Abstracts Book - IMRC 2018

• SA5-O005
TAILORING THE MICROSTRUCTURE TOWARDS CONDUCTIVE
NANOCRYSTALLINE DIAMOND FILMS FOR ENHANCED FIELD
ELECTRON EMISSION CHARACTERISTICS
Sankaran Kamatchi Jothiramalingam 1,2 , Chien-Jui Yeh 3 , Ping-Yen Hsieh 4 , Paulius Pobedinskas 1,2 ,
Key-Chyang Leou 3 , Marlies K. Van Bael 1,2 , Nyan-Hwa Tai 4 , I-Nan Lin 5 , Ken Haenen 1,2
1
Hasselt University, Institute for Materials Research, Belgium. 2 IMEC vzw, IMOMEC, Belgium.
3 National Tsing Hua University, Department of Engineering and System Science, Taiwan.
4 National Tsing Hua University, Department of Materials Science and Engineering, Taiwan.
5
Tamkang University, Department of Physics, Taiwan.
Field electron emitters (FEE) with applicable electron emission characteristics,
such as low turn-on field, large field enhancement factor and stable and high
FEE current density, find potential applications as cold cathodes in X-rays, flat
panel displays and microplasma devices. Among carbon based FEE emitters,
nanocrystalline diamond (NCD) has appealed substantial consideration in
vacuum microelectronics owing to its low electron affinity for electron emission,
strong bonding structure, good thermal and electrical conductivities to hold high
currents, and utmost hardness to withstand ion bombardment.
This work deals with the influence of varying the concentration of CH4 in the
CH4/H2/N2 gas mixtures on plasma reactivity and on NCD’s microstructural
evolution. While the NCD films grown in CH4/H2/N2 (1/96/3) plasma contain large
diamond grains, the microstructure changed considerably for the NCD films
grown using CH4/H2/N2 (5/92/3) (or CH4/H2/N2 (10/87/3)), ensuing in nano-sized
diamond grains. For CH4/H2/N2 (15/82/3) grown NCD films, well-defined needlelike
nanostructures evolve. These needle-like structured NCD films contain sp 3
phase diamond, sheathed with sp 2 bonded graphitic phases, achieving low
resistivity of 90 ohm-cm and superior FEE properties, namely, low turn-on field
of 4.3 V/μm, high FEE current density of 3.3 mA/cm 2 at an applied field of 8.6
V/μm and large field enhancement factor of 3865. The optical emission
spectroscopy studies authorize that the presence of CN and C2 species in the
growing plasma are the main factors for the changes in the microstructure of
the films. However, the increase in substrate temperature to a high enough
value (~780°C) due to the incorporation of 15% CH4 in CH4/H2/N2 plasma is the
key factor resulting in the formation of needle-like diamond grains. Especially,
the NCD films with needle-like geometry are the most auspicious ones for the
FEE, especially when they are encased in graphitic phases. The outstanding