Initial Polarization Research Articles

Impact of various mechanisms of the photorefractive effect on polarization singularity generation during the self-focusing of a Gaussian beam in an isotropic medium

The emerging of polarization singularity lines (C-lines), accompanying the self-focusing of an initially elliptically polarized Gaussian beam in an isotropic medium with various mechanisms of cubic nonlinearity, is studied numerically. Lines of circular polarization can appear in planes perpendicular to the beam axis as circles centered at the axis in both sub-threshold and super-threshold regimes of nonlinear self-action. The range of beam power values, for which the C-lines are formed, rapidly expands as the initial polarization of the beam gets closer to circular. The radius of the first formed C-line and the distance from the C-line to the border of the medium are decreasing if the beam power increases.

Using a vibratory source at Mt. Etna (Italy) to investigate the wavefield polarization at Pernicana Fault

ABSTRACTThe paper presents the results of a controlled‐source seismic experiment performed using a vibratory source capable of producing harmonic vibrations. The survey aimed at investigating the horizontal directional amplification mechanism observed at the Pernicana Fault (Mt. Etna in Sicily, Italy) along an N150°/N330° orientation. With the vibratory source (a shaker truck) working in shear‐wave mode in the frequency range 5–40 Hz, we recorded seismic data using both three‐component velocimeters and 4.5 Hz geophones. These two types of receivers were arranged in linear configuration along two orthogonal orientations: radial and transverse to the direction of the main polarization observed within the fault zone. The two lines of seismic stations allowed us to investigate the polarization evolution as a function of the distance from the source. Results show that when the shear excitation induced by the source is parallel to the direction of observed polarization of the ground motion, the seismic signal propagates efficiently, maintaining the same horizontal polarization induced by the active source. This polarization is well recorded up to distances as large as 300 m from the source. On the contrary, when the shear excitation is orthogonal to the predominant site polarization, the ground excitation loses its initial polarization in less than 50 m away from the source position. At larger distances, the transmitted energy propagates with the natural site polarization independently from the original source polarization. The observations in terms of polarization were combined with surface‐wave analysis, aimed at investigating the dispersion characteristics of the wavefield on the geophone lines. The data suggest that the experimental Rayleigh‐wave dispersion spectra show a more coherent signal over the frequency range along the same orientation of the observed site polarization, supporting a preferential direction in the propagation of surface waves. From inversion of the Rayleigh dispersion curves, we inferred the shear‐wave velocity (Vs) to be in the range of 120–450 m/s in the first 30 m deep of Quaternary volcanic sediments. The dispersion curves are not constant along transverse and radial directions, suggesting the presence of fracture‐induced seismic anisotropy in the near surface.

Precision test of the weak equivalence principle from gamma-ray burst polarization

If the weak equivalence principle (WEP) is broken, the measured values of the parametrized post-Newtonian parameter $\gamma$ from photons with left- and right-handed circular polarizations should differ slightly, leading to the arrival-time difference of these two circular components. Thus, the polarization vector of a linearly polarized light may rotate during the propagation. The rotation angle of the polarization vector depends on both the photon energy and the distance of the source. It is believed that if the rotation angle differs by more than $\pi/2$ over an energy range, then the net polarization of the signal would be significantly suppressed and could not be as high as the observed level. Thus, the detection of highly polarized photons implies that the relative rotation angle ($\Delta\Theta$) should not be too large. In this paper, we give a detailed calculation on the evolution of gamma-ray burst (GRB) polarization arising from a possible violation of the WEP, and we find that more than $60\%$ of the initial polarization degree can be conserved even if $\Delta\Theta$ is larger than $\pi/2$. In addition, to tightly constrain the WEP violation, GRBs with harder spectra and polarization observations in a wider energy range seem to be favored. Applying our formulas to the measurements of linear polarization from GRB 110721A and GRB 061122, we obtain strict limits on the differences of the $\gamma$ values as low as $\Delta\gamma<1.3\times10^{-33}$ and $\Delta\gamma<0.8\times10^{-33}$. These provide the most stringent limits to date on a deviation from the WEP, improving at least 6 orders of magnitude over previous bounds.

Spin States Protected from Intrinsic Electron-Phonon Coupling Reaching 100 ns Lifetime at Room Temperature in MoSe2.

We present time-resolved Kerr rotation measurements, showing spin lifetimes of over 100 ns at room temperature in monolayer MoSe2. These long lifetimes are accompanied by an intriguing temperature-dependence of the Kerr amplitude, which increases with temperature up to 50 K and then abruptly switches sign. Using ab initio simulations, we explain the latter behavior in terms of the intrinsic electron-phonon coupling and the activation of transitions to secondary valleys. The phonon-assisted scattering of the photoexcited electron-hole pairs prepares a valley spin polarization within the first few ps after laser excitation. The sign of the total valley magnetization, and thus the Kerr amplitude, switches as a function of temperature, as conduction and valence band states exhibit different phonon-mediated intervalley scattering rates. However, the electron-phonon scattering on the ps time scale does not provide an explanation for the long spin lifetimes. Hence, we deduce that the initial spin polarization must be transferred into spin states, which are protected from the intrinsic electron-phonon coupling, and are most likely resident charge carriers, which are not part of the itinerant valence or conduction band states.

Vibrating Powders: Eqcm Measurement of Potential Dependent IrO2 Mass Changes for Voltage Reversal Tolerant PEMFC Anodes

Oxygen evolution reaction (OER) catalysts are used to protect carbon components of polymer electrolyte membrane fuel cell (PEMFC) anodes during transient fuel starvation conditions such as start-up/shut-down [1]. OER catalysts such as IrO2 or RuO2 promote the oxidation of water instead of the corrosion of carbon components [1, 2]. However, the conditions in a PEMFC during normal operation (ca. 0 V and low pH) can induce instability in these metal oxides. IrO2 in particular can form soluble Ir3+ species [3] that migrate across the membrane electrode assembly and deposit on the cathode causing poisoning of the oxygen reduction reaction (ORR) catalyst (typically Pt/C). Currently, OER catalysts for reversal tolerant anodes (RTAs) are investigated using prototype MEA single unit cell testing which is time consuming and expensive to perform [4]. Previously, our group investigated the dissolution of different IrO2 based powder catalysts using a potential stepping stress test. The dissolution of Ir3+ from this test was compared with reversal tolerance of a membrane electrode assembly fabricated using the same IrO2 catalyst [5]. To further investigate the dissolution of IrO2 powders, we have devised a series of experiments (with potential cycling between 0.05 to 1.2, 1.4 and 1.6 V, at 100 mV s-1 30 times each and 298 K) using the electrochemical quartz crystal microbalance (EQCM) technique. The EQCM uses a vibrating quartz crystal and measures its frequency (inversely proportional to crystal mass) as a function of potential. Our method was validated using a commercially available IrO2 powder (Alfa Aesar) heat treated in air at 350, 450 and 550°C which improves durability while negatively effecting OER activity [6]. The powders were deposited (24 μ cm-2) onto a gold EQCM crystal to investigate the dissolution behavior as a function of particle size, crystallinity and electrode potential. The untreated IrO2 exhibited a large irreversible increase in vibration frequency indicating a loss of mass during the initial polarization from 1.2 to 0.05 V. The increase was on the order of 400 to 700 Hz or -7.1 to -12.4 μg cm-2 assuming a perfectly uniform and rigid layer (figure a). This frequency increase could equally be due to loss of adhesion from the surface, a change in the rigidity of the layer or dissolution of Ir3+. To confirm that frequency changes were not due to adhesion or rigidity of the film, samples of the electrolyte were taken from near the electrode surface and Ir3+ concentration was determined by inductively coupled plasma mass spectrometry (ICP-MS). We observed that the frequency of the untreated IrO2 increased by ca. 90 Hz (-1.6 μ cm-2) during a single polarization from 0.05 V to 1.2 V (figure a). Birss et al. reported the formation of an iridium oxo-hydroxide which causes a mass increase when polarizing to 0 V [6]. Conversely, the frequency of heat treated layers first decreased by ca. 200-500 Hz (1.4 to 3.5 μg) then increased again when polarizing to 1.6 V. Heat treatment induced IrO2 crystallinity changes could account for this difference in frequency response. From the first cycle to the last, there was a frequency gain for untreated IrO2 and a frequency loss for all of the heat treated IrO2 catalysts; suggesting Ir3+ dissolution and increased IrO2 layer rigidity or coverage respectively. The capacitive current of the untreated catalyst decreased slightly over the course of the test and was more than five times higher than the 550°C heat treated catalyst in its cyclic voltammogram (figure c and d). The main challenge to using EQCN for powder catalyst investigation is producing layers with consistent and repeatable frequency behavior. In this work, the IrO2 deposition conditions were tightly controlled and each experiment was repeated to ensure the consistency of the results. If these obstacles can be overcome, EQCN presents a novel, rapid and powerful tool to learn about the potential dependent reactions taking place using a myriad of catalyst materials. Ralph TR, Hudson S, Wilkinson DP (2006) ECS Trans 1:67–84.Patterson TW, Darling RM (2006) Electrochem Solid-State Lett 9:A183–A185.Danilovic N, Subbaraman R, Chang K-C, et al (2014) J Phys Chem Lett 5:2474–2478.Makharia R, Kocha S, Yu P, et al (2006) ECS Trans 1:3–18.Moore CE, Eastcott J, Cimenti M, Kremliakova N, Gyenge EL (2019) J Power Sources in review da Silva GC, Perini N, Ticianelli EA (2017) App Cat B: Env 218 287–297.Birss VI, Elzanowska H, Gottesfeld S (1991) J Electroanal Chem and Interfac Electrochem 318:327–333. Figure 1

High-Performance Oxygen Electrodes for Low Temperature Solid Oxide Cells

Solid Oxide Cells (SOCs) present an efficient, environmentally friendly, and largely scalable method for converting fuel to electricity or generating fuels via electrolysis. It is generally believed that the commercial viability of SOCs can be improved by reducing the operating temperature, e.g., ≤ 650 °C. Since low temperature SOC performance is typically limited by the oxygen electrode, current research has focused on developing new oxygen electrode materials and architectures like Ba0.5Sr0.5Co0.8Fe0.2O3-δ, Sr0.5Sm0.5­CoO3-δ, and nanostructured electrodes with high surface areas in order to achieve low temperature performance. These materials, however, suffer from several degradation phenomena such as delamination, cation segregation, chemical reactivity, and coarsening. It was recently shown that PrOx infiltrated into a Gd-doped ceria scaffold provides very low polarization resistance values at low temperature.1 However, the long term stability is not known, nor is the mechanism for its good performance or its effect on other scaffold materials, either electronic conductors or mixed ionic and electronic conductors (MIECs). Here we present results on PrOx infiltrated into Sr(Ti0.3Fe0.7-xCox)O3-δ (STFC) (0 < x < 0.15), STFC-GDC (Ce0.9Gd0.1O2-δ) composite, and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) scaffolds. Figure 1 illustrates the performance enhancing effects of PrOx infiltrated into LSCF and STFC MIEC scaffolds at 550 °C. For example, it decreases the initial polarization resistance of STFC from 0.57 to 0.22 Ω·cm2. The initial resistance decrease for LSCF+PrOx was even greater, from 2.05 to 0.58 Ω·cm2. The performance improvement is seen in the low frequency response, which is attributed to the catalytic surface processes related the addition of PrOx. Similar performance improvements are seen at 650 °C. Furthermore, the resistance values of STFC+PrOx and LSCF+PrOx are reasonably stable over ~ 1000 h life tests at 550 °C. The LSCF+PrOx result is particularly interesting since the LSCF electrode degrades considerably. The composite STFC-GDC+PrOx electrodes generally provide reduced polarization resistance compared to STFC-PrOx. References Nicollet, C., Flura, A., Vibhu, V., Rougier, A., Bassat, J.-M. & Grenier, J.-C. An innovative efficient oxygen electrode for SOFC: Pr6O11 infiltrated into Gd-doped ceria backbone. Int. J. Hydrogen Energy 2–8 (2016). doi:10.1016/j.ijhydene.2016.04.024 Figure Caption Figure 1 - Evolution of Nyquist and Bode plots during a life test at 550 °C for ~ 1000 hours of (a) La0.6Sr0.4Co0.2Fe0.8O3-δ with and without nano-infiltrated PrOx and (b) SrTi0.3Fe0.55Co0.15O3-δ with and without nano-infiltrated PrOx all supported on a Ce0.9Gd0.1O2-δ electrolyte. Figure 1

Effect of BaO impregnation on sulfur tolerance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes of solid oxide fuel cells

Oscar2019: The effect of BaO impregnation on the electrochemical activities and sulfur tolerance of La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) cathodes of solid oxide fuel cells (SOFCs) was studied. BaO nanoparticles were introduced to LSCF electrodes by solution impregnation. The resistance and tolerance of LSCF electrodes toward sulfur in air stream increased with the loading of impregnated BaO nanoparticles. For 1.08 mgcm−2 BaO impregnated LSCF electrodes, initial electrode polarization resistance RE was 0.4 Ω cm2, which was close to 0.35 Ω cm2 measured on pristine LSCF electrode at 700 °C. However, RE remained almost constant after polarization at 200 mA cm−2 for 40 h in the presence of 1 ppm SO2 at 700 °C, which was in contrast with significant increase of RE to 1.24 Ω cm2 after polarization for 20 h for the reaction on pristine LSCF under identical test conditions. The results indicate that the impregnated BaO nanoparticles served as a barrier layer, effectively inhibiting the interaction between sulfur and strontium of LSCF electrode and thus enhancing its sulfur tolerance.

Robustness of quantum correlation for accelerating two atoms coupled with electromagnetic field

In this paper, we investigate the behaviors of quantum correlation quantified by trace norm measurement-induced nonlocality (TMIN) for two uniformly accelerated atoms coupled with electromagnetic vacuum fluctuation in the Minkowski vacuum. We firstly discuss the solving process of master equation that governs the system evolution based on the Pauli matrix presentation for two-qubit state. Similar to [Y. Q. Yang et al., Phys. Rev. A 94, 032337 (2016)], we analyze the degradation, creation, revival and enhancement of quantum correlation for different initial states and polarizations of two atoms, and the influence of interatomic separation and acceleration on quantum correlation. Compared with the entanglement dynamics discussed in [Y. Q. Yang et al., Phys. Rev. A 94, 032337 (2016)], it is found that quantum correlation exhibits better robustness than entanglement. This may be helpful for quantum information processing.

Reversible Effects of Periodic Polarization on Anodic Electroactive Biofilms

AbstractAnodic electroactive biofilms (EABs) are commonly grown under continuous polarization of the underlying electrode. Their growth under appropriate periodic polarization was recently reported to considerably enhance their electrochemical properties (catalytic current and charge carriers concentration). This improvement was only investigated on relatively short term (ten days), and its resilience once the periodic polarizations are switched back to continuous (or vice versa) has not yet been assessed. Here, we first cultivated 16 Geobacter‐dominated EABs on glassy carbon electrodes under either continuous or periodic polarization for several days. The polarization mode was then switched from continuous to periodic and vice versa. The improvement induced by the initial periodic polarization was lost over only two days of continuous polarization. Conversely, it took about ten days of periodic polarization to fully improve the electroactivity of the EABs initially grown under continuous polarization. The periodic polarization favored biofilm detachments, which were followed by a full recovery of current within three days. The performance of EABs under periodic polarization was less negatively impacted under substrate‐limiting conditions, likely because of substrate replenishment during open circuit periods.

New constraints on Lorentz invariance violation with polarized gamma-ray bursts

Lorentz invariance violations (LIV) can yield vacuum birefringence, which results in an energy-dependent rotation of the polarization vector of linearly polarized emission from astrophysical sources. It is believed that if the relative rotation angle ($\Delta\Theta$) of the polarization vector of high energy photons with respect to that of low energy photons is larger than $\pi/2$, then the net polarization of the signal would be significantly depleted and could not be as high as the observed level. Hence, the measurement of high polarization implies that $\Delta\Theta$ should not be too large. In this work, we assemble recent detections of prompt emission polarization in gamma-ray bursts (GRBs), all of whom have high detection significance. Following the method shown in Lin et al. (2016), we give a detailed calculation on the polarization evolution arising from the LIV effect for each GRB, and confirm that, even if $\Delta\Theta$ is approaching to $\pi/2$, the net polarization is not severely suppressed, and more than 60\% of the initial polarization can be conserved. Applying this method to our GRB polarimetric data, we improve existing sensitivities to LIV involving photons by factors ranging from two to ten. In addition, we prove that our constraints are not greatly affected by uncertainties in the spectral parameters of GRBs.

Final taus and initial state polarization signatures from effective interactions of Majorana neutrinos at future e^{+}e^{-} colliders

We study the possibility of future e^{+}e^{-} colliders to disentangle different new physics contributions to the production of heavy sterile Majorana neutrinos in the lepton number violating channel e^{+}e^{-}rightarrow l^{+} l^{+}+ 4 {text {jets}}, with l=e, mu , tau . This is done investigating the final anti-tau polarization trails and initial beam polarization dependence of the signal on effective operators with distinct Dirac–Lorentz structure contributing to the Majorana neutrino production and decay, which parameterize new physics from a higher energy scale. We find that both analyses could well disentangle possible vectorial and scalar operators contributions.

Aurora-A Breaks Symmetry in Contractile Actomyosin Networks Independently of Its Role in Centrosome Maturation

Cell polarity is facilitated by a rearrangement of the actin cytoskeleton at the cell cortex. The program triggering the asymmetric remodeling of contractile actomyosin networks remains poorly understood. Here, we show that polarization of Caenorhabditis elegans zygotes is established through sequential downregulation of cortical actomyosin networks by the mitotic kinase, Aurora-A. Aurora-A accumulates around centrosomes to locally disrupt the actomyosin contractile activity at the proximal cortex, thereby promoting cortical flows during symmetry breaking. Aurora-A later mediates global disassembly of cortical actomyosin networks, which facilitates the initial polarization through suppression of centrosome-independent cortical flows. Translocation of Aurora-A from the cytoplasm to the cortex is sufficient to interfere with the cortical actomyosin networks independently of its roles in centrosome maturation and cell-cycle progression. We propose that Aurora-A activity serves as a centrosome-mediated cue that breaks symmetry in actomyosin contractile activity, and facilitates the initial polarization through global suppression of cortical actomyosin networks.

Numerical investigation of nanoscale electromechanical response in a ferroelectric perovskite through an atomistic field theory

An atomistic field theory was introduced to study the electromechanical response in a ferroelectric perovskite at nanoscale. Based on a shell model potential, the polarization switching process of a ferroelectric perovskite PbTiO3 under electric field and mechanical loading was investigated. The simulation results showed that external electric field applied opposite to the initial polarization direction could result in 180° polarization switching in PbTiO3 nanostructures as the external electric field increased. On the other hand, mechanical loading applied parallel to initial polarization could cause 90° nanoscale polarization rotation in PbTiO3. Ultimately, the simulation results indicated that the coupled loads of electric field and mechanical loading would influence the polarization switching in PbTiO3 nanostructures.

Electric Quadrupole Moment and the Tensor Magnetic Polarizability of Twisted Electrons and a Potential for their Measurements.

For a twisted (vortex) Dirac particle in nonuniform electric and magnetic fields, the relativistic Foldy-Wouthuysen Hamiltonian is derived including high order terms describing new effects. The result obtained shows for the first time that a twisted spin-1/2 particle possesses a tensor magnetic polarizability and a measurable (spectroscopic) electric quadrupole moment. We have calculated the former parameter and have evaluated the latter one for a twisted electron. The tensor magnetic polarizability of the twisted electron can be measured in a magnetic storage ring because a beam with an initial orbital tensor polarization acquires a horizontal orbital vector polarization. The electric quadrupole moment is rather large and strongly influences the dynamics of the intrinsic orbital angular momentum (OAM). Three different methods of its measurements, freezing the intrinsic orbital angular momentum and two resonance methods, are proposed. The existence of the quadrupole moment of twisted electrons can lead to practical applications.

YAP and TAZ limit cytoskeletal and focal adhesion maturation to enable persistent cell motility.

Cell migration initiates by traction generation through reciprocal actomyosin tension and focal adhesion reinforcement, but continued motility requires adaptive cytoskeletal remodeling and adhesion release. Here, we asked whether de novo gene expression contributes to this cytoskeletal feedback. We found that global inhibition of transcription or translation does not impair initial cell polarization or migration initiation, but causes eventual migratory arrest through excessive cytoskeletal tension and over-maturation of focal adhesions, tethering cells to their matrix. The transcriptional coactivators YAP and TAZ mediate this feedback response, modulating cell mechanics by limiting cytoskeletal and focal adhesion maturation to enable persistent cell motility and 3D vasculogenesis. Motile arrest after YAP/TAZ ablation was partially rescued by depletion of the YAP/TAZ-dependent myosin phosphatase regulator, NUAK2, or by inhibition of Rho-ROCK-myosin II. Together, these data establish a transcriptional feedback axis necessary to maintain a responsive cytoskeletal equilibrium and persistent migration.

Dynamic analysis of a nonlinear nanobeam with flexoelectric actuation

Over the past few years, several researchers have been increasingly attracted to flexoelectric transduction because of its potential application for sensing and actuation in NanoElectroMechanical Systems. The flexoelectric effect refers to coupling between polarization and strain gradient in centrosymmetric and non-centrosymmetric dielectrics. Consequently, not only piezoelectric dielectrics with an initial polarization are of interest, but also a larger range of dielectric materials. In contrast to piezoelectricity, the flexoelectric effect is scale-dependent and can exhibit large electromechanical coefficients only at small scales. This paper focuses on the effects of geometric nonlinearity, resulting from relatively large displacements and restrictive boundary conditions, on the static and dynamic responses of piezoelectric flexoelectric nanobeams. The derived equations of motion for the transverse displacement and variation of the internal electric potential are discretized using a Galerkin procedure. A closed-form solution for the nonlinear static response is proposed. The results are compared and validated with those found in the literature. For the dynamic response, a perturbation technique is used to solve analytically the nonlinear equations of motion for the primary and parametric resonances of the first mode. The analytical perturbation solution is validated using a numerical technique. The results show that a general hardening-type behavior is obtained and, therefore, several jumps are observed for the dynamic solution. High sensitivity of the solution to an applied AC voltage is also demonstrated for the principal resonance of the first mode.

Distribution of the Ferroelectric Polarization in Polyvinylidene Fluoride During Initial Poling and Polarization Reversal

Distribution of the Ferroelectric Polarization in Polyvinylidene Fluoride During Initial Poling and Polarization Reversal

Mechanisms of PrO &lt;sub&gt;x&lt;/sub&gt; Performance Enhancement of Oxygen Electrodes for Low Temperature Solid Oxide Cells

Recent developments in solid oxide cells focus on decreasing operating temperatures below 600 °C for improved cost and electrochemical stability in order to improve viability for commercialization. In this work, we improve the performance and stability of La0.6Sr0.40.2Fe0.8O3-δ (LSCF) and a recently developed electrode material, SrTi0.3Fe0.55Co0.15O3-δ (STFC), with addition of PrOx nanoparticles. Single-step PrOx infiltration improves performance of both LSCF and STFC across all tested temperatures (450 to 650 °C) with the most significant enhancements at lower temperatures. STFC modified with PrOx yields the best overall performance and stability, with the initial polarization resistance of 0.20 Ω·cm2 at 550 °C increasing over ~ 800 hours before stabilizing at 0.27 Ω·cm2. This represents a factor of ~ 10 resistance decrease compared to the LSCF electrode at 550 °C. A distribution of relaxation timesanalysis sheds light on the electrochemical mechanisms impacted by PrOx.

Alternating electric fields induce a period-dependent motion of Escherichia coli in three-dimension near a conductive surface.

It has been demonstrated that electric fields can minimize surface adhesion of bacteria, but how they affect the near-surface bacterial dynamics has remained largely overlooked. In the present study, the three-dimensional motions of Escherichia coli (E. coli) HCB1 and HCB1414 near a conductive surface under alternating-current (AC) electric fields were monitored with digital holographic microscopy. The period (T) of AC fields exhibited profound effects on near-surface bacterial behavioral patterns and thus affected the surface adhesiveness of E. coli. When T ≥ 1 s, HCB1 cells tumble frequently, and both two strain cells increasingly undergo subdiffusive motions compared to the case without electric fields. The bacterial density near the surface varies due to galvanotaxis depending on the initial polarization of the surface. For shorter periods (T ≤ 0.1 s), the electric fields reduce the near-surface bacterial density by 10%-20% with the surface as either an anode or a cathode. The AC fields directly disturb the intrinsic bacterial rotation. The bacterial body exhibits strong wobbling at T ≥ 1 s. Such wobbling was suppressed with decreasing T, which reduces the collisions between E. coli and the surface and thus leads to declining bacterial density. These results suggest that the use of low-density AC fields with tunable T may be a promising antifouling strategy and merits further investigations.

Direct Correlation of Ferroelectric Properties and Memory Characteristics in Ferroelectric Tunnel Junctions

Ferroelectric memories have made big advancements in the last years due to the discovery of ferroelectricity in already widely used hafnium oxide. Here we investigate ferroelectric tunnel junctions (FTJ) consisting of a ferroelectric hafnium zirconium oxide layer and a dielectric aluminum oxide layer. By varying the set and reset amplitude and pulse width the fraction of reversed ferroelectric domains can be controlled. Due to the statistical distribution of the coercive voltage the current can be tuned between the minimum off-state and maximum on-state current. This leads to possible multi-level information storage in our FTJs. In this paper a detailed study of the set/reset operation and the intermediate current levels is presented. Furthermore, the endurance properties of the memory device can be directly correlated to the wake-up and fatigue phenomena in the ferroelectric layer. While the usability of the memory window is still limited by the initial polarization increase and ultimately by the hard breakdown of the device, a further optimization of the ferroelectric layer itself and the ferroelectric/dielectric interface can directly improve the viability of the tunnel junction. Finally, we show that the current of our FTJs scales as expected and reproducible results across different devices are obtained.