Guided Electro-Optical Switching of Small Graphene Oxide Particles by Larger Ones in Aqueous Dispersion

Ahmad, Rana Tariq Mehmood; Shen, Tong; Masud, Aurangzeb Rashid; Ekanayaka, Thilini K.; Song, Jang‐Kun

doi:10.1021/acs.langmuir.6b03460

Cited by 23 publications

(12 citation statements)

References 35 publications

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“…An aqueous GO dispersion was prepared using the Hummers’ method, following the process that we have recently reported . The GO dispersion was cleaned about 10 times using the centrifuge cleaning method, in order to remove residual ions in the dispersion .…”

Section: Methodsmentioning

confidence: 99%

Reduced Graphene Oxide as Efficient Hole Injection Layer for Quantum‐Dot Light‐Emitting Diodes

Song

Song²,

Shen³

et al. 2018

Physica Status Solidi (a)

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Polyethylene dioxythiophene:polystyrenesulfonate (PEDOT:PSS) is widely used for preparing the solution processable hole injection layer (HIL) in quantumdot light-emitting diodes (QLEDs), but it can cause erosion of the anode, posing a critical issue for long-term stability. Graphene oxide (GO) is a promising candidate to replace PEDOT:PSS, but its performance is somewhat inferior to that of a PEDOT:PSS device. Here, we investigate the effect of reduction in a GO HIL on the hole injection ability and resulting QLED performance. We find that the hole current in reduced GO (rGO) HIL is one order of magnitude larger than that with GO HIL. The greater hole injection ability dramatically improves the current efficiency and external quantum efficiency of an rGO-QLED by more than two times. To verify the underlying mechanism, we analyze the conductivity and energy barriers, and find that both the conductivity and the energy barriers vary depending on the degree of reduction of GO. We conclude that the increasing conductivity dominantly contributes to the improved hole conductivity in rGO layer. Thus, the optimization of reduction in rGO HIL is an excellent approach to solve the anode erosion issue and to improve QLED performance, increasing the potential of applications in QLED devices.

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Section: Methodsmentioning

confidence: 99%

Reduced Graphene Oxide as Efficient Hole Injection Layer for Quantum‐Dot Light‐Emitting Diodes

Song

Song²,

Shen³

et al. 2018

Physica Status Solidi (a)

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“…The relaxation time is defined as the time taken for the system to relax once the electric field is removed. Both the response and relaxation times for graphene oxide dispersions have been found to be just under half a second, depending on the flake size distribution and concentration ( Figure 14) [39,63]. This has been shown to be affected by flake size and in particular the flake size distribution [39,63].…”

Section: Electro-optic Effectsmentioning

confidence: 95%

“…Both of these results were attributed to the higher ionic content of the aqueous dispersion [42] which occurs because the surface functional groups of graphene oxide are easily ionized in aqueous dispersions. The maximum fieldinduced birefringence has been shown to be affected by the flake size and distribution [63] ( Figure 13) but interestingly also the number of cleaning steps taken in the production of the graphene oxide [64]. Figure 13.…”

Section: Electro-optic Effectsmentioning

confidence: 99%

“…Both the response and relaxation times for graphene oxide dispersions have been found to be just under half a second, depending on the flake size distribution and concentration ( Figure 14) [39,63]. This has been shown to be affected by flake size and in particular the flake size distribution [39,63]. The higher the fraction of large flakes (>1 µm) in a mixture which otherwise contains mainly small flakes (<1 µm) the slower the response to electric fields and the slower the relaxation time when the field is removed.…”

Section: Electro-optic Effectsmentioning

confidence: 99%

“…The higher the fraction of large flakes (>1 µm) in a mixture which otherwise contains mainly small flakes (<1 µm) the slower the response to electric fields and the slower the relaxation time when the field is removed. This has been attributed to increased inter-particle friction when larger flakes are present [63]. The time taken for the graphene oxide dispersions to become fully aligned to the electric field is known as the response time.…”

Section: Electro-optic Effectsmentioning

confidence: 99%

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Lyotropic Liquid Crystals from Colloidal Suspensions of Graphene Oxide

Draude

Dierking

2019

Crystals

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Lyotropic liquid crystals from colloidal particles have been known for more than a century, but have attracted a revived interest over the last few years. This is due to the developments in nanoscience and nanotechnology, where the liquid crystal order can be exploited to orient and reorient the anisotropic colloids, thus enabling, increasing and switching the preferential properties of the nanoparticles. In particular, carbon-based colloids like carbon nanotubes and graphene/graphene-oxide have increasingly been studied with respect to their lyotropic liquid crystalline properties over the recent years. We critically review aspects of lyotropic graphene oxide liquid crystal with respect to properties and behavior which seem to be generally established, but also discuss those effects that are largely unfamiliar so far, or as of yet of controversial experimental or theoretical outcome. Crystals 2019, 9, 455 2 of 20 easy to handle, because graphene is largely insoluble in nearly all liquid solvents. This is very different for graphene-oxide (GO) which exhibits different functional groups at the edges and the plane of the graphene oxide sheets, and is readily soluble in many solvents, including water, which is a significant advantage for environmentally friendly applications (Figure 1b). At certain concentrations, roughly > 0.1-1 wt%, GO often exhibits very stable lyotropic nematic phases [11][12][13]. One of the interesting aspects of GO liquid crystals is the possibility of self-organized and self-ordered systems of graphene oxide. This order can then easily be manipulated by application of external stimuli, such as boundary conditions, mechanical shear, but possibly also electric and magnetic fields. After obtaining a certain directional order one could wash away or evaporate the solvent, leaving an ordered GO structure, which may even be reduced chemically or through heat application to produce reduced graphene oxide (rGO), which displays some of the originally desirable graphene properties. Lyotropic graphene oxide liquid crystals are thus of immense interest for nanotechnology and its applications. There have been several review articles on the properties of GO liquid crystals [14][15][16]. In this paper we want to give a short critical account of what is known, what is not yet known, and what are the controversial questions with regards to graphene oxide liquid crystals. Effects of flake size and solvent will be discussed, alignment, addition of salts and polymers, as well as electro-optic properties, and electric and magnetic field effects. Graphene and Graphene OxidePristine graphene is a two-dimensional hexagonal lattice of sp 2 hybridized carbon with a basis of two, giving rise to a honeycomb structure [10]. Graphene oxide is a very different material to graphene. Graphene is often obtained by mechanical exfoliation of graphite (the so-called Scotch Tape ® method) or grown by chemical vapor deposition. On the other hand, graphite that has undergone treatment to become graphite oxide readily exfoliates ...

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Widely Tunable GRIN Lenses Using Negative Dielectrophoretic Manipulation of Phosphate Nanosheets Colloid

Priyadharshana

Shen

Hong³

2022

Advanced Optical Materials

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Tunable gradient refractive index (GRIN) lens has attracted increasing attention from researchers due to its promising applicability in various optical and electronic applications. However, the polarization‐insensitive, large sized, and focal‐length‐controllable GRIN lens is highly difficult to implement due to the lack of available functional materials with the property of tunable refractive index. Herein, a two dimensional (2D) α‐ZrP nanocolloid is introduced to fabricate a GRIN lens in which the 2D nanosheet density distribution is precisely controlled by negative dielectrophoresis. Interestingly, the geometrical 2D shape of nanosheets plays an essential role in reducing optical light scattering in colloids and enhancing the dielectrophoretic controllability of nanosheet distribution. Moreover, despite the nematic assembly of 2D nanosheets in colloids, the birefringence effect is negligible, and polarization‐independent properties are obtained. Using a simple nanocolloidal cell with designed electrodes and various thicknesses, not only tunable lenses with either positive or negative focal lengths but also wide tunable lenses across positive and negative focal lengths are successfully demonstrated. Thus, the results reveal new possibilities for 2D nanocolloids in tunable GRIN optical applications.

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Guided Electro-Optical Switching of Small Graphene Oxide Particles by Larger Ones in Aqueous Dispersion

Cited by 23 publications

References 35 publications

Reduced Graphene Oxide as Efficient Hole Injection Layer for Quantum‐Dot Light‐Emitting Diodes

Reduced Graphene Oxide as Efficient Hole Injection Layer for Quantum‐Dot Light‐Emitting Diodes

Lyotropic Liquid Crystals from Colloidal Suspensions of Graphene Oxide

Widely Tunable GRIN Lenses Using Negative Dielectrophoretic Manipulation of Phosphate Nanosheets Colloid

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