The surface passivation effect of SF6 plasma on ZnO films for application in polymer solar cells is demonstrated.

Room-temperature deep Si etching using time-multiplexed deep reactive ion etching (DRIE) processes is investigated to fabricate ultra-high aspect ratio Si nanowires (SiNWs) perpendicular to the silicon substrate. Nanopatterning is achieved using either top-down techniques (e.g. electron beam lithography) or colloidal polystyrene (PS) sphere self-assembly. The latter is a faster and more economical method if imperfections in diameter and position can be tolerated. We demonstrate wire radii from below 100 nm to several micrometers, and aspect ratios (ARs) above 100:1 with etching rates above 1 μm min(-1) using classical mass flow controllers with pulsing rise times of seconds. The mechanical stability of these nanowires is studied theoretically and experimentally against adhesion and capillary forces. It is shown that above ARs of the order of 50:1 for spacing 1 μm, SiNWs tend to bend due to adhesion forces between them. Such large adhesion forces are due to the high surface energy of silicon. Wetting the SiNWs with water and drying also gives rise to capillary forces. We find that capillary forces may be less important for SiNW collapse/bending compared to adhesion forces of dry SiNWs, contrary to what is observed for polymeric nanowires/nanopillars which have a much lower surface energy compared to silicon. Finally we show that SiNW arrays have oleophobic and superoleophobic properties, i.e. they exhibit excellent anti-wetting properties for a wide range of liquids and oils due to the re-entrant profile produced by the DRIE process and the well-designed spacing.

A new concept of radio frequency (rf) driven atmospheric pressure dielectric barrier discharge source based on printed circuit board (PCB) is proposed for efficient and uniform large area processing of polymeric surfaces. The source comprises a perforated PCB with a metal electrode and an optional metallic (Cu) grid on its two surfaces. The source was characterized using electromagnetic simulations and electrical measurements. Different source configurations were compared concerning the existence of a Cu grid into the PCB configuration and also the cases of grid being powered or floating. Electric field simulations showed enhanced electric field peak values with the grid addition, especially for the powered grid configuration, and also high electric field uniformity over the discharge area. The electrical measurements in helium plasma confirmed that the grid existence resulted in lower breakdown voltages and higher power dissipation. Etching rate and water contact angle measurements in plasma treated poly(methyl methacrylate)/PMMA films were performed to evaluate the source efficiency in polymer processing. The etching rate increased almost two times in the presence of a grid, reaching values around 65 nm min −1 in pure He. An optimum water contact angle of 27.4° was achieved after plasma treatment with the powered grid source and this value increased to 33° after four weeks of storage indicating the enhanced hydrophilization stability.

Tuning the transition between stable hydrophilicity and high etching-rate and simultaneous hydrophilization of polymethylmethacrylate (PMMA) films was achieved in an open-air environment simply by adjusting the O2 content in He gas injection through the showerhead-type electrode of a novel atmospheric pressure dielectric barrier discharge source. A comparative study was performed for He and He-O2 plasma treatment of PMMA. Electrical and optical measurements indicated severe alteration of plasma characteristics when O2 is added in gas feed. The enhancement of oxygen emission band intensities indicates an enhanced concentration of atomic oxygen, resulting in very high PMMA etching rates of ∼320 nm/min, ∼four times higher compared to pure He. In contrast, the He plasma showed higher nitrogen emission band intensities, translated into a higher nitrogen content on the PMMA surface according to x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. This enhanced nitrogen content due to the partial substitution of ester groups of the PMMA side chain with amide groups was responsible for the more efficient hydrophilization of the PMMA surface. A water contact angle as low as ∼28° was achieved, stabilizing at ∼40° after 10 days and remained constant at least for 45 days, significantly lower than that for the untreated PMMA (∼69°).