Two-dimensional hexagonal boron nitride nanosheet as the planar-alignment agent in a liquid crystal-based electro-optic device

Basu, Rajratan; Atwood, Lukas J.

doi:10.1364/oe.27.000282

Cited by 22 publications

(20 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Therefore, the hexagonal benzene rings in the LC and the hexagonal 2D h-BN lattice structure have almost the same size. It has been experimentally shown that this nano-architectural symmetry of the hexagons in these two species leads the benzene rings of the LC to coherently align on the hexagonal lattice of h-BN [12]. This epitaxial interaction is schematically presented in Figure 1a by matching the LC benzene rings on the hexagons of the h-BN lattice.…”

Section: Methodsmentioning

confidence: 94%

“…For example, the epitaxial interactions between the nematic LC and the hexagonal lattice of graphene, molybdenum diselenide, and tungsten diselenide deposited [1][2][3][4][5][6][7][8][9][10] demonstrate that the LC can achieve a planar-aligned state on these 2D hexagonal nanostructures. Our group has recently shown that the 2D hexagonal boron nitride (h-BN) film can be successfully employed as a planar-alignment agent as well as an ion-capturing agent in electro-optic LC devices [11][12][13]. Here we report the effects of ultrafine 2D h-BN flakes as a colloidal dopant in a nematic LC.…”

Section: Introductionmentioning

confidence: 95%

“…Since W θ and γ 1 influence the dynamic electro-optic response in an LC device mainly, the electro-optic switching times for both the pure LC and LC+h-BN samples in 20 µm cells have been investigated. These response times in both the cells were measured by employing the standard electro-optical setup [6,[11][12][13], where a 5-mW He-Ne laser beam of wavelength 633 nm was sent through two crossed-polarizers and into a photodetector. The planar LC test cell was placed in-between the crossed polarizers wheren in the cell was aligned at 45 • with respect to the polarizer.…”

Section: Electro-optic Switchingmentioning

confidence: 99%

See 2 more Smart Citations

Dielectric and Electro-Optic Effects in a Nematic Liquid Crystal Doped with h-BN Flakes

2020

Self Cite

View full text Add to dashboard Cite

A small quantity of hexagonal boron nitride (h-BN) flakes is doped into a nematic liquid crystal (LC). The epitaxial interaction between the LC molecules and the h-BN flakes rising from the π−π electron stacking between the LC’s benzene rings and the h-BN’s honeycomb structure stabilizes pseudo-nematic domains surrounding the h-BN flakes. Electric field-dependent dielectric studies reveal that the LC-jacketed h-BN flakes follow the nematic director reorientation upon increasing the applied electric field. These anisotropic pseudo-nematic domains exist in the isotropic phase of the LC+h-BN system as well, and interact with the external electric field, giving rise to a nonzero dielectric anisotropy in the isotropic phase. Further investigations reveal that the presence of the h-BN flakes at a low concentration in the nematic LC enhances the elastic constants, reduces the rotation viscosity, and lowers the pre-tilt angle of the LC. However, the Fréedericksz threshold voltage stays mostly unaffected in the presence of the h-BN flakes. Additional studies show that the presence of the h-BN flakes enhances the effective polar anchoring strength in the cell. The enhanced polar anchoring strength and the reduced rotational viscosity result in faster electro-optic switching in the h-BN-doped LC cell.

show abstract

Section: Methodsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 95%

Section: Electro-optic Switchingmentioning

confidence: 99%

See 1 more Smart Citation

Dielectric and Electro-Optic Effects in a Nematic Liquid Crystal Doped with h-BN Flakes

2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…On the 2D h-BN crystal, the LC molecules can obtain three degenerate planar orientations separated by 60 degrees due to the three-fold rotational symmetry of the hexagonal structure. It is still possible to achieve uniform planar-alignment in-between two h-BN layers (without any PI) in an LC cell [58]. However, that process requires several steps to align two h-BN layers in the same direction to avoid the degenerate planar orientations in the cell [58].…”

Section: Fabrication Of the 2d H-bn Based Lc Devicementioning

confidence: 99%

“…It is still possible to achieve uniform planar-alignment in-between two h-BN layers (without any PI) in an LC cell [58]. However, that process requires several steps to align two h-BN layers in the same direction to avoid the degenerate planar orientations in the cell [58]. Here, we have used one rubbed PI layer and one h-BN layer in the cell.…”

Section: Fabrication Of the 2d H-bn Based Lc Devicementioning

confidence: 99%

Reduced ionic effect and accelerated electro-optic response in a 2D hexagonal boron nitride planar-alignment agent based liquid crystal device

Basu

Atwood

2019

Opt. Mater. Express

Self Cite

View full text Add to dashboard Cite

The presence of excess free-ion impurities in liquid crystals (LCs) gives rise to a number of problems in the electro-optical liquid crystal displays (LCDs), e.g., slow electro-optical responses and image sticking effects. Here we experimentally present that the two-dimensional (2D) hexagonal boron nitride (h-BN) nanosheet can serve as a planar-alignment agent and as an ion-capturing agent at the same time in an electro-optic LC device. The 2D h-BN nanosheet is employed as a planar-alignment agent on one side of an LC cell, where the standard planaraligning polyimide (PI) layer is used on the other side of the cell. The LC exhibits uniform planar-alignment in this h-BN/PI hybrid device. It is found that the free-ion impurities in the LC are significantly suppressed in this h-BN/PI hybrid cell compared to that in a standard PI/PI LC cell. The free-ion density is reduced in the hybrid cell due to the 2D h-BN nanosheet's ion-capturing process. The reduction of ionic impurities results in an accelerated electro-optic response of the LC in the h-BN based hybrid cell-which may have potential application for faster electro-optic devices.

show abstract

Solution‐Processed h‐BN Film as an Alignment Layer for Liquid Crystal Devices: Realization of a Non‐Polymer Approach for Unidirectional Alignment over Unprecedentedly Large Areas

Pisharody

Sahoo

Rao

et al. 2022

Adv Materials Inter

View full text Add to dashboard Cite

atomic-scale switches and transistors working at gigahertz frequencies using mechanically cleaved graphene, [3,4] ballistic transport of electrons in graphene-boron nitride heterostructures, [5] ambipolar transport in transition metal dichalcogenides and black phosphorus. [6][7] In contrast to the correlated high thermal and electrical conductivity as in carbon nanotubes or graphene, [8][9] h-BN offers a startlingly different combination of high thermal conductivity and excellent electrical insulation. [10] While the field gained attention with fabrication procedures that are easily realizable, it is the chemical vapor deposition (CVD) technique that truly made the surge ahead, especially because monolayers of large enough dimensions can be obtained. [11][12][13] The importance of aligning liquid crystal (LC) molecules for fabricating a liquid crystal display device needs hardly any emphasis. Indeed, the success mentioned above provided the impetus to employ CVD-grown 2D films as alignment layers for LC molecules. However, it has been realized that the CVD technique suffers from drawbacks such as high operational temperature, need for vacuum, usage of hazardous chemicals, and limited film thickness. [14] Besides, the process is timeconsuming as well as expensive, not to mention the high skills necessary to obtain good quality CVD-grown films. [14] It is with this background that solution processing (SP) of 2D materials, which can address the aforementioned issues in a simple and cost-effective way, is being currently considered as a viable alternative. [15] More importantly, the SP can also offer the possibility of fabricating large-area flexible devices. [16] It may be noted that the SP route has already helped to realize a plethora of devices including capacitors, supercapacitors, transistors, photodetectors, etc. [17][18][19] Despite the simplicity, the performance of the solution-processed electronic devices is reported to be inferior to those obtained by the CVD method. [20][21][22] The compromising device performance being the major hindrance for commercialization of the SP devices, it would be a significant step forward Fabrication of liquid crystal devices heavily relies on the alignment layer providing the mandatory unidirectional orientation of the nematic molecules. Drawbacks of the traditional mechanically rubbed polymer layer have prompted to find better alternatives. However, cost-effective methods for large-area unidirectional alignment are still elusive. The latest attempt has been to use 2D materials deposited through the well-known chemical vapor deposition process, invariably inviting all the associated complexities including high-temperature processing, cumbersome transfer onto the required substrate, etc. Most importantly, the achieved domain size over which the nematic molecules exhibit unidirectional planar orientation, has been too small (sub-mm 2 ) for employable devices. Here, the authors present a room temperature solution process for obtaining h-BN dispersion and directly depositing it...

show abstract

Two-dimensional hexagonal boron nitride nanosheet as the planar-alignment agent in a liquid crystal-based electro-optic device

Cited by 22 publications

References 37 publications

Dielectric and Electro-Optic Effects in a Nematic Liquid Crystal Doped with h-BN Flakes

Dielectric and Electro-Optic Effects in a Nematic Liquid Crystal Doped with h-BN Flakes

Reduced ionic effect and accelerated electro-optic response in a 2D hexagonal boron nitride planar-alignment agent based liquid crystal device

Solution‐Processed h‐BN Film as an Alignment Layer for Liquid Crystal Devices: Realization of a Non‐Polymer Approach for Unidirectional Alignment over Unprecedentedly Large Areas

Contact Info

Product

Resources

About