Electrical and morphological behavior of carbon nanotubes synthesized within porous anodic alumina templates

The synthesis of carbon nanotubes (CNTs) within porous anodic alumina (PAA) templates requires better understanding regarding their dynamic growth evolution, and how this is influenced by the geometrical features of the PAA. The growth of nanostructures, such as CNTs, becomes more complex when an exponential voltage decrease process is applied to thin the dielectric layer of the PAA matrix, because this process leads to the formation of a branched structure at the bottom of the pores. Here, we present direct evidence of the impact of the branched structure at the bottom of the PAA at different time-stages of the CNT synthesis. These studies reveal that when numerous branches are created, competition between the growing nanotubes is established during their formation. Additionally, large pores lead to flattened catalyst electrodeposition, promoting tube entanglement since more than one tube can grow in each pore. Interestingly, two different electrical behaviors are measured when considering PAA/CNT devices: linear response in the case of CNTs connecting two parallel electrodes, and nonlinear when junctions between the tubes are being promoted. These results highlight the relevance of having an in-depth understanding of the CVD growth evolution of carbon nanostructures within PAA templates, and simultaneously serve as a guiding procedure towards the fabrication of devices based on parallel organized CNT arrays.