Adhesion and Mechanical Properties of a-CSi:H Thin Films Prepared from Tetravinylsilane Monomer by Plasma Polymerization

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The adhesion of the thin film to the substrate and mechanical properties of this film are some of the most important and crucial attribute in determining the thin film's application possibilities. Thin films with controlled adhesion are essential as barrier, anti-scratch, wear-resistant, transparent and antireflective coatings for surface modified materials. The greatest potential of this research for industrial applications is in glass-fiber-reinforced polymer composites without sharp interfaces. In this study, hydrogenated amorphous silicon-carbon (a-CSi:H) thin films were studied from the point of adhesion to the silicon substrate. Silicon wafers were pretreated with argon plasma (5.7 Pa, 10 sccm, 5 W, 10 min) using continuous wave to reach reproducible thin film adhesion. Thin films were deposited by plasma-enhanced chemical vapor deposition (PECVD) from pure tetravinylsilane (TVS) monomer (2.7 Pa, 3.8 sccm), employing a radiofrequency (RF) helical coupling system, using a pulsed regime with effective power ranging from 2 W to 150 W. Prepared films were 0.1 μm thick for nanoscratch testing and 1.0 μm for nanoindentation measurement. The nanoscratch test consisted of drawing a conical diamond indenter (90°, 1 μm tip radius) over a film under linearly increasing normal loading from 1 μN up to 10 mN. The scratch length was 10 μm and was reached in 30 s. The value of the load at which adhesion failure is detected is known as the critical normal load (Lc), which is used as a semiquantitative measure of adhesion. Scratch tracks were also observed by atomic force microscopy (AFM) and correlated with loading curve (Fig. 1). Young's modulus and hardness were obtained by instrumented nanoindentation technique using Berkovich indenter (50 nm tip radius). Analysis of load-displacement curves was based on Oliver-Pharr method. It was observed that critical load increased with enhanced power from 1.6 mN (2 W) up to 4.6 mN (75 W) and was invariable for higher power 4.4 mN (150 W). The measurements showed an increase in Young's modulus in dependence on effective power, specifically from 10 GPa (2 W) to 140 GPa (150 W). Although critical load has been found to increase with enhanced power, work of adhesion is decreasing. This fact is due to the significant effect of Young's modulus, which grows vigorously, on the critical load value. Based on model Burnett and Rickerby [1] and modified by Bull et al. [2], the work of adhesion, eliminating the influence of variable Young's modulus, was used. It was found out that the adhesion of the films for 4 years was without changes, it means with no aging effect. References [1] P. J. Burnett, D. S. Rickerby, Thin Solid Films 157 (1988) 233–254. [2] S. J. Bull, D. S. Rickerby, A. Matthews, A. Leyland, A. R. Pace, J. Valli, Surf. Coat. Technol. 36 (1988) 503–517. Acknowledgement This work was supported in part by the Czech Science Foundation, grant no. 16-09161S and the BUT Specific Research, grant no. FCH-S-18-5194.

thin films, a-CSi:H, PECVD, nanoscratch test, adhesion, nanoindentation, mechanical properties, atomic force microscopy

PLICHTA, T.; BRÁNECKÝ, M.; ČECH, V.

12. 9. 2018

Vysoké učení technické v Brně, Fakulta chemická, Purkyňova 464/118, 612 00 Brno

978-80-214-5488-0

7th Meeting on Chemistry and Life 2018. Book of abstracts

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