Plasma beam alignment of liquid crystal with improved alignment stability [LCD manufacture]
A method of plasma beam treatment providing liquid crystal (LC) aligning substrates of improved alignment stability is described. In this method the aligning substrates are obliquely treated with a plasma flux containing alignment and passivation agents simultaneously. This method is applicable for the substrates of organic and inorganic origin. During this treating process, good pretilt angle stability and alignment quality are much promised.
Planar and tilted uniform alignment of liquid crystals by plasma-treated substrates
We describe a new aligning technique that yields uniform planar or tilted orientation of a nematic liquid crystal at different organic and inorganic substrates. The method is based on the oblique irradiation of an aligning substrate with a partially collimated flux of accelerated plasma. The sheet-like plasma flux is produced by an anode layer thruster with a race track geometry of the discharge channel. For liquid crystals with a positive dielectric anisotropy the technique produces two modes of uniform alignment: (1) with the easy axis in the incident plane of the plasma beam; (2) with the easy axis perpendicular to the plane of incidence. Mode 1 transforms into mode 2 as the irradiation dose increases. In mode 1, the pretilt angle can be controlled by changing the parameters of irradiation such as incidence angle, current density and particle energy. In mode 2, the pretilt angle is zero (planar alignment). The azimuthal anchoring coefficient is relatively weak (W a∼10−6 J m−2) for the first type of alignment and strong (W a≥10−4 J m−2, comparable to rubbed polymer substrates) for the second type. The two-mode alignment feature can be used to control alignment properties and to create alignment patterns. The method is free from the usual shortcomings of the traditional rubbing technique. We discuss possible mechanisms of the two-mode alignment and show that plasma-induced modifications of the substrate topography might be an important factor in liquid crystal alignment.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%