We present a new formulation for the dynamicmodeling of twisted nematic liquid crystal display cells based on aconstant charge assumption instead of the commonly used "fixedvoltage" model. This formulation is based on a tensor representationof the director field, which is solved using a combination offinite-element and finite-difference methods. It allows the accuratemodeling of liquid crystal pixel cells in thin-film-transistor-drivenactive matrix displays, extensively used in flat panel computer andtelevision displays.

In this paper a two-dimensional (2-D) dynamicmodel, based on a tensor formulation and solved numericallyby combining finite elements and finite differences, is proposedand used for analyzing nematic liquid crystal (LC) test cells withinterdigital electrodes. We compare theoretical and experimentalresults concerning the switching behavior, response mechanism,and viewing angle characteristics of nematic LC pixel structureswhich use the in-plane-switching (IPS) mode. The good agreementobserved between theory and experiment in terms of electroopticalproperties validates our modeling and demonstrates itspotential for design optimization. We show that the proposed LCtest cells, using the in-plane-switching mode, ensure switching-ON and -OFF response times of 22 and 28 ms, respectively, andexcellent viewing angle characteristics.

A molecular-dynamics study has been made of the influence of solute content on low-energy displacement cascade processes in copper containing up to 15 at. % Au in solid solution. This alloy system was chosen to illustrate the effects of heavy, oversized solute atoms in a fcc matrix. Cascades of up to 2ke Vin energy were considered. The presence of the solute was found to have a significant impact on all phases of cascade development, but not on the final defect number. The ballistic phase is increased in duration, and the number of temporarily displaced atoms is increased by the solute, and the thermal spike that follows is also increased in intensity and duration. As a consequence, the atomic mixing associated with these two phases was highest in the Cu–15% Au alloy that contained the most solute. However, as a result of self-healing in the thermal spike, the final number of Frenkel defects is independent of alloy composition. To test the influence of solute atomic mass, simulations were carried out on copper containing solute atoms with the same size as Au, but a lighter mass than copper. The alloys with this fictitious element did not show the ballistic-and thermal-spike effects exhibited by those containing "normal" gold. The results are discussed in terms of the likely roles of solutes in damage evolution in alloys under cascade-producing irradiation.

The influence of solute atoms on point-defect properties and defect generation by radiation damage in alloys is known to be important, and hence it is desirable to understand their effect on the basic mecha- nisms involved. Most computer modeling of these phenomena has only considered pure metals, but as part of a project to investigate displacement cascades in alloys, we have simulated dilute solutions of gold (Au) in copper (Cu), treating this as a "model" for a heavy, oversized solute alloy system. In the present paper, modified many-body interatomic potentials for the Cu-Au system are described that are suitable for modeling high-energy atomic collisions. The properties of point defects in pure copper and the dilute alloy, including solute-defect binding energies, are presented. The oversized solute has a larger binding energy with an interstitial atom than with a vacancy. The displacement threshold energy, Ea, of a Cu atom and a Au atom in the copper matrix has been investigated as a function of primary recoil direction, and the difference between the two species is found to be substantial. Furthermore, the pres- ence of a Au solute has a significant effect on the formation of Frenkel pairs by the replacement- collision-sequence mechanism. These results are discussed in terms of the mass and size difference of Cu and Au atoms.

Research into displacement cascade processes in alloy systems has received little attention, yet is potentially of interest because issuessuch as the effect of solutes on the displacement threshold and the defectdistribution and movement in cascades are important. As part of a widerstudy, we have initially considered the minor substitutional solute Au in a Cu matrix, and have used molecular dynamics to investigate the properties of point defects, the threshold displacement energy Ed, and temporal and spatial distribution of defects in low-energy (≤500 eV) displacement cascades. The results show that the influence of the solute on the properties of defects is important and that Edis dramatically different from its form in pure copper. In comparison with pure copper,the recoil of the Au solute gives rise to a higher peak at longer timesin the number of displaced atoms in the generation of a displacement cascade. The influence of this on defect density in the cascade and thefinal number and arrangement of defects has been investigated.