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1.
Chemistry ; 25(43): 10204-10213, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31144786

RESUMO

We present herein the synthesis, crystal structure, and electric and magnetic properties of the spin-crossover salt [Mn(5-Cl-sal-N-1,5,8,12)]TCNQ1.5 ⋅2 CH3 CN (I), where 5-Cl-sal-N-1,5,8,12=N,N'-bis(3-(2-oxy-5-chlorobenzylideneamino)propyl)-ethylenediamine, containing distinct conductive and magnetic blocks along with acetonitrile solvent molecules. The MnIII complex with a Schiff-base ligand, [Mn(5-Cl-sal-N-1,5,8,12)]+ , acts as the magnetic unit, and the π-electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ- ) is the conducting unit. The title compound (I) exhibits semiconducting behavior with room temperature conductivity σRT ≈1×10-4  ohm-1 cm-1 and activation energy Δ ≈0.20 eV. In the temperature range 73-123 K, it experiences a hysteretic phase transition accompanied by a crossover between the low-spin S=1 and high-spin S=2 states of MnIII and changes in bond lengths within the MnN4 O2 octahedra. The pronounced shrinkage of the basal Mn-N bonds in I at the spin crossover suggests that the d x 2 - y 2 orbital is occupied/deoccupied in this transition. Interestingly, the bromo isomorphic counterpart [Mn(5-Br-sal-N-1,5,8,12)]TCNQ1.5 ⋅2 CH3 CN (II) of the title compound evidences no spin-crossover phenomena and remains in the high-spin state in the temperature range 2-300 K. Comparison of the chloro and bromo compounds allows the thermal and spin-crossover contributions to the overall variation in bond lengths to be distinguished. The difference in magnetic behavior of these two salts has been ascribed to intermolecular supramolecular effects on the spin transition. Discrete hydrogen bonding exists between cations and cations and anions in both compounds. However, the hydrogen bonding in the crystals of II is much stronger than in I. The relatively close packing arrangement of the [Mn(5-Br-sal-N-1,5,8,12)]+ cations probably precludes their spin transformation.

2.
Nanoscale ; 8(43): 18454-18460, 2016 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-27778015

RESUMO

The competition between superconductivity and ferromagnetism poses great challenges and has attracted renewed interest for applications in novel spintronic devices. In order to emphasize their interactions, we fabricated a heterostructure composed of superconducting YBa2Cu3O7-δ (YBCO) film embedded with itinerant ferromagnetic SrRuO3 (SRO) mesocrystals. Starting from a doping concentration of 10 vol% of SRO mesocrystal in a YBCO matrix, corresponding to the density of SRO nanocrystals ∼5 × 109 cm-2, which exhibits the typical characteristic of a metal-superconductor transition, and then increasing the magnetic interactions as a function of SRO embedment, the electronic correlation and the interplay between superconductivity and magnetism throughout the temperature regime were investigated. A metal-insulator transition in the normal state of YBCO and a crossover between superconductivity and magnetism at low temperatures were found upon increasing the density of nano-size SRO crystallites in the YBCO matrix as a consequence of competing interactions between these two ordered phases.

3.
J Phys Condens Matter ; 28(34): 345501, 2016 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-27355241

RESUMO

The electronic structure and magnetic properties of SrMn0.5Fe0.5O3 powder and films grown on (1 0 0)-SrTiO3 (STO) and (1 0 0)-LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) were investigated by temperature dependent magnetization and soft x-ray absorption. The results exhibit characteristics of 3d (5) Fe(3+), [Formula: see text], and 3d (3) + 3d (4) [Formula: see text] Mn(4+) at room temperature in all samples. However, the features of 3d (5) Fe(3+) and 3d (3) Mn(4+) increased significantly for SMFO/LAO at 35 K, which also displayed substantial competition between antiferromagnetic and ferromagnetic order well-above the Néel temperature of SrFeO3 (T N ~ 134 K). We attributed this to being caused by charge disproportionation resulting from ligand-hole localization, which is more favorable to take place when the sample is under compressive strain.

4.
Adv Mater ; 28(4): 764-70, 2016 Jan 27.
Artigo em Inglês | MEDLINE | ID: mdl-26607052

RESUMO

The coupling of the localized surface plasmon resonance of Au nanoparticles is utilized to deliver a visible-light stimulus to control conduction at the LaAlO3 /SrTiO3 interface. A giant photoresponse and the controllable metal-insulator transition are characterized at this heterointerface. This study paves a new route to optical control of the functionality at the heterointerfaces.

5.
Sci Rep ; 5: 16385, 2015 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-26548444

RESUMO

We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.

6.
Sci Rep ; 5: 14128, 2015 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-26370337

RESUMO

Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5 eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu(0.02)Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs.

7.
ACS Nano ; 8(6): 6242-9, 2014 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-24841152

RESUMO

Self-assembled nanocomposites with a high interface-to-volume ratio offer an opportunity to overcome limitations in current technology, where intriguing transport behaviors can be tailored by the choice of proper interactions of constituents. Here we integrated metallic perovskite oxide SrRuO3-wurzite semiconductor ZnO nanocomposites to investigate the room-temperature metal-insulator transition and its effect on photoresponse. We demonstrate that the band structure at the interface can be tuned by controlling the interface-to-volume ratio of the nanocomposites. Photoinduced carrier injection driven by visible light was detected across the nanocomposites. This work shows the charge interaction of the vertically integrated multiheterostructures by incorporating a controllable interface-to-volume ratio, which is essential for optimization of the design and functionality of electronic devices.

8.
Adv Mater ; 25(34): 4753-9, 2013 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-23847088

RESUMO

A new way to induce a large magnetoresistance has been achieved by self-assembled nanostructures consisting of ferromagnetic spinel CoFe2O4 (CFO) and metallic perovskite SrRuO3 (SRO). The interdiffused Fe³âº ions in SRO have paved the way to strong magnetic couplings with CFO nanopillars, resulting in the suppression of spin-polarized electron scattering.

9.
Adv Mater ; 25(24): 3357-64, 2013 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-23666885

RESUMO

Modulation of band bending at a complex oxide heterointerface by a ferroelectric layer is demonstrated. The as-grown polarization (Pup ) leads to charge depletion and consequently low conduction. Switching the polarization direction (Pdown ) results in charge accumulation and enhances the conduction at the interface. The metal-insulator transition at a conducting polar/nonpolar oxide heterointerface can be controlled by ferroelectric doping.

10.
Phys Rev Lett ; 109(24): 246807, 2012 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-23368366

RESUMO

In this study, direct observation of the evolution of electronic structures across complex oxide interfaces has been revealed in the LaAlO(3)/SrTiO(3) model system using cross-sectional scanning tunneling microscopy and spectroscopy. The conduction and valence band structures across the LaAlO(3)/SrTiO(3) interface are spatially resolved at the atomic level by measuring the local density of states. This study directly maps out the electronic reconstructions and a built-in electric field in the polar LaAlO(3) layer. Results also clearly reveal the band bending and the notched band structure in the SrTiO(3) adjacent to the interface.

11.
Appl Opt ; 50(19): 3311-5, 2011 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-21743534

RESUMO

We use optical tweezers to trap a unilamellar phospholipid vesicle and measure the out-of-plane thermal fluctuations by using differential confocal microscopy. Bending moduli of the lipid membranes are calculated directly from the mean-square values of the fluctuation amplitudes. Owing to the refractive index contrast between the inner and outer solutions of the vesicle, optical tweezers trap the vesicle laterally and improve the reliability of the measured fluctuation amplitudes along the optical axis. Bending moduli of membranes in gel or fluid phases obtained by the combination of differential confocal microscopy and optical tweezers are close to those reported previously. We also obtain the bending modulus of sphingomyelin membranes in the gel phase, which was not reported previously.


Assuntos
Microscopia Confocal/instrumentação , Esfingomielinas/química , Lipossomas Unilamelares/química , Bicamadas Lipídicas , Microscopia Confocal/métodos , Pinças Ópticas , Óptica e Fotônica
12.
Lab Chip ; 11(4): 695-9, 2011 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-21152515

RESUMO

We combine a micro-fluidic electric-field cell-culture (MEC) chip with structured-illumination nano-profilometry (SINAP) to quantitatively study the variations of cancer cell filopodia under external direct-current electric field (dcEF) stimulations. Because the lateral resolution of SINAP is better than 150 nm in bright-field image modality, filopodia with diameters smaller than 200 nm can be observed clearly without fluorescent labeling. In the MEC chip, a homogeneous EF is generated inside the culture area that simulates the endogenous EF environment. With this MEC chip-SINAP system, we directly observe and quantify the biased growth of filopodia of lung cancer cells toward the cathode. The epidermal growth factor receptors around the cell edges are also redistributed to the cathodal side. These results suggest that cancer-cell filopodia respond to the changes in EFs in the microenvironment.


Assuntos
Técnicas Analíticas Microfluídicas/métodos , Neoplasias/patologia , Pseudópodes/efeitos da radiação , Linhagem Celular Tumoral , Campos Eletromagnéticos , Humanos , Microscopia Confocal , Microscopia de Fluorescência
13.
ACS Nano ; 4(9): 5139-46, 2010 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-20731385

RESUMO

Perovskite phase instability of BiMnO3 has been exploited to synthesize epitaxial metal oxide magnetic nanocrystals. Thin film processing conditions are tuned to promote the breakdown of the perovskite precursor into Bi2O3 matrix and magnetic manganese oxide islands. Subsequent cooling in vacuum ensures complete volatization of the Bi2O3, thus leaving behind an array of self-assembled magnetic Mn3O4 nanostructures. Both shape and size can be systematically controlled by the ambient oxygen environments and deposition time. As such, this approach can be extended to any other Bi-based complex ternary oxide system as it primarily hinges on the breakdown of parent Bi-based precursor and subsequent Bi2O3 volatization.

14.
Opt Lett ; 34(22): 3562-4, 2009 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-19927211

RESUMO

A strongly saturated waveguide-based optical-field-ionization soft-x-ray laser seeded by high harmonic generation was demonstrated for Ni-like Kr lasing at 32.8 nm. Compared with the same laser seeded only with spontaneous emission, seeding with high harmonics yields much smaller divergence, enhanced spatial coherence, and controlled polarization. The integration of high harmonic seeding, optically preformed plasma waveguide, and optical-field-ionization pumping forms one of the optimal archetypes of an ultrashort-pulse soft-x-ray laser.

15.
Opt Lett ; 34(5): 623-5, 2009 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-19252572

RESUMO

Single-shot digital holographic microscopy with an adjustable field of view and magnification was demonstrated by using a tabletop 32.8 nm soft-x-ray laser. The holographic images were reconstructed with a two-dimensional fast-Fourier-transform algorithm, and a new configuration of imaging was developed to overcome the pixel-size limit of the recording device without reducing the effective NA. The image of an atomic-force-microscope cantilever was reconstructed with a lateral resolution of 480 nm, and the phase contrast image of a 20 nm carbon mesh foil demonstrated that profiles of sample thickness can be reconstructed with few-nanometers uncertainty. The ultrashort x-ray pulse duration combined with single-shot capability offers great advantage for flash imaging of delicate samples.

16.
Appl Opt ; 47(13): 2458-64, 2008 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-18449313

RESUMO

We demonstrate the observation of gold-nanoparticle internalization in membranes of living cells by using noninterferometric widefield optical profilometry (NIWOP). The NIWOP technique can trace the height of an 80 nm gold particle on the membrane by calibrating the change of light intensity scattered from the particle along the optical axis. On the membrane, the depth resolution based on the scattering signal is similar to that based on the reflection signal, nearly 20 nm. Comparing the heights of the nanoparticle and the nearby cell membranes, we can identify the occurrence of particle internalization. Combining fluorescence microscopy with NIWOP, we also find actin aggregation around the site of the internalization process, which is an indication of endocytosis.


Assuntos
Membrana Celular/metabolismo , Nanopartículas Metálicas , Óptica e Fotônica , Células 3T3 , Animais , Membrana Celular/ultraestrutura , Ouro , Luz , Nanopartículas Metálicas/ultraestrutura , Camundongos , Espalhamento de Radiação
17.
Appl Opt ; 46(30): 7460-3, 2007 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-17952182

RESUMO

We propose an optical thin-film characterization technique, differential optical sectioning interference microscopy (DOSIM), for simultaneously measuring the refractive indices and thicknesses of transparent thin films with submicrometer lateral resolution. DOSIM obtains the depth and optical phase information of a thin film by using a dual-scan concept in differential optical sectioning microscopy combined with the Fabry-Perot interferometric effect and allows the solution of refractive index and thickness without the 2pi phase-wrapping ambiguity. Because DOSIM uses a microscope objective as the probe, its lateral resolution achieves the diffraction limit. As a demonstration, we measure the refractive indices and thicknesses of SiO2 thin films grown on Si substrate and indium-tin-oxide thin films grown on a glass substrate. We also compare the measurement results of DOSIM with those of a conventional ellipsometer and an atomic force microscope.


Assuntos
Microscopia de Interferência/métodos , Óptica e Fotônica , Calibragem , Desenho de Equipamento , Índio/química , Interferometria/métodos , Microscopia/métodos , Microscopia de Força Atômica , Microscopia Confocal , Modelos Estatísticos , Refratometria , Análise de Regressão , Silício/química , Compostos de Estanho/química
18.
Opt Lett ; 32(18): 2714-6, 2007 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-17873945

RESUMO

Sharp periodic enhancement of high-harmonic generation synchronized to prepulse-induced cluster vibration is observed. Tenfold enhancement of high-harmonic-generation efficiency is achieved by optimal selection of the prepulse-pump delay. This strong correlation between high-harmonic generation and cluster vibration also provides a new tool for studying the vibrational dynamics of nanometer atomic clusters.

19.
Opt Lett ; 31(19): 2873-5, 2006 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-16969407

RESUMO

Combining the noninterferometric wide-field optical profilometry technique with fluorescence microscopy, we observe the membrane activities of a living cell as well as the structures of its cytoskeletons. The membrane ripples of a lamellipodium are related to similar structures of the underlying actin filaments. However, we find the ripples appear prior to and disappear later than the corresponding actin filament structures, which supports the elastic Brownian ratchet model of cell motility. In addition, we measure the three-dimensional movement of a fibronectin-coated latex bead on the membrane. The bead motion is determined by the movement and branching of the actin molecules on the filament, as well as by the displacement of the filament itself.


Assuntos
Membrana Celular/ultraestrutura , Movimento Celular/fisiologia , Citoesqueleto/ultraestrutura , Fluidez de Membrana/fisiologia , Microscopia de Fluorescência/métodos , Fotometria/métodos , Células 3T3 , Animais , Membrana Celular/fisiologia , Citoesqueleto/fisiologia , Interferometria , Camundongos , Propriedades de Superfície
20.
Opt Lett ; 31(7): 984-6, 2006 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-16599232

RESUMO

Tomographic measurement of high harmonic generation in a cluster jet was demonstrated by programming the cluster density distribution with a laser machining technique. The growth of harmonic energy with the propagation of the pump pulse was resolved by scanning the end of the argon cluster distribution in the path of the pump pulse. A downstream shift of the position of rapid growth and a decrease of the slope with increasing backing pressure as results of changes in the phase-matching condition were observed, which explains the presence of an optimal backing pressure.

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