P. Evans

Electrocatalytic Properties of Ni-Based Alloys Toward Hydrogen Evolution Reaction in Acid Media

The electrocatalytic performance toward the hydrogen evolution reaction (HER) of a series of Ni-based alloys prepared by electroless deposition was studied by means of linear polarization, cyclic voltammetry, and potential step techniques. Ni-W-P and Ni-Mo-P alloy electrodes exhibit good electrocatalytic activity toward HERs, with some Ni-Mo-P alloys approaching the performance of Pt foils. The electrocatalytic activity of Ni-based alloys decreases with increasing P content but increases with increasing content of W or Mo. The experimental results can be interpreted in terms of a pronounced synergy between Ni, which has internally paired d electrons, and W or Mo, which have empty or half-filled d orbitals and therefore, bind hydrogen atoms strongly. The absorption of hydrogen in these alloys is also found to have an important effect on their activity. Electrodes with higher activity are capable to incorporate larger amounts of hydrogen during cathodic charging.

Selective metal electrodeposition through doping modulation of semiconductor surfaces

We demonstrate selective electrodeposition of magnetic layers on doped semiconductors resulting in a self-aligned pattern which replicates the doping pattern in the semiconductor surface. A Schottky barrier forms at the interface between a semiconductor substrate and the electrolyte, which upon application of a cathodic potential is biased in the forward (reverse) direction for n- or p-type semiconductors, respectively. Electron transfer from an n-type semiconductor is thus possible, while breakdown of the Schottky barrier would be necessary for deposition on a p-type substrate. The process will thus be spatially selective on a lateral modulation of the substrate doping. As an example we demonstrate the deposition of Co on GaAs.

Electrodeposited Co-Fe and Co-Fe-Ni alloy films for magnetic recording write heads

The electrodeposition of Co-Fe and Co-Fe-Ni alloys from electrolytes without any organic additives is explored. For Co-Fe alloys, the effect of the ratio of Co and Fe concentrations in the electrolyte on the composition and magnetic properties of the deposits is examined. A maximum saturation magnetization of 20.4 kG is obtained, however the films showed high coercivity (20 to 30 Oe). The addition of Ni to the solution leads to much improved soft magnetic properties. A Fe-rich alloy, Co/sub 19/Fe/sub 52/Ni/sub 29/ showed a saturation magnetization of 20.5 kG, a coercivity of about 1 Oe and saturation magnetostriction /spl lambda//sub s/, about 10/sup -6/. Best soft magnetic properties are obtained when BCC and FCC phases are seen to coexist. The films show good stability of magnetic properties upon easy axis annealing up to 200/spl deg/C. Magnetic force microscopy showed the domain pattern to be a ripple structure for films with positive magnetostriction, changing to a stripe domain structure with increasing Ni content. This corresponds to a change in sign of the magnetostriction.

Sharp ferromagnet/semiconductor interfaces by electrodeposition of Ni thin films onto n-GaAs(001) substrates

We report on the chemical, electrical, and magnetic properties of Ni/GaAs(001) interfaces prepared using electrodeposition. Electrodeposition is an equilibrium process which thus releases much less energy per absorbed atom than other deposition techniques. This allows preparation of chemically sharp interfaces which otherwise show a high degree of reactivity and interdiffusion. This is demonstrated by the example of Ni grown on GaAs(001). Photoelectron spectroscopy shows the absence of surface segregation of substrate material or diffusion into the Ni layer. This is confirmed by the electrical and magnetic properties of the films.

Electrodeposited, high-moment magnetic alloys for recording write heads

The magnetic and structural properties of Fe-Co-Ni alloys electrodeposited from solutions containing no organic additives have been investigated. The range of compositions corresponding to high moment and low coercivity is seen to correspond closely with the range of compositions where the films show a mixed FCC-BCC phase structure. The best films showed B, values in excess of 20 kG with H c < 2Oe and low magnetostriction.

Structure and magnetic properties of electrodeposited Ni films on n-GaAs(001)

We report the structural and magnetic properties of Ni films grown on GaAs(001) using electrodeposition, covering the thickness range 0–80 nm. The structure is characterized by mixed (001) and (011) epitaxial orientation of fcc Ni with a preference for the Ni(001) orientation. The magnetic anisotropy is originated by a combination of a crystalline contribution with fourfold symmetry and a uniaxial anisotropy probably caused by the asymmetry in the substrate surface structure. The saturation magnetic moment varies linearly with thickness, indicating limited intermixing between Ni film and GaAs substrate. This is ascribed to the low-energy deposition process characteristic of electrodeposition.

Evolution of interface properties of electrodeposited Ni/GaAs(001) contacts upon annealing

We demonstrate how epitaxial FM (Ni) films can be grown by ECD directly onto GaAs(001) without outdiffusion or surface segregation of As or Ga. The thickness dependence of electrical and magnetic properties (saturation magnetic moment) verify the good quality of the layers and indicate that electrochemical deposition is a suitable candidate for the growth of epitaxial Ni films with sharp interfaces on GaAs(001). X-ray photoelectron spectroscopy (XPS) analysis on electroplated (epitaxial) Ni films showed no interdiffusion for annealing up to 250 °C. Annealing at higher temperatures, up to 350 °C, significantly increases both the As outdiffusion and the Schottky barrier heights, which indicates the correlation between intermixing and the diode quality.

Photoexcited electrodeposition of Cu structures on p-Si(001)

Selective growth of metals on semiconductors has recently raised considerable interest due to its possible application in the direct formation of conduction paths and contacts on semiconductors. We produced small structures by photoexcited electroless plating of Cu on p-type Si(001). The p-type substrate forms a Schottky barrier with the solution which inhibits the plating process. Local illumination creates minority carriers which become available to discharge metal ions. Illumination was done by converging a 1–5 mW laser beam to a 1–2 μm focus diameter on the substrate in the plating solution using an optical microscope. The dimensions of the dots are determined by the diffusion length of the excited minority carriers. We analyzed the diameter of the growing dots as a function of the laser light wavelength and intensity, illumination duration, composition of the solution and charge carrier lifetime in the substrate. The lateral dimensions of the structures produced are found to decrease with reduced las...

Epitaxial growth and magnetic anisotropy of electrodeposited Ni and Co thin films grown on n-type GaAs

Summary form only given. Ferromagnetic films on semiconductors can be used in the fabrication of magnetic sensors, memories, and novel devices based on spin-dependent transport phenomena. Electrochemical deposition offers some advantages with respect to UHV techniques for the growth of these structures, such as the low temperature processing, which can limit the interdiffusion between the film and substrate, thus creating well defined interfaces. We have studied the electrochemical growth and magnetic anisotropy of Ni and Co on [001]- and [011]-oriented n-GaAs.