Application of Surface Roughness Data for the Evaluation of Depth Profile Measurements of Nanoscale Multilayers

Abstract

A secondary neutral mass spectrometric ͑SNMS͒ depth profile study of electrodeposited Co/Cu multilayers was performed. Depth profile measurements were performed both in the conventional way ͑i.e., starting the sputtering from the final deposit surface͒ and in the reverse manner ͑i.e., detaching the multilayers from the substrate and starting the analysis from the substrate side, which was very smooth as compared to the final deposit surface͒. The latter method could yield significantly larger intensity fluctuations in the SNMS spectra. Surface roughness data were measured with atomic force microscopy ͑AFM͒ for multilayers with different bilayer numbers but otherwise exhibiting the same layer structure as those used for the depth profiling. The experimental AFM surface roughness evolution was used to calculate the result of the depth profile measurements quantitatively. An excellent agreement was obtained between this calculation and the SNMS measurements. It was shown that the decrease in the intensity fluctuations during the depth profile analysis stems mainly from the increase in surface roughness of the samples studied, especially in the conventional sputtering mode. It was also concluded that the thickness fluctuation of the entire multilayer deposit and that of each layer are strongly correlated. DOI: 10.1149/1.3133182 .Nanoscale magnetic/nonmagnetic multilayers are in the forefront of materials research since the discovery of giant magnetoresistance ͑GMR͒ in these nanostructures.1,2 Multilayers are mostly produced by physical methods ͑evaporation, sputtering, and molecular beam epitaxy͒, some of them applying a fairly expensive high vacuum system. The feasibility of the electrodeposition of metallic magnetic/ nonmagnetic multilayers with GMR was demonstrated 3 a few years after the discovery of the phenomenon. Although electrodeposition has long been considered as a possible low cost alternative to the physical sample preparation techniques, the quality of the electrodeposited ͑ED͒ multilayers is still inferior to their physically produced analogs. The literature of the ED multilayer films with GMR amounts to some 140 papers, 4-6 but very little is known about why the sample quality, especially GMR, cannot achieve the properties of the samples prepared by physical methods.Although depth profile analysis is a very efficient tool for the characterization of element distribution and the interface quality of ED multilayer samples, only a few studies were published hitherto. Basile et al.7 studied the depth profile of ED Co/Cu sandwiches by Auger electron spectroscopy. They found that the observed interface width of approximately 20 nm is an inherent feature of the sample itself rather than the artifact of the sputtering method used for the depth profiling ͑although the sputtering also leads to some intermixing at a smaller depth scale 8,9 ͒. According to Tokarz et al., 10 the interface width of ED Cu͑200 nm͒/Ni͑200 nm͒ bilayers can also be estimated as being 20-30 nm, as shown by their secondary-ion mass spe...

Influence of Ag Additive to the Spacer Layer on the Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers

“…The envelope curve of the decay of the composition oscillation for depths beyond 300 nm is mainly determined by the development of the surface roughness of the sample. 46 At high depth, where the planar sputtering front crosses the tilted layer interfaces randomly, a smearing out of the concentration profile can be observed.…”

“…The surface of the resulting Cr-capped sample was as smooth as the Si wafer, making it particularly appropriate for a depth profile study. In order to achieve a sufficient spatial resolution along the depth, 46 the individual layer thicknesses in the Co/Cu(Ag) multilayers prepared for the SNMS study were chosen as high as 10 or 15 nm whereby keeping an equal thickness for the magnetic and non-magnetic layers. The total thickness of the SNMS multilayers was 400 or 450 nm.…”

On the composition depth profile of electrodeposited Fe–Co–Ni alloys

“…This new technique named as the reverse depth profile analysis [34][35][36] has shown that in ED Fe-Co-Ni alloys various zones were formed close to the substrate due to the interplay of the anomalous nature of the codeposition of Fe, Co and Ni with the depletion of the electrolyte for the ions of the magnetic elements. The composition depth profile measured [36] did not agree with any of the thickness dependence of the composition reported earlier.…”

Influence of Pb Additive to the Spacer Layer on the Structure and Giant Magnetoresistance of Electrodeposited Co/Cu Multilayers

“…A 5-nm-thick Cr adhesive layer was followed by a 20-nm-thick Cu conductive layer; both layers were produced by evaporation. The mean surface roughness of the Si/Cr/Cu substrates determined with atomic force microscopy was found to be between 1 and 3 nm [21]. A Cu sheet served as counterelectrode in each case.…”