Direct growth of carbon nanotubes on a conical tip as a micro-focused x-ray generation source: Effects of various composition ratios of co-sputtered Ni and Co catalysts

In this study, we first present the experimental results that regard the direct growth of CNTs on a conical-type tungsten (W) tip and their electron emission properties, in terms of the catalyst materials such as a nickel (Ni) and a cobalt (Co) as well as their composition ratios. Sharpening of W-tips was done by electrochemical etch and their diameters were controlled to range from 5 mum down to sub-mum. The co-sputtering method using Ni and Co targets was used to deposit the catalyst layers with various composition ratios of Ni and Co metals. The composition ratio of the co-sputtered catalysts was evaluated by using an energy dispersive X-ray spectroscopy (EDS, Oxford). CNTs were grown by inductively coupled plasma-chemical vapor deposition (ICP-CVD).