Properties and characterization of chemical vapor deposition diamond fieldemitters

The field emission properties of chemical vapor deposition (CVD) diamond th in films are investigated by measuring the field emission I-V characteristi cs, the emission site density and the field emitted electron energy distrib ution. The results are discussed with regard to field emission due to negat ive electron affinity (NEA) and classical Fowler-Nordheim emission due to g eometrical field enhancement. The requirements on the diamond films for NEA mediated field emission are discussed. These requirements are high resisti vity, low defect density and few grain boundaries. We show that diamond fil ms matching these requirements are actually bad field emitters. On the othe r hand we show that the films exhibiting good field emission properties are just opposed to the above mentioned requirements, they exhibit low resisti vity, high defect density and many grain boundaries as they are of nanocrys talline nature. The good emitting CVD diamond films are grown on p-type Si( 100) using plasma enhanced CVD at substrate temperatures around 950 degrees C and a gas mixture of 5% CH4 in H-2. Using the example of multiwalled carb on nanotube emitter (MWNT) we show how the emitter work function and the lo cal field at the emission site can be determined independently by measuring the field emitted electron energy distribution. For MWNT we find a work fu nction of 4.9 eV and a local field of 2500 V mum(-1) (for an emission curre nt of the order of 10 pA). In the case of nanocrystalline CVD diamond emitt er we find work function values around 6 eV and local electric fields again of the order of 2500 V mum(-1). The electronic structure of the nanocrysta lline CVD diamond field emitters is investigated using standard photoemissi on spectroscopy and simultaneous photoemission and field emission spectrosc opy. From the presented measurements we can clearly relate the low field el ectron emission of the investigated nanocrystalline diamond films to classi cal Fowler-Nordheim tunneling due to local geometrical field enhancement. ( C) 2001 Elsevier Science Ltd. All rights reserved.