H. M. J. Boots

Ferroelectric liquid crystal gels Network stabilized ferroelectric display

Abstract Liquid crystal (LC) mixtures of a reactive diacrylate and a commercial ferroelectric liquid crystal (FLC) mixture were produced. The mixtures were brought into cells provided with orientation layers in which various orientations such as uniaxial and twisted orientations, could be induced. When the desired orientation had been obtained, the polymerization of the reactive molecules was induced creating a three-dimensional anisotropic network containing the FLC molecules which were not chemically attached to the network (ferroelectric gels). The presence of the anisotropic network was found to have a large effect on various properties of the FLC molecules. For example, complex orientations (for example, 180° twisted) obtained by polymerization (formation of the gel) in the nematic phase remained unchanged when the gel was cooled to the FLC phase. Likewise uniaxial orientation, which cannot be realised in thick cells containing the pure FLC, could be realised when ferroelectric gels were used. For th...

Time‐resolved reflectivity measurements during explosive crystallization of amorphous silicon

Explosive crystallization of Cu implanted amorphous silicon during irradiation by a 32‐ns FWHM ruby laser pulse has been studied using time‐resolved reflectivity measurements and Rutherford backscattering spectrometry. From interferences in the reflectivity, the position and the velocity of the self‐propagating melt have been deduced as a function of time. A maximum average velocity of 13±2 m/s has been obtained. The reflectivity behavior indicates the presence of crystalline nuclei in the melt.

Direct observation of resolidification from the surface upon pulsed‐laser melting of amorphous silicon

Amorphized Si has been irradiated using a 7.5‐ns frequency‐doubled neodymium:yttrium aluminum garnet laser. For low energy density pulses, time‐resolved reflectivity measurements and Rutherford backscattering spectrometry of Cu implantation profiles show that the melted layer solidifies from the surface as well as from the liquid‐solid interface. From interferences in the reflectivity, growth from the surface is found to occur at a velocity of 1.5 m/s. At higher energy densities sufficient to obtain epitaxial regrowth of the amorphous layer, solidification from the surface does not occur.

Scaling of characteristic frequencies in RF CMOS

Device simulation of the 180-, 90-, and 65-nm CMOS generations shows that in NMOSTs, the cut-off frequency f/sub T/ and the maximum oscillation frequency f/sub max/ are roughly inversely proportional to the gate length. The voltage-gain bandwidth f/sub A/ depends only weakly on the gate length. At 40-nm gate length, f/sub T/ values of 300 GHz are predicted. For small values of the drain and source contact resistance (<10/sup -8/ /spl Omega//spl middot/cm/sup 2/), f/sub T/ can only be improved by a further reduction of the gate length. The f/sub max/ values (for zero gate resistance higher than f/sub T/) degrade strongly with increasing gate resistance. Simple approximate formulas for the dependence of f/sub T/ and f/sub A/ on the contact resistances are presented.

Anisotropic‐network‐stabilized ferroelectric gels for active matrix addressing

Ferroelectric gels have been produced by polymerization of liquid crystal (LC) diacrylates in mixtures of nonreactive molecules showing the ferroelectric LC (FLC) phase. Within the gels, the orientational, optical, and electrical properties of the nonreactive molecules are to a large extent dominated by the polymer network. For this reason the gels are also referred to as anisotropic‐network‐stabilized FLC. In this publication gels with homogeneous and hybrid orientations are described. Network molecules of various birefringences are used to show that the effective birefringence within the gels can be reduced. The extinction angle within the gels is also influenced by the anisotropy and the concentration of the network. The gels also show continuous switching over a broad range of voltages. The voltage range becomes broader and shifts to higher voltages with an increasing network concentration. This behavior of FLC gels makes them suitable for the production of grey levels in display applications. Using a...

Between explosive crystallization and amorphous regrowth: Inhomogeneous solidification upon pulsed‐laser annealing of amorphous silicon

Si amorphized by Cu implantation has been irradiated by spatially uniform pulses of 7.5 ns duration from a frequency‐doubled neodymium:yttrium aluminum garnet laser. After irradiation the samples were examined by cross‐section transmission electron microscopy. A laterally random pattern of polycrystalline Si patches was found imbedded in amorphous material. At low‐energy densities a considerable fraction of the regrown Si was polycrystalline. With increasing energy density the amount of polycrystalline Si decreased, both at the surface and in total. These results are discussed in terms of the time available for the nucleation of polycrystalline Si at a liquid‐solid interface and the temperature profile in both the liquid and the solid material.

Exact and moment equation modeling of electron transport in submicron structures

We compare I‐Vcharacteristics of a semiconducting submicron n + nn + diode as predicted by extended moment equation approximations to those obtained from the solution of the corresponding Boltzmann equation. All lower order models fail in the predominantly ballistic regime. Moreover, the conductance is inadequately predicted by these models, even in nonballistic cases due to the high build‐in electric fields.

Anhysteretic magnetization and demagnetization factor in Preisach models

The anhysteretic magnetization M/sub an/ depends on the internal field after degaussing H/sub an/ and, possibly, on the demagnetization factor N. Neels theory of the N dependence is criticized. Classes of Preisach models are identified for which M/sub an/ (H/sub an/) does not depend on N. A numerical method is presented to determine M/sub an/ (H/sub an/, N) from a Preisach model. The zero-field anhysteretic permeability is expressed in terms of the Preisach distribution up to first order in N-k, where k is the parameter of the moving Preisach model.

Multiple scattering of light from polymer dispersed liquid crystal material

Light scattering from polymer dispersed liquid crystal (PDLC) material has been studied experimentally and by Monte Carlo simulation. Light scattering was measured as a function of both scattering angle and cell thickness. The cell thicknesses of practical interest are in an intermediate regime where neither single scattering nor light diffusion applies. Both the angular and the thickness dependence of the scattering intensity can be described accurately by a Monte Carlo simulation of multiple scattering from a homogeneous distribution of independent scatterers. The model smoothly interpolates between the single scattering limit for thin cells and the diffusion limit for thick cells. It can easily be extended to include any specific feature of a scattering display system.

Dependence of the anhysteretic magnetization on the demagnetization factor

Abstract A method is presented to measure the dependence of the anhysteretic magnetization curve (the anhysteretic magnetization as a function of the internal field after degaussing) on the demagnetization factor N without physically varying N. The relation between the Preisach distribution and the N dependence of the anhysteretic magnetization curve is discussed in a way that is very close to the work of Bertotti. Classes of (moving) Preisach models are identified for which the anhysteretic magnetization curve is independent of the demagnetization factor. It is proven that the anhysteretic magnetization increases with N at fixed internal field, if the Preisach distribution decreases monotonically with increasing Hcent, the internal field value of a Preisach domain. It is shown that the Moving Preisach model may lead to a negative anhysteretic permeability.