Microscale or nanoscale patterns with specific structures on sapphire substrate can effectively reduce the dislocation defects of gallium nitride (GaN) material and improve the quality of gallium nitride crystal during the epitaxy growth of GaN-based light-emitting diodes, thus improving the internal quantum efficiency of LED luminescence. Numbers of methods have been used to fabricated patterned sapphire substrate. But most methods remain on the micron scale. In this work, the nickel annealing technique was introduced to fabricate a novel sapphire substrate, Hierarchical Patterned Sapphire Substrate (HPSS), which has typical characteristics of nano sapphire pillars on a Micro-Patterned Sapphire Substrate (MPSS) used for GaN-based Light-Emitting Diodes (LEDs). Nano-pillars with an average feature size of about 110 nm and feature surface density of ⪆2.339×109 cm-2 were obtained on commercial MPSS through this method. This nickel annealing technique provides an extremely simple, cost-effective and universal method to fabricate hierarchical patterns with two-inch wafer-scale. What’s more, the substrates can be not only sapphire but also extended to silicon, quartz and other heat-resisting materials which are widely used in photoelectric devices and micro/nanofabrication, making it a promising method to fabricate patterned substrate for industrial applications.
Here we report a series of molecular dynamics simulations to explore the hydrogen bonds (HBs) behavior of ethylammonium nitrate (EAN) protic ionic liquid(IL)-water mixtures with different concentrations at the interface with POPC bilayers. Our simulation results clearly demonstrate that the POPC–H2O and POPC–EA+ HBs are strongest among all kinds of HBs, so that all of the EA+–NO-3, EA+–H2O, NO3––H2O, and H2O–H2O HBs at the interface are enhanced compared to those in the bulk phase. Specifically, the order of these HB strength at the interface is POPC–H2O > POPC– EA+ > H2O–H2O < NO-3 –H2O < EA+–H2O > EA+–NO-3 HBs. Furthermore, increasing EAN concentration can be favorable to a further enhancement of all these HB strength at the interface, which lead to slower rotations of EA+, NO-3, and H2O as the EAN concentration increases. Accordingly, the relevant HB networks around the EA+, NO-3 and H2O are also found to change considerably with the addition of EAN protic ionic liquid. Our simulation results in this work provide some molecular-level insights into the concentration-dependent HB behavior of protic ionic liquid-water mixtures at the interface of phospholipid bilayer, which is of great importance for scientist to understand the influence of ionic liquid on the function of cell membranes.
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