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Two-dimensional ferromagnetic (2D FM) half-metal holds great potential for quantum magnetoelectronics and spintronic devices. Here, using density functional calculations and magnetic pictures, we study the electronic structure and magnetic properties of the novel van der Waals (vdW) metal-organic framework (MOF), CrCl2(N2C4H4)2, i.e. CrCl2(pyrazine)2. Our results show that CrCl2(pyrazine)2 is a 2D FM half-metal, having a strong intralayer FM coupling but a much weak interlayer one due to the vdW spacing. Its spin-polarized conduction bands are formed by the pyrazine molecular orbitals and are polarized by the robust Cr3+ local spin = 3/2. These results agree with the recent experiments [Pedersen et al., Nature Chemistry, 2018, 10, 1056]. More interestingly, CrCl2(pyrazine)2 monolayer has a strong doping tunability of the FM half-metallicity, and the FM coupling would be significantly enhanced by electron doping. Our work highlights a vital role of the organic ligand and suggests that vdW MOF is also worth exploration for new 2D magnetic materials., Comment: 9 pages, 10 figures, 4 tables

We report the synthesis, crystal structures, and thermal, optical and magnetic properties of three new metal dicyanamide frameworks comprising benzyltrimethylammonium cations (BeTriMe+) as labile guests. These compounds crystallize in two-dimensional noncentrosymmetric structures, in space group Pna21 of the orthorhombic system, in which metal cations coordinate to five N atoms from dicyanamide anions and one oxygen atom from the water molecule. Magnetic studies indicate that Mn, Co and Ni compounds order at 2.5, 2.8 and 7.0 K, respectively. Second harmonic generation (SHG) and density functional theory (DFT) studies performed for BeTriMe[Mn(dca)3(H2O)] confirm a noncentrosymmetric structure. DFT computations also provide insights into the experimentally observed low-temperature magnetic order and insulating behavior. Thus, the synthesized compounds are rare examples of dicyanamide frameworks exhibiting coexistence of polar and magnetic orders, and additionally – SHG activity. Optical studies indicate that BeTriMe[Mn(dca)3(H2O)] also exhibits red emission under 450 nm excitation. Thermal studies reveal that BeTriMe[M(dca)3(H2O)] networks dehydrate near 350–380 K resulting in structural transformations. The anhydrous BeTriMeMn also exhibits SHG activity, which is about 4 times smaller compared to the hydrated analogue. On direct contact with air the anhydrous BeTriMeMn spontaneously rehydrates, restoring the SHG response to initially observed intensity. On the other hand, if the dehydrated BeTriMeMn is sealed from air, its SHG response is essentially irreversible and stable for days. Taking BeTriMeMn as an example we demonstrate that noncentrosymmetric compounds with effectively irreversible temperature-induced change of SHG response can be potentially employed as remote nonlinear optical (NLO) markers (NLO threshold temperature sensors). The usefulness of non-contact NLO markers of this kind is based on the fact that they can inform on the thermal history of a given object, specifically, by showing whether a certain threshold temperature was achieved or not.

The Light-Emitting Electrochemical Cell (LEEC) is one of the simplest kind of electroluminescent solid-state devices. Generally, they are fabricated with only one emitting material layer (EML), so-called active emission layer, that consist of an emitter material mixed with an ionic electrolyte. Apart from the electrolyte, their structure is similar to that of a single layer organic light-emitting diode (OLED). Not only LEECs assemble most of OLEDs applications and their technological advantages, but they also bring additional ones such as (i) low dependence of the electrodes work function, (ii) low dependence to the EML thickness, (iii) low operation voltage and high brightness and finally (iv) LEECs can be printed or sprayed in large areas. To investigate the performance of ionic liquid (IL) based devices we synthesized four organic salts that were compared with devices using four inorganic salts commonly used as electrolyte for LEECs. All devices were fabricated with a commercial poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as emitter polymer. As a result, we showed that the best device performance was achieved with the Ionic Liquid 1-dodecyl-4-(hydroxymethyl)-3-methyl-1H-1,2,3-triazol-3-ium iodide (dohmtI) presenting a current efficiency of 3.6 cd/A, an external quantum efficiency (EQE) of 1.4% as well as a luminance of 3.2 × 104 cd/m2. Despite the use of MEH-PPV, a polymer not so efficient when compared to the state-of-art of the novel polymers employed nowadays, our realization showed these new ILs have been able to provide the specific requirements of the LEEC devices.

Ferroelectric molecular crystals are a promising class of materials with lower cost and environment-friendly preparation process. In this work, by combining first-principles calculations and molecular dynamics simulations, we report a systematic study of of ferroelectricity in three molecular ferroelectrics: di-isopropyl-ammonium chloride (DIPAC), di-isopropyl-ammonium bromide (DIPAB) and di-isopropyl-ammonium iodide (DIPAI). Our results agree with previous electronic structure calculations and provide new insights into the mechanism of the phase transition.

We present a theoretical model of methylhydrazinium CH3NH2NH2+ molecular cation ordering in perovskite [CH3NH2NH2][M(HCOO)3] (M = Mn, Mg, Fe, and Zn) formate frameworks, which exhibit two structural phase transitions. The proposed model is constructed by analyzing the available structural information and mapping the molecular cation states on a three-dimensional simple cubic lattice. The model includes the short-range Ising and Potts interactions between the dipolar CH3NH2NH2+ cations. We study the model using the Monte Carlo simulations as well as by the density functional theory calculations. The simulations indicate that our model accurately describes the methylhydrazinium cation arrangement in all three structural phases of the compounds. The calculated temperature dependences of the heat capacity and electric polarization are in good agreement with the experimental data. The simulations also allow us to obtain the characteristic energies of the molecular cation interactions for all members of the [CH...

Biological ferroelectric materials have great potential in biosensing and disease diagnosis and treatment. Glycine crystals form the simplest bioferroelectric materials, and here we investigate the polarizations of its β- and γ-phases. Using density functional theory, we predict that glycine crystals can develop polarizations even larger than those of conventional inorganic ferroelectrics. Further, using systematic molecular dynamics simulations utilizing polarized crystal charges, we predict the Curie temperature of γ-glycine to be 630 K, with a required coercive field to switch its polarization states of 1 V·nm–1, consistent with experimental evidence. This work sheds light on the microscopic mechanism of electric dipole ordering in biomaterials, helping in the material design of novel bioferroelectrics.

In this work, we study the structural changes of the polar [NH4][Cd(HCOO)3] hybrid perovskite under external hydrostatic pressure. We report a reversible framework rearrangement as a function of pressure characterized by: (i) a gradual modification of one formate ligand, which changes its coordination mode from a bridging syn–anti mode at atmospheric pressure (LP-phase) to a chelating-anti mode at high-pressure (HP-phase) and (ii) a change in the coordination of the Cd2+ cations from six-coordinated (LP-phase) to hepta-coordinated (HP-phase). Very interestingly, this unprecedented framework arrangement displays a large electrical polarization. For instance, the polarization value observed at p = 17.7 GPa is about four times the polarization at atmospheric pressure. Therefore, we report that the external pressure induces a novel framework rearrangement in the polar [NH4][Cd(HCOO)3] hybrid perovskite with enhanced electrical polarization. This structure–property relationship offers new insights for designing novel ferroelectric materials based on pressure-responsive hybrid perovskite materials.

A detailed study on the single-molecule ferroelectric property of Preyssler-type polyoxometalates (POMs), [M3+P5W30O110]12− (M = La, Gd, and Lu), is performed by density functional theory calculations. Linked to one H2O molecule, the cation (M3+) encapsulated in the cavity of the Preyssler framework is off-centered, and it generates a permanent dipole, which is essential for a ferroelectric ground state. Accompanied with a 180° rotation of H2O, the switching of M3+ between two isoenergetic sites on both sides of the cavity results in a calculated barrier of 1.15 eV for Gd3+, leading to the inversion of electric polarization. The height of the barrier is in good agreement with the experimentally measured barrier for the Tb3+ ion, whose ionic radius is similar to Gd3+. The total polarization value of the crystal is estimated to be 4.7 µC/cm2 as calculated by the modern theory of polarization, which is quite close to the experimental value. Considering that the order of contributions to the polarization is M3+–H2O > counter-cations (K+) > [P5W30O110]15−, the interconversion of M3+–H2O between the two isoenergetic sites is predicted to be the main origin of ferroelectricity with a polarization contribution of 3.4 µC/cm2; the K+ counter-cations contribute by 1.2 µC/cm2 and it cannot be disregarded, while the framework appears to contribute negligibly to the total polarization. Our study suggests that a suitable choice of M3+–H2O could be used to tune the single-molecule ferroelectricity in Preyssler-type polyoxometalates.

Evaluating many-body correlation effects beyond the commonly applied local or semilocal density functionals has received tremendous attention over the past few years. Using the random phase approximation to describe the correlation energy combined with the exact exchange energy, we have investigated 20 cubic $AB{\mathrm{O}}_{3}$-type perovskites and three prototypical ferroelectric (tetragonal) perovskites. A quantitative analysis and comparison of the performance of various local and semilocal exchange-correlation functionals shows that the inclusion of dynamical correlation effects allows for an excellent account of the structure and energetics of complex $AB{\mathrm{O}}_{3}$-type oxides.

Soft growing robots are proposed for use in applications such as complex manipulation tasks or navigation in disaster scenarios. Safe interaction and ease of production promote the usage of this technology, but soft robots can be challenging to teleoperate due to their unique degrees of freedom. In this paper, we propose a human-centered interface that allows users to teleoperate a soft growing robot for manipulation tasks using arm movements. A study was conducted to assess the intuitiveness of the interface and the performance of our soft robot, involving a pick-and-place manipulation task. The results show that users were able to complete the task 97% of the time and achieve placement errors below 2 cm on average. These results demonstrate that our body-movement-based interface is an effective method for control of a soft growing robot manipulator.

Density functional theory calculations were performed for the electronic and the ferroelectric properties of the bulk and the monolayer benzylammonium lead-halide (BA2PbCl4). Our calculations indicate that both the bulk and monolayer systems display a band gap of ∼3.3 eV (HSE06+SOC) and a spontaneous polarization of ∼5.4 μC/cm2. The similar physical properties of bulk and monolayer systems suggest a strong decoupling among the layers in this hybrid organic-inorganic perovskite. Both the ferroelectricity, through associated structure distortion, and the spin-orbit coupling, through splitting induced in the electronic bands, significantly influence the band gaps. Most importantly, we found for the first time in a two-dimensional hybrid organic-inorganic class of material, a peculiar spin texture topology such as a unidirectional spin-orbit field, which may lead to a protection against spin decoherence.

Removing valley degeneracy is a necessary condition for manipulating valley degrees of freedom and storing information in future spintronics. Magnetic proximity effect has been demonstrated to be an effective way to introduce exchange interactions, especially in the case of two-dimensional (2D) van der Waals (vdW) heterostructures. We have explored the electronic properties and the valley physics of 2D ${\mathrm{WSe}}_{2}/{\mathrm{CrI}}_{3}$ using first-principles calculations. Our results show that a valley splitting of 2 meV is achieved in ${\mathrm{WSe}}_{2}/{\mathrm{CrI}}_{3}$ heterostructures thanks to the coexistence of inversion and time-reversal symmetry breaking. This value corresponds to an effective magnetic field of \ensuremath{\sim}10 T in experiments. Moreover, we demonstrate that the valley splitting is a robust feature regardless of the stacking configuration and the thickness of ${\mathrm{CrI}}_{3}$. Most importantly, by reversing the magnetization in the ${\mathrm{CrI}}_{3}$ layer, the valley splitting and polarization at ${K}^{+}$ and ${K}^{\ensuremath{-}}$ points are completely switchable. Our findings provide fundamental insights into the magnetoelectric spin-orbit coupling based spintronics applications of 2D vdW heterostructures.

The hybrid organic inorganic perovskites (HOIPs) have attracted much attention for their potential applications as novel optoelectronic devices. Remarkably, the Rashba band splitting, together with specific spin orientations in k space (i.e., spin texture), has been found to be relevant for the optoelectronic performances. In this work, by using first principles calculations and symmetry analyses, we study the electric polarization, magnetism, and spin texture properties of the antiferromagnetic (AFM) HOIP ferroelectric TMCM_MnCl3 (TMCM = (CH3)3NCH2Cl, trimethylchloromethyl ammonium). This recently synthesized compound is a prototype of order disorder and displacement-type ferroelectric with a large piezoelectric response, high ferroelectric transition temperature, and excellent photoluminescence properties [You et al., Science 357, 306 (2017)]. The most interesting result is that the inversion symmetry breaking coupled to the spin orbit coupling gives rise to a Rashba-like band splitting and a related robust persistent spin texture (PST) and/or typical spiral spin texture, which can be manipulated by tuning the ferroelectric or, surprisingly, also by the AFM magnetic order parameter. The tunability of spin texture upon switching of AFM order parameter is largely unexplored and our findings not only provide a platform to understand the physics of AFM spin texture but also support the AFM HOIP ferroelectrics as a promising class of optoelectronic materials., Comment: 24pages, 4 figures

The atomic nature of topologically protected ferroelectric (FE) walls in hexagonal ReMnO3 oxides (R: Sc, Y, Er, Ho, Yb, Lu) creates an interesting playground to study effects of defects on domain walls. The 6-fold FE vortices in this multiferroic family lose the ordering by the rule of 6 in the presence of partial edge dislocations (PED) besides it can be modified by chemical doping. Therefore, it is essential to comprehend the cross coupling of FE walls and defects or vacancies in the lattice of multiferroics. Atomic resolution STEM is used to explore the correlative response of electrical polarization of FE domains in the presence of defects in multiferroic ceramics. Such level of resolution also allows the study of switching of FE domains on encounter of lattice defects. The driving force behind appearance of dispersed, small FE domains in images of piezo force microscopy is revealed by observation of lattice defects and FE boundaries simultaneously at the nano-scale. Planar defects and FE domain walls play their role of internal interfaces consequently such interplaying duly modifies the magnetic and FE properties of multiferroic oxides.

The importance of organic molecular cation orientation and interaction with surrounding inorganic framework in the optoelectronic hybrid halide perovskites is a topic of considerable interest. To that end, we study the effect of organic molecule rotations on the properties of such hybrid semiconductors using the swarm intelligence-based structure prediction method combined with ab initio density functional calculations. Adopting the cubic phases of ${\mathrm{APbI}}_{3}$ [$\mathrm{A}={\mathrm{CH}}_{3}{\mathrm{NH}}_{3}$(MA), ${\mathrm{CHNH}}_{2}{\mathrm{NH}}_{2}$(FA) and ${\mathrm{CH}}_{3}{\mathrm{CH}}_{2}{\mathrm{NH}}_{3}$(EA)], we determine the energetically stable/metastable configurations of organic molecules inside the quasicubic perovskite cages. Different cation orientations result in up to $\ensuremath{\sim}250\phantom{\rule{0.16em}{0ex}}\mathrm{meV}/\mathrm{formula}$ changes in the material free energy, reflecting the complex energy landscape of these hybrid materials containing dynamically rotating organic components. Notably, the [012] orientation of MA is found to give the most stable structure of ${\mathrm{MAPbI}}_{3}$, while the conventional [001], [011], or [111] directions remain slightly higher in energy. Molecular orientations clearly influence the fundamental electronic bandgap and also modify the magnitude of Rashba-type energy band splitting resulting in indirect gap behavior. However, the dielectric screening remains large for all orientations thus creating weakly bound excitons. Based on the analysis of many organic molecule configurations obtained through the structure search technique, our results provide insightful understanding on the effects of organic molecule rotation on optoelectronic properties and carrier dynamics of hybrid halide perovskites.

The zigzag edged graphene nanoribbon (ZGNR) is excellent for spintronics devices, and many efforts have been made to investigate its properties such as spin filtering, rectification and magnetoresistance. Here we propose a molecular spintronic transport device based on two ZGNR electrodes connected with a dibenzo[a,c]dibenzo[5,6:7,8]quinoxalino[2,3-i]phenazine (DDQP) molecule. By performing first-principles electron transport computations, we found an enhanced spin polarized current–voltage curve, giant spin filter efficiency, magnetoresistance and rectification ratio properties of the device compared to its all-carbon molecular analogue. Our systematic investigation suggests the vital role played in spin polarized electron transport by nitrogen atoms in DDQP, the ZGNR probe's width and terminal geometry, especially the increased spin filter efficiency with higher ZGNR width.

The chapter describes a computer vision-based robot-assisted system used in neurorehabilitation of post-stroke patients that allows the subjects to reach for and grasp objects in a defined workspace. The proposed computer vision technique is used to model objects that have not been preprocessed in a real setting, track them in real time, and provide their actual pose to the robotic device in order to accomplish grasping tasks. The robotic device is composed of three integrated modules: (i) a 4-DOF arm exoskeleton that supports the patient's impaired arm when reaching for the objects; (ii) a 3-DOF actuated wrist exoskeleton for optimizing the hand pose in the grasping task; and (iii) a 2-DOF (flexion/extension) underactuated hand exoskeleton designed to be automatically adjusted for different grasping tasks based on contact forces. The conducted tests have demonstrated the robustness of the proposed approach, and its performance in the neurorehabilitation scenario through reaching and grasping task experiments.

Spin-reorientation magnetic transitions are studied in Mn-doped SmFeO3., Spin reorientation is a magnetic phase transition in which rotation of the magnetization vector with respect to the crystallographic axes occurs upon a change in the temperature or magnetic field. For example, SmFeO3 shows a magnetization rotation from the c axis above 480 K to the a axis below 450 K, known as the Γ4 → Γ2 transition. This work reports the successful synthesis of the new single-crystal perovskite SmFe0.75Mn0.25O3 and finds interesting spin reorientations above and below room temperature. In addition to the spin reorientation of the Γ4 → Γ2 magnetic phase transition observed at around T SR2 = 382 K, a new spin reorientation, Γ2 → Γ1, was seen at around T SR1 = 212 K due to Mn doping, which could not be observed in the parent rare earth perovskite compound. This unexpected spin configuration has complete antiferromagnetic order without any canting-induced weak ferromagnetic moment, resulting in zero magnetization in the low-temperature regime. M–T and M–H measurements have been made to study the temperature and magnetic-field dependence of the observed spin reorientation transitions.

In this work, we focus on [(CH3)2NH2]PbI3, a member of the [AmineH]PbI3 series of hybrid organic–inorganic compounds, reporting a very easy mechanosynthesis route for its preparation at room temperature. We report that this [(CH3)2NH2]PbI3 compound with 2H-perovskite structure experiences a first-order transition at ≈250 K from hexagonal symmetry P63/mmc (HT phase) to monoclinic symmetry P21/c (LT phase), which involves two cooperative processes: an off-center shift of the Pb2+ cations and an order–disorder process of the N atoms of the DMA cations. Very interestingly, this compound shows a dielectric anomaly associated with the structural phase transition. Additionally, this compound displays very large values of the dielectric constant at room temperature because of the appearance of a certain conductivity and the activation of extrinsic contributions, as demonstrated by impedance spectroscopy. The large optical band gap displayed by this material (Eg = 2.59 eV) rules out the possibility that the observ...

Boron-based two-dimensional materials have extremely rich structures and excellent physical properties. Using a particle-swarm optimization (PSO) method and first-principles calculations, we performed a comprehensive search for the structure of a two-dimensional BeB2 monolayer. We found new configurations with lower energy compared with the previously reported α phase, namely the β, γ, and δ structures. Among those structures, the δ phase is found to have the lowest energy and we examined its dynamic as well as its thermodynamic stabilities. Then through strain engineering, we found a metal–semimetal transition in the α phase (under about 5% biaxial compressive strain) and in the δ phase (under about 3.2% and 7% biaxial tensile strain). As the compressive strain increases to 7%, the BeB2 sheets of the β phase and γ phase strongly twist, becoming more stable than the δ system. More interestingly, we found that Be atoms could penetrate the B atomic layer in the γ system under 2.5% tensile strain. All the predicted effects demonstrate the rich physical properties of the two-dimensional BeB2 monolayer.

BiFeO3 (BFO) thin films were grown by chemical solution deposition on a range of electrodes to determine their role in controlling the phase formation and microstructure of the films. The crystallization on oxide electrodes followed the sequence: amorphous → Bi2O2(CO3) → perovskite, while those on Pt crystallized directly from the amorphous phase. IrO2 electrodes promoted perovskite phase formation at the lowest temperature and LaNiO3 additionally induced local epitaxial growth. All compositions exhibited fully coherent Fe-rich precipitates within the grain interior of the perovskite matrix, whereas the incoherent Bi2Fe4O9 second phase was also observed at the grain boundaries of BFO grown on Pt electrodes. The latter could be observed by X-ray diffraction as well as transmission electron microscopy (TEM) but coherent precipitates were only observed by TEM, principally evidenced by their Z contrast in annular dark field images. These data have pronounced consequences for the extended use of BFO films under an applied field for actuator, sensor and memory applications.

Ferroelectrics with luminescent properties are promising candidates for the next generation of optical waveguides and displays. However, reports on ferroelectrics with triboluminescence properties have been very scarce so far. In this study, we demonstrate a potential hybrid molecular ferroelectric, (Ph3PO)2MnBr2, which exhibits intense green triboluminescence. Using piezoresponse force microscopy, the presence of ferroelectric domains in (Ph3PO)2MnBr2 thin films is confirmed. We also show evidence for the reversible switching of the ferroelectric domains by poling with DC biases. We believe that this combination of ferroelectricity and triboluminescence will bring about potential multifunctional optoelectronic device applications.

The theoretical ferroelectric polarization of the low-temperature (monoclinic, P21) phase and the high-temperature (hexagonal, P63) phase of hydroxyapatite Ca10(PO4)6(OH)2 is calculated based on the density functional theory (DFT). In the monoclinic structure, the value of ferroelectric polarization is found to be 9.87 μC cm−2 along the [001] direction. In the hexagonal structure, the ferroelectric polarization is 7.05 μC cm−2 along the [001] direction. The main contribution to the electric polarization comes from ordered hydroxyl OH− anions for both phases, although the inorganic Ca5(PO4)3 apatite framework also gives a non-negligible contribution. A detailed analysis of ferroelectric polarization and structural change of the hydroxyapatite is presented for a better understanding of this important biomaterial.

Correlating dopant distribution to its optical response represents a complex challenge for nanomaterials science. Differentiating the "true" clustering nature from dopant pairs formed in statistical distribution complicates even more the elucidation of doping-functionality relationship. The present study associates lanthanide dopant distribution, including all significant events (enrichment, depletion and surface segregation), to its optical response in upconversion (UPC) at the ensemble and single-nanoparticle level. A small deviation from the Er nominal concentration of a few percent is able to induce clear differences in Er UPC emission color, intensity, excited-state dynamics and ultimately, UPC mechanisms, across tetragonal to monoclinic phase transformation in rationally designed Er doped ZrO2 nanoparticles. Rare evidence of a heterogeneous dopant distribution leading to the coexistence of two polymorphs in a single nanoparticle is revealed by Z- and phase contrast transmission electron microscopy (TEM). Despite their spatial proximity, Er in the two polymorphs are spectroscopically isolated, i.e. they do not communicate by energy transfer. Segregated Er, which is well imaged in TEM, is absent in UPC, while the minor phase content overlooked by X-ray diffraction and TEM is revealed by UPC. The outstanding sensitivity of combined TEM and UPC emission to subtle deviations from uniform doping in the diluted concentration regime renders such an approach relevant for various functional oxides supporting lanthanide dopants as emitters.

In animal livestock heavy metals are widely used as feed additives to control enteric bacterial infections as well as to enhance the integrity of the immune system. As these metals are only partially adsorbed by animals, the content of heavy metals in manure and wastewaters causes soil and ground water contamination, with Zn2+ and Cu2+ being the most critical output from pig livestock. Phytoremediation is considered a valid strategy to improve the purity of wastewaters. This work studied the effect of Zn2+ and Cu2+ on the morphology and protein expression in Thelypteris palustris and Typha latifolia plants, cultured in a wetland pilot system. Despite the absence of macroscopic alterations, remodeling of cell walls and changes in carbohydrate metabolism were observed in the rhizomes of both plants and in leaves of Thelypteris palustris. However, similar modifications seemed to be determined by the alterations of different mechanisms in these plants. These data also suggested that marsh ferns are more sensitive to metals than monocots. Whereas toleration mechanisms seemed to be activated in Typha latifolia, in Thelypteris palustris the observed modifications appeared as slight toxic effects due to metal exposure. This study clearly indicates that both plants could be successfully employed in in situ phytoremediation systems, to remove Cu2+ and Zn2+ at concentrations that are ten times higher than the legal limits, without affecting plant growth.

© 2017 American Chemical Society. ABX3 (A = organic cation; B = Sn, Pb; and X = halogen) organohalide perovskites have recently attracted much attention for their photovoltaic applications. Such hybrid compounds are derived from the replacement of the inorganic monovalent metal element by an organic cation, for example, methylammonium ion (MA = CH3NH3+) and formamidinium ion (FA= +HC(NH2)2). In particular, since the organic cations are polar, it is interesting to investigate their possible long-range ordering and the corresponding Rashba spin-split bands. In this work, by using density functional theory calculations, we estimate the ferroelectric polarization corresponding to a complete ordering of dipole moments for the optimized structures of 12 perovskite halides, with A = MA, FA; B = Pb, Sn; X = Cl, Br, I. The adiabatic path and functional mode analysis have been discussed for all cases. The calculated values of the polarization may be as high as a conventional inorganic ferroelectric compound, such as BaTiO3. The concomitant inversion symmetry breaking, coupled to the sizable spin-orbit coupling of Pb and Sn, results in a fairly large Rashba spin-splitting effect for both valence and conduction bands. We highlight a rather anisotropic dispersion of spin-orbit split bands which gives rise to different Rashba parameters in different directions perpendicular to the polar axis in k-space. Furthermore, we found a weak and positive correlation between the magnitude of polarization and relevant spin-split band parameters. Since the mechanism for enhanced carrier lifetime in 3D Rashba materials is connected to the reduced recombination rate due to the spin-forbidden transition, our study could aid in the understanding of the fundamental physics of organometal halide perovskites and the optimization and design of materials for better performance.

This paper addresses the need for a fast and precise non-contact measurement system to be used to assess the quality of connectors for electrical/electronic applications and particularly it proposes a technique to measure the position of the pins that are present in various shapes and number in every connector by a stereo vision system. The proposed stereo vision system is targeted to the automotive industry, but the same approach can be translated to many other sectors. The measurement of the position of the pins is a crucial aspect in assessing the quality both of the connectors (from the point of view of the connectors suppliers) and of the equipment where the connectors are used. It is of primary importance to verify the position of the pins not only in the 2D plane where they lie, but also to measure their height to verify that they can guarantee the continuity of the electrical circuit. In this paper, a technique based on the stereo vision principle is proposed to perform such an analysis. The stereo vision system, developed for a real production line, is compared against other available non-contact techniques and its advantages in terms of resolution, speed and robustness are pointed out. The system is described in terms of hardware, layout and software. System calibration and performance are described and verified. Afterwards, the on line implementation is described and the advantages and critical points are highlighted.

A displacive-type mechanism, which accounts for the occurrence of ferroelectricity in most inorganic ferroelectrics, is rarely found in molecule-based ferroelectrics. Its role is often covered by the predominant order–disorder one. Herein, we report a lone-pair-electron-driven displacive-type ferroelectric organic–inorganic hybrid compound, [H2dmdap][SbCl5] (1; dmdap = N,N-dimethyl-1,3-diaminopropane). The structure of 1 features a typical zigzag chain of [SbCl5]∞ containing cis-connected anionic octahedra. The compound undergoes a second-order paraelectric–ferroelectric phase transition at 143 K (P21/c ↔ Pc) with a saturation polarization of 1.36 μC·cm–2 and a coercive field of 3.5 kV·cm–1 at 119 K. Theoretical study discloses the ferroelectricity mainly originating from the relative displacements of the Sb and Cl ions in the crystal lattice, which are driven by the 5s2 lone-pair electrons of the SbIII center. Furthermore, on the basis of analysis, possible routes are suggested to enhance ferroelectric p...

There is increasing interest in the development of new magnetic polymeric carriers for biomedical applications such as trigger-controlled drug release, magnetic hyperthermia (MH) for the treatment of cancer, and as contrast agents in magnetic resonance imaging (MRI). This work describes the synthesis of sub-micrometer and magnetic polymer nanocomposite capsules (MPNCs) by combining in one single platform the biodegradable polymer poly-e-caprolactone (PCL) and different concentrations of ∼8 nm oleic acid (OA)-functionalized magnetite nanoparticles (Fe3O4@OA), employing the oil-in-water emulsion/solvent evaporation method. The MPNCs showed a significant increase in particle size from ∼400 to ∼800 nm as the magnetic loading in the organic–inorganic hybrids increases from 1.0% to 10%. The MPNCs presented high incorporation efficiency of Fe3O4@OA nanoparticles, good colloidal stability, and super-paramagnetic properties. Interestingly, electron microscopy results showed that the Fe3O4@OA nanoparticles were pre...

High-quality single crystals of perovskite-like (CH3NH3)3Bi2I9 hybrids have been synthesized, using a layered-solution crystal-growth technique. The large dielectric constant is strongly affected by the polar ordering of its constituents. Progressive dipolar ordering of the methylammonium cation upon cooling below 300 K gradually converts the hexagonal structure (space group P63/mmc) into a monoclinic phase (C2/c) at 160 K. A well-pronounced, ferrielectric phase transition at 143 K is governed by in-plane ordering of the bismuth lone pair that breaks inversion symmetry and results in a polar phase (space group P21). The dielectric constant is markedly higher in the C2/c phase above this transition. Here, the bismuth lone pair is disordered in-plane, allowing the polarizability to be substantially enhanced. Density functional theory calculations estimate a large ferroelectric polarization of 7.94 μC/cm(2) along the polar axis in the P21 phase. The calculated polarization has almost equal contributions of the methylammonium and Bi(3+) lone pair, which are fairly decoupled.

This work deals with the successful synthesis, spectroscopic properties (Raman and infrared) and theoretical calculations of some quinoline derivatives, namely 4-azido-7-chloroquinoline and the commercially available 4,7-dichloroquinoline, quinolin-8-ol. The analysis of the Raman and infrared spectra of the quinoline derivatives, supported by DFT calculations, for the first time has afforded the opportunity to characterize unambiguously the main vibrational bands for these important molecules, which are mainly used as anti-malaria compounds. Despite the very similar structures of these quinolines the Raman and infrared spectra exhibit significant wavenumber shifts for several key bands. A characteristic band at ca. 1580 cm −1 can be assigned involving a δ(OH) mode for quinolin-8-ol (QNO) as well as the band at ca. 1090 cm −1 attributed to δ(CCl) for 4,7-dichloroquinoline (DCQN). The compound 4-azido-7-chloroquinoline (ACQN) shows a very characteristic marker band at ca. 1300 cm −1 , which has been assigned to the ν(NN) mode of the azide group.

In developing physical theories, analogical reasoning has been found to be very powerful, as attested by a number of important historical examples. An analogy between two apparently different phenomena, once established, allows one to transfer information and bring new concepts from one phenomenon to the other. Here, we discuss an important analogy between two widely different physical problems, namely, the Jahn–Teller distortion in molecular physics and the Rashba spin splitting in condensed matter physics. By exploring their conceptual and mathematical features and by searching for the counterparts between them, we examine the orbital texture in Jahn–Teller systems, as the counterpart of the spin texture of the Rashba physics, and put forward a possible way of experimentally detecting the orbital texture. Finally, we discuss the analogy by comparing the coexistence of linear Rashba + Dresselhaus effects and Jahn–Teller problems for specific symmetries, which allow for nontrivial spin and orbital textures, respectively.

The perovskite azido compound [(CH3)4N][Mn(N3)3], which undergoes a first-order phase change at Tt=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN6] octahedral as well as order/disorder and off-center shifts of the [(CH3)4N]+ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low-temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH3)4N][Mn(N3)3] is a singular material in which three ferroic orders coexist even above room temperature. Triple-ferroic hybrid perovskite: The azido perovskite compound [(CH3)4N][Mn(N3)3] is a singular multiferroic material in which the three ferroic orders (electric, elastic, and magnetic) coexist even above room temperature (see figure).

We report the synthesis, single crystal X-ray diffraction, and thermal, dielectric, Raman and infrared studies of a novel heterometallic formate [C2H5NH3][Na0.5Fe0.5(HCOO)3] (EtANaFe). The thermal studies show that EtANaFe undergoes a second-order phase transition at about 360 K. X-ray diffraction data revealed that the high-temperature structure is monoclinic, space group P2(1)/n, with dynamically disordered ethylammonium (EtA(+)) cations. EtANaFe possesses a polar low-temperature structure with the space group Pn and, in principle, is ferroelectric below 360 K. Dielectric data show that the reciprocal of the real part of dielectric permittivity above and below the phase transition temperature follows the Curie-Weiss, as expected for a ferroelectric phase transition. Based on theoretical calculations, we estimated the polarization as (0.2, 0, 0.8) μC cm(-2), i.e., lying within the ac plane. The obtained data also indicate that the driving force of the phase transition is ordering of EtA(+) cations. However, this ordering is accompanied by significant distortion of the metal formate framework.

The present study reports a comprehensive analysis regarding the formation of Mg–Nb combined active rock salt nanoparticles (Mg x Nb y O x+y ) in MgH 2 /Nb 2 O 5 composite hydrogen storage system. This phase exhibit close crystallographic features to MgO and, hence was overlooked for years until recently. In order to explore the evolution of this phase in-situ in a MgH 2 –Nb 2 O 5 hydrogen storage system, Nb 2 O 5 was mixed with MgH 2 in various concentrations and the mechanochemical reaction products were monitored through 8 different compositions in three sets of reaction times, 1 h, 10 h and 30 h (totally 24 samples). Our study confirms the formation of rock salt type Mg x Nb y O x+y nanostructure over a wide compositional range in the MgH 2 + nNb 2 O 5 (n = 0.083, 0.10, 0.123, 0.167, 0.25, 0.50, 1.0 and 1.5) system. In contrast to MgO, which is a well-known barrier layer in MgH 2 system, the Nb dissolved MgO phases are shown to promote the hydrogen desorption performance of MgH 2 .

High-quality CuInSe2 (CISe) nanowires have been prepared by a one-step evaporation process. The presented growth process results in a composite material consisting of CISe NWs on top of a polycrystalline CISe base layer. The nanowires were extensively characterized by transmission electron microscopy, confirming their composition and atomic-scale crystal structure with a very low number of structural defects. From these analyses, we infer that the growth axis is along the [111] direction. The polycrystalline base layer has a tetragonal chalcopyrite structure and is optically active as confirmed by X-ray diffraction and photoluminescence (PL) analysis, respectively. Potential applications of this composite CISe NW/base-layer material for photovoltaic energy conversion are supported by the reduced reflectivity of the material and its strong PL intensity. The presented growth method is based on elemental evaporation under vacuum conditions, which makes the process compatible with the fabrication of photovoltaic devices., The authors would like to acknowledge the CAPES (CAPES-INL 04/14), CNPq, and FAPEMIG funding agencies for financial support. We acknowledge the collaboration project with IMM-CSIC (AIC-B-2011-0806). P. M. P. S. acknowledges financial support from EU through the FP7 Marie Curie IEF 2012 Action No. 327367. The projects RECI/FIS-NAN/0183/2012 (COMPETE: FCOMP-01-0124-FEDER-027494) and UID/CTM/50025/2013 from the Fundação para a Ciência e a Tecnologia (Portugal) are also acknowledged.

We report on a high responsivity at zero bias in infrared photodetectors based on InAlAs quantum dots due to the formation of an Al-rich wetting layer which acts as an electron barrier. This layer has a larger bandgap and results from the low segregation and low surface diffusion of the Al atoms that mostly remain inside the wetting layer. These photovoltaic infrared photodetectors could operate up to 80 K and presented a detectivity similar to the one of a conventional photoconductive photodetector based on InAs quantum dots, despite the lack of optimization for photovoltaic operation. Such InAlAs devices might be good candidates for focal plane arrays that require low dark current, low noise, and low current consumption.

Animal production is a source of heavy metals in livestock wastewater and also a key link in the food chain, with negative impacts on human and animal health. In intensive animal production systems, the most critical elements are zinc and copper. In order to development of innovative non-invasive strategies to reduce the environmental impact of livestock, this study assessed the ability of two plants, Typha latifolia and Thelypteris palustris, to bioaccumulate the heavy metals used in animal nutrition, from wastewater. Four mesocosms (width 2.0 m, length 2.0 m, 695 L of water, 210 kg of soil) were assembled outdoors at the Botanical Garden. Two of them were planted with T. latifolia (TL treated, n = 30; TL control, n = 30) and two with T. palustris (TP treated, n = 60; TP control, n = 60). In T0 a solution of a mineral additive premix (Zn 44.02 mg/L; Cu 8.63 mg/L) was dissolved in the treated mesocosms. At T0, d 15 (T1) and d 45 (T2) samples of roots, leaves, stems, soil and water were collected, dried, mineralized and analyzed using ICP-MS in order to obtain HMs content. We found that T. latifolia and T. palustris accumulate and translocate Zn, Cu from contaminated wastewater into plant tissues in a way that is directly related to the exposure time (T2 for Zn: 271.64 ± 17.70, 409.26 ± 17.70 for Cu: 47.54 ± 3.56, 105.58 ± 3.56 mg/kg of DM, respectively). No visual toxicity signs were observed during the experimental period. This phytoremediation approach could be used as an eco-sustainable approach to counteract the output of heavy metals.

We design a compound belonging to a class of materials designated as polar half-metallic ferromagnets, where a 100% spin polarization coexists with polar distortions that globally lift inversion symmetry. Using electronic structure calculations, we predict that the ultrashort period ${({\mathrm{LaNiO}}_{3})}_{1}/{({\mathrm{YCrO}}_{3})}_{1}$ superlattice belongs to this materials class, exhibiting an integer magnetic moment of $4\phantom{\rule{3.33333pt}{0ex}}{\ensuremath{\mu}}_{B}$. The minority channel electric polarization, as computed using Berry phase theory, is as high as $\ensuremath{\sim}13.0\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, and we discuss experimental strategies to access the polarization. We propose that polar ferromagnetic half-metals exhibit multiferroism and can be exploited to realize nonreciprocal effects and directional anisotropy owing to the absence of both space-inversion and time-reversal symmetries.

Magnetic insulators are often antiferromagnetic (AFM) and layered AFM compounds usually show low ordering temperature. On the other hand, layered ferromagnetic (FM) insulators with high-TC are very rare although they could be quite useful for spintronic applications. Here, using crystal field level analysis in combination with density functional theory calculations as well as Monte Carlo simulations, we predict that the layered insulator Sr2NiRuO4 would have a strong FM coupling with TC as high as 240 K. The tetragonal crystal field in the Ni-O-Ru square plane stabilizes the S=1/2 Ni+ and S=3/2 Ru3+ states. The unique level ordering and occupation optimize the FM Ni-Ru superexchange interactions in the checkerboard arrangement, thus suggesting Sr2NiRuO4 as an unusual high-TC layered FM insulator. This work highlights the potential of charge-spin-orbital degrees of freedom for stabilizing strong FM coupling in layered oxides., 17 pages, 7 figures, 1 table

Transition-metal dichalcogenides (TMDs) monolayers have been considered as important two-dimensional semiconductor materials for the study of fundamental physics in the field of spintronics. However, the out-of-plane mirror symmetry in TMDs may constrain electrons' degrees of freedom and it may limit spin-related applications. Recently, a newly synthesized Janus TMDs MoSSe was found to intrinsically possess both the in-plane inversion and the out-of-plane mirror-symmetry breaking. Here we performed first-principles calculations in order to systematically investigate the electronic band structures of a series of Janus monolayer TMDs with chemical formula $MXY\phantom{\rule{0.16em}{0ex}}(M=\mathrm{Mo},\phantom{\rule{0.16em}{0ex}}\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{and}\phantom{\rule{0.16em}{0ex}}X,Y=\mathrm{S},\phantom{\rule{0.16em}{0ex}}\mathrm{Se},\phantom{\rule{0.16em}{0ex}}\mathrm{Te})$. It is found that they possess robust electronic properties like their parent phases. We explored also the effect of perpendicular external electric field and in-plane biaxial strain on the Rashba spin splittings. The Zeeman-type spin splitting and valley polarization at $K({K}^{\ensuremath{'}})$ point are well preserved and we observed a Rashba-type spin splitting around the $\mathrm{\ensuremath{\Gamma}}$ point for all the $MXY$ systems. We have also found that these spin splittings can be enhanced by an external electric field collinear with the local electric field derived by the polar bonds and by the compressive strain. The Rashba parameters change linearly with the external electric field, but nonlinearly with the biaxial strain. The compressive strain is found to enhance significantly the anisotropic Rashba spin splitting.

Background Green synthesis is an ecological technique for the production of well characterized metallic nanoparticles using plants. This study investigated the synthesis of silver nanoparticles (AgNPs) using a Caesalpinia ferrea seed extract as a reducing agent. Methods The formation of AgNPs was identified by instrumental analysis, including ultraviolet–visible (UV–Vis) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) of the AgNPs, and surface-enhanced Raman scattering (SERS) spectra of rhodamine-6G (R6G). We studied the physicochemical characterization of AgNPs, evaluated them as an antifungal agent against Candida albicans, Candida kruzei, Candida glabrata and Candida guilliermondii, and estimated their minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values. Lastly, this study evaluated the cytotoxicity of the AgNPs in murine L929 fibroblasts cells using an MTT assay. Results The UV–Vis spectroscopy, SERS, SEM and XRD results confirmed the rapid formation of spheroidal 30–50 nm AgNPs. The MIC and MFC values indicated the antifungal potential of AgNPs against most of the fungi studied and high cell viability in murine L929 fibroblasts. In addition, this study demonstrated that C. ferrea seed extracts may be used for the green synthesis of AgNPs at room temperature for the treatment of candidiasis.

Spin-valley and electronic band topological properties have been extensively explored in quantum material science, yet their coexistence has rarely been realized in stoichiometric two-dimensional (2D) materials. We theoretically predict the quantum spin Hall effect (QSHE) in the hydrofluorinated bismuth (Bi2HF) nanosheet where the hydrogen (H) and fluorine (F) atoms are functionalized on opposite sides of bismuth (Bi) atomic monolayer. Such Bi2HF nanosheet is found to be a 2D topological insulator with a giant band gap of 0.97 eV which might host room temperature QSHE. The atomistic structure of Bi2HF nanosheet is noncentrosymmetric and the spontaneous polarization arises from the hydrofluorinated morphology. The phonon spectrum and ab initio molecular dynamic (AIMD) calculations reveal that the proposed Bi2HF nanosheet is dynamically and thermally stable. The inversion symmetry breaking together with spin-orbit coupling (SOC) leads to the coupling between spin and valley in Bi2HF nanosheet. The emerging valley-dependent properties and the interplay between intrinsic dipole and SOC are investigated using first-principles calculations combined with an effective Hamiltonian model. The topological invariant of the Bi2HF nanosheet is confirmed by using Wilson loop method and the calculated helical metallic edge states are shown to host QSHE. The Bi2HF nanosheet is therefore a promising platform to realize room temperature QSHE and valley spintronics.

In this work, we propose an improved version of our algorithm for real-time robotic assistance tuning in robot-based therapy with any kind of active device for upper-limb rehabilitation. In particular, the work describes in detail how to extract accurate performance indices from the subject’s execution, and how to correlate them with the amount of assistance to be correspondingly provided over time. The algorithm also aims at enhancing subject’s efforts for a more effective recovery, tailoring the therapy to the patient without prior knowledge of his/her clinical status. Finally, an assessment phase illustrates the effectiveness of the procedure, showing how the system tunes the assistance required by the subjects to perform specific tasks.

The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon- germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low- temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000C. A peak figure of merit zT = 0:88 at 900C is observed and comparatively insensitive to the aforementioned param- eter variations.

We report for the first time the effective transfer of hydrophobic oleate-capped iron oxide nanoparticles to an aqueous phase upon treatment with a base bath cleaning solution. We discuss the mechanism of the phase transfer, which involves the elimination of the organic capping agent followed by ionic stabilization of the nanoparticles due to negatively charged Fe–O− surface species. The resultant superparamagnetic aqueous nanocolloid shows excellent protein immobilization capability.

Multiferroics and magnetoelectrics with coexisting and coupled multiple ferroic orders are materials promising new technological advances. While most studies have focused on single-phase or heterostructures of inorganic materials, a new class of materials called metal–organic frameworks (MOFs) has been recently proposed as candidate materials demonstrating interesting new routes for multiferroism and magnetoelectric coupling. Herein, we report on the origin of multiferroicity of (CH3)2NH2Mn(HCOO)3 via direct observation of ferroelectric domains using second-harmonic generation techniques. For the first time, we observe how these domains are organized (sized in micrometer range), and how they are mutually affected by applied electric and magnetic fields. Calculations provide an estimate of the electric polarization and give insights into its microscopic origin., npj Quantum Materials, 1, ISSN:2397-4648

By means of density functional theory based calculations, we study the role of spin-orbit coupling in the new family of ABC hyperferroelectrics [Phys. Rev. Lett. 112, 127601 (2014)]. We unveil an extremely rich physics strongly linked to ferroelectric properties, ranging from the electric control of bulk Rashba effect to the existence of a three dimensional topological insulator phase, with concomitant topological surface states even in the ultrathin film limit. Moreover, we predict that the topological transition, as induced by alloying, is followed by a Weyl semi-metal phase of finite concentration extension, which is robust against disorder, putting forward hyperferroelectrics as promising candidates for spin-orbitronic applications., 5 pages, 3 figures

First-principles calculations are performed on magnetic multidomain structures in the $\mathrm{SmFe}{\mathrm{O}}_{3}$ rare-earth orthoferrite compound. We focus on the magnetic symmetry breaking at (001)-oriented antiphase domain walls, treating magnetism in the simplest (collinear) approximation without any relativistic (spin-orbit coupling) effects. We found that the number of $\mathrm{Fe}{\mathrm{O}}_{2}$ layers inside the domains determines the electrical nature of the whole system: multidomains with odd number of layers are paraelectric, while multidomains with even number of layers possess an electric polarization aligned along $b$ axis and a resulting multiferroic $Pmc{2}_{1}$ ground state. Our ab initio data and model for ferroelectricity induced by spin order reveal that this polarization is of the improper type and originates from an exchange striction mechanism that drives a polar displacement of the oxygen ions located at the magnetic domain walls. Additional calculations ratify that this effect is general among magnetic perovskites with an orthorhombic $\mathrm{SmFe}{\mathrm{O}}_{3}\text{\ensuremath{-}}\mathrm{like}$ structure.