Quality control liquid crystals

T. Inada and T. Fukuda, Direct Synthesis and Growth of Indium Phosphide by the Liquid Phosphorous Encapsulated Czochralski Method O. Oda, K. Katagiri, K. Shinohara, S. Katsura, Y. Takahashi, K. Kainosho, K. Kohiro, and R. Hirano, InP Crystal Growth, Substrate Preparation and Evaluation K. Tada, M. Tatsumi, M. Morioka, T. Araki, and T. Kawase, InP Substrates Production and Quality Control... 

In the Kyropoulos method, the top of the melt is only slightly above its melting temperature and a seed crystal, which is cooled externally by attaching it to a water cooled heat sink, is placed in contact with the liquid to induce crystallization. The crystal may be rotated and continues to grow in the melt (Figures 37a and b). The size and quality of the crystal produced depends on the temperature gradient induced by the external coolant and the degree to which the temperature of the furnace can be controlled. 

Several elementary aspects of mass diffusion, heat transfer and fluid flow are considered in the context of the separation and control of mixtures of liquid metals and semiconductors by crystallization and float-zone refining. First, the effect of convection on mass transfer in several configurations is considered from the viewpoint of film theory. Then a nonlinear, simplified, model of a low Prandtl number floating zone in microgravity is discussed. It is shown that the nonlinear inertia terms of the momentum equations play an important role in determining surface deflection in thermocapillary flow, and that the deflection is small in the case considered, but it is intimately related to the pressure distribution which may exist in the zone. However, thermocapillary flows may be vigorous and can affect temperature and solute distributions profoundly in zone refining, and thus they affect the quality of the crystals produced. 

Active matrix displays using thin film transistors (TFTs) as electrical switches to control the transmission state of liquid crystal pixels offer excellent image quality and are commonly employed for direct-view displays [5,6]. Figure 10.7 shows the device structure of a... 

See also Applied Mathematics Applied Physics Computer Engineering Computer Science Electrochemistry Electronic Materials Production Electronics and Electronic Engineering Graphics Technologies Liquid Crystal Technology Nanotechnology Quality Control Surface and Interfece Science Transistor Technologies. 

The superiority of using lasers for material studies often lies in its spatial and temporal flexibilities, that is, the material can selectively excited and probed in space and time. These qualities may allow us to elucidate fundamental material properties not accessible to conventional techniques. The location, dimension, direction, and duration of the material excitation can be readily controlled through adjustment of the beam spot, direction, polarization, and pulse width of the exciting laser field. The flexibilities can be further enhanced when two or more light waves are used to induce excitations. Such a technique, however, has not yet been fully explored in liquid-crystal research. Although the recent studies of optical-field-induced molecular reorientation in nematic liquid-crystal films have demonstrated the ability of the technique to resolve spatial variation of excitations, corresponding transient phenomena induced by pulsed optical fields have not yet been reported in the literature. Because of the possibility of using lasers to induce excitations on a very short time scale, such studies could provide rare opportunities to test the applicability of the continuum theory in the extreme cases. 

We should note that because all the physical properties of the final mixture are interconnected and defined by the molecular structure of the components, it is impossible to change arbitrarily one or another liquid crystal parameter without affecting the rest. This is why to develop a new liquid crystal material requires a delicate touch, the way of certain compromises. The problem seems to be even more complicated because the list of parameters, required for application control, is not limited by the physical properties considered in this chapter. However, a detailed description of quality estimations of the material is beyond the firamework of this book. Sometimes this control is even considered as the Know-How of the producer. 

A color difference ratio allows us not only to evaluate the usual luminance contrast (4.59), but also to evaluate a color purity and the color hue that makes the human eye very sensitive to the variation of CDR. Reference [170] demonstrates the increase by a factor of three of the number of distinguished rows of the display when evaluating by the colorimetry methods. This effect may be understood by the fact that the human eye is more sensitive to the color contrast than to the luminance one, as the hue and the chroma both contribute to the former. Color differences between on and off display states could be optimized by a special choice of polarizers [170-172], concentration of a dichroic dye (guest) in a liquid crystal matrix (host) [166, 173], using the reflective screens [173], etc. Colorimetric evaluations are very useful in the quality control of both the guest host and twist displays [172, 174]. 

Nematic and cholesteric liquid crystals can be used for the nondestructive study of electrical defects in transistors and integrated circuits [81, 82], for the detection defects in film capacitors prepared by vacuum deposition [83], for the visualization of electrically active defects or rapidly diffusing dopants, as well as for quality control at various stages of integrating circuits production [84-86]. The most suitable effect for this purpose would appear to be the B effect [85] and the fiexoelectric effect in spatially nonuniform field [84, 86], which permits the distribution of the electrical potential in operating the integrated circuits to be visualized. 

Jeon Young Jae, Lee Gae Hwang, Jang Jae Eun, et al. Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles. Liq. Cryst. 39 no. 11 (2012) 1314-1319. 

---