Imaging of ferroelectric thin films by X-ray photoemission electron microscopy (XPEEM)

We performed X-ray photoemission electron microscopy (XPEEM) measurements at the Nanospectroscopy Beamline of the synchrotron light source ELETTRA, Trieste, Italy, to demonstrate the principal possibility of imaging ferroelectric thin films by low-energy photoelectrons. Due to the insulating properties of ferroelectric films, severe surface charging was the major experimental challenge to overcome. This was achieved by grounding an array of gold inter-digital electrodes (with 5 microm blank intervals between them) deposited on top of the films. The images taken with BaTiO(3) films revealed 50-100 nm-sized holes (material discontinuities) on the surface, an observation confirmed by high-resolution scanning electron microscopy (HRSEM). Finer details, e.g. a granular structure, which has been resolved with HRSEM, could not be observed in the XPEEM images. Our measurements indicate that despite some residual charging, a 50 nm lateral resolution can be achieved in XPEEM measurements with ferroelectric films.     

Nonaqueous chromatography of biopolymers by means of their poly(ethylene glycol)-mediated solubilization in alcohols

Freeze-drying of aqueous solutions of biopolymers and excess poly(ethylene glycol)s leads to formation of hydrophobic complex. Complexation with PEG increases solubility of low molecular weight DNA, RNA, and several proteins in neat ethanol and methanol. Solubilized nucleic acids can be fractionated, and proteins separated by nonaqueous reversed phase HPLC. © 1995 John Wiley & Sons, Inc.     

Kinetics of interaction of HIV fusion protein (gp41) with lipid membranes studied by real-time AFM imaging

One of the most important steps in the process of viral infection is a fusion between cell membrane and virus, which is mediated by the viral envelope glycoprotein. The study of activity of the glycoprotein in the post-fusion state is important for understanding the progression of infection. Here we present a first real-time kinetic study of the activity of gp41 (the viral envelope glycoprotein of human immunodeficiency virus—HIV) and its two mutants in the post-fusion state with nanometer resolution by atomic force microscopy (AFM). Tracking the changes in the phosphatidylcholine (PC) and phosphatidylcholine–phosphatidylserine (PC:PS) membrane integrity over one hour by a set of AFM images revealed differences in the interaction of the three types of protein with zwitterionic and negatively charged membranes. A quantitative analysis of the slow kinetics of hole formation in the negatively charged lipid bilayer is presented. Specifically, analysis of the rate of roughness change for the three types of proteins suggests that they exhibit different types of kinetic behavior.     

XUV laser-plasma source based on solid Ar filament

We present a laser driven soft x-ray source based on a novel solid argon filament. The continuously flowing micron-sized filament (diameter approximately 56 microm, flow speed approximately 5 mms) was used as a laser target in order to generate a plasma source of high brightness in the "water window" (2.2-4.4 nm) spectral range. The emission properties of the source were characterized in detail with respect to crucial parameters such as positional and energy stability using an extreme ultraviolet (XUV) sensitive pinhole camera and an XUV spectrometer. The results are compared with an argon plasma based on a gas puff target operated under the same experimental conditions showing an increase of the brilliance by a factor of 84. By changing the capillary geometry from a constant diameter to a convergent shape the flow speed of the filament was significantly increased up to 250 mms, facilitating the operation at higher repetition rates.     

NSOM the fourth dimension: Integrating nanometric spatial and femtosecond time resolution

Photonic devices are becoming the cornerstone of next generation systems for computing and information processing. This paper reports on the first steps in the development of methods to understand these devices with nanometric (10^?7 cm) spatial and femtosecond (10^?15 s) time resolution. The basis of this achievement is the dramatic developments that have occurred in the past few years in a new area of optics called near-field optics. Near-field optics is a form of lensless optics with a resolution that is subwavelength and which is independent of the wavelength of the light being employed. We report in this paper the transmission of pulses with tens of femtosecond duration through subwavelength, near-field optical elements. We also report on a femtosecond near-field optical light source with cross-correlating capabilities and on the growth of GaAs in the tip of micropipettes for use as an ultra-fast electro-optical switch which can cross-correlate optical, electrical, and electro-optical effects. These developments are especially relevant in the investigation of photonic devices since such devices can alter their characteristics as a function of size in the mesoscopic regime from just below lens-based optical resolutions to dimensions that approach atomic scales of ～1 nm (10^?7 cm). In view of the fact that these devices and the processes that govern them also exhibit ultrafast speeds, the combination of state of the art femtosecond laser spectroscopy with the unique features of near-field optics is a critical step in advancing our next generation understandings of such materials and structures so that their full potential in information processing can be achieved.     

Antiferromagnetic Inverse Spinel Oxide LiCoVO4 with Spin-Polarized Channels for Water Oxidation

Exploring highly efficient catalysts for the oxygen evolution reaction (OER) is essential for water electrolysis. Cost-effective transition-metal oxides with reasonable activity are raising attention. Recently, OER reactants' and products' differing spin configurations have been thought to cause slow reaction kinetics. Catalysts with magnetically polarized channels could selectively remove electrons with opposite magnetic moment and conserve overall spin during OER, enhancing triplet state oxygen molecule evolution. Herein, antiferromagnetic inverse spinel oxide LiCoVO₄ is found to contain d⁷ Co²⁺ ions that can be stabilized under active octahedral sites, possessing high spin states S = 3/2 (t_2g⁵e_g²). With high spin configuration, each Co²⁺ ion has an ideal magnetic moment of 3 µ_B, allowing the edge-shared Co²⁺ octahedra in spinel to be magnetically polarized. Density functional theory simulation results show that the layered antiferromagnetic LiCoVO₄ studied contains magnetically polarized channels. The average magnetic moment (µ_ave) per transition-metal atom in the spin conduction channel is around 2.66 µ_B. Such channels are able to enhance the selective removal of spin-oriented electrons from the reactants during the OER, which facilitates the accumulation of appropriate magnetic moments for triplet oxygen molecule evolution. In addition, the LiCoVO₄ reported has been identified as an oxide catalyst with excellent OER activity.     

Hydrogels of polyvinylpyrrolidone (PVP) and poly(acrylic acid) (PAA) synthesized by photoinduced crosslinking of homopolymers

A novel method of covalent crosslinking between polyvinylpyrrolidone (PVP) and poly(acrylic acid) (PAA) resulting in hydrogels has been developed. The hydrogels were formed by photocrosslinking in oxygen-free aqueous solutions containing hydrogen peroxide as a source of hydroxyl radicals. The crosslinking was achieved via irradiation within the broad wavelength range from 200 to 800 nm, as well as by the light cut-off at λ > 300 nm. The obtained PAA-PVP gels were sensitive to pH. Protonation of the PAA carboxylic groups with decreasing pH promoted hydrogen bonding between the PAA and PVP segments within the crosslinked structure and caused the gel to collapse. This property enabled the use of the hydrogels as a simple chemical sensor. When loaded with glucose oxidase, the PAA-PVP gel's opacity and sedimentation due to the clearly observable phase separation were triggered by the presence of glucose due to a drop in pH caused by the enzymatic reaction.     

Synthesis and Evaluation of a Series of Bis(pentylpyridinium) Compounds as Antifungal Agents

A series of bis(4‐pentylpyridinium) compounds with a variety of spacers between the pyridinium headgroups was synthesised, and the antifungal activity of these compounds was investigated. Lengthening the alkyl spacer between the pentylpyridinium headgroups from 12 to 16 methylene units resulted in increased antifungal activity against C. neoformans and C. albicans, but also resulted in increased hemolytic activity and cytotoxicity against mammalian cells. However, inclusion of an ortho‐substituted benzene ring in the centre of the alkyl spacer resulted in decreased cytotoxicity and hemolytic activity, while maintaining antifungal potency. Replacement of the alkyl and aromatic‐containing spacers by more hydrophilic ethylene glycol groups resulted in a loss of antifungal activity. Some of the compounds inhibited fungal PLB1 activity, but the low correlation of this inhibition with antifungal potency indicates PLB1 inhibition is unlikely to be the predominant mode of antifungal action of this class of compounds, with preliminary studies suggesting they may act via disruption of fungal mitochondrial function.     

Radiation-Induced Fault Simulation of SOI/SOS CMOS LSI’s Using Universal Rad-SPICE MOSFET Model

The methodology of modeling and simulation of environmentally induced faults in radiation hardened SOI/SOS CMOS IC’s is presented. It is realized at three levels: CMOS devices – typical analog or digital circuit fragments – complete IC’s. For this purpose, a universal compact SOI/SOS MOSFET model for SPICE simulation software with account for TID, dose rate and single event effects is developed. The model parameters extraction procedure is described in great depth taking into consideration radiation effects and peculiarities of novel radiation-hardened (RH) SOI/SOS MOS structures. Examples of radiation-induced fault simulation in analog and digital SOI/SOS CMOS LSI’s are presented for different types of radiation influence. The simulation results show the difference with experimental data not larger than 10–20% for all types of radiation.