John L. Makous

Superconducting and structural properties of sputtered thin films of YBa2Cu3O7−x

We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Post‐annealing in pure O2 after sputtering resulted in superconducting films with a Tc onset as high as 89 K and a midpoint Tc of 75 K. We report preliminary results of films deposited on sapphire, MgO and sol‐gel coatings of ZrO2 on sapphire, with and without buffer layers of Ag. The chemical and physical structures of these films were analyzed by using several x‐ray diffraction techniques and Rutherford backscattering spectroscopy.

Elastic constants of, and Stonely waves in, molybdenum films measured by Brillouin scattering

The dispersion of Rayleigh, Stonely, and Sezawa acoustic waves guided by deposited thin molybdenum films has been used to evaluate selected elastic constants and film homogeneity. This work includes the first experimental observation of Stonely waves by Brillouin scattering.

Integer monolayer metallic superlattices

Abstract We report the fabrication of metallic superlattices modulated by integer number of atomic planes of Mo and Ta. The set of superlattices reported here retain structural coherence and exhibit metallic resistivity behavior over the entire range of wavelengths down to the monolayer limit. These results contrast with structural and transport behavior observed in other metal-metal superlattices previously studied.

Elastic and structural properties of Mo/Ta superlattices

Abstract Previously1 we reported the fabrication, structure, and electrical transport properties of Mo/Ta superlattices. This present paper reports a more quantitative analysis used to explain an observed wavelength-dependent strain perpendicular to the layers in terms of the van der Merwe2,3 model for epitaxial superlattices. These results are correlated with an anomalous decrease in the c44 elastic stiffness constant of Mo/Ta for 20 A

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.

Metallic Superlattices with Monolayer Modulation

We report the preparation and characterization of sputtered Mo/Ta superlattices where the wavelengths are modulated by integer numbers of atomic monolayers. Resistivity and tunnel junction measurements on Mo/Ta superlattices with wavelengths in the range from 153 atomic planes each of Mo and Ta to the monolayer limit of 1 atomic plane of each are found to be consistent with their structural properties as determined by x-ray analyses. In addition, these results are consistent with earlier studies on the phonon structure of Mo/Ta using Brillouin scattering.

Contamination Effects in Mo/Ni Superlattices

A softening of the shear elastic constant c 44 has been observed previously in Mo/Ni superlattices as a function of decreasing bilayer thickness below approximately 100 A.[1] We have prepared a series of Mo/Ni superlattice films by ion beam sputtering doped with varying concentrations of either aluminum or oxygen. The chemical and structural properties of these films were then determined using x-ray diffraction (XRD) and Auger electron spectroscopy (AES). The shear elastic properties were characterized by measuring the surface acoustic wave (SAW) velocity of the deposited films. We demonstrate structural and elastic property effects resulting from Al and O impurity incorporation in Mo/Ni multilayers.

dV/dI Double Peak Structures in Superlattice-Based Tunnel Junctions

We realized high quality tunnel junctions using bcc-bcc Mo-Ta superlattices in the modulation wavelength range 16–450 A as the first electrode. The dV/dI vs. V characteristics showed a double peak structure in the wavelength range 50–250 A. We fitted the temperature behavior of these structures using both a two band model and the proximity effect theory. Preliminary calculations of a possible microscopic explanation of this data are presented.

Structural, electrical, and magnetic properties of Fe/Pd superlattices (abstract)

We have made Fe/Pd superlattices with periodic modulation wavelength Λ ranging from 33.2 to 188.4 A. Long‐range structural coherency is inferred from several x‐ray diffraction techniques. Fe and Pd were found to grow (110) and (111) parallel to the substrate, respectively. The in‐plane electrical resistivity was measured in the range 7.5–300 K by the four‐point probe method. The dependence of the resistivity on Λ will be explained by a model using interfacial scattering of electrons. Room‐temperature magnetic properties of the samples were measured using conversion electron Mossbauer spectroscopy and vibrating sample magnetometry. We found all the samples to be ferromagnetic. Both the intrinsic hyperfine magnetic field and the saturation magnetization show an increase as Λ decreases. We found that both of these physical quantities strongly depend on the number of atomic layers of (110) Fe in Λ. We did not find any induced magnetism in (111) Pd to within the experimental error. We determined the magnetic m...