Marius Iosif Boamfa

Observation of surface and bulk phase transitions in nematic liquid crystals

The behaviour of liquid crystal (LC) molecules near a surface is of both fundamental and technological interest: it gives rise to various surface phase-transition and wetting phenomena, and surface-induced ordering of the LC molecules is integral to the operation of LC displays. Here we report the observation of a pure isotropic–nematic (IN) surface phase transition—clearly separated from the bulk IN transition—in a nematic LC on a substrate. Differences in phase behaviour between surface and bulk are expected, but have hitherto proved difficult to distinguish, owing in part to the close proximity of their transition temperatures. We have overcome these difficulties by using a mixture of nematic LCs: small, surface-induced composition variations lead to complete separation of the surface and bulk transitions, which we then study independently as a function of substrate and applied magnetic field. We find the surface IN transition to be of first order on surfaces with a weak anchoring energy and continuous on surfaces with a strong anchoring. We show that the presence of high magnetic fields does not change the surface IN transition temperature, whereas the bulk IN transition temperature increases with field. We attribute this to the interaction energy between the surface and bulk phases, which is tuned by magnetic-field-induced order in the surface-wetting layer.

Compartmentalized Multistable Liquid Crystal Alignment

A novel method for compartmentalized multistable liquid crystal alignment is presented (see figure). The compartmentalization allows planar-aligned liqid crystal domains to be switched independently under vertical electric fields. This work opens new routes for the design and fabrication of multistage liquid crystal devices, switchable viewing-angle displays and tunable structures of guest materials within liquid crystal host.

Two-Dimensional Optical Storage Mastering: Adding a New Dimension to Liquid Immersion Mastering

We present a novel-mastering concept of Two-dimensional structures using a single writing spot. We describe its implementation for the existing liquid immersion mastering set-up, from initial concept and feasibility analysis to mastered discs of up to 60 GB/layer data density.

Liquid immersion deep-UV optical disc mastering for high data capacity ROM discs

In this paper we describe the liquid immersion mastering technique and its application to the mastering of ROM discs for the Blu-ray Disc system and for ROM discs with considerably higher data densities. Replicated 25GB BD-ROM discs were evaluated using a standard blue test player (λ=405nm, NA=0.85). A bottom jitter value with limit equalizer of less than 5% was measured. Also the values of asymmetry, normalized push pull and symbol error rate were well within the Blu-ray Disc format specification, offering a large process window. Full-format BD-ROM test discs with high definition video content were mastered and their successful read-back was demonstrated. In addition we show that liquid immersion mastering can successfully be applied for mastering of considerably higher densities. Measurements on replicated discs up to data densities above 40GB per layer are discussed. The present results demonstrate that liquid immersion mastering is a proven technology for the mass-production of high data capacity ROM discs.