Most of the artificial superhydrophobic surfaces that have been fabricated to date are not biodegradable, renewable, or mechanically flexible and are often expensive, which limits their potential applications. In contrast, cellulose, a biodegradable, renewable, flexible, inexpensive, biopolymer which is abundantly present in nature, satisfies all the above requirements, but it is not superhydrophobic. Superhydrophobicity on cellulose paper was obtained by domain-selective etching of amorphous portions of the cellulose in an oxygen plasma and subsequently coating the etched surface with a thin fluorocarbon film deposited via plasma-enhanced chemical vapor deposition using pentafluoroethane as a precursor. Variation of plasma treatment yielded two types of superhydrophobicity : "roll-off" (contact angle (CA), 166.7 degrees +/- 0.9 degrees ; CA hysteresis, 3.4 degrees +/- 0.1 degrees ) and "sticky" (CA, 144.8 degrees +/- 5.7 degrees ; CA hysteresis, 79.1 degrees +/- 15.8 degrees ) near superhydrophobicity. The nanometer scale roughness obtained by delineating the internal roughness of each fiber and the micrometer scale roughness which is inherent to a cellulose paper surface are robust when compared to roughened structures created by traditional polymer grafting, nanoparticle deposition, or other artificial means.

Silicon surface hydrophobicity has been varied by using silane treatments on silicon pyramid surfaces generated by KOH anisotropic etching. Results demonstrated that by altering the surface hydrophobicity, the apparent contact angle changed in accord with the Wenzel equation for surface structures with inclined side walls. Hierarchical structures were also constructed from Si pyramids where nanostructures were added by Au-assisted electroless HF/H2O2 etching. Surface hydrophobicity and superhydrophobicity were achieved by surface modification with a variety of silanes. Stability of the Cassie state of superhydrophobicity is described with respect to the Laplace pressure as indicated by the water droplet meniscus in contact with the hierarchical structures. The contact angle hysteresis observed is also discussed with respect to water/substrate adhesion.

The removal of copper oxide using acetic acid at low temperatures was investigated. Acetic acid removes a variety of copper oxides, including cuprous oxide, cupric oxide, and cupric hydroxide without attacking the underlying copper film. The removal of these oxides was determined by X-ray photoelectron spectroscopy. Acetic acid can tolerate up to 4 vol % water dilution without hindering the oxide removal while producing an oxide-free surface. However, if a deionized water rinse is performed after an acetic acid treatment, a surface film of cupric hydroxide forms immediately. An acetic acid treatment at 35°C without a water rinse removes the native copper oxide and produces an oxide-free, streak-free copper surface.

No abstract

The gas-phase kinetics and plasma chemistry of high density oxygen discharges are studied. A self-consistent spatially averaged model is developed to determine positive ion, negative ion, and electron densities, ground state and metastable free radical densities, and electron temperature as functions of gas pressure, microwave input power, and cylindrical source diameter and length. For an electron cyclotron resonance discharge, the reduction in radial transport due to the confining magnetic field is also modeled. The kinetic scheme includes excitation, dissociation, and ionization of neutrals due to electron impact, electron attachment and detachment, and ion-ion neutralization. In addition, ion neutralization at the reactor walls is included. Model results show that for a low neutral pressure, high plasma density discharge, oxygen molecules are almost completely dissociated to form oxygen atoms, and the dominant positive ion is O § rather than Q. The metastable species are not important for the pressure range studied (0.5 to 100 mTorr), and the confining magnetic field significantly affects the plasma chemistry, the total positive ion density, and the electron temperature. Comparisons are made with experimental data, and qualitative agreement between experiment and model is observed.