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Elastic constants of WC-a-C:H composite films studied by Brillouin spectroscopy

: Jiang, X.; Faßbender, J.; Hillebrands, B.


Physical Review. B 49 (1994), Nr.19, S.13815-13819
ISSN: 0163-1829
ISSN: 1098-0121
ISSN: 0556-2805
Fraunhofer IST ()
Brillouin light scattering; Brillouinlichtstreuung; composite film; Compositschicht; elastic constant; elastische Konstante; phonon; Rayleigh mode; Rayleigh-Welle; Schallgeschwindigkeit; sound velocity; WC-a-C-H

Brillouin light scattering experiments have been performed on tungsten carbide containing amorphous hydrogenated carbon (WC-a-C:H) films which were prepared on (111) silicon wafers by a reactive rf sputtering process. From the measured velocity of the Rayleigh surface modes the shear modulus G is calculated as a function of the tungsten carbide volume fraction, reflecting a phase transition of the films from an a-S divide H dominant to a crystalline beta-WC dominant WC-a-C divide H mixture. The determined elastic constants meet well the results obtained from depth-sensing indentation measurements. The theoretical calculation of the elastic constant of the composite was also performed as a function of WC volume fraction. The result show a small deviation from the experimental data in the range of low WC fraction which is probably caused by the phase change of the a-C:H matrix. The relatively large discrepancy of the theoretical calculation in the high WC fraction region may be a result of the invalidity of the theory.