Structure and property features of the catalyst-assisted carbon nanostructures on Si wafer by catalyst ion implantation and ECR-CVD

Abstract

Experiments to examine effects of ion-implanted catalyst on the structure and property features of carbon nanotubes (CNTs) and nanostructures on Si wafer were conducted by electron cyclotron resonance chemical vapor deposition (ECR-CVD) with CH4 and H-2 as source gases, under both ion-implanted and PVD-coated catalysts with different H-plasma pretreatment conditions. The deposited CNTs and substrates at every processing step were characterized by FESEM, TEM, SIMS, XRD and Raman spectroscopy. The results show that the growth mechanism of the CNTs under condition with the ion-implanted catalyst is different from that with the PVD-coated catalyst. It results in a greater hollow size of the tubes for the former condition. Furthermore, under conditions of a higher catalyst dosage and higher H-plasma concentration pretreatment, it indicates better field emission properties, more Co-silicide formation and more percentage of base-growth CNTs due to an increase in the amount of Co source and process temperature. The main effect of the implanted catalyst is essentially to enhance the adhesion strength of CNTs with the substrate through the Co-silicide formation and embedding the catalyst into the substrate, as shown by XRD and SIMS analyses. Additionally, it is also favor to form CNTs with a lower I-D/I-G ratio and so a lower defect density. Under the present conditions, the best field emission properties are: turn-on voltage similar to 6 V/mu m and current density > 0.72 mA/cm(2). In summary, the structure, growth mode, adhesion strength with the substrate, defect density and field emission properties of CNTs can be manipulated by changing the ion-implantation dosages and H-plasma pretreatment conditions, which may not be able to be produced by other methods. (c) 2005 Elsevier B.V. All rights reserved.