Vertically Aligned CNTs Embedded in Cr/TiO2 Membranes For Realization of Ion Sources

Abstract

AbstractPECVD-grown carbon nanotubes on (100) silicon membranes have been realized and exploited for electron and ion emission applications. The growth of CNT's is achieved by a mixture of hydrogen and acetylene gases in a CVD reactor and a 5-10nm thick nickel is used as the seed for the growth. The presence of a DC-plasma yields a vertical growth of carbon nanotubes. The as-grown nanotubes are encapsulated by means of an insulating TiO2 layer. The formation of a thin membrane is possible by means of a chemical anisotropic etching technique. The membrane is then removed from the back side to fully suspend the CNT-holding TiO2 layer. Upon exposure to a plasma ashing step the nanotubes are partially removed and a both-end opened hollow nanostructure is formed which can be used as a miniaturized ion source. The CNT-holding substrate can be exploited as a grid to extract the ions from an ionization chamber just underneath the membrane. Applying a proper accelerating electric field, positive ions made inside a DC discharge cavity can form a beam-shape emission of ions towards the opposite negative electrode. The beam is well suited for a source of ion lithography. In which, the emission has the ability of direct writing on a photo-resist coated substrates. Preliminary nano-scale dots have been created with sizes between 50 and 80nm. Scanning electron microscopy has been used to investigate the results.