On the Cholesteric-Nematic Phase-Change Transition in Layers with Homeotropically Orienting Surfaces

Lattice-model calculations of the energies of surface director-configurations are presented. These configurations mediate between the homeotropic surface conditions and the bulk fingerprint texture of cholesteric layers. Their energy determines the asymptotic behaviour of the cholesteric-nematic threshold field in the limit of thick layers. The dependence of their energies on the elastic constant ratios could be brought into a simple scaling form. This form is in agreement with existing and newly presented measurements.

Download Full-text

Threshold field of phase change memory materials measured using phase change bridge devices

Applied Physics Letters ◽

10.1063/1.3210792 ◽

2009 ◽

Vol 95 (8) ◽

pp. 082101 ◽

Cited By ~ 96

Author(s):

Daniel Krebs ◽

Simone Raoux ◽

Charles T. Rettner ◽

Geoffrey W. Burr ◽

Martin Salinga ◽

...

Keyword(s):

Phase Change ◽

Phase Change Memory ◽

Threshold Field ◽

Change Memory

Download Full-text

Extremely small twist elastic constants in lyotropic nematic liquid crystals

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1922275117 ◽

2020 ◽

Vol 117 (44) ◽

pp. 27238-27244 ◽

Cited By ~ 1

Author(s):

Clarissa F. Dietrich ◽

Peter J. Collings ◽

Thomas Sottmann ◽

Per Rudquist ◽

Frank Giesselmann

Keyword(s):

Liquid Crystals ◽

Elastic Constant ◽

Elastic Constants ◽

Nematic Phase ◽

Elastic Moduli ◽

Building Blocks ◽

Lyotropic Liquid Crystals ◽

Order Of Magnitude ◽

Typical Range ◽

Special Case

Recent measurements of the elastic constants in lyotropic chromonic liquid crystals (LCLCs) have revealed an anomalously small twist elastic constant compared to the splay and bend constants. Interestingly, measurements of the elastic constants in the micellar lyotropic liquid crystals (LLCs) that are formed by surfactants, by far the most ubiquitous and studied class of LLCs, are extremely rare and report only the ratios of elastic constants and do not include the twist elastic constant. By means of light scattering, this study presents absolute values of the elastic constants and their corresponding viscosities for the nematic phase of a standard LLC composed of disk-shaped micelles. Very different elastic moduli are found. While the splay elastic constant is in the typical range of 1.5 pN as is true in general for thermotropic nematics, the twist elastic constant is found to be one order of magnitude smaller (0.30 pN) and almost two orders of magnitude smaller than the bend elastic constant (21 pN). These results demonstrate that a small twist elastic constant is not restricted to the special case of LCLCs, but is true for LLCs in general. The reason for this extremely small twist elastic constant very likely originates with the flexibility of the assemblies that are the building blocks of both micellar and chromonic lyotropic liquid crystals.

Download Full-text

Phase behavior and local structure of a binary mixture in pores: Mean-field lattice model calculations for analyzing neutron scattering data

The Journal of Chemical Physics ◽

10.1063/1.1867372 ◽

2005 ◽

Vol 122 (12) ◽

pp. 124510 ◽

Cited By ~ 9

Author(s):

Dirk Woywod ◽

Sebastian Schemmel ◽

Gernot Rother ◽

Gerhard H. Findenegg ◽

Martin Schoen

Keyword(s):

Binary Mixture ◽

Neutron Scattering ◽

Phase Behavior ◽

Lattice Model ◽

Local Structure ◽

Mean Field ◽

Scattering Data ◽

Model Calculations

Download Full-text

Lattice model calculations for dx2−y2-wave Josephson junctions

Physica C Superconductivity ◽

10.1016/s0921-4534(00)01716-0 ◽

2001 ◽

Vol 352 (1-4) ◽

pp. 165-168 ◽

Cited By ~ 2

Author(s):

Hiroki Tsuchiura ◽

Yukio Tanaka ◽

Masao Ogata ◽

Satoshi Kashiwaya

Keyword(s):

Lattice Model ◽

Josephson Junctions ◽

Model Calculations

Download Full-text

Amorphized Length and Variability in Phase Change Memory Line Cells

10.3762/bxiv.2020.58.v1 ◽

2020 ◽

Author(s):

Nafisa Noor ◽

Sadid Muneer ◽

Raihan Sayeed Khan ◽

Anna Gorbenko ◽

Helena Silva

Keyword(s):

Phase Change ◽

Phase Change Memory ◽

Amorphous State ◽

Critical Parameters ◽

Threshold Field ◽

Electrical Measurements ◽

Threshold Switching ◽

Reset Voltage ◽

Threshold Voltages ◽

Change Memory

The dimensions of amorphized regions in phase-change memory cells are critical parameters to design devices for different applications but are difficult to determine by direct imaging. In this work, the length of amorphized regions in multiple, identical Ge2Sb2Te5 (GST) line cells was extracted from electrical measurements. After each cell was programmed to an amorphous state, a sequence of increasing amplitude post-reset voltage pulses separated by low-amplitude read DC-sweeps was applied. When a sufficient amplitude post-reset voltage pulse was applied to a given cell, the measured current and the post-pulse resistance increased drastically, indicating the cell re-amorphized after threshold switching, melting, and quenching. The amorphized length was calculated using the measured voltage at which threshold switching took place and the expected drifted threshold field at that time. The measured threshold voltages, hence, the extracted amorphized lengths, generally increase linearly with the programmed resistance levels, but significant variability arises from the intrinsic uniqueness in the crystallization and amorphization processes in these devices. For example, cells programmed to ~50 MΩ amorphous resistance show threshold voltages of ~5-7 V, corresponding to amorphized lengths of ~240-360 nm. This unpredictable programming feature in phase-change memory devices can be utilized in hardware security applications.

Download Full-text