3 research outputs found
Highly Enhanced Light-Outcoupling Efficiency in ITO-Free Organic Light-Emitting Diodes Using Surface Nanostructure Embedded High-Refractive Index Polymers
We
develop the high-performance internal light-outcoupling (HRLOC) system
based on the high-refractive index polyimide (PI) and metal oxide
nanoparticles for organic light-emitting diodes (OLEDs) with silver
nanowires (AgNWs). The spontaneously formed nanobump structures, high
refractive index, and light-scattering properties of HRLOC significantly
enhance the light-extraction efficiency of OLEDs. Not only do the
outcoupling structures improve the light-extraction efficiency, but
also remarkably enhance the electrical properties of OLEDs. HRLOC
leads to the regular and smooth formation of AgNWs, resulting in the
improvement of the electrical properties of devices by preventing
electrical shorts and leakage currents. The power efficiency of the
AgNW-based OLEDs with PI is improved by a factor of 1.31 compared
to the reference device with indium tin oxide (ITO) transparent electrode
at a luminance of 20 000 cd/m<sup>2</sup>. The efficiency is
further improved by incorporating TiO<sub>2</sub> nanoparticles into
the PI matrix by a factor of 1.69. To our knowledge, the optically
and electrically enhanced OLEDs show one of the highest enhancement
factors reported for ITO-free OLEDs with internal outcoupling structures.
In addition, the outcoupling structures are solution processable,
thermally stable, and can be scaled up to 200 Ă— 200 mm<sup>2</sup> for large-area applications. We believe that the light-outcoupling
structures developed here have great potential for efficient, low-cost,
and flexible ITO-free OLEDs
Rapid, Microwave-Assisted Synthesis of Cubic, Three-Dimensional, Highly Porous MOF-205 for Room Temperature CO<sub>2</sub> Fixation via Cyclic Carbonate Synthesis
A dual-porous, three-dimensional,
metal–organic framework [Zn<sub>4</sub>OÂ(2,6-NDC)Â(BTB)<sub>4/3</sub>] (MOF-205, BET = 4200 m<sup>2</sup>/g) has been synthesized
using microwave power as an alternative energy source for the first
time, and its catalytic activity has been exploited for CO<sub>2</sub>–epoxide coupling reactions to produce five-membered cyclic
carbonates under solvent-free conditions. Microwave synthesis was
performed at different time intervals to reveal the formation of the
crystals. Significant conversion of various epoxides was obtained
at room temperature, with excellent selectivity toward the desired
five-membered cyclic carbonates. The importance of the dual porosity
and the synergistic effect of quaternary ammonium salts on efficiently
catalyzed CO<sub>2</sub> conversion were investigated using various
experimental and physicochemical characterization techniques, and
the results were compared with those of the solvothermally synthesized
MOF-205 sample. On the basis of literature and experimental inferences,
a rationalized mechanism mediated by the zinc center of MOF-205 for
the CO<sub>2</sub>–epoxide cycloaddition reaction has been
proposed
Atomic Layer Etching Mechanism of MoS<sub>2</sub> for Nanodevices
Among
the layered transition metal dichalcogenides (TMDs) that can form
stable two-dimensional crystal structures, molybdenum disulfide (MoS<sub>2</sub>) has been intensively investigated because of its unique
properties in various electronic and optoelectronic applications with
different band gap energies from 1.29 to 1.9 eV as the number of layers
decreases. To control the MoS<sub>2</sub> layers, atomic layer etching
(ALE) (which is a cyclic etching consisting of a radical-adsorption
step such as Cl adsorption and a reacted-compound-desorption step
via a low-energy Ar<sup>+</sup>-ion exposure) can be a highly effective
technique to avoid inducing damage and contamination that occur during
the reactive steps. Whereas graphene is composed of one-atom-thick
layers, MoS<sub>2</sub> is composed of three-atom-thick S<sub>(top)</sub>î—¸Mo<sub>(mid)</sub>î—¸S<sub>(bottom)</sub> layers; therefore,
the ALE mechanisms of the two structures are significantly different.
In this study, for MoS<sub>2</sub> ALE, the Cl radical is used as
the adsorption species and a low-energy Ar<sup>+</sup> ion is used
as the desorption species. A MoS<sub>2</sub> ALE mechanism (by which
the S<sub>(top)</sub>, Mo<sub>(mid)</sub>, and S<sub>(bottom)</sub> atoms are sequentially removed from the MoS<sub>2</sub> crystal
structure due to the trapped Cl atoms between the S<sub>(top)</sub> layer and the Mo<sub>(mid)</sub> layer) is reported according to
the results of an experiment and a simulation. In addition, the ALE
technique shows that a monolayer MoS<sub>2</sub> field effect transistor
(FET) fabricated after one cycle of ALE is undamaged and exhibits
electrical characteristics similar to those of a pristine monolayer
MoS<sub>2</sub> FET. This technique is also applicable to all layered
TMD materials, such as tungsten disulfide (WS<sub>2</sub>), molybdenum
diselenide (MoSe<sub>2</sub>), and tungsten diselenide (WSe<sub>2</sub>)