Iron zirconium multilayer films were prepared by electron beam evaporation and by sputter deposition. Layer thicknesses were varied from 50 monolayers of each constituent down to 2 monolayers. Conversion electron Mössbauer spectroscopy, x-ray diffraction, and Auger spectroscopy have been used to characterize multilayers in the as-deposited and annealed state. Amorphous phase formation occurs during thermal anneals, and samples with layer thicknesses of 5 monolayers or less of each constituent are amorphous as deposited. Amorphous interfaces are observed in all samples, with this interface region being larger in the electron beam evaporated samples than in the sputter deposited samples.

Titanium-silicon and molybdenum-silicon multilayers have been investigated in cross-section using a high resolution TEM with a point-to-point resolution of .22 nm. This resolution has allowed us to confirm the amorphous nature both of the intermixed layers which form at the metal-silicon interfaces on sputter deposition, and of the Ti-Si reaction product which forms at temperatures below which crystalline silicides nucleate.

The bulk studies are complemented by in-situ annealing experiments in the high-resolution microscope. Phase reactions in the multilayers can be followed in real time, allowing direct observation of the formation of the amorphous alloy, the appearance of rows of Kirkendall voids, and the crystallization and growth of silicide phases.

Amorphous Si/Ge artificial multilayers have been implanted with Si and B at liquid nitrogen temperature, and partially ion mixed with Ar at different temperatures. In all cases, the square of the mixing length was found to be proportional to the dose. Annealing of Si-implanted samples showed that after relaxation the diffusivity appeared unaffected by the implantation process. Annealing of the B-implanted samples showed an enhancement of the diffusivity at the higher dose. The diffusive component of the square of the mixing length in the Ar-ion mixed samples has an Arrhenius-type temperature dependence, with an activation enthalpy of 0.22 eV.

We discuss recent measurements of relaxation, interdiffusion and crystallization in amorphous hydrogenated semiconductors and insulators prepared as periodic multilayers. The stability of multilayer structures depends upon temperature, repeat distance and the nature of the materials. Crystallization of amorphous silicon in amorphous silicon/amorphous silicon dioxide layers is inhibited when the silicon thickness is reduced below 20 nm.

SixGe1−x strained layer superlattices are known to be metastable in that they can be grown fully commensurate with layer thickness higher than the equilibrium, calculated Tc at which dislocation formation becomes energetically favorable. In this paper, we describe the mechanism of relaxation in such multilayers. Both plane-view and cross-sectional transmission electron microscopy (TEM) were used to examine the formation of dislocation at the different interfaces. RBS was used to follow interdiffusion. We found two competing mechanisms for relaxation: The preferred mode for relaxation is the creation of dislocation networks at each of the interfaces. This process can be stopped or considerably inhibited by the difficulty of forming new dislocations in samples which are perfectly commensurate after growth; Some dislocations appear necessary in order to generate more dislocations during annealing. When this is not the case, the only possible way to attain relaxation is through diffusion. In such a case, stress-enhanced diffusion is observed, with a diffusion coefficient 200 times higher than expected.

Differential Scanning Calorimetry (DSC) and Debye-Scherrer X-ray diffraction have been used to characterize silicide formation in nickel/amorphous-silicon multilayer films. Two different Ni:Si layer thickness ratios were investigated, 3:11 and 1:1. Films with layer thickness ratio of 3:11 first formed Ni2Si followed by NiSi at a temperature 25°C higher. Multilayer films with 1:1 thickness ratios formed only Ni2Si. Activation energies for these reaction were determined and found to be in agreement with previous results on bilayer films. The temperature at which Ni 2Si formation was complete in the 1:1 films was found to decrease with decreasing layer thickness. Analysis of this phenomenon allowed determination of the interdiffusivity during silicide formation, also in agreement with previous results. Films with 1:1 layer thickness ratios and layer thickness of 125 Å or less were found to sometimes undergo explosive silicidation. This presumably occurs because the rate of heat generation at the reacting interfaces exceeds the rate of heat dissipation.

The relaxation of misfit strain in metastable structures by plastic flow is described using a continuum model based on Haasen's picture of plastic flow in bulk diamond-phase semiconductors and the concept of excess stress. This model provides a unified explanation of the equilibrium critical thickness, the relaxation behavior of metastable strained-layer structures, and the “metastable” critical thicknesses reported in many semiconductor strained-layer geometries.

We report two new epitaxial systems, prepared by MBE: basal plane epitaxy of the rare earth metal Dy onto LaF3 films and vice versa. SQUID magnetometry studies indicate that buried epitaxial Dy films, of ∼300Å thick, order ferromagnetically at similar temperatures to bulk Dy crystals.These epitaxial systems are one member of a new family of epitaxial systems of basal plane epitaxy of rare earth metals on rare earth fluorides and vice versa. Such systems may be used to probe the effects of strain and dimensionality on magnetic ordering in rare earth metal films and multilayers.

We have generalised our x-ray diffraction results from amorphous/crystalline multilayers, to include random interfacial disorder of a gaussian type. A general relation is obtained which can be applied to both crystalline/crystalline and crystalline/amorphous multilayers. This gaussian fluctuation or “roughness” can strongly reduce the long-range atomic order along the growth direction of the multilayer. Using classical structure factor calculations, we simulate the evolution of x-ray patterns as a function of the fluctuation amplitude, the superlattice wavelength, and the interatomic distances. Applying this model to the crystalline/crystalline case we fit the experimental Nb/Cu data, deduce a fluctuation amplitude of about 0.4 Å, and relate it to the lattice mismatch between Nb and Cu. For crystalline/amorphous systems (Pb/Ge) this amplitude can be significantly larger (2 Å).

The stability of Pb/Ge and Pb/C multilayers has been studied over a broad temperature range by x-ray diffraction experiments. In the Pb/Ge system an amorphous to microcrystalline phase transformation of the Ge-layers was already observed at ≃ 100 °C. This transition destroys the modulation structure and improves the Pb(111) texture. In the Pb/C multilayers, the layered structure was still present at temperatures higher than the melting temperature of Pb. Contrary to recent publications, no depression of the melting temperature of the two-dimensional Pb layers could be observed.

A general scheme for determining which metal-Si systems undergo solidphase amorphization (SPA) upon rapid thermal annealing is presented and used to investigate Ni-Si, Ti-Si, V-Si, Co-Si and Cr-Si reactions. SPA occurs only in the first three systems. With the glaring exception of Co-Si, the results agree with the thermodynamic predictions of SPA in systems in which the free energy of a glassy phase is significantly lower than the free energy of the separate components. The amorphization may also be influenced by the diffusing species and contamination. Following SPA, the first crystalline compound is determined by nucleation kinetics.

The reactions in sputter deposited Si-Ti-Si diffusion couples were investigated with X-ray diffraction, Auger electron spectroscopy and cross-section transmission electron microscopy. Anneals at a temperature of 400°C resulted in the growth of an amorphous phase at the Si-Ti interfaces. Crystalline silicides were only found after an anneal at temperatures of 500°C or higher.

It was demonstrated that an amorphous layer of approximately 8 nm thickness sustained a concentration gradient from about 73% Si at the Si side to about 28% Si at the Ti side of the diffusion couple. The measured width of the phase field agreed with the width predicted from a calculated free energy versus composition diagram. Actually the observed phase field was found to be so wide, that it contains the stoichiometry of all equilibrium silicides. The consequences of our results for the explanation of silicide first phase nucleation were discussed.

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 surface-Brillouin zone interactions to the behaviour of these materials to be assessed.

Ellipsometric and magneto-optical properties of amorphous Dy (3.5 Å) and amorphous Fe (25 Å to 12.5 Å) multilayers were investigated over the spectral range from 3000 Å to 8000 Å in magnetic fields to 0.21 Tesla. In this range of layer thickness the magnetic anisotropy is vertical. Kerr rotations, θk, were weakly spectrally dependent, and as large as 0.1 degrees. The diagonal and off-diagonal elements of the optical dielectric response function were determined over the full spectral range, and were found to be dependent on iron layer thickness.

We report on magnetic exchange coupling phenomena between Fe and TbFe thin films. The structures are grown utilizing D.C. magnetron sputtering from separate Tb and Fe targets and their magnetic characteristics are measured utilizing VSM and Longitudinal Kerr Rotation. In addition, Auger depth profiling and x-ray diffraction studies were conducted to study film composition and structure.

Uniaxial alignment of the Fe moment in the plane of the substrate is revealed by the longitudinal Kerr measurements. The coercivity of the Fe layer varies from 19 Oe to 130 Oe depending on the azimuthal angle between the normal to the plane of the bilayer and the direction of the external field. The hysterisis loops vary in shape from rectangular in the alignment direction to S-shape in the direction orthogonal to this direction.

These effects are discussed in terms of magnetic exchange coupling interactions between the ferromagnetic layer and the ferrimagnetic alloy.

Multilayered structures containing sputter-deposited films of amorphous TbFeCo can exhibit magneto-optical Kerr rotation and are leading candidates for erasable optical storage media. Ellipsometric characterization of optically active multilayered media is desirable during media development, testing and production, but traditional ellipsometry does not account for the presence of optical activity. A novel ellipsometer is described that can characterize both the dielectric overcoat and the optically active layers. Reflectivity measurements are collected for different incident angles and polarizations using a differential detector while the magnetic reversibility of the active film layer is exploited to enhance the magneto-optical signal from the TbFeCo. A multilayer film model is used to process observations and estimate media characteristics. The model explicitly accounts for the optical activity of the TbFeCo layer, and is parameterized in terms of the index of refraction and thickness of the overcoat, and the real and imaginary parts of the elements of the dielectric tensor of the active layer.

A series of TbFeCo films with varying composition, rf-sputter deposited on quartz substrates with Al2O3 dielectric protective overcoats, is characterized. Both Tb-rich and Fe-rich samples were deposited, with room temperature coercivities ranging from 1.6kOe to about 4kOe, and film-side Kerr rotations between 21 minutes and 28 minutes. Reflectivity data versus angle of incidence, and estimated dielectric tensor elements for the TbFeCo layers are presented. A standard figure of merit, based on the off-diagonal tensor elements, is used to compare competing media in terms of their optimal performance in a multilayered structure.

We have made and tested several sliced multilayer structures which can function as transmissive x-ray optical elements (diffraction gratings, zone plates, and phase gratings) at 8 keV. Our automated multilayer sputtering system is optimized to sputter layers of arbitrary thickness for very large total deposits at high deposition rates. Diffraction patterns produced by the multilayer devices closely match theoretical predictions. Such transmissive optics have the potential for wide application in high resolution microscope and spectrometer systems.

Raman scattering has been used to examine strained-layer GaSb/AlSb superlattices for a variety of growth imperfections. Analysis of zone-folded acoustic phonon spectra permit a determination of the superlattice period, the individual layer widths, some estimate of the interfacial widths, and evidence for variations in layer thicknesses.

The integrated absorption of the Si-H, Ge-H and Si-H2 IR stretching modes were measured for three series of superlattices where: a) the well to barrier thickness ratio was kept constant while the period was varied; b) the barrier thickness was kept constant while the well thickness was varied and c) the well thickness was kept constant while the barrier thickness was varied. The dark (σd) and photo (σph) conductivities, the photoconductivity exponent γ and the activation energy of the dark conductivity Ea were measured perpendicularly to the plane of the layers for series a) and b). Structural changes induced by sandwiching were documented by IR absorption and correlated with the optoelectronic properties of the thin films.

Interdiffusion in a two-dimensional compositionally modulated lattice has been studied by Monte-Carlo simulations. In the initial stages, the interdiffusion coefficient has been observed to change with time due to the development of short-range order simultaneously with the interdiffusion process. When the short-range order parameter approached its limiting value, the diffusion coefficient approached a constant value. The dependence of the interdiffusion coefficient on the modulation wavelength does not agree with the prediction of one-dimensional theories. For ordering alloy systems, the effective interdiffusion coefficient is positive, i.e., an initially present modulation decays in time, for all wavelengths.