Kinetic roughening of amorphousZr65Al7.5Cu27.5films investigatedin situwith scanning tunneling microscopy

Abstract

The isotropic nature of metallic glasses, lacking in long-range structural order, suggests an advantage for surface growth studies. In the present work the surface topography of vapor quenched amorphous ${\mathrm{Zr}}_{65}{\mathrm{Al}}_{7.5}{\mathrm{Cu}}_{27.5}$ films is investigated in situ with scanning tunneling microscopy. The development of surface morphology on mesoscopic length scales is analyzed with respect to an increasing film thickness. Vertical roughness and in-plane correlation are statistically analyzed by a height-height correlation function. With film thickness less than 30 nm, the surface roughness evolves with a growth exponent $\beta$ of approximately 0.2. Above a film thickness of 30 nm we find strong deviations from a self-affine scaling behavior. A roughening transition is observed, at which the lateral size of the characteristic surface structures converges to a maximum value. Moreover, the size of the uniform surface structures is increased with elevated substrate temperature during film deposition. We show that the in-plane size of these structures is governed by surface diffusion. In an approximation, neglecting nonlinear corrections, the experimental results are analyzed with respect to a growth model proposed by Wolf and Villain [Europhys. Lett. 13, 389 (1990)].