrays have attracted wide attention due to their wide range of applicability, particularly in fabricating devices containing scalable and controllable junctions. In this work, highly ordered carbon nanotube (CNT) arrays grown directly on Si substrates were fabricated, and their electronic transport properties as a function of wall thickness were explored. The CNTs were synthesized by chemical vapor deposition inside porous alumina membranes, previously fabricated on n-type Si substrates. The morphology of the CNTs, controlled by the synthesis parameters, was characterized by electron microscopies and Raman spectroscopy, revealing that CNTs exhibit low crystallinity (LC). A study of conductance as a function of temperature indicated that the dominant electric transport mechanism is the 3D variable range hopping. The electrical transport explored by I-V curves was approached by an equivalent circuit based on a Schottky diode and resistances related to the morphology of the nanotubes. These junction arrays can be applied in several fields, particularly in this work we explored their performance in gas sensing mode and found a fast and reliable resistive response at room temperature in devices containing LC-CNTs with wall thickness between 0.4 nm and 1.1 nm.

Patterning of metallic nanoparticles for the growth of carbon nanotubes

We report a straightforward method of patterning large ordered arrays of metallic nanoparticles using existing semiconductor processing technology. The topographies of contact holes created on full 200 mm wafers serve as templates to pattern Ni or Co nanoparticles. Over a large range of synthesis conditions, these patterned nanoparticles are demonstrated to successfully catalyse the growth of carbon nanotubes (CNTs) selectively in the patterned areas of the wafer. This approach to catalyst deposition is scalable and fully compatible with existing semiconductor processing technology. Thus, it can be exploited for a variety of applications where confinement of materials in nanometric domains is necessary. These results represent a further step towards the integration of CNTs into conventional Si-based technology.