Effect of the Gas Chemistry, Total Pressure, and Microwave Power on the Grain Size and Growth Rate of Polycrystalline Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition Technique

Ultrananocrystalline Diamond Coatings for Next-Generation High-Tech and Medical Devices

“…Figure 1.7b,c shows that films grown at 60 mbar and 80 mbar pressure, with the same H 2 (98%)/CH 4 (2%) chemistry, for 2 h, exhibit the highest thickness (~2500 nm) and grain size of ~230 nm, and 1500 nm thickness and ~230 nm grain size, respectively. The Raman spectra of the films grown at 20 and 40 mbar show the typical low end of NCD (~14 nm) structure, close to UNCD (3-7 nm [22]) (Figure 1.7d), while the Raman spectra of the films grown at 60 and 80 mbar (Figure 1.7d) show a small, sharp peak at 1332 cm -1 , indicative of the more noticeable sp 3 -type C atomic bond from diamond, indicative of grain sizes in the hundreds of nanometer range, as described above (see figures 3 and 4 in [73]). XRD analysis of the polycrystalline diamond films (Figure 2b in [73]) reveal only peaks corresponding to diamond, indicating that no graphite was formed in any of the grown films.…”

“…The Raman spectra of the films grown at 20 and 40 mbar show the typical low end of NCD (~14 nm) structure, close to UNCD (3-7 nm [22]) (Figure 1.7d), while the Raman spectra of the films grown at 60 and 80 mbar (Figure 1.7d) show a small, sharp peak at 1332 cm -1 , indicative of the more noticeable sp 3 -type C atomic bond from diamond, indicative of grain sizes in the hundreds of nanometer range, as described above (see figures 3 and 4 in [73]). XRD analysis of the polycrystalline diamond films (Figure 2b in [73]) reveal only peaks corresponding to diamond, indicating that no graphite was formed in any of the grown films. The intensity of the peaks increased with increasing pressure, indicative of thicker films with larger grains due to grain growth with film thickness.…”

“…For a gas chemistry of H 2 (98%)/CH 4 (2%), the film grown at 20 mbar total pressure for 2 h was only ~60 nm thick (Figure 1.7aright) and the surface morphology was characteristic of NCD film structure, with grains ~14 nm, as calculated from the Debye-Scherrer equation using parameters from XRD measurements (Figure 1.7aleft), mainly due to the fact that at low pressure the amount of C-based species is much lower than for the higher pressures, resulting in a film with initial nucleation nanoscale grains. SEM imaging of films grown at 40 mbar pressure (not shown heresee figure 3b in [73]), also for 2 h, showed a thickness of ~850 nm and grain size also of ~14 nm. Figure 1.7b,c shows that films grown at 60 mbar and 80 mbar pressure, with the same H 2 (98%)/CH 4 (2%) chemistry, for 2 h, exhibit the highest thickness (~2500 nm) and grain size of ~230 nm, and 1500 nm thickness and ~230 nm grain size, respectively.…”

“…To finish this section reviewing the growth of UNCD films using the conventional wet chemical seeding plus MPCVD processes, it is relevant to give a brief review of recent research [73], focused on exploring, in a systematic series of studies, the combined effect of total gas pressure (20-80 mbar), precursor gas chemistry (Ar/ CH 4 /H 2 ), and microwave power on the grain size, atoms' chemical bonding, and growth rate of polycrystalline diamond films grown by MPCVD [73], with a particular focus on determining the conditions that can produce UNCD films even with the inclusion of H 2 gas flow in the gas chemistry. Figure 1.7 shows a series of SEM images and Raman analysis spectra which provide very revealing information about the mechanism for growing UNCD to MCD diamond films using a tailored combination of gas chemistry and flows, total pressure and power in the MPCVD process.…”

Growth of Nitrogen Incorporated Ultrananocrystalline Diamond Coating on Graphite by Hot Filament Chemical Vapor Deposition

“…Figure 3 c (Raman spectrum), and corresponding Figure 3 f (SEM Image of N-UNCD film’s surface) corresponds to the N-UNCD film of sample 4, grown by HFCVD with filament-substrate distance at 3 cm and NG surface temperature at 575 °C. The Raman spectrum reveals peaks at 1345 cm −1 , which encapsulates the 1332 cm −1 peak correlated with sp 3 C atoms bonds characteristic of diamond in the grains, and sp 2 bonds of C atoms in the grain boundaries, expected for N-UNCD films, as shown in those grown by MPCVD [ 16 ]. The Raman spectrum shown in Figure 3 c and Figure 4 c,d are considered N-UNCD thin films, since they show the TPA peaks at 1150 ane1480 cm-1 characteristic of UNCD films [ 17 ], although the D and G peaks are a bit sharper and higher than the peaks observed in thick N-UNCD films produced by MPCVD [ 5 , 6 ] or thicker N-UNCD films grown recently by HFCVD [ 8 , 18 ] on Si substrate.…”