We investigated the phenomena of a metallic photonic crystal (MPC) immersed in liquid crystal. According to our
design, the photonic crystal has specific photonic band gap (PBG) and can be utilized as a filter. The device is filled with
nematic liquid crystal (NLC), MDA-00-3461. The refractive indices of NLC can be magnetically controlled by
reorienting the NLC molecules. Consequently, the corresponding PBG and the filtering performance of the device are
tunable. According to our experimental results, the low frequency boundary of PBG at 0.121 THz can be blue shifted by
6.17 GHz, and the high frequency boundary of PBG at 0.175 THz can be shifted to the blue by 11.04 GHz. As a tunable
THz filter, the peak transmittance at 0.187 THz can be blue shifted by 3.66 GHz.
A method for liquid crystal surface alignment by using a one-step, ion beam sputtering on glass substrates is
demonstrated. Pre-coating by polyimide is not necessary. We use a diode-type sputter to treat the glass substrates with Ar
ion-beam. The homeotropic alignments for nematic liquid crystals are achieved. The alignments are characterized by
using the polarizing optical microscope and the conoscope. To find out the alignment mechanism, the studies by using
super conducting quantum interference device and scanning probe microscopy are carried out. The surveyed surface
morphology reveals that the films are amorphous and composed of nanoparticles with dimensions around 30 nm. The
magnetization anisotropy of the sputtered magnetic films is analyzed. The polar anchoring strengths of the coated films
with different thicknesses are measured and compared with their saturation magnetization. We deduce that the
homeotropic alignment is achieved due to the orientation of the diamagnetic nematogenic molecules in the magnetic
field caused by the γ-Fe2O3 ferrimagnetic thin films. A simple model of alternatively distributed magnetic moments with
opposite direction is proposed. The profile of magnetic field strength near the surface is then calculated to compare with
the measured alignment strength.
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