Helga Hildebrand

Selective palladium electrochemical deposition onto AFM-scratched silicon surfaces

The present work investigates the selective electrochemical deposition of palladium nano-structures into scratches produced through thin oxide layers covering p -Si (1 0 0) surfaces. Using an atomic force microscope equipped with a single-crystalline diamond tip scratches in the 100 nm range were produced through a 10 nm thick dry oxide layer. Pd deposition was carried out in PdCl2 (0.01 g l � 1 )� /HCl (0.1 M) by cathodic potential steps. Investigation of the palladium nucleation and growth processes onto silicon surfaces is presented. Under optimized conditions sub-100 nm palladium structures can be obtained with a very high selectivity. # 2003 Elsevier Ltd. All rights reserved.

Challenges in the surface analytical characterisation of anodic TiO2 films : a review

Abstract Surface analytical findings of thick anodic passive layers on titanium are discussed and analysed in order to give a critical overview about possible artefacts for the system Ti/TiO2. In line with previous studies, the pretreatment of the surface can have an influence on the morphology of the passive film. On polycrystalline surfaces, the oxide film shows a different composition and morphology on differently oriented grains, but although the crystallographic orientation of the substrate influences the thickness and the morphology of the passive layer the defect density does not seem to depend so strongly on the substrate condition. Ion sputtering strongly alters the TiO2 surface morphology and composition which can be directly seen in SEM images of the surface and indirectly from the change in XPS spectra throughout a sputter depth profile. The material removal is not homogeneous and sputtering leads to reduction of the surface oxide. In AES experiments the passive layer on titanium undergoes changes induced by the primary electron beam that is used for the analysis. All these effects make the Ti/Ti-oxide a challenging system particularly when employing surface analytical methods for its investigation. Recent developments like the growth of nanotube structures on titanium give the system a renewed importance.

A significant cathodic shift in the onset potential of photoelectrochemical water splitting for hematite nanostructures grown from Fe–Si alloys

Thermal oxidation of Fe to nanostructured hematite (wires, flakes) is currently widely investigated to produce efficient photoanodes for photoelectrochemical water splitting. The process carried out on pure iron, however, has the key drawback that not only hematite but a layered structure of Fe2O3–Fe3O4–FeO is formed where the thick suboxide layer underneath the Fe2O3 is highly detrimental to the photoresponse. In the present work, we show that suboxide formation can be largely suppressed if hematite nanowires/nanoflakes are thermally grown on Fe–Si alloys. For hematite structures grown on a Fe–Si alloy with 5 at% Si, a photocurrent onset potential as low as 0.6 VRHE can be reached (under AM 1.5 illumination and 1 M KOH). We believe that the results represent a key finding towards the formation of optimized hematite nanostructures using a thermal oxidation method.

Metal-insulator transition in nanocomposite VOx films formed by anodic electrodeposition

The ability to grow VO2 films by electrochemical methods would open a low-cost, easily scalable production route to a number of electronic devices. We have synthesized VOx films by anodic electrodeposition of V2O5, followed by partial reduction by annealing in Ar. The resulting films are heterogeneous, consisting of various metallic/oxide phases and including regions with VO2 stoichiometry. A gradual metal insulator transition with a nearly two order of magnitude change in film resistance is observed between room temperature and 140 °C. In addition, the films exhibit a temperature coefficient of resistance of ∼ −2.4%/ °C from 20 to 140 °C.

Electron Beam Induced Writing of Corrosion Protection

Carbon patterns (C layers) were deposited on iron surfaces by electron-beam induced contamination decomposition writing. Chemical and electrochemical etching were used to investigate the protective nature of these C layers against metal corrosion. The results clearly show that E-beam written C patterns can be very corrosion resistant. The key factor controlling the degree of protectiveness, under given conditions of attack, is the deposition dose, i.e., the layer thickness. For sufficiently high doses, the iron surface can be completely protected against corrosion. Therefore, this direct masking approach opens new perspectives for highly precise and controlled local corrosion suppression.

Effect of Al on the passivity of Ti base implant alloys

Abstract The influence of Al as an alloying element in Ti on the passive behavior was studied. Fast open-circuit activation of native passive films on Ti-6A1-4V, Ti-6Al-7Nb and Ti-50A1 - in contrast to commercially-pure Ti - takes place in 0.5 M H2SO4. Passivation in an acidic solution, however, leads to a higher protectiveness of the passive films, as well as to a higher stability against open-circuit activation. Surface analytical experiments were carried out, with the aim to correlate the composition of the passive film with its stability (resistance against activation in acidic solutions) and protective quality.