We investigate two types of internal light-extraction layer structures for organic light-emitting diodes (OLEDs) that consist of silica nanoparticles (NPs) embedded in high-refractive-index TiO₂ matrices. The composite of silica NPs and TiO₂ matrices was coated on the glass substrate and fabricated with and without a SiO₂ planarization layer. An increase in the optical out-coupling efficiency by a factor of 2.0 was obtained at a high luminance of 3,000 cd/m² from OLEDs containing the silica NPs embedded in TiO₂ matrices between glass substrates and Zn-doped In₂O₃ (IZO) electrodes after additional planarization processes. This is consistent with the analytical result using the finite-difference time-domain (FDTD) method. Randomly distributed silica NPs acting as scattering centers could reduce the optical loss when extracting light. By using additional planarization processes with a PECVD-derived SiO₂ layer, one can assure that smoother surfaces provide higher out-coupling efficiency, which attain 100% and 97% enhancements in power (lm/W) and current (cd/A) efficiencies, respectively.
A sliding object on a crystal surface with a nanoscale contact will always experience stick-slip movement. However, investigation of the slip motion itself is rarely performed due to the short slip duration. In this study, we performed molecular dynamics simulation and frictional force microscopy experiments for the precise observation of slip motion between a graphene layer and a crystalline silicon tip. The simulation results revealed a hierarchical structure of stick and slip motion. Nanoscale stick and slip motion is composed of sub-nanoscale stick and slip motion. Sub-nanoscale stick and slip motion occurred on a timescale of a few ps and a force scale of 10(-1) nN. The relationship between the trajectories of the silicon tip and stick-slip peak revealed that in-plane and vertical motions of the tip provide information about stick and slip motion in the sub-nanoscale and nanoscale ranges, respectively. Parametric studies including tip size, scan angle, layer thickness, and flexibility of the substrate were also carried out to compare the simulation results with findings on lateral force microscopy.
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