Oblique Evaporation Method

In the oblique evaporation process, a micro columnar structure is realized on the substrate surface, due to the self shadowing effect as shown in Fig. 3.3.1. When a nematic liquid crystal contacts such a surface, elastic deformation of the liquid crystal along the surface induces an interaction energy between the surface and the nematic material. This is thought to be the driving force for alignment of the nematic director. 

The surface structure of the oblique evaporated film changes with the evaporation angle (the angle between evaporation beam and substrate normal). The structure of stepwise grooves and the array of columns change their angle and density. 

The surface structure of the oblique evaporated film is illustrated schematically as in Fig. 3.3.2. There are many grooves and columns, the features of which vary with evaporation angle and change in the nematic alignment direction and pretilt angle. 

3 Evaporation angle dependence of the liquid crystal alignment. Position G and C are illustrated in Pig. 3.3.2. 

O 2005 KcMd Takatoh, Masald Hasegawa, Mitsiihiro Koden, Nobi oiki Itoh, Ray Has wa and Masanori Sakamoto 

5 2005 KohM Takatoh, MasaM Hasegawa, Mitsuhiro Koden, Nobuyuki Itoh, Ray Hasegawa and Masanori Sakamoto 

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Finally, although they are not described in this chapter, we must note some important and interesting studies such as those of the oblique evaporation method [43], the twisted FLC [44], an oblique layered structure that exhibits an analogue grey scale [45], etc. 

T. Uemura, N. Obba, N. Mfekita. R Ohnishi, and 1. Ola. AUgnmem of chiral smectic C liquid crystal by oblique evaporation method, Proc. 6A tat. DispL Res. Caaf.. Japaa Display S6," Tbkyo, 1986, pp. 464-467. 

In order to make a more qualitative discussion, it will be necessary to find a method to measure the coefficients k and Att, which determine the value of a, and to measure the surface order parameter S . Furthermore, the direction of the easy axis must be determined for the oblique evaporated surface exactly... 

Obliquely evaporated SiO, which forms a saw-tooth profile at the surface, was first reported by Janning. Similar to the Berremann s model in these cases, the easy axis is determined by the evaporation direction. We note that, in special evaporation directions and SiO thickness ranges, this method could provide bistable anchoring conditions leading to bistable nematic devices." ... 

One of the standard techniques often used for this purpose is the preparation of a perfectly aligned smectic A sample. Liquid crystal often undergoes the following phase sequence isotropic phase (nematic) smectic A => smectic C. The nematic phase (if it exists) could be oriented by traditional methods, such as the rubbing of polymer films or the evaporation of inorganic films at an oblique angle (< 10 ) [135]. The quality of orientation improves for lower values of the specific heat at the nematic smectic A transition and the minimum amount of crystallization centers. 

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