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The valence band structure of well-ordered Fe3O4(0 0 1) films was investigated in situ by angle-resolved photoemission spectroscopy (ARPES) at room temperature (RT) and 90 K. A band gap of about 70 meV below the Fermi level (E F) can be observed at 90 K, suggesting a ‘metal–insulator’ transition. With temperature reduced from RT to 90 K, O 2p-derived features shown in ARPES spectra change substantially. Meanwhile, the feature near E F of the Fe3O4(0 0 1) film at 90 K becomes about 0.1 eV deeper than that at RT. The results are compared with recent theoretical studies.

Fabrication of micrometer-sized, three-dimensional ͑3-D͒ Ni/Cu multilayered structures consisting of a stack of different sized disks using a wet process is investigated. A cylindrical micrometer-sized Ni/Cu multilayered structure is first fabricated using electroplating aided by photolithography, with Ni layers in the resulting structure then selective etched. The behavior of the oxidative dissolution of Ni and Cu films was studied electrochemically. Parameters for Ni film deposition were chosen to produce a film with a smooth surface morphology that was resistant to passivation by adding S to the plating bath. Cu film parameters were chosen to give a Cu layer with a smooth surface morphology. This allowed Ni layers in the Ni/Cu multilayered structures to be selectively etched under potentiostatic condition in sulfuric acid.Fabrication of metallic microstructures by electrodeposition processes such as the lithography, electroplating, molding process has been investigated in recent years. 1-11 Sacrificial materials are commonly used in fabrication of three-dimensional ͑3-D͒ microstructures to produce sacrificial volumes. [12][13][14][15][16][17][18][19] Schwartz et al. reported on the in situ formation of a sacrificial layer in electrodeposited FeNi alloys using a pulsed electrolyte agitation technique to fabricate 3-D microstructures. 20 The present authors previously reported the fabrication of micrometer-sized, 3-D Cu/Ni multilayered structures consisting of a stack of different sized disks using a wet process with the aid of photolithography. 21 To control the shape of the micrometer-sized structures, multilayered structures were fabricated by electroplating followed by selective chemical etching of Cu layers using an acidic thiourea solution.An attempt to fabricate similar micrometer-sized, 3-D Ni/Cu multilayered structures by selective etching of Ni layers is presented in this paper. Multilayered microstructures like these can be expected to be used, for example, as a microradiator. In particular, as Cu has large thermal conductivity, these structures are suitable for use in radiators.The standard redox potentials of Ni 2ϩ ϩ 2e Ϫ ϭ Ni and Cu 2ϩ ϩ 2e Ϫ ϭ Cu are Ϫ0.25 V vs. saturated hydrogen electrode ͑SHE͒ and ϩ0.34 V vs. SHE, respectively. Because of this, Ni layers of Ni/Cu multilayered structures would be expected to selectively dissolve into Ni 2ϩ in an acidic solution. However, Ni is susceptible to passivation and therefore does not dissolve easily in an acidic solution. The passivation of Ni has been reported to be restricted in the presence of Cl Ϫ . 22,23 Therefore, Ni is expected to dissolve oxidatively into an acidic solution containing Cl Ϫ , such as HCl solution. However, in the presence of dissolved oxygen, Cu is also susceptible to oxidative dissolution in HCl solution. Passivation of Ni has been found to be inhibited by the addition of sulfur, 24-28 and electrodeposition of a passivation-resistant Ni film containing S from a plating bath containing colloidal S has been reported previously. 29...

Nickel plating containing intentionally introduced S was produced to obtain Ni film that is resistant to passivation, and the oxidative dissolution of the film was investigated. Dull Watt's and bright Watt's baths were used as base baths. In order to prepare the plating baths for the production of S-containing Ni films, colloidal S formed by decomposition of Na 2 S 2 O 3 was dispersed into the base baths. The colloidal S dispersion allowed Ni films with high S contents to be obtained from these baths, with a maximum S content of 3.8 atom % achieved. The Ni films produced using the plating baths containing dispersed colloidal S inhibited the passivation of the Ni films, with this suppression increasing with increasing S content. The Ni film obtained from the bright Watt's bath had higher concentration of S relative to the Ni film obtained from the dull Watt's bath and inhibited the passivation more strongly.

Structural and magnetic properties, and the valence band structure of pure and Co-doped (up to 33%) Fe3O4(100) films were investigated. Reconstruction of the Fe3O4(100) surface is found to be blocked by Co doping. Doped Co ions in Fe3O4 are in a charge state of 2 + and substitute the Fe2+ in the B site of Fe3O4. All the films exhibit room temperature ferromagnetism. Co doping changes the coercivity and reduces saturation magnetization. The density of states near the Fermi level is reduced by Co doping due to the decrease of Fe2+ in the B site, which might responsible for the decrease in conductivity and magnetoresistance of Co-doped Fe3O4. The Verwey transition in the range of 100–120 K is observed for the pure Fe3O4 film, while no transition could be detected for Co-doped Fe3O4 films.