Ferroelectric phase transition in individual single-crystalline BaTiO3 nanowires

We report scanned probe characterizations of the ferroelectric phase transition in individual barium titanate (BaTiO3) nanowires. Variable-temperature electrostatic force microscopy is used to manipulate, image, and evaluate the diameter-dependent stability of ferroelectric polarizations. These measurements show that the ferroelectric phase transition temperature (TC) is depressed as the nanowire diameter (dnw) decreases, following a 1/dnw scaling. The diameter at which TC falls below room temperature is determined to be approximately 3 nm, and extrapolation of the data indicates that nanowires with dnw as small as 0.8 nm can support ferroelectricity at lower temperatures. We also present density functional theory (DFT) calculations of bare and molecule-covered BaTiO3 surfaces. These calculations indicate that ferroelectricity in nanowires is stabilized by molecular adsorbates such as OH and carboxylates. These adsorbates are found to passivate polarization charge more effectively than metallic electrodes, explaining the observed stability of ferroelectricity in small-diameter BaTiO3 nanowires.     

Spatial distribution of TCPM-H and TCPM-OH in blue mussel and fish from the Gulf of Gdańsk, Baltic Sea

We describe a pre-embedding immunocytochemical method for visualization of the lysosomal enzyme cathepsin D in cultured cells. The protein was demonstrated at both light and electron microscopic levels by neutral-pH silver enhancement of ultrasmall (0.8-nm) gold particles conjugated to the antibodies. The best morphological preservation and the highest labeling density were achieved by initial fixation for 20 min at 4C in 4% paraformaldehyde (PFA) and 0. 05% glutaraldehyde (GA) in 0.15 M sodium cacodylate buffer, followed by permeabilization in sodium borohydride. Three cell types were used: human foreskin fibroblasts, histocytic lymphoma (J-774) cells, and primary rat heart myocytes. In all three, cathepsin D was demonstrated in lysosome-like structures. The rat heart myocytes were also exposed to the redox cycling substance naphthazarin (5, 8-dihydroxy-1,4-naphthoquinone) to induce oxidative stress. This was done for such a short period of time that the cells initially did not show any signs of morphological damage and retained normal plasma membrane stability, although an early and clear redistribution of cathepsin D from membrane-bound structures to the cytosol was apparent. This redistribution was followed by cell degeneration and, eventually, by cell death.     

Analytical Solutions for Stress Intensity Factor,T-Stress and Weight Function for the Edge-Cracked Half-Space

An analytical solution for the linear-elastic problem of an edge-cracked semi-infinite body was given already in 1957. For the numerical evaluation of this solution an iteration procedure had to be applied. This might be the reason why the related analysis was not commonly used. By means of powerful mathematical tools developed in the last years it is now possible to evaluate highly-precise stress intensity factors, T-stress terms, weight functions etc. This will be shown in this paper in detail.     

Exposure of populations to dioxins and related compounds

The present situation with respect to the exposure of the general human population to PCDDs, PCDFs and (dioxin-like) PCBs and specific issues that should be taken into consideration for a risk assessment of these exposures have been summarized. The information is based on studies performed in The Netherlands and Germany in the last 10 years. Additional data have been collected through a literature search and through many contacts with researchers and national authorities. The most important route for human exposure to PCDDs, PCDFs and (dioxin-like) PCBs is food consumption contributing over 90% of total exposure, with products of animal origin and fish making the greatest contribution to this exposure. The dietary intake of PCDDs and PCDFs by the general population of industrialized countries is on average 1-3 picograms of (i)-TEQ per kilogram body weight per day. If the contribution of dioxin-like PCBs are also considered, the daily TEQ intake can be a factor of two to three higher. Special consumption habits and consumption of highly contaminated foodstuffs may lead to lower and higher TEQ intakes. In general, TEQ intake increases during childhood and stabilizes in adults of about 20 years of age. However, when normalized by body weight exposure is found to decrease with childhood age due to increasing body weight. Exposure has been shown to have fallen over time in all countries where data are available. Countries that started to implement measures to reduce dioxin emissions in the late 1980s, such as The Netherlands, United Kingdom and Germany, clearly show decreasing PCDD/PCDF and PCB levels in food and consequently a significantly lower dietary intake of these compounds by almost a factor of 2 within the past 7 years.     

Surface Pyroelectricity in Cubic SrTiO3

Symmetry‐imposed restrictions on the number of available pyroelectric and piezoelectric materials remain a major limitation as 22 out of 32 crystallographic material classes exhibit neither pyroelectricity nor piezoelectricity. Yet, by breaking the lattice symmetry it is possible to circumvent this limitation. Here, using a unique technique for measuring transient currents upon rapid heating, direct experimental evidence is provided that despite the fact that bulk SrTiO₃ is not pyroelectric, the (100) surface of TiO₂‐terminated SrTiO₃ is intrinsically pyroelectric at room temperature. The pyroelectric layer is found to be ≈1 nm thick and, surprisingly, its polarization is comparable with that of strongly polar materials such as BaTiO₃. The pyroelectric effect can be tuned ON/OFF by the formation or removal of a nanometric SiO₂ layer. Using density functional theory, the pyroelectricity is found to be a result of polar surface relaxation, which can be suppressed by varying the lattice symmetry breaking using a SiO₂ capping layer. The observation of pyroelectricity emerging at the SrTiO₃ surface also implies that it is intrinsically piezoelectric. These findings may pave the way for observing and tailoring piezo‐ and pyroelectricity in any material through appropriate breaking of symmetry at surfaces and artificial nanostructures such as heterointerfaces and superlattices.     

Direct in situ determination of the polarization dependence of physisorption on ferroelectric surfaces

The ability to manipulate dipole orientation in ferroelectric oxides holds promise as a method to tailor surface reactivity for specific applications. As ferroelectric domains can be patterned at the nanoscale, domain-specific surface chemistries may provide a method for fabrication of nanoscale devices. Although studies over the past 50 yr have suggested that ferroelectric domain orientation may affect the energetics of adsorption, definitive evidence is still lacking. Domain-dependent sticking coefficients are observed using temperature-programmed desorption and scanning surface potential microscopy, supported by first-principles calculations of the reaction coordinate. The first unambiguous observations of differences in the energetics of physisorption on ferroelectric domains are presented here for CH(3)OH and CO(2) on BaTiO(3) and Pb(Ti(0.52)Zr(0.48))O(3) surfaces.     

Remote Photodamaging of DNA by Photoinduced Energy Transport

Local DNA photodamaging by light is well-studied and leads to a number of structurally identified direct damage, in particular cyclobutane pyrimidine dimers, and indirect oxidatively generated damage, such as 8-oxo-7,8-hydroxyguanine. Similar damages have now been found at remote sites, at least more than 105 Å (30 base pairs) away from the site of photoexcitation. In contrast to the established mechanisms of local DNA photodamaging, the processes of remote photodamage are only partially understood. Known pathways include those to remote oxidatively generated DNA photodamages, which were elucidated by studying electron hole transport through the DNA about 20 years ago. Recent studies with DNA photosensitizers and mechanistic proposals on photoinduced DNA-mediated energy transport are summarized in this minireview. These new mechanisms to a new type of remote DNA photodamaging provide an important extension to our general understanding to light-induced DNA damage and their mutations.     

On-Growth and In-Growth Osseointegration Enhancement in PM Porous Ti-Scaffolds by Two Different Bioactivation Strategies: Alkali Thermochemical Treatment and RGD Peptide Coating

A lack of primary stability and osteointegration in metallic implants may result in implant loosening and failure. Adding porosity to metallic implants reduces the stress shielding effect and improves implant performance, allowing the surrounding bone tissue to grow into the scaffold. However, a bioactive surface is needed to stimulate implant osteointegration and improve mechanical stability. In this study, porous titanium implants were produced via powder sintering to create different porous diameters and open interconnectivity. Two strategies were used to generate a bioactive surface on the metallic foams: (1) an inorganic alkali thermochemical treatment, (2) grafting a cell adhesive tripeptide (RGD). RGD peptides exhibit an affinity for integrins expressed by osteoblasts, and have been reported to improve osteoblast adhesion, whereas the thermochemical treatment is known to improve titanium implant osseointegration upon implantation. Bioactivated scaffolds and control samples were implanted into the tibiae of rabbits to analyze the effect of these two strategies in vivo regarding bone tissue regeneration through interconnected porosity. Histomorphometric evaluation was performed at 4 and 12 weeks after implantation. Bone-to-implant contact (BIC) and bone in-growth and on-growth were evaluated in different regions of interest (ROIs) inside and outside the implant. The results of this study show that after a long-term postoperative period, the RGD-coated samples presented higher quantification values of quantified newly formed bone tissue in the implant’s outer area. However, the total analyzed bone in-growth was observed to be slightly greater in the scaffolds treated with alkali thermochemical treatment. These results suggest that both strategies contribute to enhancing porous metallic implant stability and osteointegration, and a combination of both strategies might be worth pursuing.     

Epitaxial TiOx Surface in Ferroelectric BaTiO3: Native Structure and Dynamic Patterning at the Atomic Scale

Surfaces and interfaces of ferroelectric oxides exhibit enhanced functionality, and therefore serve as a platform for novel nano and quantum technologies. Experimental and theoretical challenges associated with examining the subtle electro‐chemo‐mechanical balance at metal‐oxide surfaces have hindered the understanding and control of their structure and behavior. Here, combined are advanced electron‐microscopy and first‐principles thermodynamics methods to reveal the atomic‐scale chemical and crystallographic structure of the surface of the seminal ferroelectric BaTiO₃. It is shown that the surface is composed of a native <2 nm thick TiO_x rock‐salt layer in epitaxial registry with the BaTiO₃. Using electron‐beam irradiation, artificial TiO_x sites with sub‐nanometer resolution are successfully patterned, by inducing Ba escape. Therefore, this work offers electro‐chemo‐mechanical insights into ferroelectric surface behavior in addition to a method for scalable high‐resolution beam‐induced chemical lithography for selectively driving surface phase transitions, and thereby functionalizing metal‐oxide surfaces.