Variable liquid crystal pretilt angles on various compositions of alignment layers

The authors introduce variable liquid crystal (LC) pretilt angles via ion beam (IB) irradiation of silicon carbide (SiC) layers of various compositions. To control the composition of the SiC layer, the authors altered the rf power ratio between the graphite target and silicon target. The pretilt angle of the silicon-rich SiC layer was constant regardless of IB irradiation angle; however, the carbon-rich SiC layer showed variable pretilt angles, depending on IB irradiation angle. The authors attribute variable pretilt angle to the competition between van der Waals interactions, favoring the vertical alignment, and pi-pi interactions, favoring the LC alignment parallel to IB direction. (c) 2007 American Institute of Physics.