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1.
Artigo em Inglês | MEDLINE | ID: mdl-32929952

RESUMO

Introducing point defects in complex metal oxides is a very effective route to engineer crystal symmetry and thereby control physical properties. However, the inversion symmetry breaking, which is vital for many tantalizing properties, such as ferroelectricity and chiral spin structure, is usually hard to be induced in bulk crystal by point defects. By designing oxygen vacancies formation energy profile and migration path across oxide heterostructure, our first principles density functional theory (DFT) calculations demonstrate that the point defects can effectively break the inversion symmetry and hence to create novel ferroelectricity in superlattices comprised of otherwise non-ferroelectric materials SrTiO3 and SrRuO3. This induced ferroelectricity can be significantly enhanced by reducing SrTiO3 thickness. Inspired by theory calculation, SrTiO3/SrRuO3 superlattices were experimentally fabricated and are found to exhibit surprising strong ferroelectric properties. Our finding paves a simple and effective pathway to engineer the inversion symmetry and thus properties by point defect control in oxide heterostructures.

2.
Artigo em Inglês | MEDLINE | ID: mdl-32285661

RESUMO

A dielectric loss-type electromagnetic wave (EMW) absorber, especially over a broad frequency range, is important yet challenging. As the most typical dielectric attenuation absorber, carbon-based nanostructures were highly pursued and studied. However, their poor impedance-matching issues still exist. Here, to further optimize dielectric properties and enhance reflection loss, ultrathin MoS2 nanosheets encapsulated in hollow carbon spheres (MoS2@HCS) were prepared via a facile template method. The diameter and shell thickness of the as-prepared HCSs were ∼250 and ∼20 nm. The encapsulated MoS2 nanosheets presented high dispersity and crystallinity. Compared to a pure HCS or MoS2 absorber, MoS2@HCS exhibited an optimized impedance characteristic, which can be attributed to the synergistic effects between HCSs (ensuring rapid electron transmission and compensating the low conductivity of MoS2) and MoS2 nanosheets (exposing sufficient numbers of active sites for polarizations and multi-reflection). Consequently, the MoS2@HCS was endowed with -65 dB EMW attenuation ability under 2 mm and the effective attenuation bandwidth under -20 dB was ∼3.3 GHz over the K-band under 1.2 mm and ∼3.4 GHz over the Ka-band under merely 0.7 mm. These results suggested that the MoS2@HCS is a promising dielectric absorber for practical applications. Meanwhile, this work introduces a facile and versatile strategy, which could in principle be extended to other transition metal sulfide@HCS for designing novel EMW absorbers.

3.
Artigo em Inglês | MEDLINE | ID: mdl-32043353

RESUMO

A stretchable electronic skin (e-skin) requires a durable elastomeric matrix to serve in various conditions. Therefore, excellent and balanced properties such as elasticity, water proof capability, toughness, and self-healing are demanded. However, it is very difficult and often contradictory to optimize them at one time. Here, a polyurethane (BS-PU-3) containing a polydisperse hard segment, hydrophobic soft segment, and a dynamic disulfide bond was prepared by one-pot synthesis. Unlike the normal two-pot reaction, BS-PU-3 obtained through the one-pot method owned a higher density of self-healing points along the main chain and a faster self-healing speed, which reached 1.11 µm/min in a cut-through sample and recovered more than 93% of virgin mechanical properties in 6 h at room temperature. Moreover, a remarkable toughness of 27.5 MJ/m3 assures its durability as an e-skin matrix. Even with a 1 mm notch (half of the total width) on a standard dumbbell specimen, it could still bear the tensile strain up to 324% without any crack propagation. With polybutadiene as the soft segment, the shape, microstructure, and conductivity in BS-PU-3 and BS-PU-3-based stretchable electronics kept very stable after soaking in water for 3 days, proving the super waterproof property. An e-skin demo was constructed, and self-healing in pressure sensitivity, mechanical, and electrical properties were verified.

4.
ACS Nano ; 13(2): 2634-2642, 2019 02 26.
Artigo em Inglês | MEDLINE | ID: mdl-30730696

RESUMO

The rapid development of artificial intelligence techniques and future advanced robot systems sparks emergent demand on the accurate perception and understanding of the external environments via visual sensing systems that can co-locate the self-adaptive detecting, processing, and memorizing of optical signals. In this contribution, a simple indium-tin oxide/Nb-doped SrTiO3 (ITO/Nb:SrTiO3) heterojunction artificial optoelectronic synapse is proposed and demonstrated. Through the light and electric field co-modulation of the Schottky barrier profile at the ITO/Nb:SrTiO3 interface, the oxide heterojunction device can respond to the entire visible light region in a neuromorphic manner, allowing synaptic paired-pulse facilitation, short/long-term memory, and "learning-experience" behavior for optical information manipulation. More importantly, the photoplasticity of the artificial synapse has been modulated by heterosynaptic means with a sub-1 V external voltage, not only enabling an optoelectronic analog of the mechanical aperture device showing adaptive and stable optical perception capability under different illuminating conditions but also making the artificial synapse suitable for the mimicry of interest-modulated human visual memories.

5.
Nat Commun ; 10(1): 736, 2019 02 13.
Artigo em Inglês | MEDLINE | ID: mdl-30760719

RESUMO

Memristors with enormous storage capacity and superior processing efficiency are of critical importance to overcome the Moore's Law limitation and von Neumann bottleneck problems in the big data and artificial intelligence era. In particular, the integration of multifunctionalities into a single memristor promises an essential strategy of obtaining a high-performance electronic device that satisfies the nowadays increasing demands of data storage and processing. In this contribution, we report a proof-of-concept polymer memristive processing-memory unit that demonstrates programmable information storage and processing capabilities. By introducing redox active moieties of triphenylamine and ferrocene onto the pendants of fluorene skeletons, the conjugated polymer exhibits triple oxidation behavior and interesting memristive switching characteristics. Associated with the unique electrochemical and electrical behavior, the polymer device is capable of executing multilevel memory, decimal arithmetic operations of addition, subtraction, multiplication and division, as well as simple Boolean logic operations.

6.
Chem Soc Rev ; 48(6): 1531-1565, 2019 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-30398508

RESUMO

The explosive increase in digital communications in the Big Data and internet of Things era spurs the development of universal memory that can run at high speed with high-density and nonvolatile storage capabilities, as well as demonstrating superior mechanical flexibility for wearable applications. Among various candidates for the next-generation information storage technology, resistive switching memories distinguish themselves with low power consumption, excellent downscaling potential, easy 3D stacking, and high CMOS compatibility, fulfilling key requirements for high-performance data storage. Employing organic and hybrid switching media in addition allows light weight and flexible integration of molecules with tunable device performance via molecular design-cum-synthesis strategy. In this review, we present a timely and comprehensive review of the recent advances in organic and hybrid resistive switching materials and devices, with particular attention on their design principles for electronic property tuning and flexible device performance. The current challenges posed with development of organic and hybrid resistive switching materials and flexible memory devices, together with their future perspectives, are also discussed.

7.
Nat Commun ; 9(1): 3813, 2018 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-30232336

RESUMO

The development of ultrasensitive, anti-jamming, and durable sensors that can precisely distinguish different human body motions are of great importance for smart health monitoring and diagnosis. Physical implementation of such flexible sensors is still a challenge at the moment. Combining the designs of advanced material showing excellent electrochemical properties with the facilitative structure engineering, high-performance flexible sensors that satisfy both signal detecting and recognition requirements may be made possible. Here we report the first metal-organic framework-based strain sensor with accurate signal detection and noise-screening properties. Upon doping the tricarboxytriphenyl amine-based metal-organic framework nanofilm with iodine, the two-terminal device exhibits ultrahigh sensitivity with a gauge factor exceeding 10,000 in the 2.5% to 3.3% deformation range for over 5000 dynamic operating cycles and out-of-scale noise-screening capability. The high-performance strain sensor can easily differentiate the moderate muscle hyperspasmia from subtle swaying and vigorous sporting activities.


Assuntos
Estruturas Metalorgânicas/química , Nanopartículas/química , Estresse Mecânico , Cristalização , Eletricidade , Corpo Humano , Humanos , Simulação de Dinâmica Molecular , Movimento (Física)
8.
Nat Commun ; 9(1): 2255, 2018 06 08.
Artigo em Inglês | MEDLINE | ID: mdl-29884868

RESUMO

The anomalous Hall effect, observed in conducting ferromagnets with broken time-reversal symmetry, offers the possibility to couple spin and orbital degrees of freedom of electrons in ferromagnets. In addition to charge, the anomalous Hall effect also leads to spin accumulation at the surfaces perpendicular to both the current and magnetization direction. Here, we experimentally demonstrate that the spin accumulation, subsequent spin backflow, and spin-charge conversion can give rise to a different type of spin current-related spin current related magnetoresistance, dubbed here as the anomalous Hall magnetoresistance, which has the same angular dependence as the recently discovered spin Hall magnetoresistance. The anomalous Hall magnetoresistance is observed in four types of samples: co-sputtered (Fe1-xMn x )0.6Pt0.4, Fe1-xMn x /Pt multilayer, Fe1-xMn x with x = 0.17-0.65 and Fe, and analyzed using the drift-diffusion model. Our results provide an alternative route to study charge-spin conversion in ferromagnets and to exploit it for potential spintronic applications.

9.
ACS Appl Mater Interfaces ; 10(7): 6453-6462, 2018 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-29388428

RESUMO

Resistive random access memory (RRAM) with inherent logic-in-memory capability exhibits great potential to construct beyond von-Neumann computers. Particularly, unipolar RRAM is more promising because its single polarity operation enables large-scale crossbar logic-in-memory circuits with the highest integration density and simpler peripheral control circuits. However, unipolar RRAM usually exhibits poor switching uniformity because of random activation of conducting filaments and consequently cannot meet the strict uniformity requirement for logic-in-memory application. In this contribution, a new methodology that constructs cone-shaped conducting filaments by using chemically a active metal cathode is proposed to improve unipolar switching uniformity. Such a peculiar metal cathode will react spontaneously with the oxide switching layer to form an interfacial layer, which together with the metal cathode itself can act as a load resistor to prevent the overgrowth of conducting filaments and thus make them more cone-like. In this way, the rupture of conducting filaments can be strictly limited to the tip region, making their residual parts favorable locations for subsequent filament growth and thus suppressing their random regeneration. As such, a novel "one switch + one unipolar RRAM cell" hybrid structure is capable to realize all 16 Boolean logic functions for large-scale logic-in-memory circuits.

10.
ACS Nano ; 11(11): 11298-11305, 2017 11 28.
Artigo em Inglês | MEDLINE | ID: mdl-29028312

RESUMO

Memristive devices are able to store and process information, which offers several key advantages over the transistor-based architectures. However, most of the two-terminal memristive devices have fixed functions once made and cannot be reconfigured for other situations. Here, we propose and demonstrate a memristive device "memlogic" (memory logic) as a nonvolatile switch of logic operations integrated with memory function in a single light-gated memristor. Based on nonvolatile light-modulated memristive switching behavior, a single memlogic cell is able to achieve optical and electrical mixed basic Boolean logic of reconfigurable "AND", "OR", and "NOT" operations. Furthermore, the single memlogic cell is also capable of functioning as an optical adder and digital-to-analog converter. All the memlogic outputs are memristive for in situ data storage due to the nonvolatile resistive switching and persistent photoconductivity effects. Thus, as a memdevice, the memlogic has potential for not only simplifying the programmable logic circuits but also building memristive multifunctional optoelectronics.

11.
Adv Mater ; 29(39)2017 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-28833612

RESUMO

Nanoscale manipulation of materials' physicochemical properties offers distinguished possibility to the development of novel electronic devices with ultrasmall dimension, fast operation speed, and low energy consumption characteristics. This is especially important as the present semiconductor manufacturing technique is approaching the end of miniaturization campaign in the near future. Here, a superior metal-insulator transition (MIT) of a 1D VO2 nanochannel constructed through an electric-field-induced oxygen ion migration process in V2 O5 thin film is reported for the first time. A sharp and reliable MIT transition with a steep turn-on voltage slope of <0.5 mV dec-1 , fast switching speed of 17 ns, low energy consumption of 8 pJ, and low variability of <4.3% is demonstrated in the VO2 nanochannel device. High-resolution transmission electron microscopy observation and theoretical computation verify that the superior electrical properties of the present device can be ascribed to the electroformation of nanoscale VO2 nanochannel in V2 O5 thin films. More importantly, the incorporation of the present device into a Pt/HfO2 /Pt/VO2 /Pt 1S1R unit can ensure the correct reading of the HfO2 memory continuously for 107 cycles, therefore demonstrating its great possibility as a reliable selector in high-density crossbar memory arrays.

12.
Sci Rep ; 7(1): 2837, 2017 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-28588254

RESUMO

We investigated the magnetic anisotropy and the high-frequency property of flexible Fe60Co26Ta14 (FeCoTa) thin films obtained by oblique sputtering onto a wrinkled surface. The sinuously wrinkled topography is produced by growing Ta layer on a pre-strained polydimethylsiloxane (PDMS) membrane. Due to the enhanced effect of shadowing, the oblique deposition of FeCoTa layer gives rise to a shift of wrinkle peak towards the incident atomic flux. With increasing the PDMS pre-strain or increasing the oblique sputtering angle, both the uniaxial magnetic anisotropy and the ferromagnetic resonance frequency of FeCoTa films are enhanced, but the initial permeability decreases. The magnetization reversal mechanism of wrinkled FeCoTa films can be interpreted by a two-phase model composed of both coherent rotation and domain wall nucleation. With the enhancement of uniaxial magnetic anisotropy, the domain wall nucleation becomes pronounced in FeCoTa films.

13.
Nanoscale ; 9(21): 7037-7046, 2017 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-28252131

RESUMO

Flexible and transparent resistive switching memories are highly desired for the construction of portable and even wearable electronics. Upon optimization of the microstructure wherein an amorphous-nanocrystalline hafnium oxide thin film is fabricated, an all-oxide based transparent RRAM device with stable resistive switching behavior that can withstand a mechanical tensile stress of up to 2.12% is obtained. It is demonstrated that the superior electrical, thermal and mechanical performance of the ITO/HfOx/ITO device can be ascribed to the formation of pseudo-straight metallic hafnium conductive filaments in the switching layer, and is only limited by the choice of electrode materials. When the ITO bottom electrode is replaced with platinum metal, the mechanical failure threshold of the device can be further extended.

14.
Adv Mater ; 28(35): 7658-65, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27346164

RESUMO

Direct, nonvolatile, and reversible control of nanomagnetism in solid-state ferromagnetic thin films is achieved by controlling the chemical composition of the film through field-driven ion redistribution. The electric field-driven de-intercalation/intercalation of lithium ions can result in ≈100% modulation of the magnetization and drives domain wall motion over ≈100 nm. High-speed and multilevel magnetic information storage is further demonstrated.

15.
ACS Appl Mater Interfaces ; 8(24): 15551-6, 2016 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-27244645

RESUMO

Switching luminescence of lanthanide-based molecules through an external electric field is considered as a promising approach toward novel functional molecule-based devices. Classic routes use casted films and liquid electrolyte as media for redox reactions. Such protocol, even if efficient, is relatively hard to turn into an effective solid-state device. In this work, we explicitly synthesize lanthanide-based dimers whose luminescent behavior is affected by the presence of Cu(2+) ions. Excellent evaporability of the dimers and utilization of Cu(2+)-based solid-state electrolyte makes it possible to reproduce solution behavior at the solid state. Reversible modulation of Cu(2+) ions transport can be achieved by an electric field in a solid-state device, where lanthanide-related luminescence is driven by an electric field. These findings provide a proof-of-concept alternative approach for electrically driven modulation of solid-state luminescence and show promising potential for information storage media in the future.

16.
ACS Nano ; 10(4): 4403-9, 2016 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-27032033

RESUMO

A strain-relief structure by combining the strain-engineered periodic wrinkles and the parallel ribbons was employed to fabricate flexible dual spin valves onto PDMS substrates in a direct sputtering method. The strain-relief structure can accommodate the biaxial strain accompanying with stretching operation (the uniaxial applied tensile strain and the induced transverse compressive strain due to the Poisson effect), thus significantly reducing the influence of the residual strain on the giant magnetoresistance (GMR) performance. The fabricated GMR dual spin-valve sensor exhibits the nearly unchanged MR ratio of 9.9%, magnetic field sensitivity up to 0.69%/Oe, and zero-field resistance in a wide range of stretching strain, making it promising for applications on a conformal shape or a movement part.

17.
Chem Commun (Camb) ; 52(26): 4828-31, 2016 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-26967024

RESUMO

A bio-memristor fabricated with ferritin exhibits novel resistive switching characteristics wherein memory switching and threshold switching are made steadily coexistent and inter-convertible through controlling the magnitude of compliance current presets.

18.
Sci Rep ; 5: 17734, 2015 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-26639108

RESUMO

We report an investigation of anisotropic magnetoresistance (AMR) and anomalous Hall resistance (AHR) of Rh and Pt thin films sputtered on epitaxial Y(3)Fe(5)O(12) (YIG) ferromagnetic insulator films. For the Pt/YIG hybrid, large spin-Hall magne toresistance (SMR) along with a sizable conventional anisotropic magnetoresistance (CAMR) and a nontrivial temperature dependence of AHR were observed in the temperature range of 5-300 K. In contrast, a reduced SMR with negligible CAMR and AHR was found in Rh/YIG hybrid. Since CAMR and AHR are characteristics for all ferromagnetic metals, our results suggest that the Pt is likely magnetized by YIG due to the magnetic proximity effect (MPE) while Rh remains free of MPE. Thus the Rh/YIG hybrid could be an ideal model system to explore physics and devices associated with pure spin current.

19.
Sci Rep ; 5: 16164, 2015 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-26530132

RESUMO

Solid state cooling technologies based on electrocaloric, magnetocaloric and mechanocaloric effects have received much attention during the past decade. To further improve the cooling efficiency and reduce the driving field, it is desirable to combine multiple effects in a single system. Here, we report on the caloric effects induced by both electric field and strain in PbZr0.95Ti0.05O3 films deposited on 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 substrate. The isothermal entropy change (ΔS) induced by the antiferroelectric-ferroelectric phase transition of PbZr0.95Ti0.05O3 films is calculated to be 6.78 J K(-1) kg(-1). Furthermore, the strain from 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 substrate can reduce the electric field where ΔS reaches the maximum by as much as 50 kV/cm. The electrocaloric efficiency is also increased from 0.366 to 0.378 by the strain effect. The electrocaloric effect in an antiferroelectric material assisted by strain may lead to more efficient solid state cooling technology.

20.
J Am Chem Soc ; 137(26): 8572-83, 2015 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-26062868

RESUMO

Research on stable open-shell singlet diradicaloids recently became a hot topic because of their unique optical, electronic, and magnetic properties and promising applications in materials science. So far, most reported singlet diradicaloid molecules have a symmetric structure, while asymmetric diradicaloids with an additional contribution of a dipolar zwitterionic form to the ground state were rarely studied. In this Article, a series of new push-pull type oligo(N-annulated perylene)quinodimethanes were synthesized. Their chain length and solvent-dependent ground states and physical properties were systematically investigated by various experimental methods such as steady-state and transient absorption, two-photon absorption, X-ray crystallographic analysis, electron spin resonance, superconducting quantum interference device, Raman spectroscopy, and electrochemistry. It was found that with extension of the chain length, the diradical character increases while the contribution of the zwitterionic form to the ground state becomes smaller. Because of the intramolecular charge transfer character, the physical properties of this push-pull system showed solvent dependence. In addition, density functional theory calculations on the diradical character and Hirshfeld charge were conducted to understand the chain length and solvent dependence of both symmetric and asymmetric systems. Our studies provided a comprehensive understanding on the fundamental structure- and environment-property relationships in the new asymmetric diradicaloid systems.

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