Synthesis of Crystalline Carbon Nitride by Chemical Vapor Deposition
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EXPERIMENT A rf diode plasma assisted hot filament CVD system in a stainless steel bell jar chamber was used in this work. One electrode of the rf diode was mounted 3cm above a tungsten filament in the chamber, and the other one was around the stainless steel chamber surface. 2 The substrate was 8cm under the filament. The typical rf plasma power was 19 Wcmand the rf frequency was 13.6MHZ. The filament temperature and substrate temperature were about 2100 'C and 900 'C , respectively. The reactant gas was a mixture of CH 4 , NH 3 and H 2 [(CH 4 +NH 3 ) 2% vol. in H 2]. The ratio of NH 3 to CH 4 was kept at 5. The total flow rate of the gaseous mixture was 150 sccm, passing through a stainless steel pipe below the inner rf electrode to the hot tungsten filament toward the substrate surface. The deposition pressure was 120 Pa.
RESULTS The deposited films adhere well to the polycrystalline Ni substrate. Auger spectra and energy-dispersive x-ray spectra (EDX) have been used to analyze the composition of the deposited films. The results show that the films are composed primarily of C and N with very small amount of 0, Ni, and W contaminants. However, the semi-quantitative results are not accurate enough for absolutely analyzing the stoichiometry of the films.
(a)
lOjiM
(b)
WP-MO
FIG.1 SEM micrographs of a crystalline C-N film grown on a polycrystalline Ni substrate. Images (a) and (b) are obtained for different regions of the film
with different magnifications.
Figs.1 (a) and (b) show the typical SEM micrographs of the crystalline carbon nitride films with the film-thickness of -6 am deposited for 5 hours on a polycrystalline Ni substrate. Individual crystals [see Fig.l(a)] as well as tortuous chain-like islands and film-like regions formed from the attachment of crystalline grains [see Fig.1(b) ] were observed. Crystalline grains up to ,-10 um in size can be observed with relatively clear crystal facets and crystal edges. TABLE I. The experimental results of XRD for a crystalline C-N film deposited on polycrystalline Ni substrate and the matching diffraction data of the proposed materials. The s, m, w, and vw represent strong, medium, weak, and very weak diffraction intensities, respectively. d, and d 2 represent the groups of interplanar spacings of /3-C 3 N4 with, respectively, the theoretical lattice and a proposed lattice from the calculation of the experimental transmission electron microscopy of possible f-C 3 N4 particles contained in an amorphous C-N thin film from Yu at al.'s study [5]. I/Io is the intensity ratio of every diffraction peak to the strongest peak [d, (210)].
318
Measured
XRD
Calculated
d (A)
(I/Io)
di(A)
5.565
f3-C3 N4
(hid)
d2(A) (hkl) Intensity
9 9 7 16 48 14 85 34 48 58 35 100 41 38 30 39 7 54 11 11 16 10 12 12 17 14 16 26 27 23 17 21 19 14 6 7 12 10 9 11 20 9
patterns
m
(100)
5.46 3.931 3.358 3.206 3.091 2.818 2.786 2.551 2.504 2.422 2.277 2.250 2.148 2.058 1.973 1.949 1.876 1.824 1.779 1.759 1.745 1.688 1.565 1.551 1.451 1.416 1.366 1.353 1.334 1.316 1.303 1.291 1.
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