Nanocrystalline Diamond Films Prepared with Different Diamond Seeding Processes of 4 Nm and 0.25 Μm Diamond Powders

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The growth of diamond films in metastable condition occurs in two steps: nucleation and growth of crystals. Studies have shown that the nucleation process is the most critical step and essential to optimize the properties of the diamond, but its understanding is still very limited. Furthermore, the nucleation process is directly related to the pretreatment applied to the surface of the substrate: cleaning the surface and seeding. When the substrate is silicon, it is cleaned with acetone and scratching with diamond particles dispersed in a suitable solvent followed by ultrasonic agitation (nucleation rate = 109 part/cm2). However, research has demonstrated that the use of diamond nanoparticles (ND) prepared with the use of a powerful ultrasound (750W) provides nucleation density much higher (1012 part/cm2) compared to that processed with larger size particles. This work demonstrates that diamond films prepared with ND different solutions exhibit differences in relation to diamond films prepared using diamond particle dispersed in an organic solvent. Morphological analysis and the quality of the films were evaluated by Scanning Electron Microscopy, Optical Perfilometry and Raman Scattering Spectroscopy.

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Edited by:

Francisco Ambrozio Filho and Aloisio Nelmo Klein

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146-151

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M. Santos et al., "Nanocrystalline Diamond Films Prepared with Different Diamond Seeding Processes of 4 Nm and 0.25 Μm Diamond Powders", Materials Science Forum, Vol. 802, pp. 146-151, 2014

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December 2014

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[12] The Fig. 3 e 4 show the composition change of surface functional groups, i. e. the oxidation of some surface groups such as hydrocarbon groups increasing the relative amount and density of carboxyl on ND surface. When a large amount of carboxyl groups are formed on the ND surface by heat treatment, the deprotonation of carboxyl will be still dominant in acidic media, and then ND particles can be strongly negatively charged in the whole observed pH range. Fig. 3 - The oxidation of some surface groups such as hydrocarbon groups. carboxyl anion carboxyl group Fig. 4 – Dissociation of carboxyl groups in water. Thus, this analysis confirms the importance of functionalize the substrate surface when ND particles are used in the seeding process. The next step of this study was to analyze the influence of seeding process in growth rate of diamond films. Fig. 5 shows the comparative SEM cross section images of the films obtained from the experiments I and II(b), respectively. According them, the film thicknesses were similar for both, around 3μm. These images show that the films do not exhibit columnar growth, indicating that the films present growth similar to ultrananocrystalline diamond (UNCD) films.

DOI: https://doi.org/10.1007/978-1-4684-7218-9_5

[13] 2μm 2μm I II(b) II(b) I Fig. 5 - Comparative SEM cross section images of the films obtained from the experiments I and II(b), respectively. After that, the quality of films was evaluated as shown in Fig. 6. It is possible to observe that the Raman spectra of films obtained from seeding experiments I and II (b) are very similar. The diamond peak was visible and shifted to a lower wavenumber (1300 cm-1). The D (1350 cm-1) and G (1550 cm-1) bands are related to high part of sp2-bonded carbon in these films. The shoulders at 1150 cm-1 and 1490 cm-1 are related to transpolyacetylene (TPA) segments at the grain boundaries of the NCD surface.

DOI: https://doi.org/10.1107/s1600577514024047/co5056sup1.pdf

[14] Fig. 6 - Raman spectra of the UNCD films from the experiments I and II(b). In the Table 2 are presented the average roughness obtained from film surface while in Fig. 7 are showed the OP images of these films. The perfilometric analysis showed that the major roughness was obtained in the film of the experiment II(b), as expected. Table 2 Average roughness (Ra) Experiment Average roughness (Ra) (nm) I 107, 72 II(b) 201, 56 I II(b) Fig. 7 - The OP images of UNCD films from the experiments I and II (b). Conclusions The results indicated that the growth of BDND films is strongly affected by the seeding pre-treatment used on silicon substrate. ND solution (4nm) and 0. 25μm diamond disperse in organic solvent exhibit different routes in nucleation phases and growth process. The use of ND solution with PDDA seems to be a pre-treatment fast and more efficient in getting diamond films. The results also evidenced that the diamond powder size principally affects the nucleation density and permit to control the film morphology, growth rate, and roughness. The characteristics of BDND film obtained by seeding experiment II (b) makes it more suitable for the experiments of electrochemical degradation due to its larger surface area that may create more active sites in the electrode/electrolyte interface. Acknowledgments Special thanks to FAPESP, CAPES, CNPq for financial support, for Mrs. Maria Lúcia Brison by the SEM analyses and to Fatec Pindamonhangaba (Centro Paula Souza). Referências.

DOI: https://doi.org/10.1533/9780857093295.1.60

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