Mechanical displacement in commonly used piezoelectric materials is typically restricted to linear or biaxial in nature and to a few percent of the material dimensions. Here, we show that free-standing BaTiO3 membranes exhibit non-conventional electromechanical coupling. Under an external electric field, these superelastic membranes undergo controllable and reversible "sushi-rolling-like" 180° folding-unfolding cycles. This crease-free folding is mediated by charged ferroelectric domains, leading to a giant > 3.8 and 4.6 µm displacements for a 30-nm thick membrane at room temperature and 60 °C, respectively. Further increasing the electric field above the coercive value changes the fold curvature, hence augmenting the effective piezoresponse. Finally, it is found that the membranes fold with increasing temperature followed by complete immobility of the membrane above the Curie temperature, allowing us to model the ferroelectric-domain origin of the effect.The electromechanical power conversion of piezoelectrics is the basis for a broad range of sensing, actuating, and communication technologies, including ultrasound imaging and cellular phones. 1-3 Recent interest in electromechanical energy harvesting 4,5 as well as in flexible electronics for wearable devices, 6,7 nano motors, 8 and medical applications 9-11 raises a need for flexible piezoelectric materials and devices. Modern applications of piezoelectrics hinge on thin films, 12-14 however, the substrate in such geometries is typically rigid, preventing the development of flexible devices. Flexible piezoelectric devices are therefore typically based on either nanowires 4 or on thin-film systems, but with substrates that have been designed especially for such applications. 15,16 Most piezoelectric applications rely on lead-based materials, which exhibit strong piezoelectric coefficients. Nevertheless, the toxicity of these materials is undesirable for environmental considerations, while it also disqualifies them for medical or wearable applications. Likewise, traditional thin-film geometries limit the electromechanical excitation modes. That is, usually, uniaxial electric field results in either parallel or perpendicular uniaxial or biaxial mechanical deformation (or vice versa).Nevertheless, the interest in flexible-electronic technologies raises a need for advanced electromechanical excitation modes, e.g., for motorized devices, including microscale aerial vehicles. 17 Substrate removal for piezoelectric films or membranes augments their functional properties, 18-21 mainly thanks to mechanically-induced ferroic-domain reorganization. 22 However, the preparation of completely stand-alone substrate-free films has remained a challenge. Lu et al. 23 demonstrated lately a general method to prepare oxide materials in the form of membranes, i.e., continuous free-standing thin films with no substrate. More recently, Dong et al. 24 used this method to process BaTiO3 membranes, which is a well-known lead-free piezoelectric and ferroelectric material. This work show...

A series of magnesium and zinc tetraarylporphyrins and their porphyrinoxidized derivatives were studied by UV/Vis, ESR, and resonance Raman spectroscopy at various temperatures. The series included tetra(mefa-dichloropheny1)porphyrinatozinc (S), tetra(orrh0-dichloropheny1)porphyrinatozinc (6), tetra(orfho-difluoropheny1)porph yrinatozinc and -magnesium (9 and lo), and tetra(pentafluoropheny1)porphyrinatozinc and -magnesium (7 and 8). The radical cations (3a-10a) were isolated by chemical one-electron oxidation of their neutral precursors (3-10). Despite the structural similarity of all these radicals, their electronic ground state varied within the series. The position of the chloro groups was found to play a key role. While the radical cation of the mera-dichloro-substituted derivative 5a exhibited A , , spectroscopic features, the orrho-dichlorophenyl derivative (6a) showed A , , spectral features. Radicals of the fluoro-substituted porphyrins, especially that of 10. were found to have state-admixed ( A ,JAZu) Keywords electronic structure 1 frontier orbitals metatloporphyrins -radical cations electronic structures, and the relative contributions of the two states was found to vary with temperature and to depend on the axial ligand. The results indicate that the fluoro-substituted porphyrins are primarily A,, at low temperature, even though their room temperature spectroscopic features resemble those of A , , cations. The elucidation of factors that affect the electronic structures of the radicals in the present series is helpful in providing a greater understanding of the spin-spin interactions in the intermediates of heme-dependant enzymatic reactions and their synthetic analogues.

Here, we optimized ultrathin films of granular NbN on SiO and of amorphous αWSi. We showed that hybrid superconducting nanowire single-photon detectors (SNSPDs) made of 2 nm thick αWSi films over 2 nm thick NbN films exhibit advantageous coexistence of timing (<5 ns reset time and 52 ps timing jitter) and efficiency (>96% quantum efficiency) performance. We discuss the governing mechanism of this hybridization via the proximity effect. Our results demonstrate saturated SNSPDs performance at 1550 nm optical wavelength and suggest that such hybridization can significantly expand the range of available superconducting properties, impacting other nano-superconducting technologies. Lastly, this hybridization may be used to tune properties, such as the amorphous character of superconducting films.

No abstract

Surfaces and interfaces of ferroelectric oxides exhibit enhanced functionality, and therefore serve as a platform for novel nano and quantum technologies. Experimental and theoretical challenges associated with examining the subtle electro-chemo-mechanical balance at metal-oxide surfaces have hindered the understanding and control of their structure and behavior. Here, combined are advanced electron-microscopy and firstprinciples thermodynamics methods to reveal the atomic-scale chemical and crystallographic structure of the surface of the seminal ferroelectric BaTiO 3 . It is shown that the surface is composed of a native <2 nm thick TiO x rock-salt layer in epitaxial registry with the BaTiO 3 . Using electronbeam irradiation, artificial TiO x sites with sub-nanometer resolution are successfully patterned, by inducing Ba escape. Therefore, this work offers electro-chemo-mechanical insights into ferroelectric surface behavior in addition to a method for scalable high-resolution beam-induced chemical lithography for selectively driving surface phase transitions, and thereby functionalizing metal-oxide surfaces.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10. 1002/adfm.201902549. in oxidation states of the participating ions. Hence, functional-oxide surfaces and interfaces constitute a rich platform for novel phases that are attractive for high-performance miniaturized electronic devices [7,8] as well as for chemical catalyses. [9] Because ferroelectric oxides comprise regions with varying crystallographic and electric polarization orientations, there has been a growing interest in their outer surface and domain wall functionality, which is expressed as enhanced conductivity, [10][11][12] magnetism, [4] and even superconductivity. [13] The chemical origin of such a functional behavior is typically attributed to either oxygen vacancy dynamics [14][15][16][17] or cation segregation, [18] while other studies look at the effects of intrinsic symmetry breaking. [4] Despite the accumulated knowledge on domain walls, the structure and behavior of ferroelectric surfaces, which are responsible for domain stabilization and are attractive for, e.g., nano lithography [19][20][21][22][23] and catalysis, [9,[24][25][26][27] have remained elusive. Specifically, the longstanding challenge in understanding how the surface mediates between the absence of electric and mechanical fields in the vacuum and the polarization, and strain in the bulk is not merely experimental or theoretical, but even conceptual. [28] Hence, computational methods that were developed to explain the electro-chemical [29] and electro-mechanical [30] atomic-scale interactions in ferroelectrics have been adopted to describe experimental observations of the surface behavior. For example, Tsurumi et al. [31,32] combined dielectric measurements and density functional theory (DFT) calculations to demonstrate that nanoparticles (NPs) of the seminal nontoxic ferroelectric, BaTiO 3 , organize in a core-shell...