Evaluation of Multilayers for Soft X-Ray Fabricated by Ion Beam Sputtering
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EVALUATION OF MULTILAYERS FOR SOFT X-RAY FABRICATED
BY ION BEAM SPUTTERING. I.KATAOKA,
I.YAMADA,
K.ETO and K.ITO
Japan Aviation Electronics
Industry,
Musashino 3-chome, Akishima-shi,
Limited,
Akishima Plant,
1-1
Tokyo 196 Japan.
ABSTRACT Multilayer
structures
of
Li 2 0
and Ni were deposited onto
polished fused quartz by the dual ion beam sputtering method.
tical
and
physical
Reflectivity of multilayer
evaluated.
at
mirrors
angle of 79.6 deg. was 17% for 44A(C-K line). agreement with the calculated value considering roughness
Op-
properties of the multilayer structure were
and residual oxygen contamination in
an
incident
There was good the interface
the Ni layer from
the background of Li2O deposition. INTRODUCTION It is well known that the protein of the cell can be observed without absorption of water by X-rays of wavelengths from 23.3A to 44A; because in the above mentioned wavelength region. the absorption coefficient of carbon for X-rays is bigger by about ten times than that of oxygen[l]. A number of studies on soft X-ray optics for biological use have been made, and we are also investigating these optics and materials for rcfIecl, ix'e layers. Furthermore we have been paying attention to the characteristic feature of this field, namely, a wide selection of* materials for multilayers is available because the problem of Xray durability is
thought to be small in
the biological field.
Then we can select the materials mainly with a view of getting high reflectivity without considering X-ray durability. In the previous paper[2], we proposed that the use oxides or hydrides for space layers gives very high reflectivity in this wavelength region. In this paper we prepare multilayer structures of Li 2 O/Ni by the dual ion beam sputtering method and evaluate the optical and physical properties. CALCULATION OF REFLECTIVITY In order to select a combination of materials, we calculated peak reflectivity of the multilayers with many material combinations in the wavelength region from 10A to 50A, which includes the region of interest for biological microscopic studies. In Figure 1 we show the spectral dependence of the calculated reflectivity of multilayer mirrors. Peak reflectivity is obtained for 199 layers with the incident angle 8 =70 deg. when the thickness of each layer is optimized at each wavelength. We determined the thickness by the method of linking the reflectivity line for each material to the point where an overall smooth curve is made on the complex plane[2]. The reflectivity was calculated by solving the asymptotic equation, using Fresnel's coefficient. The index of materials used for the calculation were taken from Henke's f data book[3]. Space layers should be made of a material with index close to unity and an absorption coefficient as small as possible. Figure 1 shows the calculated results using Li, LiH, Li 2 O and Be Mat. Res. Soc. Symp. Proc. Vol. 128. ' 1989 Materials Research Society
514
7,0.0 0.0 24
00.0 30.0
-
5,0.
40.0
30.0
20.0
WAVELENGTH A
Figure 1. Th
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