All-Quantum-Dot Multilayer LEDs Prepared Using Layer-by-Layer Solution Processing Show High Brightness
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catalog of 388 individual grain boundaries in pure nickel. At a given temperature they found that each grain boundary was either a smooth atomic-structured boundary with very low mobility, or rough atomic-structured boundaries with high mobility. After reaching a transition temperature, which differs from boundary to boundary, the grain boundary structure changes from smooth to rough and the mobility decreases. Holm and Foiles applied these data to a mesoscale simulation for a polycrystalline microstructure using the Monte Carlo Potts model for grain growth. When smooth/slow bound-
All-Quantum-Dot Multilayer LEDs Prepared Using Layer-by-Layer Solution Processing Show High Brightness The quest for cheap and energy-efficient lighting and light-emitting displays has resulted in robust efforts to develop technologies for light-emitting diodes (LEDs). The use of quantum dots (QDs) in LEDs offers the advantages of high color purity and easy tunability of emission. High brightness has been achieved with very thin QD layers (one-to-two monolayers), but challenges in research on QD LEDs remain. Increasing the devices’ lifetime, brightness, and homogeneous deposition over large areas, as well as avoiding the use of toxic materials, would make them serious alternatives to organic devices. W.K. Bae, K.H. Char, C.H. Lee, S.H. Lee, and co-workers from the Seoul National University have recently demonstrated the large-area deposition of multicolored allQD (QDs with core and chemical composition gradient shell structure—mostly CdSe/ZnS) LEDs prepared by the spinassisted layer-by-layer assembly method. As reported in the July 14th issue of Nano Letters (DOI: 10.1021/nl100168s; p. 2368), the research team fabricated allquantum-dot LEDs with well-controlled vertical and horizontal structures. Quantum dots were treated with cysteamine (CAm) or mercaptopropionic acid (MPA) and dispersed in water to obtain positive and negative charges on the surface of the nanocrystals. Alternate spincoating depositions of positively and negatively charged nanocrystals allowed the build-up of multilayered thin films con-
2011 MRS Spring Mee Meeting eting April 25-29, 2011 San Fran cisco, Californ ia Francisco, California
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aries are present, the researchers found that grain growth plateaus at a finite grain size value which decreased as the fraction of smooth/slow boundaries increases. In addition, they found that stagnant grain size increases with temperature. These results suggested that the boundary roughening transition could influence grain growth stagnation. Holm and Foiles performed another MD simulation, a grain growth in a realistic three-dimensional nanocrystalline nickle grain structure. At the temperatures analyzed, simulation results showed that after a short initial transient state, normal grain
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growth occurs. However, after some time, grain growth slows and grain size appears to stagnate. Moreover, the stagnant grain sizes observed were consistent with results from mesoscale simulations. Simulation results from different method
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