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In this work, immobilization of the often unwanted filaments in dielectric barrier discharges (DBD) is achieved and used for one‐step deposition of patterned coatings. By texturing one of the dielectric surfaces, a discharge containing stationary plasma filaments is ignited in a mix of argon and propargyl methacrylate (PMA) in a reactor operating at atmospheric pressure. From PMA, hydrophobic and hydrophilic chemical and topographical contrasts at sub‐millimeter scale are obtained on silicon and glass substrates. Chemical and physical characterizations of the samples are performed by micrometer‐scale X‐ray photoelectron spectroscopy and infrared imaging and by water contact angle and profilometry, respectively. From the latter and additional information from high‐speed imaging of the plasma phase and electrical measurements, it is suggested that filaments, denser in energetic species, lead to higher deposition rate with higher fragmentation of the precursor, while surface discharges igniting outwards the filaments are leading to smoother and slower deposition. This work opens a new route for a one‐step large‐area chemical and morphological patterning of surfaces at sub‐millimeter scales. Moreover, the possibility to separately deposit coatings from filaments and the surrounding plasma phase can be helpful to better understand the processes occurring during plasma polymerization in filamentary DBD. [ABSTRACT FROM AUTHOR]

Multifunctional polymer surfaces exhibiting both hydrophilic and hydrophobic functionality were created using self-organized plasma "streamer" microdischarges occurring in atmospheric pressure dielectric barrier discharges (DBD) operating with argon and air. Surface chemistry and wettability change of polymethylmethacrylate (PMMA) were found to spatially correlate with self-organized streamer patterns. Gas atmosphere was found to play a significant role on streamer density, pattern stability, and lateral contrast of plasma-induced physicochemical property changes across the surface. Stable streamer patterns, with each streamer surrounded by a glowlike discharge, were obtained in argon; discharges in air had more transient and chaotic streamers that were surrounded by dark "plasma free"-like zones. Air plasma streamer treatment of PMMA resulted in hybrid hydrophilic/phobic surfaces with water contact angles (WCA) ranging from 30° to 100° (PMMA WCA = 75°), depending on processing conditions and location. WCA and XPS mapping after treatment revealed that surface chemistry is preferentially modified near streamers, and moreover, that streamer exposure in air locally renders the surface more hydrophilic, surrounded by regions that are more hydrophobic. Overall, this work demonstrates that self-organized streamers in DBD plasmas could be used for scalable and localized modification of surfaces. [ABSTRACT FROM AUTHOR]

Chemical etching and Al2O3 dielectric passivation were used to minimize nonradiative sidewall defects in InGaN/GaN microLEDs (mesa diameter = 2–100 μm), resulting in an increase in external quantum efficiency (EQE) as the LED size was decreased. Peak EQEs increased from 8%–10% to 12%–13.5% for mesa diameters from 100 μm to 2 μm, respectively, and no measurable leakage currents were seen in current density–voltage (J–V) characteristics. The position and shape of EQE curves for all devices were essentially identical, indicating size-independent ABC model (Shockley–Read–Hall, radiative, and Auger recombination) coefficients-behavior that is not typical of microLEDs as the size decreases. These trends can be explained by enhancement in light extraction efficiency (LEE), which is only observable when sidewall defects are minimized, for the smallest LED sizes. Detailed ray-tracing simulations substantiate the LEE enhancements. [ABSTRACT FROM AUTHOR]