Hitoshi Homma

Interfacially initiated crystallization in amorphous germanium films

The amorphous to microcrystalline phase transition of Ge in Pb/Ge multilayers has been extensively studied. During crystallization, the x‐ray diffraction peaks of the modulated structure disappear and the Pb texture improves. It is shown that the crystallization temperature decreases with decreasing amorphous Ge thickness and is strongly affected by the texture of the metallic component. These results imply that the crystallization is interfacially initiated.

Phase diagram and oxygen stoichiometry of Y‐Ba‐Cu‐O thin films

We have performed an exhaustive study of the phase diagram of Y‐Ba‐Cu‐O thin films using chemical analysis, energy dispersive x‐ray spectroscopy, Auger electron spectroscopy, and x‐ray diffraction. We show that Raman scattering can provide information regarding impurity phases and oxygen stoichiometry in thin films

Epitaxial film growth and metastable phases of single crystal Dy by molecular beam epitaxy

We have grown two novel epitaxial phases of dysprosium (Dy) on vanadium (V) by the molecular beam epitaxy technique. Surface structures are studied by in situ reflection high‐energy electron diffraction, and bulk structures are studied by x‐ray diffraction after removal from the growth chamber. The new hcp phases are ∼4% expanded uniformly in the (0001) plane and ∼9% and ∼4% expanded out of plane, along the c axes, for noninterrupted and interrupted deposition cases, respectively. We also observed (2×2), (3×3), and (4×4) Dy surface reconstruction patterns and a series of structural changes as the Dy film thickness increases.

Superconductivity in Coupled Pb/Ge and Pb/C Multilayers

We report on measurements of the dimensional crossover effect in superconducting Pb/Ge and Pb/C multilayers. The critical field data indicate the presence of a proximity effect at the interface between the Pb and the Ge or C. Using the model of Tachiki and Takahashi, we calculate the finite density of states near the Fermi-level in the Ge and C layers.

Influence of the interface on the crystallization of amorphous Ge in Pb/Ge multilayers

The amorphous to crystalline phase transition of Ge in contact with Pb has been extensively investigated in Pb/Ge multilayers. We find that the Ge crystallizes at reduced temperatures in the range of 100-200°C depending on the thickness of the Ge and the Pb. Simultaneously the texture of the Pb improves and the layered structure completely disappears. It is suggested that the basis for the reduction of the crystallization temperature is the enhanced diffusion kinetics at the interface, caused by the adjacent Pb layer.

Nature of coupling and dimensional crossover in superconducting multilayers

Comparaison entre les champs critiques superieurs dependant de la temperature dans des multicouches couplees par effet Josephson et par effet de proximite

ELECTRONIC TRANSPORT IN Mo/Ni SUPERLATTICES

Abstract An experimental relationship between superconductivity, magnetism and localization is explored in short-wavelength (14A ⩽ ⋀ ⩽ 40A) sputtered Mo/Ni superlattices. A crossover to a superconducting state is observed for ⋀

Structural Study Of Multilayered Vanadium/Nickel Superlattices

We have studied the microstructure of V/Ni metallic superlattice, using x-ray and neutron diffraction. We find a sharp and broad rocking curves around the first order Bragg peak, and attribute them to a columnar structure which gives rise to two modulation structures; one the ordinary layered structure within the columns and the other the averaged modulation structure which produces the sharp rocking peak.

Interface Induced Loss of Coherence in Superlattices

Extending our x-ray diffraction results obtained on amorphous/crystalline multilayers, we model the disorder at the interface of multilayered structures. In an actual x-ray scattering experiment, peak positions are related to atomic and layer periodicities (using Bragg’s equation), while linewidths are related (using Scherrer’s equation) to the number of scatterers whose positions obey these periodicities. The “coherence length”, evaluated for a periodicity, is this number times the periodicity. Assuming a perfect atomic structure of both materials in the multilayer, all loss of range order is induced by fluctuations at the interface. These fluctuations are either continuous variations in the distance between the two materials, and (or) are discrete variations in the number of atoms building up each layer, both giving rise to “roughness”. Obviously the latter will mainly influence the long range periodicities, while the small range periodicities (corresponding to high angle diffraction peaks) conserve their coherence length.

The Effect of Interfacial Disorder on the X-Ray Diffraction of Superlattices

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 A, and relate it to the lattice mismatch between Nb and Cu. For crystalline/amorphous systems (Pb/Ge) this amplitude can be significantly larger (2 A).