Electron Field Emission from Nano-Diamond Films
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Electron Field Emission From Nano-Diamond Films S.G. Wang, Q. Zhang, S.F. Yoon, J. Ahn, Q. Wang, D.J. Yang, Q.F. Huang Microelectronics Centre, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore. ABSTRACT In this paper, the field emission properties of nano-diamond films were investigated by measuring the curves of emission current density (J) versus applied electric field (E). The nanodiamond films were prepared on n-type (100) silicon substrate by microwave plasma enhanced chemical vapor deposition (MPECVD) technique using a gas mixture of nitrogen-methanehydrogen. Field emission results show that, with increasing hydrogen gas flow ratio of [H2] / [N2+CH4+H2] from 0 to 10 %, diamond grain size increases from 5 to 60 nm, threshold electric field for electron field emission increases from 1.2 to 5.75 V/µm, and emission current density decreases from 820 to 560 µA/cm2, demonstrating that small grain size nano-diamond films are promising as a cathode material for low-field electron emitters.
INTRODUCTION CVD diamond is known for its excellent chemical, mechanical and thermal properties, and low or negative electron affinity (NEA) [1-6]. These unique characteristics make CVD diamondbased electron emitters more favorable for emitting electrons at a lower electric field and for a longer time under a higher emission current density, compared to silicon and other metallic emitters [7]. However, it has been found that negative electron affinity only plays a limited role in the electron field emission. The electron emission from CVD diamond films is strongly affected by several other factors. Nano or fine grain size diamond has been shown good electron field emission properties [8-14]. Besides, high nitrogen incorporation in polycrystalline diamond films has been reported to reduce the emission turn-on voltage significantly [15]. Incorporated non-diamond phases with sp2 hybrid bonded carbon (especially graphite clusters) can greatly enhance the emissivity [16-18]. In this paper, the preparation of nano-diamond films by MPECVD using a gas mixture of nitrogen-methane-hydrogen is presented. Electron field emission behavior from nano-diamond films with different grain size deposited with hydrogen gas flow ratio from 0 to 10 % is investigated.
EXPERIMENTAL DETAILS Diamond films under investigation were deposited on n-type (100) silicon substrates by MPECVD using an ASTeX microwave plasma system. During the deposition, the deposition pressure, substrate temperature and microwave power were maintained at 28 Torr, 720 oC and 1.3 KW, respectively. A gas mixture of nitrogen, methane and hydrogen was used as reactant gases. The hydrogen gas flow ratio of [H2] / [N2+CH4+H2] was varied from 0 to 10 %. Methane
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flow ratio of [CH4] / [N2+CH4+H2] was kept at 2.5 % for initial 30 min for nucleation and then at 1 % for 210 min for film growth. The total gas flow rate was 200 sccm. Prior to film deposition, the substrates were scratched using 2.5 µm and 5 nm diamond particl
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