Carbon Nanotubes for Future Field Electron Emission Devices

摘要

Today there is only one mature technology to produce field emitter arrays. This technology is the so-called Spindt type metal microtip process. The drawbacks of the Spindt type process are the expensive production, the critical lifetime in technical vacuum and the high operating voltage. Carbon nanotubes (CNT) can be regarded as the potential second-generation technology to the Spindt type metal microtips. The advantages of CNT are above all a potentially longer lifetime due to chemical inertness and the lower operating voltage due to higher local field enhancement. In the present contribution we show that the field electron emission (FE) of CNT thin films can be accurately described by Fowler-Nordheim tunneling and that the field enhancement factor β influences the emission properties most prominently. Therefore the FE of a CNT thin film can be understood in terms of the local field enhancement β(x,y), which can be determined with scanning anode field emission. To characterize the FE properties of thin film emitters we introduce the concept of the field enhancement distribution function f(β). In this context f(β)·dβ gives the number of emitters on a unit surface with field enhancement factors within the interval [β,β+dβ]. We show that the field enhancement distribution f(β) gives an almost complete characterization of the field emission properties, contrary to the threshold field F_(thr) of thin emitters. Though the fundamental properties of CNT's are very favorable for the use as field emission tips, these properties alone will not guarantee their success in this area. Our investigations clearly show that only a perfect control of the catalytic CNT growth process will result in a successful CNT technology for field emitters, at least for high current applications.