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1.
Sci Adv ; 5(11): eaav4355, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31700996

RESUMO

Recently, several captivating topological structures of electric dipole moments (e.g., vortex, flux closure) have been reported in ferroelectrics with reduced size/dimensions. However, accurate polarization distribution of these topological ferroelectric structures has never been experimentally obtained. We precisely measure the polarization distribution of an individual ferroelectric vortex in PbTiO3/SrTiO3 superlattices at the subunit cell level by using the atomically resolved integrated differential phase contrast imaging in an aberration-corrected scanning transmission electron microscope. We find, in vortices, that out-of-plane polarization is larger than in-plane polarization, and that downward polarization is larger than upward polarization. The polarization magnitude is closely related to tetragonality. Moreover, the contribution of the Pb─O bond to total polarization is highly inhomogeneous in vortices. Our precise measurement at the subunit cell scale provides a sound foundation for mechanistic understanding of the structure and properties of a ferroelectric vortex and lattice-charge coupling phenomena in these topological ferroelectric structures.

2.
Phys Chem Chem Phys ; 21(38): 21381-21388, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31531469

RESUMO

In multiferroics, electromagnons have been recognized as a noticeable topic due to their indispensable role in magnetoelectric, magnetodielectric, and magnetocapacitance effects. Here, the electromagnons of Bi1-xNdxFeO3 (x = 0-0.2) nanoparticles are studied via terahertz time-domain spectroscopy, and the impacts of doping concentrations on electromagnons have been discussed. We found that the electromagnons in Bi1-xNdxFeO3 nanoparticles are associated with their phase transition. The total coupling weight of electromagnons is gradually increased in polar R3c structures and then reduces in the antipolar Pbam phase, and the weight in the antipolar phase is less than that of the pure R3c phase. Interestingly, a colossal electromagnon is observed at polar-antipolar and antiferromagnetic-ferromagnetic phase boundaries. Our work offers an avenue for designing and choosing materials with better magnetodielectric and magnetocapacitance properties.

3.
Nanoscale Res Lett ; 14(1): 254, 2019 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-31350697

RESUMO

The HfO2-based ferroelectric field effect transistor (FeFET) with a metal/ferroelectric/insulator/semiconductor (MFIS) gate stack is currently being considered as a possible candidate for high-density and fast write speed non-volatile memory. Although the retention performance of the HfO2-based FeFET with a MFIS gate stack could satisfy the requirements for practical applications, its memory window (MW) and reliability with respect to endurance should be further improved. This work investigates the advantage of employing ZrO2 seed layers on the MW, retention, and endurance of the Hf0.5Zr0.5O2 (HZO)-based FeFETs with MFIS gate stacks, by using fast voltage pulse measurements. It is found that the HZO-based FeFET with a ZrO2 seed layer shows a larger initial and 10-year extrapolated MW, as well as improved endurance performance compared with the HZO-based FeFET without the ZrO2 seed layer. The results indicate that employing of a direct crystalline high-k/Si gate stack would further improve the MW and reliability of the HfO2-based FeFETs.

4.
ACS Appl Mater Interfaces ; 11(2): 2205-2210, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30408951

RESUMO

Self-assembled heteroepitaxial nanostructures have played an important role for miniaturization of electronic devices, e.g., the ultrahigh density ferroelectric memories, and cause for great concern. Our first principle calculations predict that the materials with low formation energy of the interface ( Ef) tend to form matrix structure in self-assembled heteroepitaxial nanostructures, whereas those with high Ef form nanopillars. Under the guidance of the theoretical modeling, perovskite BiFeO3 (BFO) nanopillars are swimmingly grown into CeO2 matrix on single-crystal (001)-SrTiO3 (STO) substrates by pulsed laser deposition, where CeO2 has a lower formation energy of the interface ( Ef) than BFO. This work provides a good paradigm for controlling self-assembled nanostructures as well as the application of self-assembled ferroelectric nanoscale memory.

5.
ACS Appl Mater Interfaces ; 10(36): 30574-30580, 2018 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-30118205

RESUMO

In the era of Internet of Things, the demand for flexible and transparent electronic devices has shifted to the forefront of materials science research. However, the radiation damage to key performance of transparent devices under radiative environment remains as a critical issue. Here, we present a promising technology for nonvolatile transparent electronic devices based on flexible oxide heteroepitaxy. A direct fabrication of epitaxial lead lanthanum zirconate titanate on transparent flexible mica substrate with indium tin oxide electrodes is presented. The transparent flexible ferroelectric heterostructures not only retain their superior performance, thermal stability, reliability, and mechanical durability, but also exhibit remarkably robust properties against to a strong radiation exposure. Our study demonstrates an extraordinary concept to realize transparent flexible nonvolatile electronic devices for the design and development of next-generation smart devices with potential application in electronics, automotive, aerospace, and nuclear systems.

6.
J Vis Exp ; (134)2018 04 08.
Artigo em Inglês | MEDLINE | ID: mdl-29683441

RESUMO

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.


Assuntos
Eletrônica/métodos , Memória/fisiologia
7.
Nat Commun ; 9(1): 685, 2018 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-29449561

RESUMO

Emergent physical properties often arise at interfaces of complex oxide heterostructures due to the interplay between various degrees of freedom, especially those with polar discontinuities. It is desirable to explore if these structures may generate pure and controllable spin currents, which are needed to attain unmatched performance and energy efficiency in the next-generation spintronic devices. Here we report the emergence of a spin-polarized two-dimensional electron gas (SP-2DEG) at the interface of two insulators, SrTiO3 and PbZr0.2Ti0.8O3. This SP-2DEG is strongly localized at the interfacial Ti atoms, due to the interplay between Coulomb interaction and band bending, and can be tuned by the ferroelectric polarization. Our findings open a door for engineering ferroelectric/insulator interfaces to create tunable ferroic orders for magnetoelectric device applications and provide opportunities for designing multiferroic materials in heterostructures.

8.
Sci Adv ; 3(6): e1700121, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28630922

RESUMO

We present a promising technology for nonvolatile flexible electronic devices: A direct fabrication of epitaxial lead zirconium titanate (PZT) on flexible mica substrate via van der Waals epitaxy. These single-crystalline flexible ferroelectric PZT films not only retain their performance, reliability, and thermal stability comparable to those on rigid counterparts in tests of nonvolatile memory elements but also exhibit remarkable mechanical properties with robust operation in bent states (bending radii down to 2.5 mm) and cycling tests (1000 times). This study marks the technological advancement toward realizing much-awaited flexible yet single-crystalline nonvolatile electronic devices for the design and development of flexible, lightweight, and next-generation smart devices with potential applications in electronics, robotics, automotive, health care, industrial, and military systems.

9.
Sci Rep ; 5: 13655, 2015 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-26351109

RESUMO

Regelation, i.e., ice melts under compression and freezes again when the pressure is relieved, remains puzzling since its discovery in 1850's by Faraday. Here we show that hydrogen bond (O:H-O) cooperativity and its extraordinary recoverability resolve this anomaly. The H-O bond and the O:H nonbond possesses each a specific heat ηx(T/ΘDx) whose Debye temperature ΘDx is proportional to its characteristic phonon frequency ωx according to Einstein's relationship. A superposition of the ηx(T/ΘDx) curves for the H-O bond (x=H, ωH~3200 cm(-1)) and the O:H nonbond (x=L, ωL~200 cm(-1), ΘDL=198 K) yields two intersecting temperatures that define the liquid/quasisolid/solid phase boundaries. Compression shortens the O:H nonbond and stiffens its phonon but does the opposite to the H-O bond through O-O Coulomb repulsion, which closes up the intersection temperatures and hence depress the melting temperature of quasisolid ice. Reproduction of the Tm(P) profile clarifies that the H-O bond energy EH determines the Tm with derivative of EH=3.97 eV for bulk water and ice. Oxygen atom always finds bonding partners to retain its sp3-orbital hybridization once the O:H breaks, which ensures O:H-O bond recoverability to its original state once the pressure is relieved.

10.
Phys Chem Chem Phys ; 16(42): 22987-94, 2014 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-25198167

RESUMO

Consistency in experimental observations, numerical calculations, and theoretical predictions have revealed that the skins of water and ice share the same attribute of supersolidity characterized by an identical H-O vibration frequency of 3450 cm(-1). Molecular undercoordination and inter-electron-pair repulsion shortens the H-O bond and lengthens the O:H nonbond, leading to a dual process of nonbonding electron polarization. This relaxation-polarization process enhances the dipole moment, elasticity, viscosity, and thermal stability of these skins with a 25% density loss, which is responsible for the hydrophobicity and toughness of the water skin and results in the slippery behavior of ice.

11.
Phys Chem Chem Phys ; 16(42): 22995-3002, 2014 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-25253165

RESUMO

The Mpemba paradox, that is, hotter water freezes faster than colder water, has baffled thinkers like Francis Bacon, René Descartes, and Aristotle since B.C. 350. However, a commonly accepted understanding or theoretical reproduction of this effect remains challenging. Numerical reproduction of observations, shown herewith, confirms that water skin supersolidity [Zhang et al., Phys. Chem. Chem. Phys., DOI: ] enhances the local thermal diffusivity favoring heat flowing outwardly in the liquid path. Analysis of experimental database reveals that the hydrogen bond (O:H-O) possesses memory to emit energy at a rate depending on its initial storage. Unlike other usual materials that lengthen and soften all bonds when they absorb thermal energy, water performs abnormally under heating to lengthen the O:H nonbond and shorten the H-O covalent bond through inter-oxygen Coulomb coupling [Sun et al., J. Phys. Chem. Lett., 2013, 4, 3238]. Cooling does the opposite to release energy, like releasing a coupled pair of bungees, at a rate of history dependence. Being sensitive to the source volume, skin radiation, and the drain temperature, the Mpemba effect proceeds only in the strictly non-adiabatic 'source-path-drain' cycling system for the heat "emission-conduction-dissipation" dynamics with a relaxation time that drops exponentially with the rise of the initial temperature of the liquid source.

12.
Tumour Biol ; 35(6): 5055-9, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24609902

RESUMO

Osteosarcoma is the most commonly diagnosed primary malignant bone tumor, with similar global incidence rate across childhood and adolescence. Patients with localized disease have a 5-year survival period of 80 %; however, the prognosis is poor in those with metastatic osteosarcoma. The origin of the primary tumor is most frequently the metaphyseal (actively growing) regions of the distal femur, proximal tibia, and proximal humerus, although the tumor can develop in any bone, and the most likely sites for metastasis are the lungs and bone. Ezrin is a member of the ezrin-radixin-moesin (ERM) family of proteins that functions as a cross-linker between the actin cytoskeleton and the plasma membrane, and ezrin also plays a positive role in maintaining cell shape and polarity and facilitates membrane-trafficking pathways, cell migration, cell signaling, growth regulation, and differentiation. There is strong evidence to suggest that ezrin is necessary for osteosarcoma metastasis. The objective of the current review is to summarize the know-how about metastatic progression in osteosarcoma, with a focus on ezrin. Despite the promise that preliminary studies on ezrin have shown, there is a great need to further analyze the role of ezrin in osteosarcoma metastasis and to determine its usefulness as a biomarker for the disease.


Assuntos
Neoplasias Ósseas/patologia , Proteínas do Citoesqueleto/fisiologia , Osteossarcoma/secundário , Animais , Humanos , Receptores de Hialuronatos/fisiologia , Sistema de Sinalização das MAP Quinases/fisiologia , Proteínas Proto-Oncogênicas c-akt/fisiologia
13.
Chemistry ; 20(19): 5815-20, 2014 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-24664534

RESUMO

Iron fluoride cathodes have been attracting considerable interest due to their high electromotive force value of 2.7 V and their high theoretical capacity of 237 mA h g(-1) (1 e(-) transfer). In this study, uniform iron fluoride hollow porous microspheres have been synthesized for the first time by using a facile and scalable solution-phase route. These uniform porous and hollow microspheres show a high specific capacity of 210 mA h g(-1) at 0.1 C, and excellent rate capability (100 mA h g(-1) at 1 C) between 1.7 and 4.5 V versus Li/Li(+) . When in the range of 1.3 to 4.5 V, stable capacity was achieved at 350 mA h g(-1) at a current of 50 mA g(-1) .

14.
Chemistry ; 20(3): 824-30, 2014 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-24339205

RESUMO

Spinel cathode materials consisting of LiMn2 O4 @LiNi0.5 Mn1.5 O4 hollow microspheres have been synthesized by a facile solution-phase coating and subsequent solid-phase lithiation route in an atmosphere of air. When used as the cathode of lithium-ion batteries, the double-shell LiMn2 O4 @LiNi0.5 Mn1.5 O4 hollow microspheres thus obtained show a high specific capacity of 120 mA h g(-1) at 1 C rate, and excellent rate capability (90 mAhg(-1) at 10 C) over the range of 3.5-5 V versus Li/Li(+) with a retention of 95 % over 500 cycles.

15.
J Phys Chem B ; 117(43): 13639-45, 2013 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-24090472

RESUMO

A combination of the Lagrangian mechanics of oscillators vibration, molecular dynamics decomposition of volume evolution, and Raman spectroscopy of phonon relaxation has enabled us to resolve the asymmetric, local, and short-range potentials pertaining to the hydrogen bond (O:H-O) in compressed ice. Results show that both oxygen atoms in the O:H-O bond shift initially outwardly with respect to the coordination origin (H), lengthening the O-O distance by 0.0136 nm from 0.2597 to 0.2733 nm by Coulomb repulsion between electron pairs on adjacent oxygen atoms. Both oxygen atoms then move toward right along the O:H-O bond by different amounts upon being compressed, approaching identical length of 0.11 nm. The van der Waals potential VL(r) for the O:H noncovalent bond reaches a valley at -0.25 eV, and the lowest exchange VH(r) for the H-O polar-covalent bond is valued at -3.97 eV.


Assuntos
Gelo , Ligações de Hidrogênio , Simulação de Dinâmica Molecular
16.
Sci Rep ; 3: 3005, 2013 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-24141643

RESUMO

The structural symmetry and molecular separation in water and ice remain uncertain. We present herewith a solution to unifying the density, the structure order and symmetry, the size (H-O length dH), and the separation (d(OO) = d(L) + d(H) or the O:H length d(L)) of molecules packing in water and ice in terms of statistic mean. This solution reconciles: i) the d(L) and the d(H) symmetrization of the O:H-O bond in compressed ice, ii) the d(OO) relaxation of cooling water and ice and, iii) the d(OO) expansion of a dimer and between molecules at water surface. With any one of the d(OO), the density ρ(g·cm⁻³), the d(L), and the d(H), as a known input, one can resolve the rest quantities using this solution that is probing conditions or methods independent. We clarified that: i) liquid water prefers statistically the mono-phase of tetrahedrally-coordinated structure with fluctuation, ii) the low-density phase (supersolid phase as it is strongly polarized with even lower density) exists only in regions consisting molecules with fewer than four neighbors and, iii) repulsion between electron pairs on adjacent oxygen atoms dictates the cooperative relaxation of the segmented O:H-O bond, which is responsible for the performance of water and ice.


Assuntos
Gelo , Água/química , Elétrons , Ligações de Hidrogênio , Modelos Moleculares , Conformação Molecular , Oxigênio/química
17.
Phys Chem Chem Phys ; 15(40): 17658-63, 2013 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-24042730

RESUMO

Toward engineering high performance anode alloys for Li-ion batteries, we proposed a useful method to quantitatively estimate the bulk modulus of binary alloys in terms of metallic electronegativity (EN), alloy composition and formula volume. On the basis of our proposed potential viewpoint, EN as a fundamental chemistry concept can be extended to be an important physical parameter to characterize the mechanical performance of Li-Si and Li-Sn alloys as anode materials for Li-ion batteries. The bulk modulus of binary alloys is linearly proportional to the combination of average metallic EN and atomic density of alloys. We calculated the bulk moduli of Li-Si and Li-Sn alloys with different Li concentrations, which can agree well with the reported data. The bulk modulus of Li-Si and Li-Sn alloys decreases with increasing Li concentration, leading to the elastic softening of the alloys, which is essentially caused by the decreased strength of constituent chemical bonds in alloys from the viewpoint of EN. This work provides a deep understanding of mechanical failure of Si and Sn anodes for Li-ion batteries, and permits the prediction of the composition dependent bulk modulus of various lithiated alloys on the basis of chemical formula, metallic EN and cell volume (or alloy density), with no structural details required.

18.
Chemistry ; 19(30): 9811-6, 2013 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-23788047

RESUMO

Charged up: A general soft-template route for the synthesis of uniform hollow carbon microspheres embedded with transition-metal oxide nanocrystals (OHCMs) has been developed (see figure). The obtained OHCMs possess a microsized spherical shape, embedded transition-metal oxide nanocrystals, and fully encapsulating conductive carbon shells, which endow the resulting anode materials with high specific capacities, rate capabilities, electrode densities, and cycle stabilities.

19.
J Phys Chem Lett ; 4(15): 2565-70, 2013 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-26704426

RESUMO

Goldschmidt-Pauling contraction of the H-O polar-covalent bond elongates and polarizes the other noncovalent part of the hydrogen bond (O:H-O), that is, the O:H van der Waals bond, significantly, through the Coulomb repulsion between the electron pairs of adjacent oxygen (O-O). This process enlarges and stiffens those H2O molecules having fewer than four neighbors such as molecular clusters, hydration shells, and the surface skins of water and ice. The shortening of the H-O bond raises the local density of bonding electrons, which in turn polarizes the lone pairs of electrons on oxygen. The stiffening of the shortened H-O bond increases the magnitude of the O1s binding energy shift, causes the blue shift of the H-O phonon frequencies, and elevates the melting point of molecular clusters and ultrathin films of water, which gives rise to their elastic, hydrophobic, highly-polarized, ice-like, and low-density behavior at room temperature.

20.
J Phys Chem Lett ; 4(19): 3238-44, 2013 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-26706381

RESUMO

The specific-heat difference between the O:H van der Waals bond and the H-O polar-covalent bond and the Coulomb repulsion between electron pairs on adjacent oxygen atoms determine the angle-length-stiffness relaxation dynamics of the hydrogen bond (O:H-O), which is responsible for the density and phonon-stiffness oscillation of water ice over the full temperature range. Cooling shortens and stiffens the part of relatively lower specific-heat, and meanwhile lengthens and softens the other part of the O:H-O bond via repulsion. Length contraction/elongation of a specific part always stiffens/softens its corresponding phonon. In the liquid and in the solid phase, the O:H bond contracts more than the H-O elongates, hence, an O:H-O cooling contraction and the seemingly "regular" process of cooling densification take place. During freezing, the H-O contracts less than the O:H elongates, leading to an O:H-O elongation and volume expansion. At extremely low temperatures, the O:H-O angle stretching lowers the density slightly as the O:H and the H-O lengths change insignificantly. In ice, the O-O distance is longer than it is in water, resulting in a lower density, so that ice floats.

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