Morphology of amorphous ${\mathrm{Fe}}_{91}{\mathrm{Zr}}_9∕{\mathrm{Al}}_2{\mathrm{O}}_3$ multilayers: Dewetting and crystallization

Amorphous ${\mathrm{Fe}}_{91}{\mathrm{Zr}}_9∕{\mathrm{Al}}_2{\mathrm{O}}_3$ multilayers grown by magnetron sputtering have been studied using x-ray reflectometry, x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy. It could be demonstrated that on the interface between the ${\mathrm{Fe}}_{91}{\mathrm{Zr}}_9$ and the ${\mathrm{Al}}_2{\mathrm{O}}_3$, crystalline grains are formed, that for very small repetition thicknesses destroy the periodicity of the multilayers by accumulative roughness. Understanding these effects would enable substantial improvement of the quality of nanolaminated amorphous layers.

Figure 1

X-ray reflectivity curves for samples with varied metal layer thickness as indicated. Increase of metal layer thickness leads to higher-order multilayer peaks. Scans are offset for clarity.

Figure 2

Bright field TEM micrograph of sample with $130\mathrm{\AA }$ FeZr and $18\mathrm{\AA }$ ${\mathrm{Al}}_2{\mathrm{O}}_3$ layers on Si with native oxide. Grains within the FeZr appear preferentially at the lower interfaces (arrows).

Figure 3

Bright field TEM micrograph of sample with $25\mathrm{\AA }$ FeZr and $11\mathrm{\AA }$ ${\mathrm{Al}}_2{\mathrm{O}}_3$ layers. An increased waviness and variation in thickness of the layers as compared to the sample in Fig. 2 is apparent.

Figure 4

High-resolution TEM micrograph of the sample shown in Fig. 3 ($25\mathrm{\AA }$ FeZr and $11\mathrm{\AA }$ ${\mathrm{Al}}_2{\mathrm{O}}_3$ layers). Crystalline grains extending through the entire thickness of the metal layer are clearly seen.

Figure 5

High-resolution TEM micrograph of the sample shown in Fig. 2 ($130\mathrm{\AA }$ FeZr and $18\mathrm{\AA }$ ${\mathrm{Al}}_2{\mathrm{O}}_3$ layers). Local crystallization appears, mainly on the lower interfaces, as indicated by the arrow.

Figure 6

Symmetric scans of samples with different interface densities. Sample compositions are given in the figure. The increase in intensity toward lower $Q$ values is consistent with the diffuse ring in the electron diffraction pattern in Fig. 7. The forbidden Si(002) reflection from the substrate is also marked.

Figure 7

Selected area electron diffraction pattern (top-view geometry) of a sample with $50\mathrm{\AA }$ thick FeZr layers. Rings correspond to polycrystalline iron and diffuse rings are from the amorphous material. Indices of diffracting lattice planes are indicated. The scale was calibrated using the Si substrate of the same sample.

Figure 8

(Color online) RBS spectrum of a sample with $130\mathrm{\AA }$ metal and $18\mathrm{\AA }$ aluminum oxide, repeated ten times. The simulated curve corresponds to the composition of ${\mathrm{Fe}}_{91}{\mathrm{Zr}}_9$. For the silicon substrate, slight channeling results in lower intensity than expected from the simulation.