Nanocomposite thin films synthesized by plasma nanotechnology

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Thin amorphous films with incorporated grains of different mechanical properties can be synthesized simultaneously from tetravinylsilane monomer using plasma-enhanced chemical vapor deposition (PECVD). Thin films in a form of hydrogenated amorphous carbon-silicon (a-SiC:H) alloy of thickness from 25 nm to 1 micron were deposited at an RF power ranging from 10 to 70 W (self-bias 120-680 V) and a mass flow rate of 3.8 sccm (3.0 Pa). The films synthesized at a power of 10 W (120 V) were of grain structure with a diameter of grains about 29 nm. The diameter of some grains increased up to 0.5 micron with enhanced power at an expense of smaller ones, whose magnitude decreased. The bigger grains formed isolated islands in a relatively smooth matrix at a power of 50 W (530 V) and the density of bigger grains increased forming agglomerates at a power of 70 W (680 V). The grain structure of all the films was extensively investigated by atomic force microscopy (AFM) using height, magnitude, phase, and atomic force acoustic microscopy (AFAM) modes. Nanoindentation measurements were used to determine mechanical properties of the smooth matrix and bigger grains. The Youngs modulus and hardness of the matrix increased with enhanced power (10-70 W) from 12 GPa (0.8 GPa) to 81 GPa (8.8 GPa), respectively. Nevertheless, the mechanical constants of bigger grains were lower than those of the matrix, e.g., the Youngs modulus (hardness) was 42 GPa (3.5 GPa) for grains formed at a power of 70 W, i.e., half a magnitude in contrast to the matrix. The difference between mechanical properties of the matrix and grains was partly explained (simulations using finite element analysis) by grain geometry that influenced the nanoindentation measurements. However, the AFAM measurements confirmed lower mechanical properties of grains with respect to the smooth matrix. Typically, hard particles are used to reinforce a softer matrix in composite films. However, our films include softer grains in a stiffer matrix resulting in higher toughness of deposited films - a new type of coatings. The size of grain and its mechanical properties are controlled by the deposition conditions.

thin film, nanocomposite, low-temperature plasma, AFAM

ČECH, V.; PÁLESCH, E.; LASOTA, T.

31. 12. 2011

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