Field emission properties of carbon nanotubes grown on a conical tungsten tip for the application of a microfocus x-ray tube

Experimental results relating to the structural properties of carbon nanotube (CNTs) and the field-emission characteristics of conical-type tungsten tips coated with the CNTs are presented. CNTs have been grown on conical W-tips by inductively coupled plasma-chemical vapor deposition (ICP-CVD) with or without coating a TiN-buffer prior to the formation of Ni catalysts. For all the CNTs grown, their nanostructures, morphologies, and crystalline structures are analyzed by FESEM, HRTEM, and Raman spectroscopy. Furthermore, the emission properties of CNT-based field-emitters are characterized to estimate the maximum current density, threshold voltage, and spatial distribution of electron beams. Prolonged stability testing for the CNT-emitters has also been performed. All the experimental results obtained in this study indicate that the emission current level, focused beam area, and emission stability are satisfactory and desirable for application of microfocus x-ray systems, particularly for the CNT-based field emitter without a TiN-buffer layer.