Electronic and Mechanical Properties of DC Sputtered Compositionally Modulated Metal Films
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ELECTRONIC AND MECHANICAL PROPERTIES OF DC SPUTTERED COMPOSITIONALLY MODULATED METAL FILMS J.S. DREWERY AND A.L. GREER University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, Cambridge CB2 3QZ, United Kingdom.
ABSTRACT We describe a recently constructed apparatus for the measurement of the Young's modulus and Poisson's ratio of free-standing sputtered multilayer films. In comparison with more conventional methods, this is expected to permit both measurement with lower uncertainties and interpretation which is more straightforward. A separate apparatus for the accurate measurement of the conductivity, magnetoresistance, and Hall coefficient of such systems has been prepared which will enable the contribution of Fermi surfaceBrillouin zone interactions to the behaviour of these materials to be assessed.
1.
A NOVEL APPARATUS FOR ELASTICITY MEASUREMENTS
Previous measurements of elastic moduli in thin films have fallen into two classes. (1) Indirect determinations based on measurements of the velocity of sound or on vibrating reed techniques. The former are adversely affected by surface reflections. In the latter, distortion of the film leads to an enhancement of the effective stiffness, and possibly to deviations from harmonic behaviour; to take account of the distortion several resonances of the film must be found [1]. (2) Direct determination of the stress-strain relationship in microtensile apparatus or in a bulge test [2]. Here the strain is difficult to determine because of slip where the thin film is gripped. The measurements are complicated by the uncertainty in the length of the film over which the strain is uniform and by possible non-rigidity of the mounting points. We have constructed an apparatus less sensitive to the above problems, independent of the movement of the grips, which detects the strain in the sample by optical diffraction from a grating pattern on the sample surface. The change in the angle of the diffracted spots of light from a gridiron pattern grating can be used to study the in-plane Poisson's ratio, which has not previously been measured.
1.1. The Apparatus A diagram of the overall arrangement is given in fig. 1, and of the sample mounting assembly in fig. 2. Two large piezoelectric tubes are used to strain the samples. A large DC voltage, on to which an AC modulation can be superimposed, is applied to the outside of the tubes. The inner surfaces are earthed as are the end plates. This provides a screened environment in the cavity. The stress in the sample is measured using a pair of piezoelectric rings whose end faces are connected to the inputs of a lock-in amplifier (Brookdeal 9206) so that the voltage output is proportional to the sum of the measured stresses. Stresses due to translational motion of the sample are thereby eliminated. The connection from the sample to the sensors is made via a light titanium shaft. The lower sensor is connected Mat. Res. Soc. Symp. Proc. Vol. 103. 19g8 Materials Research Society
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