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1.
Nat Commun ; 12(1): 6420, 2021 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-34741042

RESUMO

The electrical control of antiferromagnetic moments is a key technological goal of antiferromagnet-based spintronics, which promises favourable device characteristics such as ultrafast operation and high-density integration as compared to conventional ferromagnet-based devices. To date, the manipulation of antiferromagnetic moments by electric current has been demonstrated in epitaxial antiferromagnets with broken inversion symmetry or antiferromagnets interfaced with a heavy metal, in which spin-orbit torque (SOT) drives the antiferromagnetic domain wall. Here, we report current-induced manipulation of the exchange bias in IrMn/NiFe bilayers without a heavy metal. We show that the direction of the exchange bias is gradually modulated up to ±22 degrees by an in-plane current, which is independent of the NiFe thickness. This suggests that spin currents arising in the IrMn layer exert SOTs on uncompensated antiferromagnetic moments at the interface which then rotate the antiferromagnetic moments. Furthermore, the memristive features are preserved in sub-micron devices, facilitating nanoscale multi-level antiferromagnetic spintronic devices.

4.
Adv Mater ; 33(44): e2105199, 2021 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-34569647

RESUMO

Practical sensing applications such as real-time safety alerts and clinical diagnoses require sensor devices to differentiate between various target molecules with high sensitivity and selectivity, yet conventional devices such as oxide-based chemo-resistive sensors and metal-based surface-enhanced Raman spectroscopy (SERS) sensors usually do not satisfy such requirements. Here, a label-free, chemo-resistive/SERS multimodal sensor based on a systematically assembled 3D cross-point multifunctional nanoarchitecture (3D-CMA), which has unusually strong enhancements in both "chemo-resistive" and "SERS" sensing characteristics is introduced. 3D-CMA combines several sensing mechanisms and sensing elements via 3D integration of semiconducting SnO2 nanowire frameworks and dual-functioning Au metallic nanoparticles. It is shown that the multimodal sensor can successfully estimate mixed-gas compositions selectively and quantitatively at the sub-100 ppm level, even for mixtures of gaseous aromatic compounds (nitrobenzene and toluene) with very similar molecular structures. This is enabled by combined chemo-resistive and SERS multimodal sensing providing complementary information.

5.
Adv Sci (Weinh) ; 8(19): e2100640, 2021 10.
Artigo em Inglês | MEDLINE | ID: mdl-34363354

RESUMO

Noble metal-based surface-enhanced Raman spectroscopy (SERS) has enabled the simple and efficient detection of trace-amount molecules via significant electromagnetic enhancements at hot spots. However, the small Raman cross-section of various analytes forces the use of a Raman reporter for specific surface functionalization, which is time-consuming and limited to low-molecular-weight analytes. To tackle these issues, a hybrid SERS substrate utilizing Ag as plasmonic structures and GaN as charge transfer enhancement centers is presented. By the conformal printing of Ag nanowires onto GaN nanopillars, a highly sensitive SERS substrate with excellent uniformity can be fabricated. As a result, remarkable SERS performance with a substrate enhancement factor of 1.4 × 1011 at 10 fM for rhodamine 6G molecules with minimal spot variations can be realized. Furthermore, quantification and multiplexing capabilities without surface treatments are demonstrated by detecting harmful antibiotics in aqueous solutions. This work paves the way for the development of a highly sensitive SERS substrate by constructing complex metal-semiconductor architectures.

6.
Adv Sci (Weinh) ; 8(20): e2100895, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34390224

RESUMO

Thermoelectric properties are frequently manipulated by introducing point defects into a matrix. However, these properties often change in unfavorable directions owing to the spontaneous formation of vacancies at high temperatures. Although it is crucial to maintain high thermoelectric performance over a broad temperature range, the suppression of vacancies is challenging since their formation is thermodynamically preferred. In this study, using PbTe as a model system, it is demonstrated that a high thermoelectric dimensionless figure of merit, zT ≈ 2.1 at 723 K, can be achieved by suppressing the vacancy formation via dopant balancing. Hole-killer Te vacancies are suppressed by Ag doping because of the increased electron chemical potential. As a result, the re-dissolution of Na2 Te above 623 K can significantly increase the hole concentration and suppress the drop in the power factor. Furthermore, point defect scattering in material systems significantly reduces lattice thermal conductivity. The synergy between defect and carrier engineering offers a pathway for achieving a high thermoelectric performance by alleviating the power factor drop and can be utilized to enhance thermoelectric properties of thermoelectric materials.

7.
Sci Adv ; 7(30)2021 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-34290086

RESUMO

Unsupported Pt electrocatalysts demonstrate excellent electrochemical stability when used in polymer electrolyte membrane fuel cells; however, their extreme thinness and low porosity result in insufficient surface area and high mass transfer resistance. Here, we introduce three-dimensionally (3D) customized, multiscale Pt nanoarchitectures (PtNAs) composed of dense and narrow (for sufficient active sites) and sparse (for improved mass transfer) nanoscale building blocks. The 3D-multiscale PtNA fabricated by ultrahigh-resolution nanotransfer printing exhibited excellent performance (45% enhanced maximum power density) and high durability (only 5% loss of surface area for 5000 cycles) compared to commercial Pt/C. We also theoretically elucidate the relationship between the 3D structures and cell performance using computational fluid dynamics. We expect that the structure-controlled 3D electrocatalysts will introduce a new pathway to design and fabricate high-performance electrocatalysts for fuel cells, as well as various electrochemical devices that require the precision engineering of reaction surfaces and mass transfer.

8.
ACS Nano ; 15(6): 10464-10471, 2021 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-34115490

RESUMO

Nanoimprint lithography (NIL) is typically performed by filling up of molds by heated polymers or UV-curable liquid resists, inevitably requiring subsequent pattern-transfer processes. Although direct NIL techniques have been suggested alternatively, they usually require precursors or ink-type resists containing undesired organic components. Here, we demonstrate extreme-pressure imprint lithography (EPIL) that effectively produces well-defined multiscale structures with a wide range from 10 nm to 10 mm on diverse surfaces even including pure or alloy metals without using any precursors, heating, UV exposure, or pattern transfer. In particular, EPIL is accomplished through precise control of room-temperature plastic deformation in nanoscale volumes, which is elucidated by finite element analyses and molecular dynamics simulations. In addition to scalability to macroscopic areas, we confirm the outstanding versatility of EPIL via its successful applications to Ni, Cu, steel, and organics. We expect that the state-of-the-art EPIL process combined with other emerging nanopatterning technologies will be extendable to the future large-area nanofabrication of various devices.

9.
Nat Commun ; 12(1): 40, 2021 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-33397946

RESUMO

Interaction between metal and oxides is an important molecular-level factor that influences the selectivity of a desirable reaction. Therefore, designing a heterogeneous catalyst where metal-oxide interfaces are well-formed is important for understanding selectivity and surface electronic excitation at the interface. Here, we utilized a nanoscale catalytic Schottky diode from Pt nanowire arrays on TiO2 that forms a nanoscale Pt-TiO2 interface to determine the influence of the metal-oxide interface on catalytic selectivity, thereby affecting hot electron excitation; this demonstrated the real-time detection of hot electron flow generated under an exothermic methanol oxidation reaction. The selectivity to methyl formate and hot electron generation was obtained on nanoscale Pt nanowires/TiO2, which exhibited ~2 times higher partial oxidation selectivity and ~3 times higher chemicurrent yield compared to a diode based on Pt film. By utilizing various Pt/TiO2 nanostructures, we found that the ratio of interface to metal sites significantly affects the selectivity, thereby enhancing chemicurrent yield in methanol oxidation. Density function theory (DFT) calculations show that formation of the Pt-TiO2 interface showed that selectivity to methyl formate formation was much larger in Pt nanowire arrays than in Pt films because of the different reaction mechanism.

10.
ACS Nano ; 2020 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-33270433

RESUMO

Deterministic positioning and assembly of colloidal nanoparticles (NPs) onto substrates is a core requirement and a promising alternative to top-down lithography to create functional nanostructures and nanodevices with intriguing optical, electrical, and catalytic features. Capillary-assisted particle assembly (CAPA) has emerged as an attractive technique to this end, as it allows controlled and selective assembly of a wide variety of NPs onto predefined topographical templates using capillary forces. One critical issue with CAPA, however, lies in its final printing step, where high printing yields are possible only with the use of an adhesive polymer film. To address this problem, we have developed a template dissolution interfacial patterning (TDIP) technique to assemble and print single colloidal AuNP arrays onto various dielectric and conductive substrates in the absence of any adhesion layer, with printing yields higher than 98%. The TDIP approach grants direct access to the interface between the AuNP and the target surface, enabling the use of colloidal AuNPs as building blocks for practical applications. The versatile applicability of TDIP is demonstrated by the creation of direct electrical junctions for electro- and photoelectrochemistry and nanoparticle-on-mirror geometries for single-particle molecular sensing.

11.
Nat Commun ; 11(1): 4921, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-33004820

RESUMO

Despite highly promising characteristics of three-dimensionally (3D) nanostructured catalysts for the oxygen evolution reaction (OER) in polymer electrolyte membrane water electrolyzers (PEMWEs), universal design rules for maximizing their performance have not been explored. Here we show that woodpile (WP)-structured Ir, consisting of 3D-printed, highly-ordered Ir nanowire building blocks, improve OER mass activity markedly. The WP structure secures the electrochemically active surface area (ECSA) through enhanced utilization efficiency of the extended surface area of 3D WP catalysts. Moreover, systematic control of the 3D geometry combined with theoretical calculations and various electrochemical analyses reveals that facile transport of evolved O2 gas bubbles is an important contributor to the improved ECSA-specific activity. The 3D nanostructuring-based improvement of ECSA and ECSA-specific activity enables our well-controlled geometry to afford a 30-fold higher mass activity of the OER catalyst when used in a single-cell PEMWE than conventional nanoparticle-based catalysts.

12.
Opt Express ; 28(18): 26519-26530, 2020 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-32906924

RESUMO

We propose an optimal outcoupling structure of a quantum-dot light-emitting diode (QLED) and present material properties based on numerical calculations via the ray-tracing method, in which light extraction properties are obtained according to the surface wrinkles on a substrate. After analyzing the designed microstructure elements, the optimal model was derived and applied to the QLEDs; consequently, the outcoupling efficiency enhanced by 31%. The liquid crystalline polymer forming the random surface wrinkles not only achieves an excellent light extraction through plasma crosslinking but also facilitates large-area processes. We propose an optical design rule for high-efficiency QLED design by analyzing the electro-optical efficiency, emission spectrum, and angular radiation pattern of the optical device.

13.
Small ; 16(40): e2002109, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32930494

RESUMO

Environmentally friendly ZnSe/ZnS core/shell quantum dots (QDs) as an alternative blue emission material to Cd-based QDs have shown great potential for use in next-generation displays. However, it remains still challenging to realize a high-efficiency quantum dot light-emitting diode (QLED) based on ZnSe/ZnS QDs due to their insufficient electrical characteristics, such as excessively high electron mobility (compared to the hole mobility) and the deep-lying valence band. In this work, the effects of QDs doped with hole transport materials (hybrid QDs) on the electrical characteristics of a QLED are investigated. These hybrid QDs show a p-type doping effect, which leads to a change in the density of the carriers. Specifically, the hybrid QDs can balance electrons and holes by suppressing the overflow of electrons and improving injection of holes, respectively. These electrical characteristics help to improve device performance. In detail, an external quantum efficiency (EQE) of 6.88% is achieved with the hybrid QDs. This is increased by 180% compared to a device with pure ZnSe/ZnS QDs (EQE of 2.46%). This record is the highest among deep-blue Cd-free QLED devices. These findings provide the importance of p-type doping effect in QD layers and guidance for the study of the electrical properties of QDs.

14.
ACS Appl Mater Interfaces ; 12(41): 46678-46685, 2020 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-32931243

RESUMO

Archimedean spirals in nanometer scale have shown remarkable plasmonic responses derived from their linear and rotational asymmetry. Despite the unique optical properties of nanoscale spirals, their applications have been limited due to the difficulty in fabricating large-scale arrays with uniform and systematic control of the morphology. Here, we report simulation results of spiral morphologies, which are used to design a scalable fabrication process for nanoscale spirals and predict their plasmonic responses. First, self-consistent field theory (SCFT) simulations were performed to design optimal templates to guide self-assembly into spiral morphologies. Using the SCFT results, we developed a scalable fabrication process, which is based on the micron-scale assembly of microspheres combined with glancing angle deposition and nanoscale assembly of block copolymers, to induce the formation of uniform nanospirals with diverse size, handedness, orientation, and winding number. Finally, finite-difference time-domain simulation results show linear dichroism and electric field intensity enhancement effects of these nanospirals, which are highly dependent on the winding number of the spirals, indicating the importance of precise control of the structural parameters.

15.
Sci Adv ; 6(31): eabb6462, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32832691

RESUMO

Nanotransfer printing (nTP) has attracted considerable attention due to its good pattern resolution, process simplicity, and cost-effectiveness. However, the development of a large-area nTP process has been hampered by critical reliability issues related to the uniform replication and regular transfer printing of functional nanomaterials. Here, we present a very practical thermally assisted nanotransfer printing (T-nTP) process that can easily produce well-ordered nanostructures on an 8-inch wafer via the use of a heat-rolling press system that provides both uniform pressure and heat. We also demonstrate various complex pattern geometries, such as wave, square, nut, zigzag, and elliptical nanostructures, on diverse substrates via T-nTP. Furthermore, we demonstrate how to obtain a high-density crossbar metal-insulator-metal memristive array using a combined method of T-nTP and directed self-assembly. We expect that the state-of-the-art T-nTP process presented here combined with other emerging patterning techniques will be especially useful for the large-area nanofabrication of various devices.

16.
ACS Nano ; 14(8): 10376-10384, 2020 08 25.
Artigo em Inglês | MEDLINE | ID: mdl-32706577

RESUMO

Alzheimer's disease (AD), the most common age-related neurodegenerative disorder, accompanies a massive degradation of neurons including axonal injury. Being an axonal neuron-specific protein, neurofilament light (NfL) is a blood biomarker that reflects the neurodegeneration in AD, but no attempt has been made yet to develop sensing platforms that target NfLs in blood serum or plasma. Here, we report three-dimensional cross-stacked Pt nanowire arrays for the ultrasensitive photoelectrochemical (PEC) detection of NfLs. We constructed a woodpile-like Pt nanowire array (PtWP)-based biocathode by printing multilayer Pt nanowire arrays in an orthogonal configuration and conjugating them with NfL-specific DA2 antibodies. According to our collective electrochemical analyses, the five-layered PtWP electrode modified with DA2 antibodies exhibited high oxygen reduction activities due to the large electrochemical active surface area and the effective electron transfer properties. We have combined the DA2-PtWP biocathode with a water-oxidizing, iron oxyhydroxide-deposited bismuth vanadate (FeOOH/BiVO4) photoanode to assemble a bias-free PEC detection system. Powered by a white-light-emitting diode, the unbiased PEC platform accurately recognizes NfLs in blood plasma with the limit-of-detection of 38.2 fg/mL and limit-of-quantification of 853 fg/mL, which is 40 times lower than the NfL levels in AD patients' blood.


Assuntos
Doença de Alzheimer , Nanoestruturas , Biomarcadores , Humanos , Filamentos Intermediários , Proteínas de Neurofilamentos
17.
Nat Commun ; 11(1): 3040, 2020 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-32546822

RESUMO

The next-generation wearable near-eye displays inevitably require extremely high pixel density due to significant decrease in the viewing distance. For such denser and smaller pixel arrays, the emissive material must exhibit wider colour gamut so that each of the vast pixels maintains the colour accuracy. Electroluminescent quantum dot light-emitting diodes are promising candidates for such application owing to their highly saturated colour gamuts and other excellent optoelectronic properties. However, previously reported quantum dot patterning technologies have limitations in demonstrating full-colour pixel arrays with sub-micron feature size, high fidelity, and high post-patterning device performance. Here, we show thermodynamic-driven immersion transfer-printing, which enables patterning and printing of quantum dot arrays in omni-resolution scale; quantum dot arrays from single-particle resolution to the entire film can be fabricated on diverse surfaces. Red-green-blue quantum dot arrays with unprecedented resolutions up to 368 pixels per degree is demonstrated.

18.
ACS Nano ; 14(7): 8335-8342, 2020 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-32539337

RESUMO

The interfacial effect between a metal catalyst and its various supporting transition metal oxides on the catalytic activity of heterogeneous catalysis has been extensively explored; engineering interfacial sites of metal supported on metal oxide has been found to influence catalytic performance. Here, we investigate the interfacial effect of Pt nanowires (NWs) vertically and alternatingly stacked with titanium dioxide (TiO2) or cobalt monoxide (CoO) NWs, which exhibit a strong metal-support interaction under carbon monoxide (CO) oxidation. High-resolution nanotransfer printing based on nanoscale pattern replication and e-beam evaporation were utilized to obtain the Pt NWs cross-stacked on the CoO or TiO2 NW on the silicon dioxide (SiO2) substrate with varying numbers of nanowires. The morphology and interfacial area were precisely determined by means of atomic force microscopy and scanning electron microscopy. The cross-stacked Pt/TiO2 NW and Pt/CoO NW catalysts were estimated with CO oxidation under 40 Torr CO and 100 Torr O2 from 200 to 240 °C. Higher catalytic activity was found on the Pt/CoO NW catalyst than on Pt/TiO2 NWs and Pt NWs, which indicates the significance of nanoscale metal-oxide interfaces. As the number of nanowire layers increased, the catalytic activity became saturated. Our study demonstrates the interfacial role of nanoscale metal-oxide interfaces under CO oxidation, which has intriguing applications in the smart design of catalytic materials.

19.
Adv Mater ; 32(35): e1907500, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32319170

RESUMO

For the last few decades, nanoscale materials and structures have been extensively studied and developed, making a huge impact on human sustainability. For example, the introduction of nanostructures has brought substantial development in electrocatalysts and optical sensing applications. However, there are still remaining challenges that need to be resolved to further improve their performance, reliability, and cost-effectiveness. Herein, long-range ordered 3D nanostructures and their design principles are introduced with an emphasis on electrocatalysts for energy conversion and plasmonic nanostructures for optical sensing. Among the various fabrication techniques, sequential solvent-injection-assisted nanotransfer printing is suggested as a practical fabrication platform for tunable long-range ordered 3D nanostructures composed of ultrahigh-resolution building blocks. Furthermore, the importance of understanding and controlling the 3D design parameters is discussed to realize more efficient energy conversion as well as effective surface-enhanced Raman spectroscopy analyses, suggesting new solutions for clean energy and healthcare issues.

20.
Nano Lett ; 20(4): 2576-2584, 2020 04 08.
Artigo em Inglês | MEDLINE | ID: mdl-32207951

RESUMO

Surface-enhanced Raman spectroscopy (SERS)-based protein analysis is a promising alternative to existing early stage diagnoses. However, SERS research conducted thus far accompanies challenges such as nonuniformity of plasmonic nanostructures, irregular coating of analytes, and denaturation of proteins, which seriously limit the practicability of suggested approaches. Here, we introduce a carboxylic acid-functionalized and graphitic nanolayer-coated three-dimensional SERS substrate (CGSS) fabricated by sequential nanotransfer printing. The substrate consists of well-defined, uniform gold nanowire arrays for effective Raman signal enhancement and a strong protein-immobilization layer. With an enhancement factor (EF) of 5.5 × 105, on par with the highest ever reported values, the CGSS allows the detection of protein conformational changes and the determination of protein concentration via Raman measurements. Exploiting the CGSS, we successfully measured the SERS spectra of Alzheimer's biomarkers, tau protein and amyloid ß, based on which secondary structural changes were analyzed quantitatively.


Assuntos
Doença de Alzheimer/diagnóstico , Peptídeos beta-Amiloides/análise , Grafite/química , Nanoestruturas/química , Análise Espectral Raman/métodos , Proteínas tau/análise , Biomarcadores/análise , Ácidos Carboxílicos/química , Desenho de Equipamento , Ouro/química , Humanos , Nanoestruturas/ultraestrutura , Nanofios/química , Nanofios/ultraestrutura , Análise Espectral Raman/instrumentação
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