A. Deyneka

Comprehensive portrait of cholesterol containing oxidized membrane.

Biological membranes are under significant oxidative stress caused by reactive oxygen species mostly originating during cellular respiration. Double bonds of the unsaturated lipids are most prone to oxidation, which might lead to shortening of the oxidized chain and inserting of terminal either aldehyde or carboxylic group. Structural rearrangement of oxidized lipids, addressed already, is mainly associated with looping back of the hydrophilic terminal group. This contribution utilizing dual-focus fluorescence correlation spectroscopy and electron paramagnetic resonance as well as atomistic molecular dynamics simulations focuses on the overall changes of the membrane structural and dynamical properties once it becomes oxidized. Particularly, attention is paid to cholesterol rearrangement in the oxidized membrane revealing its preferable interaction with carbonyls of the oxidized chains. In this view cholesterol seems to have a tendency to repair, rather than condense, the bilayer.

Lead Excess in Pb(Zr,Ti)O3 Thin Films Deposited by Reactive Sputtering at Low Temperatures

Pb(Zr,Ti)O 3 thin films deposited by multi-target reactive sputtering at low substrate temperatures are characterized by a significant lead excess without a measurable second phase formation. The presence of Pb 4 + sites was detected by means of the lead X-ray photoelectron spectroscopy spectra. Besides the Pb (4f 7/2 ) and Pb (4f 5/2 ) peaks of Pb 2 + two smaller peaks at higher energy were obtained, which should be assigned to a higher lead valence. A disordered structure enhances the temperature dependence of the optical gap in the temperature region between two second order phase transitions at 200 and 290°C. At these temperatures, the dielectric properties exhibit a Debye-type or Maxwell-Wagner-type relaxor contribution. The ternary phase diagram of a PbTiO 3 -PbZrO 3 -PbPbO 3 solution shows that about one third of the Zr-sites is occupied by Pb 4 + .

Self-Polarized PZT Thin Films: Deposition, Characterization and Application

The aim of this work is the characterization of self-polarized PZT thin films. The laser-intensity-modulation method (LIMM) was applied for the investigation of the self-polarization profile. Pyroelectric coefficient profiles were reconstructed from the pyrocurrent spectrum measured up to frequencies of 2 MHz using MATLAB-software containing algorithms for the inverse solution of the appropriate Fredholm integral equation and a Tikhonov regularization method for stable numerical solutions. Measurement uncertainties and resolution of this measurement technique are discussed. The application of self-polarized IR sensor arrays in presence detection and IR imaging is demonstrated.

DEPOSITION OF NANOCRYSTALLINE AND MICROCRYSTALLINE BaXSr1-XTiO3 BY MEANS OF PULSE MODULATED LOW PRESSURE PLASMA JET SYSTEM

ABSTRACT RF plasma jet system was used for deposition of BaxSr1-xTiO3 (BSTO) and SrTiO3 (STO) thin films. Optical emission spectroscopy was used for control of concentration of particles sputtered from the hollow cathode. Relation between ratio of spectral intensity of Ba, Ba+, Sr and Sr+ lines and ratio of Ba and Sr concentration in the deposited film was found. Deposited thin films were analyzed by XRD, which confirmed presence of BSTO perovskite phase in the films. All prepared films with high enough Ba concentration (0.5 ≤ x ≤ 0.9) revealed good shaped dielectric hysteresis loops typical for ferroelectric phase.

Phase Transitions in PbZr1-xTixO3 Ceramics Prepared by Different Techniques

In this work, we present our study of the phase transitions and the temperature dependence of the optical properties of the PbZr0.235Ti0.765O3 films prepared by multi-target reactive sputtering and sol-gel methods. Optical measurements were performed with the J. A. Woollam spectral ellipsometer operating in rotating analyzer mode. The main ellipsometric angles Ψ and Δ were measured in the spectral range from 300 to 1200 nm. High-temperature measurements were performed in a specially designed thermostat system. The samples were heated to 500°C to reach the paraelectric phase. The temperature dependences of the refractive index and the absorption coefficient at fixed wavelengths, and the optical gap Eg obtained from isoabsorption curves at a=1000 cm-1 were obtained from ellipsometric experiment.

BaxSr1-xTiO3 thin films deposited by RF hollow cathode plasma jet technique

The RF modulated plasma jet system was used for the deposition of Ba x Sr1− x TiO3 (BST), and SrTiO3 (STO) thin films on Si and multi-layer system Si/SiO2/TiO2/Pt substrates. BSTO and STO thin films were analyzed using X-ray diffraction. During deposition, the substrate was heated at 500°C. Emission spectroscopy of the plasma was used to control the concentration of sputtered particles from the hollow cathode, mainly Sr and Ba atoms. XRD diffraction confirmed the presence of BSTO and STO perovskite phase in the films. The optical band gap obtained from spectroscopic ellipsometry was correlated with composition.

Luminescence and Absorption Spectroscopy of Weakly Mn-Doped SrTiO3 Crystals

The emission and excitation spectra of photoluminescence of the as-grown and reduced SrTiO 3 :Mn (280 ppm) crystal were studied within wide temperature (12 – 300 K) and spectral (300 – 1600 nm) regions. The emission spectra consist of two overlapping bands. The first one corresponds to the emission of Mn 4 + ions substituted in octahedral coordinated Ti 4+ sites with zero-phonon line peaking at 723.23 nm at 12 K. The second broad emission band peaking near 870 nm was observed on SrTiO3:Mn crystals for the first time. Temperature behavior of photoluminescence intensity and the origin of this new Mn related emission band are discussed.

Phase Transition Shift in Lead-Excess PZT Films Under UV Illumination

Self-polarized PZT are ferroelectrics with a preferred polarization orientation at room temperature and becomes a paraelectric at high temperatures of about 460°C. The ferroelectric-paraelectric phase transition temperature depends on stoichiometry of the PZT material and therefore on preparation technology. In this work, we present an ellipsometric study of lead excess Pb1 + xZr0.235Ti0.765O3 (PZT) films exhibiting a strong self-polarization in the temperature range of 20 to 500°C under UV illumination. We obtained a shift of the ferroelectric-paraelectric phase transition temperature to lower values and an increase of the optical gap E03. The temperature dependences of the optical gap E03, the refractive index and the absorption coefficient at fixed wavelengths were determined.

Stability of Space Charge Compensated Ferroelectrics

In this work, the long-term stability of self-polarized ferroelectrics thin films consisting of a negative space charge region near the bottom electrode was investigated. This space charge acts against domain motion and polarizes the film when cooled down below the paraelectric-ferroelectric transition temperature. Self-polarized perovskite PZT layers were deposited by planar multi target sputtering on platinized silicon wafers. Ellipsometric measurements were performed for refractive index profiling in order to investigate the temperature stability of the space charge induced refractive index profile near the bottom Pt electrode. Self-polarized negative space charge compensated ferroelectric thin films were found to meet the life-time requirements for device application.

Relaxor-Like Behavior of Self-Polarized Pb(Zr,Ti)O3 Thin Films

Self-polarized Pb(Ti,Zr)O3 thin films deposited under lead enriched conditions by multitarget reactive sputtering at low substrate temperatures are characterized by tetravalent B-site occupation of excess lead. The imaginary part of the dielectric constant of such films shows a relaxor-like behavior. Evidence of a Pb2+/Pb4+ mixed valence is given by the temperature and frequency dependence of the ac conductivity. PbO volatility starts to deplete the growing film at a critical temperature of 500°C and Pb4+ formation disappears.