The Surface and Photoluminescence Properties of GaAs Passivated by Wet Chemical Method

The optical and chemical properties of gallium arsenide (GaAs) surfaces treated by ammonium sulfide ((NH4)2S) treatments were studied via low-temperature photoluminescence (PL). From the PL mapping and Atomic Force Microscope (AFM) results, the treatment process by (NH4)2S is quite effective to remove the oxide layer of GaAs.The PL intensity of (NH4)2S-passivated sample was higher than the untreated sample, and the homogeneity of passivated surface was much better. This strategy provides superior promising passivation method for III-V compound semiconductor material in high-speed and optoelectronic device applications.

The Corrosion Resistance of Zn-Plated Samples with Blackish Green Passivation Film

The corrosion resistance of blackishgreen passivation films on zinc-plated steel sheet was studied by polarization curve measurement, electrochemical impedance spectroscopy and neutral salt spray test. The passivated sample featured a more positive corrosion potential and much lower corrosion current density as compared to non-passivated sample in 5% (mass fraction) NaCl solution. The Nyquist plots of the samples with and without passivation were characterized as two complete capacitive arcs, indicating that the corrosion is controlled by electrochemical process. The radii of capacitive arcs of the passivated sample are larger than those of non-passivated sample, because the passivation film formed on the sample surface increases the reaction resistance in corrosion process, thus the corrosion resistance of the sample is improved. The anti-white rust time of the passivation film in neutral salt spray test is 400 h.

The atomic force microscope as a mechano–electrochemical pen

We demonstrate a method that allows the controlled writing of metallic patterns on the nanometer scale using the tip of an atomic force microscope (AFM) as a “mechano–electrochemical pen”. In contrast to previous experiments, no voltage is applied between the AFM tip and the sample surface. Instead, a passivated sample surface is activated locally due to lateral forces between the AFM tip and the sample surface. In this way, the area of tip–sample interaction is narrowly limited by the mechanical contact between tip and sample, and well-defined metallic patterns can be written reproducibly. Nanoscale structures and lines of copper were deposited, and the line widths ranged between 5 nm and 80 nm, depending on the deposition parameters. A procedure for the sequential writing of metallic nanostructures is introduced, based on the understanding of the passivation process. The mechanism of this mechano–electrochemical writing technique is investigated, and the processes of site-selective surface depassivation, deposition, dissolution and repassivation of electrochemically deposited nanoscale metallic islands are studied in detail.