R.E. Somekh

Differential scanning calorimetry studies of solid state amorphization in multilayer NiZr

Abstract The reduction in free energy which accompanies solid state amorphization arises primarily from the negative enthalpy of mixing the elements which constitute the diffusion couple. This evolution of enthalpy enables the amorphization reaction to be analysed using differential scanning calorimetry (DSC) and quantitative thermodynamic and kinetic data to be obtained. We present a diffusion-controlled layer growth model for computing DSC traces given by sputtered thin film Ni Zr diffusion couples. We also examine mechanisms which can affect the layer thickness of amorphous alloy formed at interfaces in d.c. magnetron sputtered Ni Zr multilayers during deposition. We discuss phenomena which may cause decreases in the rate of reaction during annealing of Ni Zr multilayers with large modulation wavelengths.

Metastable phases formed by nanosecond laser-quenching of metals and binary alloys

Abstract A Ndue5f8YAG laser giving 5 ns pulses is used to melt sputter-deposited thin films which then cool rapidly (1010−1012 K s−1). The laser-quenched structures of pure iron and zirconium, and Coue5f8Ti and Nbue5f8Ni alloys are studied. In the pure metals, solid state transformations are suppressed but either low or high temperature polymorphs form from the melt. In alloys, solute addition can give heavy faulting in the rapidly grown supersaturated solid solutions and there is a transition from collision-limited to diffusion-limited growth, leading to glass formation.

A differential scanning calorimetry study of solid state amorphization in multilayer Ni/Zr☆

Abstract The reduction in free energy which accompanies solid state amorphization is due primarily to the negative enthalpy of mixing the elements which constitute the diffusion couple. This evolution of enthalpy enables the amorphization reaction to be analysed using differential scanning calorimetry (DSC) and quantitative thermodynamic and kinetic data to be obtained. We use DSC and X-ray diffraction to study amorphization in two different materials: d.c.-magnetron-sputtered thin film Ni/Zr multilayers which were deposited with different modulation wavelengths and using different magnetron powers; bulk Ni/Zr composites made by swaging and wire drawing. In the former case, we relate the forms of the curves to the structures of the asdeposited multilayers. In the latter case, we discuss our results in terms of models for termination of amorphous phase growth in composites with large modulation wavelengths.

Electron microscopic study of CrTi alloys

Abstract Our attempts to amorphize alloys of chromium and titanium by annealing the metastable b.c.c. β-phase as suggested in existing literature have not been successful. We report our results on bulk and thin films of Crue5f8Ti and compare them with previous work. Of particular interest is the prominent diffuse scattering seen in the electron diffraction patterns of the β-phase. The stability of the β-phase is discussed.

The thermodynamic factor in interdiffusion: A strong effect in amorphous Ni-Zr

Abstract Simultaneous determinations of the interdiffusivity in amorphous Ni-Zr and of the self-diffusivity of Ni in the same phase permit the determination of the thermodynamic enhancement factor for interdiffusion. Using thin compositionally graded films containing an initially thin layer enriched in 62Ni, the evolution on annealing of the composition profile was determined by Rutherford backscattering spectrometry and that of the 62Ni profile by secondary ion mass spectrometry. The effective thermodynamic factor in a-Ni57Zr43 at 623 K is found to be 33 ± 8 in the first hour of annealing of an as-deposited film, decreasing on prolonged annealing. This factor, larger than any previously reported, is somewhat in excess of the value expected from the Darken analysis, but does not deviate markedly as has been suggested by recent calculations questioning the validity of the mean-field approach in that analysis.

Rapid solidification of cobalt-titanium alloys induced by nanosecond laser pulses

Abstract Phase formation is studied in thin films of Coue5f8Ti alloys, both as sputtered and after quenching following melting by a 5 ns laser pulse. The composition ranges for glass formation are established, and the significance of crystal growth kinetics is examined. The Coue5f8Ti system exhibits many types of intermetallic compounds and a wide variety of behaviours is found around their compositions.

Indiffusion of cobalt in amorphous Co–Zr

Abstract By use of trilayers consisting of ∼ 35 nm cobalt ∼ 45 nm amorphous Coue5f8Zr, and ∼ 35 nm cobalt, the indiffusion of cobalt into the amorphous structure was studied by means of Rutherford Backscattering Spectroscopy (RBS). At temperatures between 650 K and 690 K, an initially high diffusion essentially stopped after 20–40 min annealing before equilibrium was reached. It is proposed that the effect is related to the diffusional asymmetry in the amorphous phase. The relatively immobile zirconium atoms cannot relax their configuration to permit cobalt indiffusion up to the equilibrium value.

Study of the diffusion of Ni into amorphous Ni50Zr50 and the resulting strain formation

Abstract A set of multilayers of Ni/amorphous Ni50Zr50 of various periodicities was deposited using dc planar magnetron sputtering. The diffusion of Ni into the amorphous phase and the strain build-up in the Ni layers were measured in situ from the reduction and shift in Bragg peak intensity and angle respectively. For short periodicities, a lowered interdiffusivity was observed in agreement with other earlier experimental observations and theoretical predictions of stress effects in some amorphous multilayers with a high viscosity. Furthermore, direct evidence of stress formation owing to an unbalanced diffusional flow of the two species in Ni-Zr was obtained. These findings give further support for Stephensons theory for lowered interdiffusion due to restricted stress relaxation in amorphous alloys.

The Deposition, Fabrication and Characteristics of High Critical Temperature Devices

In the first section of this paper the sputter deposition of thin films of YBa 2 Cu 3 O 7−x is considered. In the second section low and high temperature heat treatments are discussed in the light of the thermodynamics of the material and in the third the development, fabrication and current-voltage (IV) characteristics of a variety of device structures are described, including the hysterctic characteristics of certain YBa 2 Cu 3 O 7−x / YBa 2 Cu 3 O 7−x devices that reveal Josephson supcrcurrcnt tunnelling.

Structural Characterisation of Fe-Cu Multilayers of Differing Fe Thicknesses Using Transmission Electron Microscopy

In-plane and out-of-plane lattice parameters were measured in a series of coherent Fe-Cu multilayers using non-axial high resolution electron microscopy (HREM). The results indicate that the multilayers are tetragonally distorted with the magnitude of the distortion varying with the thickness of the Fe component. These distortions preclude an understanding of the multilayer structure in terms of conventional elasticity theory. The breakdown of epitaxy for thicker Fe layers was also investigated and it was found that the b.c.c. Fe grew with [110] parallel to [001] of the coherent f.c.c. multilayer.