Applied Surface Science 320 (2014) 798–803 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Photo- and thermionic emission of MWPECVD nanocrystalline diamond films G. Cicala a,∗ , V. Magaletti b , A. Valentini c , M.A. Nitti c , A. Bellucci d , D.M. Trucchi d a CNR-IMIP, Via Amendola 122/D, 70126 Bari, Italy b ALTA S.p.A., Via Gherardesca 5, 56121 Ospedaletto, Pisa, Italy c Department of Physics, University of Bari “A. Moro”, Via Orabona 4, 70126 Bari, Italy d CNR-ISM UOS Montelibretti, Via Salaria km 29.300, 00015 Monterotondo Scalo, RM, Italy a r t i c l e i n f o Article history: Received 29 July 2014 Received in revised form 12 September 2014 Accepted 12 September 2014 Available online 20 September 2014 Keywords: MWPECVD NCD Photoemission Thermoemission a b s t r a c t Nanocrystalline diamond (NCD) films with and without a diamond buffer layer (BL) have been grown on p- type silicon substrates by microwave plasma enhanced chemical vapor deposition technique at different values of deposition temperature (652–884 ◦ C). The photo- and thermionic electron emission properties of NCD films have been investigated, illustrated and explained by analyzing the surface morphology and the grain shape determined by atomic force microscopy, the chemical-structural properties by Raman spectroscopy and nanocrystallites size by X-ray diffraction. The NCD films with BL grown at the highest deposition temperature have shown the highest photo- and thermionic emission currents. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Nanocrystalline diamond (NCD) is an emerging technological material with a variety of applications such as photo- and thermo- emitters [1], biomedical devices [2], MEMS/NEMS [3] and so on. Specifically, the very low and even negative electron affinity (NEA) that can be achieved by hydrogenated surface of single crystal [4], homoepitaxial diamond [5], poly- [6–9] and nano-crystalline dia- mond [10–12], obtained by using a microwave plasma enhanced chemical vapor deposition (MWPECVD) technique, is the key requirement for improving the photo-emission [4,6,7,10] and the thermionic emission [5,8,11,12]. In some cases, the NEA character- istics of diamond surface along with suitable dopant (nitrogen, N [13] or phosphorus, P [14]) lead to efficient thermoemission and a reduced work function. For this, the NCD films are attractive not only in displays and cold cathodes in vacuum microelectronics, but also as cathode neutralizers for ion sources in aerospace propul- sions and for energy conversion in solar concentrating systems [15,16]. Indeed, thermionic emission is a significant effect that can disclose energy conversion applications from high temperature ∗ Corresponding author. Tel.: +39 0805929518; fax: +39 0805929520. E-mail address: grazia.cicala@ba.imip.cnr.it (G. Cicala). thermal sources. On one hand efficient diamond photocathodes have been demonstrated to be more stable than conventional mate- rials such as CsI [17], on the other hand efficient thermoemitters are proposed using an emitter surface made by CVD diamond whose work function can be engineered as a function of the hydrogen content. Many authors found that the photoemission [18] and ther- moemission [19] properties depend on the defects or impurities localized at the grain boundaries (GBs) such as hydrogen (H) incor- poration and sp 2 hybridized carbon (i.e., non-diamond phases). The amount of H content can be tuned by changing the grain size; the reduction of the grain size leads to increase the GBs and conse- quently the H content located at the GBs. In this paper, the different hydrogenation extent of NCD films deposited on p-type silicon sub- strates by means of MWPECVD technique has been obtained by changing the deposition temperature in the range between 652 and 884 ◦ C and by introducing a microcrystalline diamond interlayer, in order to understand how the grain shape and size and, there- fore, the amount of incorporated hydrogen affects the emission performances. 2. Experimental The deposition of about 3 m thick NCD films was carried out in a home-made cylindrical stainless steel MWPECVD reac- tor. NCD films were produced starting from CH 4 /Ar/H 2 (1/89/10%) http://dx.doi.org/10.1016/j.apsusc.2014.09.075 0169-4332/© 2014 Elsevier B.V. All rights reserved.