Highly mobile ferroelastic domain walls in compositionally graded ferroelectric thin films.

Domains and domain walls are critical in determining the response of ferroelectrics, and the ability to controllably create, annihilate, or move domains is essential to enable a range of next-generation devices. Whereas electric-field control has been demonstrated for ferroelectric 180° domain walls, similar control of ferroelastic domains has not been achieved. Here, using controlled composition and strain gradients, we demonstrate deterministic control of ferroelastic domains that are rendered highly mobile in a controlled and reversible manner. Through a combination of thin-film growth, transmission-electron-microscopy-based nanobeam diffraction and nanoscale band-excitation switching spectroscopy, we show that strain gradients in compositionally graded PbZr1-xTixO3 heterostructures stabilize needle-like ferroelastic domains that terminate inside the film. These needle-like domains are highly labile in the out-of-plane direction under applied electric fields, producing a locally enhanced piezoresponse. This work demonstrates the efficacy of novel modes of epitaxy in providing new modalities of domain engineering and potential for as-yet-unrealized nanoscale functional devices.

Giant elastic tunability in strained BiFeO3 near an electrically induced phase transition.

Elastic anomalies are signatures of phase transitions in condensed matters and have traditionally been studied using various techniques spanning from neutron scattering to static mechanical testing. Here, using band-excitation elastic/piezoresponse spectroscopy, we probed sub-MHz elastic dynamics of a tip bias-induced rhombohedral-tetragonal phase transition of strained (001)-BiFeO3 (rhombohedral) ferroelectric thin films from ∼10(3) nm(3) sample volumes. Near this transition, we observed that the Young's modulus intrinsically softens by over 30% coinciding with two- to three-fold enhancement of local piezoresponse. Coupled with phase-field modelling, we also addressed the influence of polarization switching and mesoscopic structural heterogeneities (for example, domain walls) on the kinetics of this phase transition, thereby providing fresh insights into the morphotropic phase boundary in ferroelectrics. Furthermore, the giant electrically tunable elastic stiffness and corresponding electromechanical properties observed here suggest potential applications of BiFeO3 in next-generation frequency-agile electroacoustic devices, based on the utilization of the soft modes underlying successive ferroelectric phase transitions.

Ultrathin limit of exchange bias coupling at oxide multiferroic/ferromagnetic interfaces.

Exchange bias coupling at the multiferroic- ferromagnetic interface in BiFeO3 /La0.7 Sr0.3 MnO3 heterostructures exhibits a critical thickness for ultrathin BiFeO3 layers of 5 unit cells (2 nm). Linear dichroism measurements demonstrate the dependence on the BiFeO3 layer thickness with a strong reduction for ultrathin layers, indicating diminished antiferromagnetic ordering that prevents interfacial exchange bias coupling.

Phase transitions, phase coexistence, and piezoelectric switching behavior in highly strained BiFeO(3) films.

Highly strained BiFeO3 films transition into a true tetragonal state at 430 °C but remain polar to much higher temperatures (∼800 °C). Piezoelectric switching is only possible up to 300 °C, i.e., at temperatures for which strain stabilizes the stripe-like coexistence of multiple polymorphs.

Ferroelectricity in strain-free SrTiO3 thin films.

Biaxial strain is known to induce ferroelectricity in thin films of nominally nonferroelectric materials such as SrTiO3. By a direct comparison of the strained and strain-free SrTiO3 films using dielectric, ferroelectric, Raman, nonlinear optical and nanoscale piezoelectric property measurements, we conclude that all SrTiO3 films and bulk crystals are relaxor ferroelectrics, and the role of strain is to stabilize longer-range correlation of preexisting nanopolar regions, likely originating from minute amounts of unintentional Sr deficiency in nominally stoichiometric samples. These findings highlight the sensitive role of stoichiometry when exploring strain and epitaxy-induced electronic phenomena in oxide films, heterostructures, and interfaces.

Nanoscale mapping of ion diffusion in a lithium-ion battery cathode.

The movement of lithium ions into and out of electrodes is central to the operation of lithium-ion batteries. Although this process has been extensively studied at the device level, it remains insufficiently characterized at the nanoscale level of grain clusters, single grains and defects. Here, we probe the spatial variation of lithium-ion diffusion times in the battery-cathode material LiCoO(2) at a resolution of ∼100 nm by using an atomic force microscope to both redistribute lithium ions and measure the resulting cathode deformation. The relationship between diffusion and single grains and grain boundaries is observed, revealing that the diffusion coefficient increases for certain grain orientations and single-grain boundaries. This knowledge provides feedback to improve understanding of the nanoscale mechanisms underpinning lithium-ion battery operation.

Deterministic control of ferroelastic switching in multiferroic materials.

Multiferroic materials showing coupled electric, magnetic and elastic orderings provide a platform to explore complexity and new paradigms for memory and logic devices. Until now, the deterministic control of non-ferroelectric order parameters in multiferroics has been elusive. Here, we demonstrate deterministic ferroelastic switching in rhombohedral BiFeO(3) by domain nucleation with a scanning probe. We are able to select among final states that have the same electrostatic energy, but differ dramatically in elastic or magnetic order, by applying voltage to the probe while it is in lateral motion. We also demonstrate the controlled creation of a ferrotoroidal order parameter. The ability to control local elastic, magnetic and torroidal order parameters with an electric field will make it possible to probe local strain and magnetic ordering, and engineer various magnetoelectric, domain-wall-based and strain-coupled devices.

Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films.

Many interesting materials phenomena such as the emergence of high-Tc superconductivity in the cuprates and colossal magnetoresistance in the manganites arise out of a doping-driven competition between energetically similar ground states. Doped multiferroics present a tantalizing evolution of this generic concept of phase competition. Here, we present the observation of an electronic conductor-insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO3 through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p-n junction can be created, erased and inverted in this material. A 'dome-like' feature in the doping dependence of the ferroelectric transition is observed around a Ca concentration of approximately 1/8, where a new pseudo-tetragonal phase appears and the electric modulation of conduction is optimized. Possible mechanisms for the observed effects are discussed on the basis of the interplay of ionic and electronic conduction. This observation opens the door to merging magnetoelectrics and magnetoelectronics at room temperature by combining electronic conduction with electric and magnetic degrees of freedom already present in the multiferroic BiFeO3.

Conduction at domain walls in oxide multiferroics.

Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO(3). The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.

Inhibition of degranulation of human polymorphonuclear leukocytes by complement factor D.

A degranulation inhibiting protein could be isolated from human plasma ultrafiltrate by a three-step purification method including ion-exchange chromatography, gelfiltration and affinity-chromatography. The protein was identified as complement factor D by means of sequence analysis. Its degranulation inhibiting activity was determined with regard to its effect on the FNLPNTL-induced lactoferrin secretion of human polymorphonuclear leukocytes. Complement factor D caused a dose-dependent decrease of the FNLPNTL-stimulated lactoferrin degranulation down to 34% of stimulated controls.

Induction of UDP-Glucose:Salicylic Acid Glucosyltransferase in Oat Roots.

A UDP-glucose:salicylic acid 3-O-glucosyltransferase (EC 2.4.1.35) (GTase) from oat (Avena sativa L. cv Dal) root extracts was assayed in vitro using [(14)C]salicylic acid (SA) and an ion exchange column to separate SA from beta-glucosylsalicylic acid. The GTase, present at a very low constitutive level, was inducible to 23 times the constitutive level. When excised roots were exposed to SA at pH 6.5, the specific activity of the enzyme increased within 1.5 h, peaked after 8 to 10 h, and then declined. The increase in specific activity depended on the concentration of SA in the induction medium. Among 16 phenolics and phenolic derivatives tested, GTase induction showed high specificity toward SA and acetylsalicylic acid. Specific activity of the enzyme was induced to higher levels in roots from 7-d-old seedlings than roots from younger plants. GTase activity was less inducible in basal compared with median or apical root sections. Induction of GTase activity was a result of de novo RNA and protein synthesis. Candidate peptides for the GTase were identified by comparison of two-dimensional electrophoresis gels of proteins labeled with [(35)S]methionine during incubation of roots in the presence or the absence of SA and a gel of a partially purified GTase preparation.

Partial purification and properties of an inducible uridine 5'-diphosphate-glucose-salicylic Acid glucosyltransferase from oat roots.

A salicylic acid (SA)-inducible uridine 5'-diphosphate (UDP)-glucose:SA 3-O-glucosyltransferase was extracted from oat (Avena sativa L. cv Dal) roots. Reverse phase high-performance liquid chromatography or anion exchange chromatography was used to separate SA from the product, beta-O-d-glucosylsalicylic acid. The soluble enzyme was purified 176-fold with 5% recovery using a combination of pH fractionation, anion exchange, gel filtration, and chromatofocusing chromatography. The partially purified protein had a native molecular weight of about 50,000, an apparent isoelectric point at pH 5.0, and maximum activity at pH 5.5. The enzyme had a K(m) of 0.28 mm for UDP-glucose and was highly specific for this sugar donor. More than 20 hydroxybenzoic and hydroxycinnamic acid derivatives were assayed as potential glucose acceptors. UDP-glucose:SA 3-O-glucosyltransferase activity was highly specific toward SA (K(m) = 0.16 mm). The enzyme was inhibited by UDP and uridine 5'-triphosphate but not by up to 7.5 mm uridine 5'-monophosphate.

Herbicide clomazone does not inhibit in vitro geranylgeranyl synthesis from mevalonate.

Clomazone reduced the chlorophyll and carotenoid contents of spinach (Spinacia oleracea L.), barley (Hordeum vulgare L.), velvetleaf (Abutilon theophrasti Medik.), and soybean (Glycine max L. Merr.) seedlings. The order of species sensitivity was velvetleaf > spinach > barley > soybean. Clomazone (100 micromolar) did not affect the in vitro activities of spinach isopentenyl pyrophosphate isomerase or prenyl transferase. Clomazone also did not affect the synthesis of isopentenyl pyrophosphate from mevalonic acid. Thus, clomazone had no direct in vitro effect on the synthesis of geranylgeranyl pyrophosphate from mevalonic acid. Greening seedlings of both soybean and velvetleaf metabolized clomazone. No qualitative differences in the metabolites were detected between soybean and velvetleaf. Thus, differential metabolism of clomazone to a toxic chemical that inhibits terpenoid synthesis is unlikely. Clomazone has either a mode of action not yet identified or a metabolite that is selective in that it is much more active in sensitive than tolerant species.

Uptake and accumulation of the herbicide bentazon by cultured plant cells.

Cellular absorption of the herbicide bentazon, a weak acid with pK(a) 3.45, was investigated using suspension-cultured cells of velvetleaf (Abutilon theophrasti Medic.). Bentazon accumulated rapidly to concentrations approximately four times that of the external medium. Bentazon accumulation against a concentration gradient was not due to its conversion to metabolites, partitioning into lipids, or binding onto cellular constituents. Bentazon uptake was related linearly to the external bentazon concentration, implying that movement of the herbicide into cells was not carrier-mediated. Bentazon was able to diffuse freely and extensively out of the cells, indicating that bentazon can readily diffuse across cell membranes. Potassium cyanide and carbonyl cyanide m-chlorophenyl hydrazone inhibited bentazon accumulation as did nitrogen gas when bubbled through the uptake medium. Absorption was pH-dependent with the greatest amount of bentazon accumulating at acidic external pH. Calculations indicated that conversion of uncharged bentazon to bentazon anion in the cytoplasm accounts for cellular accumulation of bentazon. These results provide evidence that bentazon is absorbed across membranes via simple diffusion and that bentazon accumulates in plant cells via an energy-dependent, ion-trapping mechanism which results in bentazon accumulation in the cytoplasm.

Diclofop-methyl increases the proton permeability of isolated oat-root tonoplast.

Diclofop-methyl (methyl ester of 2-[4-(2',4'-dichlorophenoxy)phenoxy]propionate; 100 micromolar) and diclofop (100 micromolar) inhibited both ATP- and PPi-dependent formation of H(+) gradients by tonoplast vesicles isolated from oat (Avena sativa L., cv Dal) roots. Diclofop-methyl (1 micromolar) significantly reduced the steady-state H(+) gradient generated in the presence of ATP. The ester (diclofop-methyl) was more inhibitory than the free acid (diclofop) at pH 7.4, but this relative activity was reversed at pH 5.7. Neither compound affected the rate of ATP or PPi hydrolysis by the proton-pumping enzymes. Diclofop-methyl (50, 100 micromolar), but not diclofop (100 micromolar), accelerated the decay of nonmetabolic H(+) gradients established across vesicle membranes. Diclofop-methyl (100 micromolar) did not collapse K(+) gradients across vesicle membranes. Both the (+)- and (-)-enantiomers of diclofop-methyl dissipated nonmetabolic H(+) gradients established across vesicle membranes. Diclofop-methyl, but not diclofop (each 100 micromolar), accelerated the decay of H(+) gradients imposed across liposomal membranes. These results show that diclofop-methyl causes a specific increase in the H(+) permeability of tonoplast.

Characterization of the inhibition of k absorption in oat roots by salicylic Acid.

The phenolic compounds salicylic acid (o-hydroxybenzoic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) inhibited K(+) ((86)Rb(+)) absorption in excised oat (Avena sativa L. cv. Goodfield) root tissue. Salicylic acid was the most inhibitory. The degree of inhibition was both concentration- and pH-dependent. With decreasing pH, the inhibitory effect of the phenolic increased. During the early stages of incubation, the time required to inhibit K(+) absorption was also pH- and concentration-dependent. At pH 4.0, 5x10(-4) molar salicylic acid inhibited K(+) absorption about 60% within 1 minute; whereas, at pH 6.5, this concentration affected absorption only after 10 to 15 minutes. However, at 5 x 10(-3) molar and pH 6.5, salicylic acid was inhibitory within 1 minute. The capacity of the tissue to recover following a 1-hour treatment in 5 x 10(-4) molar salicylic acid ranged from no recovery at pH 4.5 to complete recovery at pH 7.5. The absorption of salicylic acid was pH-dependent, also. As pH decreased, more of the phenolic compound was absorbed by the tissue. The increased absorption of the compound at low pH most likely contributed to apparent tissue damage at pH 4.5 and might have accounted for the lack of recovery of K(+) absorption as pH decreased.Under the proper conditions of pH and concentration, phenolic acids such as salicylic acid could significantly affect mineral absorption by plants in the field.

Inhibition of adenosine triphosphatase activity of the plasma membrane fraction of oat roots by diethylstilbestrol.

Diethylstibestrol (DES) inhibited noncompetitively the ATPase in the plasma membrane fraction from Avena sativa L. cv. Goodfield roots when assayed in the presence of MgSO(4) or MgSO(4) plus KCl. In the presence of MgSO(4), 7.1x10(-5) molar DES inhibited the enzyme 50%; whereas in the presence of MgSO(4) and KCl, 1.3x10(-4) molar DES was required for the same inhibition. Dixon plots indicated that in the presence of MgSO(4), one molecule of DES bound to one molecule of ATPase; however, in the presence of MgSO(4) and KCl, two or more molecules bound to one ATPase molecule. These results suggested that KCl causes a conformational change in the enzyme which exposes additional binding sites for DES, but that these sites are not as inhibitory as the first binding site.In addition to KCl, other factors also affected the DES inhibition of the ATPase. Plasma membrane vesicles warmed to 38 C were inhibited more than vesicles kept on ice prior to assay. DES inhibited the Triton X-100-treated ATPase less than the ATPase which was not detergent-treated. Finally, studies with DES analogs showed that the hydroxyl groups of DES were essential for inhibition and that steric configurations of the molecule were important.DES inhibition of the ATPase suggests that DES inhibits K(+) absorption in oat roots by inhibiting the ATPase. Inhibition of K(+) absorption was greater than inhibition of the ATPase, and thus DES may also inhibit other aspects of metabolism that are involved with ion absorption.

Effect of diethylstilbestrol on ion fluxes in oat roots.

Effects of diethylstilbestrol (DES) on ion fluxes in oat roots (Avena sativa L.) were investigated by measuring K(+) and Cl(-) absorption and K(+) efflux. DES rapidly decreased the absorption of K(+) ((86)Rb) and (36)Cl(-) by excised roots; 10(-4) molar DES inhibited Cl(-) absorption in 1 minute and K(+) absorption in 1 to 2 minutes. With a 10-minute incubation period, K(+) and Cl(-) absorption were inhibited 50% by 1.1x10(-5) molar and 8.4x10(-6) molar DES, respectively. Treatment for 3 minutes with 10(-4) molar DES caused irreversible inhibition of K(+) absorption. Increasing concentrations of KCl in the absorption media decreased the DES inhibition. Experiments with the DES analogs, DES dipropionate, dienestrol and hexestrol, showed that the steric configuration and the hydroxyl group of the DES molecule are important in determining the inhibitory capacity of the compound.DES increased the efflux of (86)Rb from excised roots only after a 10-minute lag period. In 10(-4) molar DES, roots lost 82% of their radionuclide content in 1 hour. Comparison of efflux curves for roots loaded for 20 hours and those loaded for 15 minutes suggested that DES increased the permeability of the plasma membrane after about 10 minutes and the permeability of the tonoplast after 10 to 20 minutes. Oligomycin and dinitrophenol also increased the loss of (86)Rb, but the lag period was about 4 hours.The rapid effect of DES on ion absorption and the slower effect on ion efflux suggest that DES initially inhibits ion uptake by affecting the transport mechanism at the plasma membrane in some manner other than alteration of membrane permeability.

Comparison of Reductions in Adenosine Triphosphate Content, Plasma Membrane-associated Adenosine Triphosphatase Activity, and Potassium Absorption in Oat Roots by Diethylstilbestrol.

The possibility was investigated that diethylstilbestrol (DES) inhibits potassium absorption in oat (Avena sativa L. cv. Goodfield) roots by inhibiting mitochondrial functions in addition to inhibiting the plasma membrane ATPase. DES at 10(-6) molar stimulated the mitochondrial ATPase slightly, but higher concentrations had no effect. Oxidative phosphorylation by isolated mitochondria was inhibited 50% by 2.6 x 10(-5) molar DES; concentrations of 10(-4) molar or greater were completely inhibitory. After a lag of about 2 minutes, 10(-4) molar DES produced a linear decrease in ATP content of excised roots. After 20 minutes, the ATP content of the tissue was about 50% of the control and remained at that level after 30 minutes in DES.Comparison of changes in ATP content, plasma membrane ATPase activity, and K(+) absorption rate with time in the presence of DES showed that the rapid decrease in K(+) absorption rate corresponded more closely with the decrease in ATPase activity than the decrease in ATP content. Total inhibition of the ATPase was calculated by multiplying together the percentage decreases in ATPase activity and ATP content. At times greater than 10 minutes this "net" ATPase activity corresponded very closely with the K(+) absorption rate.These results show that DES can inhibit potassium absorption by reducing mitochondrial ATP production in addition to inhibiting the plasma membrane ATPase. However, the rapid (less than 5 minutes) inhibition of absorption is caused by direct inhibition of the ATPase rather than a reduced ATP supply because the ATP content is lowered only slightly whereas the ATPase is inhibited dramatically in that time. The relationship between plasma membrane ATPase activity and K(+) absorption rate as inhibited by DES supports the hypothesis that the ATPase is involved in cation absorption by plant roots.