Metal/Al 2 O 3 Multilayers As High-Temperature X-Ray Mirrors
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363 Mat. Res. Soc. Symp. Proc. Vol. 382 p 1995 Materials Research Society
In-situ Resistance
4104-
w
10 .. .. . 1 . . 1'o .. .
.5? . . 20
t [nml
Fig.1
In-situ resistance measurements for Co, Pt, and W on Sapphire.
TEM observations The preparation of perpendicular slices of our hard though extremely smooth sapphire substrates was impossible. Therefore, we present in Fig.2 a) a TEM photograph of a Pt/A120 3 multilayer sputtered on a Si(100) substrate. Although the sample quality on Si(100) does not reach the high level found on sapphire substrates, we clearly observe 15 smooth and well separated double-layers of Pt (dark) and A120 3 (light). In Fig.2 b) we add an electron diffraction image of the same sample. Near the primary beam we find a sequence of equally separated maxima, which are due to the artificial multilayer period.
Fig.2 a) : TEM-photograph of a [Pt2.1,,/A1203
2.9nm]15
multilayer.
364
b) : Electron diffraction image of the same sample.
X-ray scattering In Figs.3-5 we present x-ray reflectivity spectra (a) and Bragg-scans (b) of the three systems investigated here. From the reflectivity measurements we obtain layer thicknesses, interface roughnesses, and thickness fluctuations by fitting a density profile to the experimental data. The Bragg-scans reveal the crystalline structure and the coherency of the samples. Additionally, we performed rocking scans which characterize the specular fraction of the scattered intensity as well as the orientation of the crystal growth with respect to the physical surface of the film. Our x-ray studies clearly reveal the high thermal stability of the multilayers, which ranges from 8000C for Co and Pt to 9000C for W as the metallic component. The large number of satellite reflections up to high scattering angles indicates the very low interface roughness in our multilayers. From fits we obtain roughness parameters between 0.25 nm for Co/A12 0 3 and 0.18 nm for W/A120 3.
Fig.3
[Co4.snm/A120 3 3.7nm]10;
Reflectivity SC°(lll
Bragg-Range
)f,,
Co(O002)hp
a0=0.25nm 0
00
50
2e
100
I
C
9000C
700 0C
700 0C
300C
300C
150
400
a) reflectivity;
450
2e
500
550
b) Bragg-scans
Of particular interest is the development of the layer thicknesses upon annealing. In Fig.6 we show the nominal change of the single layer thicknesses t of all three analyzed samples. Each multilayer system exhibits a characteristic behaviour. In the case of Co/A120 3 , t(Co) decreases linearly in the same way as t(A12 0 3 ) increases which indicates a strong reaction of Co at the interfaces. For Pt/A12 0 3 we observe a significant reduction of both layer thicknesses beyond 8000C, which can be interpreted in terms of recrystallisation processes within the multilayer. W/A12 0 3 exhibits a weak increase of the multilayer period beyond 8000 C.
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Fig.4 : [Pt 3.2nm/A12 0 3 3.8nm]15;
Reflectivity
Bragg-Range
1000 0C
9000C
0
9000C 8200C 7000C 6000 C 40000C 30 C
0
820 C 0
6)
7000C 6000C 4000 C 300C
20 b) Bragg-scans.
a) reflectivity;
Fig.5
: [W 2.Onm/A12 0 3 2.7nm]
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