Reflection anisotropy spectroscopy: A probe of rubbed polyimide liquid crystal alignment layers

Macdonald, B. F.; Zheng, Weihui; Cole, Richard

doi:10.1063/1.1559423

Cited by 15 publications

(9 citation statements)

References 24 publications

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“…The potential of RAS as a quality control tool in this field has been demonstrated [325][326][327]. Figures 37(a) and (b) show, respectively, the reflectivity and RAS amplitude of a repeatedly rubbed 80 nm thick polyimide (PI) film on ITO coated glass, as used in commercial devices [328]. The dependence of the RAS amplitude on rubbing number is shown in figure 37(c).…”

Section: Monitoring Liquid Crystal Device Fabricationmentioning

confidence: 99%

Reflection anisotropy spectroscopy

et al. 2005

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Reflection anisotropy spectroscopy (RAS) is a non-destructive optical probe of surfaces that is capable of operation within a wide range of environments. In this review we trace the development of RAS from its origins in the 1980s as a probe of semiconductor surfaces and semiconductor growth through to the present where it is emerging as a powerful addition to the wide range of existing ultra-high vacuum (UHV) surface science techniques. The principles, instrumentation and theoretical considerations of RAS are discussed. The recent progress in the application of RAS to investigate phenomena at metal surfaces is reviewed, and applications in fields including electrochemistry, molecular assembly, liquid crystal device fabrication and remote stress sensing are discussed. We show that the experimental study of relatively simple surfaces combined with continuing progress in the theoretical description of surface optics promises to unlock the full potential of RAS. This provides a firm foundation for the application of the technique to the challenging fields of ambient, high pressure and liquid environments. It is in these environments that RAS has a clear advantage over UHVbased probes for investigating surface phenomena, and its surface sensitivity, ability to monitor macroscopic areas and rapidity of response make it an ideal complement to scanning probe techniques which can also operate in such environments.

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Section: Monitoring Liquid Crystal Device Fabricationmentioning

confidence: 99%

Reflection anisotropy spectroscopy

et al. 2005

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“…However, if the bulk is not truly amorphous but, consists of anisotropic domains, then the RAS will be the sum of the contributions from these domains which again, may or may not, cancel out. In the simplest case, in which the optical signal arises from a single dipole transition located in a plane perpendicular to the direction of the incident light, then rotation of the specimen through an angle in the plane of the dipole, q a technique termed azimuthally dependent RAS (ADRAS), 15,16 will yield an ADRAS signal that varies in intensity as cos 2q. If the dipole orientation is not in the azimuthal plane, then the angular variation of the ADRAS signal will be more complicated and, if there are several dipole transitions with different orientations, the ADRAS signal will be the superposition of these signals.…”

Section: Reflection Anisotropy Spectroscopy Methodologymentioning

confidence: 99%

Fundamental differences in model cell-surface polysaccharides revealed by complementary optical and spectroscopic techniques

et al. 2012

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“…Buffed polyimide polymer layers can be optically anisotropic, with an average refractive index in the visible of about 1.5 − 1.8 depending on chemical structure and morphology [31,32,33]. Our cells do not show appreciable birefringence, so we model the PI layer with a single principal dielectric function.…”

Section: Pi Layermentioning

confidence: 99%

Optical characterization of dyed liquid crystal cells

Addai1¹,

Xiao²,

Zheng³

et al. 2022

Preprint

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The guest-host liquid crystal display, first proposed in 1968, relies on controlling the orientation of dichroic dyes dissolved in a nematic liquid crystal host. Controlling the orientation of the liquid crystal and of the dissolved dye with an electric field allows control of the transmittance of the cell. Knowing the dielectric properties at optical frequencies of the dye and liquid crystal mixtures is crucial for the optimal design of guest-host liquid crystal devices. In this work, the dielectric functions of various layers in liquid crystal cells are described by models obeying the Kramers-Kronig relations: the Sellmeier equation for transparent layers and causal Gaussian oscillator model for absorbing layers. We propose a systematic way to accurately model the dielectric response of each layer by minimizing the sum of squared differences between the measured transmittance spectrum of a guest-host cell in the near-UV/vis range and the prediction of the transmittance of the modeled multilayer structure. By measuring the transmittance for incident light polarized parallel and perpendicular to the nematic director allows us to separately characterize the two principal dielectric functions of the uniaxial sample. Our results show that the causal Gaussian oscillator model can accurately characterize the dielectric functions of dyes in liquid crystals.

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Reflection anisotropy spectroscopy: A probe of rubbed polyimide liquid crystal alignment layers

Abstract: Relation between the molecular orientations of a very thin liquid crystal layer and an underlying rubbed polyimide film

Cited by 15 publications

References 24 publications

Reflection anisotropy spectroscopy

Reflection anisotropy spectroscopy

Fundamental differences in model cell-surface polysaccharides revealed by complementary optical and spectroscopic techniques

Optical characterization of dyed liquid crystal cells

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