Growth mode and asymptotic smoothing of sputtered Fe/Au multilayers studied by x-ray diffuse scattering

Abstract

The interfacial roughness of sputtered Fe͓15 Å͔/Au͓21 Å͔ crystalline multilayers on MgO͑001͒ was studied using x-ray specular and nonspecular reflectivity. The nonspecular scattering was collected using an image plate detector that allowed us to map the very weak x-ray diffuse intensity in one in-plane (q x ) and one out-of-plane (q z ) momentum-transfer direction. We have evaluated the interfacial static and dynamic roughness exponents from the in-plane diffuse scattering and the roughness conformality, and found them to be ␣ ϭ0.43Ϯ0.05 and zϭ1.61Ϯ0.15, respectively. From this result we show that the growth of this metallic thin film is described well by the Kardar-Parisi-Zhang ͑KPZ͒ model. By following the evolution of the interfacial roughness of this multilayer, starting from the MgO/Fe/Au heterostructure used to initiate a coherent lattice, we observe a tendency toward saturation in the growth and interfacial smoothing after the deposition of 40 bilayers. This asymptotic smoothing is induced by the mechanisms of the KPZ model and results in a reduction of the interfacial slope as a function of time, according to (t)ϰt Ϫ0.31 . We have also found that the in-plane roughness cutoff length remains finite throughout the multilayer and does not increase to the lateral length of the sample, even after 100 bilayers have been grown.

Maximal- and minimal-height distributions of fluctuating interfaces

“…However, there is a large number of real interfaces where the up-down symmetry is broken [13], such as those described by the nonlinear growth models of Kardar-Parisi-Zhang (KPZ) [14] and of Villain-Lai-Das Sarma (VLDS) for molecular beam epitaxy [15], which raises the question whether MAHD and MIHD are the same in those systems. This is particularly important for two-dimensional interfaces due to the variety of real growth processes which show KPZ [16,17] and VLDS scaling [18]. Recent works on persistence in VLDS growth also motivate such study, since different exponents for positive and negative height persistence were obtained [19].…”

Surface/interface roughness effects on magneto-electrical properties of thin films

“…Generally, GMR is sensitive to the roughness exponent H [17], and also to the cross-correlation between roughness of consecutive interfaces [18]. For magnetic multilayers (i.e., Fe/Au, Co/Cu, Fe/Cr), the roughness exponents in the range 0:3 < H < 1 have been found experimentally by X-ray scattering measurements [13][14][15]. Moreover, experimental data show that GMR increases with increasing roughness [14].…”

Roughness effect on the measurement of interface stress

“…The nanometer scale topology of vapor-deposited single/multi-layer thin films can be quantified in many cases in terms of self-affine roughness [12][13][14][15][18][19][20][21]. In general, any physical self-affine surface or interface is characterized by a finite lateral correlation length x, an rms roughness amplitude s, and a roughness exponent H (0 Ͻ H Ͻ 1) [12][13][14][15].…”

“…Stimulated by Spaepen's work we have extended his approach to the more general cases of random self-affine and mound rough interfaces, which are commonly observed during multi-layer growth [18][19][20][21], as well as mound interface roughness that develops during epitaxial growth [8][9][10][11]22]. Our work is in both cases executed in the weak roughness limit because in many cases of thin film growth the corresponding ratio of vertical, out-of-film-plane roughness amplitude to lateral, in-plane correlation length is equal or lower than 0.1 [12][13][14][15][18][19][20][21].…”

“…Our work is in both cases executed in the weak roughness limit because in many cases of thin film growth the corresponding ratio of vertical, out-of-film-plane roughness amplitude to lateral, in-plane correlation length is equal or lower than 0.1 [12][13][14][15][18][19][20][21].…”