Ion Beam Mixing of Alternate Layers of Ni-Nb and Ni-Cr
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The thicknesses of e-beam evaporation (10-6 torr) on Si substrates. Individual layers were chosen to provide a 50% Ni and 50% Nb composition Similarly, 1OOA of Ni and 110A of Cr alternate in the mixed layer. layers with a total thickness of 840A were deposited on Si to obtain The films were irradiated with 350 keV NitoCr 50 in the mixed layer. The projected ranges of at a dose of 2 x 101 6 ions cm2 . Cr 350 keV Cr÷ in Ni-Nb and Ni-Cr are 1200A and 1150A, respectively. All the depositions and ion bombardment were done at room temperature. There are no phases present in the equilbrium phase diagrams for these A homogeneous N14 5Cr55 film of systems at 50:50 composition. thickness - 6900A was sputter deposited from a composite Ni-Cr This film was irradiated with 2.5 MeV Ni (projected range target. 7000A) at a dose of 2 x 10 16 ions cmRESULTS AND DISCUSSION Typical high resolution RBS spectra for the as deposited and ion implanted alternate Ni-Nb and Ni-Cr layers are shown in Figures la and Signals from individual films in the alternating layers of 1 b. as-deposited films appear as oscillations in the backscattering intensity in the case of Ni-Nb after implantation with which disappear 350 keV Cr4 , 2 X 1016 ions cm- 2 indicating that the mixing has taken place. Ion mixed Ni-Cr films still shows the oscillations indicating that the Ni-Cr films do not mix well. 700
900-
800C
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5, --
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sjlc 80 AS DEPOSITED50
\
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AS DEPOSITED 2
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350key Cr* 2XIO'*o8
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ENERGY
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Figure 1(a). RBS spectra of the as deposited and ion mixed (350 keY Cr+, 2 x 1016 ions cm-2) Ni-Nb alternating layers
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ENERGY
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Figure l(b). RBS spectra of the as deposited and ion mixed (350 keY Cr 2 x 1016 ions cm-2) Ni-Cr alternating layers
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TEN analysis of the as-deposited NI-Nb and NI-Cr films reveals the polycrystalline nature of the film. Figure 2 represents the cross-sectional bright field micrograph of the ion mixed NI-Nb film. Featureless amorphous NI-Nb film is clearly found to be present. Also a polycrystalline layer (- 150 A wide) at the Interface region of Si and Ni-Nb amorphous layer is observed. The structure of this polycrystalline layer was determined from TED pattern and found to be. FCC (a = 4.2gA). It has not been possible at present to identify the chemical nature of this crystalline compound. It should be noted that the surface layer (3200 - 3300 A) of Si substrate also becomes amorphous after ion beam mixing. Figure 2. Cross-sectional micrograph of 4 + Cr keV (350 mixed ion 2 X 1016 ions cm-2) Ni-Nb alternating layers
390A
Figures 3(a,b) show the cross-sectional bright field micrograph and the TED pattern of the ion mixed (350 key Cr+, 2 X 1016 ions cm-2) Ni-Cr film. Absence of any diffuse ring and the presence of spotty diffraction rings in the TED pattern indicate that the Ni-Cr film does not amorphise and remains polycrystalline after ion mixing.
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Figure 3.(a) Cross-sectional micrograph and (b)
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