Wayne R. Bennett

Metal-Metal Superlattices

An introduction to metal-metal superlattices is presented, along with a brief review of some of the materials which have been made, and phenomena which have been observed so far. We describe in detail the results of a number of structural characterization techniques applied to these materials, including Bragg θ-2θ x-ray diffraction, transmission and reflection Laue diffraction, wide film Debye-Scherrer diffraction, Rutherford Backscattering Spectroscopy (RBS) and Auger Electron Spectroscopy (AES). Particular emphasis is placed on recent results obtained with Ta/Mo superlattices produced by sputtering techniques.

Polarized neutron reflection used to characterize cobalt/copper multilayers

The polarized neutron reflectivity (PNR) of cobalt/copper multilayer films has been measured close to the critical edge for total reflection. Prominent features in the scattered neutron intensity, such as the superlattice diffraction peaks and the positions of the critical edge for total reflection, are sensitive to both the magnetic and structural properties of films, making PNR a useful tool for the characterization of magnetic metallic superlattices. The films were prepared by sputter deposition and the sample composition was measured by Rutherford backscattering spectroscopy. It has been found that while the density of the sputtered copper/cobalt multilayers is approximately 5% less than the bulk metals, the cobalt magnetic dipole moment per atom is little changed compared to the bulk. Evidence is also found for oxidation of the top cobalt layers.

Determination of effective optical constants of magnetic multilayers

The effective optical and magneto‐optical constants of a series of Cu/Co multilayer films are determined experimentally and compared with a theoretical thin‐film model based on the bulk optical constants of Cu and Co. In the multilayer series, the atomic percentages of Cu and Co were kept fixed and the period varied from 0.4 to 13.6 nm. Deviations from bulk‐like behavior in the effective optical constants are observed for multilayers with periods less than 3 nm.

Fabrication and structure of Mo/Ta superlattices

Mo/Ta superlattices with superlattice wavelengths in the range 20–180 A were made by alternately sputtering these components. We present the results of a variety of x‐ray diffraction studies used to structurally characterize these samples.

Competing Interactions in Metallic Superlattices

Metallic superlattices provide an excellent system to study in a controlled manner a variety of physical phenomena, including superconductivity, magnetism, and electrical transport properties. As will be discussed in this paper, changes in certain of these properties as a function of superlattice modulation wavelength A are found to be correlated with structural changes and elastic property anomalies. The properties of two particular metallic superlattices, Cu/Nb and Mo/Ta, will be discussed in this paper, as examples of how competing interactions manifest themselves in the physical properties of these superlattices.

Crystal Structure and Magnetic Characteristics of Tb/Fe Multilayers

We have grown Tb/Fe multilayers with modulation wavelengths in the range of 10 to 200 A by alternately sputtering these components. The individual layer thicknesses were kept constant to within ±0.3% over the entire sample thickness of ≈0.2 μm by feedback control of the sputtering rates and microprocessor control of the substrate rotation. Composition of the samples was determined from calibrated sputtering rates, and was confirmed using Rutherford backscattering spectrometry. The layered structure was demonstrated by low angle x-ray diffraction. High angle x-ray results show that the Tb and Fe layers are polycrystalline for high modulation wavelengths, but are amorphous for low modulation wavelengths. A vibrating sample magnetometer was used to measure the coercivity and saturation magnetization over the temperature range 200 to 430 K. Comparing results for pure Fe, pure Tb, and Tb/Fe multilayers demonstrates that the Tb and Fe multilayers couple to form an antiferromagnetic film.

Short range bonding interaction at metal-metal interfaces

Using the techniques discussed by Falco, Bennett, and Boufelfel (in this volume), freshly deposited Mo surfaces were exposed to a beam of sputtered Ta atoms for varying, controlled lengths of time. The resultant number of deposited Ta atoms/cm2 (from here on referred to as Ta coverage) was subsequently measured using Rutherford Backscattering (RBS).