Masatoshi Saitou

Amorphous Structures and Kinetics of Phosphorous Incorporation in Electrodeposited Ni-P Thin Films

Microstructures and mechanisms of phosphorous incorporation into electrodeposited Ni-P thin films are studied using X-ray diffraction (XRD) and electron probe microanalyzer (EPMA). An atomic pair distribution function calculated from the XRD pattern exhibits the nearest neighbor distance of 2.5 A and a split double peak at the second neighbor distance that is observed in amorphous structures. The electrodeposited Ni-P alloy is found to have an amorphous structure similar to rapid-quenched Ni-P alloys. The phosphorous concentrations in the Ni-P deposits measured by EPMA decrease with an increase in current densities. The dependence of the phosphorous concentration on the current density is analyzed with respect to the kinetics of chemical reactions in Ni-P electrodeposition. The experimental result agrees well with a solution of rate equations that describe the indirect incorporation of phosphorous.

Surface Roughening in the Growth of Direct Current or Pulse Current Electrodeposited Nickel Thin Films

The surface roughening in the growth of direct current or pulse current electrodeposited nickel thin films at a low current density is investigated using atomic force microscopy (AFM). The growth exhibits scaling behaviors characterized by the roughness exponent a and growth exponent β. The analysis of the AFM images of the nickel thin films reveals that (i) for direct current electrodeposition: α = 0.96 and β = 0.78, and (ii) for pulse current electrodeposition: α = 0.92 and β = 0.65. Each value of α for the two techniques is almost in agreement with that predicted by a statistical model of linear diffusion dynamics. X-ray diffraction of the nickel thin films indicates the presence of preferred growth orientations that are related to the growth exponent β > 1/2.

Characterization of electrodeposited nickel film surfaces using atomic force microscopy

Abstract Microstructures of nickel surfaces electrodeposited on indium tin oxides coated glasses are investigated using atomic force microscopy. The fractal dimension D and Hurst exponent H of the nickel surface images are determined from a frequency analysis method proposed by Aguilar et al. [J. Microsc. 172 (1993) 233] and from Hurst rescaled range analysis. The two methods are found to give the same value of the fractal dimension D ∼2.0. The roughness exponent α and growth exponent β that characterize scaling behaviors of the surface growth in electrodeposition are calculated using the height-difference correlation function and interface width in Fourier space. The exponents of α ∼1.0 and β ∼0.8 show that the surface growth does not belong to the universality classes theoretically predicted by statistical growth models.

Scaling behavior of internal stress in electrodeposited nickel thin films

We have investigated the effects of the current density, film thickness, temperature, and additive agent on the internal stress in electrodeposited nickel thin films using a bent strip measurement. The internal stress is found to obey a scaling law expressed in terms of the current density and film thickness. The additive agent is shown to behave as a noise leading to different exponents in the dynamic scaling theory. In addition, the Arrhenius temperature dependence of the internal stress indicates the presence of thermal activation related to grain growth.

Shape and stability of a floating liquid zone between two solids

The shape and stability of a floating liquid zone between two solids are analytically investigated using the principle of variation. The formulas for its shape and stability are obtained.

A Study on Transient Changes of Surface Morphologies in Ag and Sb Coelectrodeposition

We have investigated transient changes in surface morphologies of Ag-Sb electrodeposits. Microscopic images of the Ag-Sb electrodeposits reveal that the surface morphology comprising Sb-poor and Sb-rich Ag deposits are described by a scaling function that is characterized by scaling exponents related to the growth mechanism of the Ag and Sb coelectrodeposition. The values of the scaling exponents indicate that Sb atoms which arrive at electrodes diffuse only in a local area. On the basis of a scenario that perturbations of ion concentrations in the electrolyte caused by Sb electrodeposition develop with time, a condition for the transient changes in the surface morphology is derived using linearized perturbation equations of the rate equations. The experimental results qualitatively support the instability condition.

Novel process for electrodeposition of Bi2S3 thin films

Abstract A novel method for electrochemical deposition of Bi 2 S 3 from an aqueous acid bath comprising Na 2 S 2 O 3 and Bi(NO 3 ) 3 complexed with disodium salt of ethylene diamine tetraacetic acid (Na 2 EDTA) is proposed using SO 3 −2 ions as a sulfur source. For stoichiometric deposition, the initial concentrations of Na 2 S 2 O 3 and Bi(NO 3 ) 3 in the solution are determined from the experimental current–potential relations based on a current model under diffusion control. X-ray diffraction reveals that the deposits have no single substance and compound other than Bi 2 S 3 within experimental uncertainties. This indicates that the system in this study obeys the current model under diffusion control.

Surface Growth of Ni Thin Films Electrodeposited on Ni(100) Surfaces

Surface growth of Ni thin films electrodeposited on Ni(100) substrates has been investigated using atomic force microscopy. In the early stage of growth, islands nucleated on the Ni(100) substrates, which appear to be rectangular in cross section, grow laterally in the same crystallographic orientation. Growth surfaces display a normal scaling behavior characterized by the linear surface diffusion universality class. Along the time evolution, instability in growth occurs and a transition from two- to three-dimensional growth is observed. In this stage, surface growth obeys anomalous scaling characterized by a local roughness exponent ζ loc = 1.0, global scaling exponent ζ = 2.1, and dynamic exponent z = 1.0.

Schwoebel effect and dynamic scaling behavior in nickel film growth by electrodeposition

Abstract Two kinds of growth rate of nickel films prepared by electrodeposition were measured by use of columnar photoresists formed on indium–tin oxide (ITO) glass plates. The ratio of the mean growth rate at the edge to that of the nickel layer was 1.5, which indicates direct evidence for the Schwoebel effect [R.L. Schwoebel, J. Appl. Phys. 40 (1969) 614]; i.e., the presence of anisotropy between the up and down step incorporation probabilities of adatoms. The growth exponent of 0.3 was obtained from atomic force microscopy (AFM) images of the nickel film surface. This suggests that the nickel growth by electrodeposition has a dynamic scaling property.

Anomalous dimension in pitting corrosion of SUS304 in a NaCl solution

The current–potential relations of SUS304 for a NaCl solution in water ranging from 0.01 to 2 mol/dm3 over a 298–333 K temperature range were investigated in order to exhibit the presence of anomalous dimensions that characterize the phase transition such as pitting corrosion. Using the anomalous dimension, all the experimental current points can be represented by a single curve in a reduced variable.