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1.
Phys Chem Chem Phys ; 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32519688

RESUMO

Organic-inorganic hybrid perovskite is a leading successor for the next generation of electronic and optoelectronic applications, owing to its unique optical and electrical properties. In this perspective, tunable optical and electrical properties are discussed, based on the nanostructured morphologies of hybrid perovskites. The current methodologies used in creating semiconducting channels are highlighted, followed by a detailed discussion of the recent advances in unique electronics and optoelectronic applications such as light-emitting transistors, phototransistors, and perovskite-2D hybrid devices. Finally, the current technological challenges and their possible solutions are addressed to identify future research directions.

2.
Sci Adv ; 6(4): eaay4045, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-32042900

RESUMO

Achieving perovskite-based high-color purity blue-emitting light-emitting diodes (LEDs) is still challenging. Here, we report successful synthesis of a series of blue-emissive two-dimensional Ruddlesden-Popper phase single crystals and their high-color purity blue-emitting LED demonstrations. Although this approach successfully achieves a series of bandgap emissions based on the different layer thicknesses, it still suffers from a conventional temperature-induced device degradation mechanism during high-voltage operations. To understand the underlying mechanism, we further elucidate temperature-induced device degradation by investigating the crystal structural and spectral evolution dynamics via in situ temperature-dependent single-crystal x-ray diffraction, photoluminescence (PL) characterization, and density functional theory calculation. The PL peak becomes asymmetrically broadened with a marked intensity decay, as temperature increases owing to [PbBr6]4- octahedra tilting and the organic chain disordering, which results in bandgap decrease. This study indicates that careful heat management under LED operation is a key factor to maintain the sharp and intense emission.

3.
ACS Nano ; 2020 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-32057230

RESUMO

Halide perovskites have many important optoelectronic properties, including high emission efficiency, high absorption coefficients, color purity, and tunable emission wavelength, which makes these materials promising for optoelectronic applications. However, the inability to precisely control large-scale patterned growth of halide perovskites limits their potential toward various device applications. Here, we report a patterning method for the growth of a cesium lead halide perovskite single crystal array. Our approach consists of two steps: (1) cesium halide salt arrays patterning and (2) chemical vapor transport process to convert salt arrays into single crystal perovskite arrays. Characterizations including energy-dispersive X-ray spectroscopy and photoluminescence have been employed to confirm the chemical compositions and the optical properties of the as-synthesized perovskite arrays. This patterning method enables the patterning of single crystal cesium lead halide perovskite arrays with tunable spacing (from 2 to 20 µm) and crystal size (from 200 nm to 1.2 µm) in high production yield (almost every pixel in the array is successfully grown with converted perovskite crystals). Our large-scale patterning method renders a platform for the study of fundamental properties and opportunities for perovskite-based optoelectronic applications.

4.
ACS Appl Mater Interfaces ; 12(4): 4707-4714, 2020 Jan 29.
Artigo em Inglês | MEDLINE | ID: mdl-31878774

RESUMO

Artificial neural networks (ANNs) based on synaptic devices, which can simultaneously perform processing and storage of data, have superior computing performance compared to conventional von Neumann architectures. Here, we present a ferroelectric coupled artificial synaptic device with reliable weight update and storage properties for ANNs. The artificial synaptic device, which is based on a ferroelectric polymer capacitively coupled with an oxide dielectric via an electric-field-permeable, semiconducting single-walled carbon-nanotube channel, is successfully fabricated by inkjet printing. By controlling the ferroelectric polarization, synaptic dynamics, such as excitatory and inhibitory postsynaptic currents and long-term potentiation/depression characteristics, is successfully implemented in the artificial synaptic device. Furthermore, the constructed ANN, which is designed in consideration of the device-to-device variation within the synaptic array, efficiently executes the tasks of learning and recognition of the Modified National Institute of Standards and Technology numerical patterns.


Assuntos
Nanotubos de Carbono/química , Redes Neurais de Computação , Transistores Eletrônicos , Inteligência Artificial , Desenho de Equipamento , Humanos , Plasticidade Neuronal , Sinapses/química , Sinapses/fisiologia
5.
Proc Natl Acad Sci U S A ; 116(47): 23404-23409, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31685626

RESUMO

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In+/In3+) inorganic halide perovskite with the composition of Cs2In(I)In(III)Cl6 in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I4/m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

6.
J Am Chem Soc ; 141(43): 17081-17085, 2019 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-31613614

RESUMO

The synthesis of a new anionic 3D metal-catecholate framework, termed MOF-1992, is achieved by linking tetratopic cobalt phthalocyanin-2,3,9,10,16,17,23,24-octaol linkers with Fe3(-C2O2-)6(OH2)2 trimers into an extended framework of roc topology. MOF-1992 exhibits sterically accessible Co active sites together with charge transfer properties. Cathodes based on MOF-1992 and carbon black (CB) display a high coverage of electroactive sites (270 nmol cm-2) and a high current density (-16.5 mA cm-2; overpotential, -0.52 V) for the CO2 to CO reduction reaction in water (faradaic efficiency, 80%). Over the 6 h experiment, MOF-1992/CB cathodes reach turnover numbers of 5800 with turnover frequencies of 0.20 s-1 per active site.

7.
ACS Nano ; 13(10): 11392-11400, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31553884

RESUMO

MXenes, an emerging class of two-dimensional (2D) transition metal carbides and nitrides, have potential for application as high-performance, low-cost electrodes in organic field-effect transistors (OFETs) because of their water dispersibility, high conductivity, and work-function tunability. In this study, we successfully fabricated a large-scale, uniform Ti3C2Tx MXene electrode array on a flexible plastic substrate for application in high-performance OFETs. The work function of the Ti3C2Tx MXene electrodes was also effectively modulated via chemical doping with NH3. The fabricated OFETs with Ti3C2Tx MXene electrodes exhibited excellent device performance, such as a maximum carrier mobility of ∼1 cm2·V-1·s-1 and an on-off current ratio of ∼107 for both p-type and n-type OFETs, even though all the electrode and dielectric layers were fabricated on the plastic substrate by solution processing. Furthermore, MXene-electrode-based complementary logic circuits, such as NOT, NAND, and NOR, were fabricated via integration of p-type and n-type OFETs. The proposed approach is expected to expand the application range of MXenes to other OFET-based electronic devices, such as organic light-emitting displays and electronic skins.

8.
J Am Chem Soc ; 141(33): 13028-13032, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31386354

RESUMO

The self-assembly of nanoparticles, a process whereby nanocrystal building blocks organize into even more ordered superstructures, is of great interest to nanoscience. Here we report the layer-by-layer assembly of 2D perovskite nanosheet building blocks. Structural analysis reveals that the assembled superlattice nanocrystals match with the layered Ruddlesden-Popper perovskite phase. This assembly proves reversible, as these superlattice nanocrystals can be reversibly exfoliated back into their building blocks via sonication. This study demonstrates the opportunity to further understand and exploit thermodynamics to increase order in a system of nanoparticles and to study emergent optical properties of a superlattice from 2D, weakly attracted, perovskite building blocks.

9.
Chem Rev ; 119(15): 9153-9169, 2019 08 14.
Artigo em Inglês | MEDLINE | ID: mdl-31282661

RESUMO

All-photonic integrated circuits are promising platforms for future systems beyond the limitation of Moore's law. Over the last several decades, one-dimensional (1D) nanowires have demonstrated great potential in photonic circuitry because of their unique 1D structure to effectively generate and tightly confine optical signals as well as easily tunable optical properties. In this Review, we categorize nanowires based on the optical properties (i.e., semiconducting, metallic, and dielectric nanowires) for their potential photonic applications (as light emitters or plasmonic and photonic waveguides). We further discuss the recent efforts in integration of nanowire-based photonic elements toward next-generation optical information processors. However, there are still several challenges remaining before the nanowires are fully utilized as photonic building blocks. The scientific and technical challenges and outlooks are provided to indicate the future directions.

10.
J Phys Chem Lett ; 10(3): 493-499, 2019 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-30642181

RESUMO

Layered indium selenide (InSe) is a van der Waals solid that has emerged as a promising material for high-performance ultrathin solar cells. The optoelectronic parameters that are critical to photoconversion efficiencies, such as hot carrier lifetime and surface recombination velocity, are however largely unexplored in InSe. Here, these key photophysical properties of layered InSe are measured with femtosecond transient reflection spectroscopy. The hot carrier cooling process is found to occur through phonon scattering. The surface recombination velocity and ambipolar diffusion coefficient are extracted from fits to the pump energy-dependent transient reflection kinetics using a free carrier diffusion model. The extracted surface recombination velocity is approximately an order of magnitude larger than that for methylammonium lead-iodide perovskites, suggesting that surface recombination is a principal source of photocarrier loss in InSe. The extracted ambipolar diffusion coefficient is consistent with previously reported values of InSe carrier mobility.

11.
ACS Appl Mater Interfaces ; 10(44): 38193-38200, 2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30299078

RESUMO

Ultrafast synthesis of high-quality transition-metal dichalcogenide nanocrystals, such as molybdenum disulfide (MoS2), is technologically relevant for large-scale production of electronic and optoelectronic devices. Here, we report a rapid solid-state synthesis route for MoS2 using the chemically homogeneous molecular precursor, (NH4)2Mo3S13·H2O, resulting in nanoparticles with estimated size down to 25 nm only in 10 s at 1000 °C. Despite the extreme nonequilibrium conditions, the resulting porous MoS2 nanoparticles remain aggregated to preserve the form of the original rod shape bulk morphology of the molecular precursor. This ultrafast synthesis proceeds through the rapid decomposition of the precursor and rearrangement of Mo and S atoms coupled with simultaneous efficient release of massive gaseous species, to create nanoscale porosity in the resulting isomorphic pseudocrystals, which are composed of the MoS2 nanoparticles. Despite the very rapid escape of massive amounts of NH3, H2O, H2S, and S gases from the (NH4)2Mo3S13·H2O mm sized crystals, they retain their original shape as they convert to MoS2 rather than undergo explosive destruction from the rapid escape process of the gases. The obtained pseudocrystals are made of aggregated MoS2 nanocrystals exhibit a Brunauer-Emmett-Teller surface area of ∼35 m2/g with an adsorption average pore width of ∼160 Å. The nanoporous MoS2 crystals are solution processable by dispersing in ethanol and water and can be cast into large-area uniform composite films. Photodetectors fabricated from these films show more than 2 orders of magnitude higher conductivity (∼6.25 × 10-6 S/cm) and photoconductive gain (20 mA/W) than previous reports of MoS2 composite films. The optoelectronic properties of this nanoporous MoS2 imply that the shallow defects that originate from the ultrafast synthesis act as sensitizing centers that increase the photocurrent gain via two-level recombination kinetics.

12.
Nat Commun ; 9(1): 4095, 2018 10 05.
Artigo em Inglês | MEDLINE | ID: mdl-30291247

RESUMO

Directed placement of solution-based nanomaterials at predefined locations with nanoscale precision limits bottom-up integration in semiconductor process technology. We report a method for electric-field-assisted placement of nanomaterials from solution by means of large-scale graphene layers featuring nanoscale deposition sites. The structured graphene layers are prepared via either transfer or synthesis on standard substrates, and then are removed once nanomaterial deposition is completed, yielding material assemblies with nanoscale resolution that cover surface areas >1 mm2. In order to demonstrate the broad applicability, we have assembled representative zero-dimensional, one-dimensional, and two-dimensional semiconductors at predefined substrate locations and integrated them into nanoelectronic devices. Ultimately, this method opens a route to bottom-up integration of nanomaterials for industry-scale applications.

13.
Nano Lett ; 18(10): 6515-6520, 2018 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-30252485

RESUMO

Generating and amplifying light in silicon (Si) continues to attract significant attention due to the possibility of integrating optical and electronic components in a single material platform. Unfortunately, silicon is an indirect band gap material and therefore an inefficient emitter of light. With the rise of integrated photonics, the search for silicon-based light sources has evolved from a scientific quest to a major technological bottleneck for scalable, CMOS-compatible, light sources. Recently, emerging two-dimensional materials have opened the prospect of tailoring material properties based on atomic layers. Few-layer phosphorene, which is isolated through exfoliation from black phosphorus (BP), is a great candidate to partner with silicon due to its layer-tunable direct band gap in the near-infrared where silicon is transparent. Here we demonstrate a hybrid silicon optical emitter composed of few-layer phosphorene nanomaterial flakes coupled to silicon photonic crystal resonators. We show single-mode emission in the telecommunications band of 1.55 µm ( Eg = 0.8 eV) under continuous wave optical excitation at room temperature. The solution-processed few-layer BP flakes enable tunable emission across a broad range of wavelengths and the simultaneous creation of multiple devices. Our work highlights the versatility of the Si-BP material platform for creating optically active devices in integrated silicon chips.

14.
Adv Mater ; 30(38): e1802990, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30095182

RESUMO

Layered indium selenide (InSe) presents unique properties for high-performance electronic and optoelectronic device applications. However, efforts to process InSe using traditional liquid phase exfoliation methods based on surfactant-assisted aqueous dispersions or organic solvents with high boiling points compromise electronic properties due to residual surface contamination and chemical degradation. Here, these limitations are overcome by utilizing a surfactant-free, low boiling point, deoxygenated cosolvent system. The resulting InSe flakes and thin films possess minimal processing residues and are structurally and chemically pristine. When employed in photodetectors, individual InSe nanosheets exhibit a maximum photoresponsivity of ≈5 × 107 A W-1 , which is the highest value of any solution-processed monolithic semiconductor to date. Furthermore, the surfactant-free cosolvent system not only stabilizes InSe dispersions but is also amenable to the assembly of electronically percolating InSe flake arrays without posttreatment, which enables the realization of ultrahigh performance thin-film photodetectors. This surfactant-free, deoxygenated cosolvent approach can be generalized to other layered materials, thereby presenting additional opportunities for solution-processed thin-film electronic and optoelectronic technologies.

15.
ACS Nano ; 12(8): 7875-7882, 2018 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-29986135

RESUMO

The crystallographic orientation of battery electrode materials can significantly impact electrochemical performance, such as rate capability and cycling stability. Among the layered transition metal dichalcogenides, rhenium disulfide (ReS2) has the largest anisotropic ratio between the two main axes in addition to exceptionally weak interlayer coupling, which serves as an ideal system to observe and analyze anisotropy of electrochemical phenomena. Here, we report anisotropic lithiation and sodiation of exfoliated ReS2 at atomic resolution using in situ transmission electron microscopy. These results reveal the role of crystallographic orientation and anisotropy on battery electrode electrochemistry. Complemented with density functional theory calculations, the lithiation of ReS2 is found to begin with intercalation of Li-ions, followed by a conversion reaction that results in Re nanoparticles and Li2S nanocrystals. The reaction speed is highly anisotropic, occurring faster along the in-plane ReS2 layer than along the out-of-plane direction. Sodiation of ReS2 is found to proceed similarly to lithiation, although the intercalation step is relatively quicker. Furthermore, the microstructure and morphology of the reaction products after lithiation/sodiation show clear anisotropy along the in-plane and out-of-plane directions. These results suggest that crystallographic orientation in highly anisotropic electrode materials can be exploited as a design parameter to improve battery electrochemical performance.

16.
Small ; 14(23): e1703915, 2018 06.
Artigo em Inglês | MEDLINE | ID: mdl-29733549

RESUMO

Carbon nanotubes (CNTs) exhibit a number of physicochemical properties that contribute to adverse biological outcomes. However, it is difficult to define the independent contribution of individual properties without purified materials. A library of highly purified single-walled carbon nanotubes (SWCNTs) of different lengths is prepared from the same base material by density gradient ultracentrifugation, designated as short (318 nm), medium (789 nm), and long (1215 nm) SWCNTs. In vitro screening shows length-dependent interleukin-1ß (IL-1ß) production, in order of long > medium > short. However, there are no differences in transforming growth factor-ß1 production in BEAS-2B cells. Oropharyngeal aspiration shows that all the SWCNTs induce profibrogenic effects in mouse lung at 21 d postexposure, but there are no differences between tube lengths. In contrast, these SWCNTs demonstrate length-dependent antibacterial effects on Escherichia coli, with the long SWCNT exerting stronger effects than the medium or short tubes. These effects are reduced by Pluronic F108 coating or supplementing with glucose. The data show length-dependent effects on proinflammatory response in macrophage cell line and antibacterial effects, but not on collagen deposition in the lung. These data demonstrate that over the length scale tested, the biological response to highly purified SWCNTs is dependent on the complexity of the nano/bio interface.


Assuntos
Escherichia coli/efeitos dos fármacos , Pulmão/efeitos dos fármacos , Nanotubos de Carbono/toxicidade , Testes de Toxicidade , Animais , Antibacterianos/farmacologia , Linhagem Celular , Citocinas/biossíntese , Escherichia coli/crescimento & desenvolvimento , Escherichia coli/ultraestrutura , Humanos , Hidrodinâmica , Inflamação/patologia , Mediadores da Inflamação/metabolismo , Camundongos Endogâmicos C57BL , Nanotubos de Carbono/ultraestrutura , Poloxâmero/farmacologia , Eletricidade Estática
17.
Chem Soc Rev ; 47(9): 3265-3300, 2018 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-29667676

RESUMO

Graphene and related two-dimensional materials provide an ideal platform for next generation disruptive technologies and applications. Exploiting these solution-processed two-dimensional materials in printing can accelerate this development by allowing additive patterning on both rigid and conformable substrates for flexible device design and large-scale, high-speed, cost-effective manufacturing. In this review, we summarise the current progress on ink formulation of two-dimensional materials and the printable applications enabled by them. We also present our perspectives on their research and technological future prospects.

18.
Acc Chem Res ; 50(4): 943-951, 2017 04 18.
Artigo em Inglês | MEDLINE | ID: mdl-28240855

RESUMO

Exfoliation of single-layer graphene from bulk graphite and the subsequent discovery of exotic physics and emergent phenomena in the atomically thin limit has motivated the isolation of other two-dimensional (2D) layered nanomaterials. Early work on isolated 2D nanomaterial flakes has revealed a broad range of unique physical and chemical properties with potential utility in diverse applications. For example, the electronic and optical properties of 2D nanomaterials depend strongly on atomic-scale variations in thickness, enabling enhanced performance in optoelectronic technologies such as light emitters, photodetectors, and photovoltaics. Much of the initial research on 2D nanomaterials has relied on micromechanical exfoliation, which yields high-quality 2D nanomaterial flakes that are suitable for fundamental studies but possesses limited scalability for real-world applications. In an effort to overcome this limitation, solution-processing methods for isolating large quantities of 2D nanomaterials have emerged. Importantly, solution processing results in 2D nanomaterial dispersions that are amenable to roll-to-roll fabrication methods that underlie lost-cost manufacturing of thin-film transistors, transparent conductors, energy storage devices, and solar cells. Despite these advantages, solution-based exfoliation methods typically lack control over the lateral size and thickness of the resulting 2D nanomaterial flakes, resulting in polydisperse dispersions with heterogeneous properties. Therefore, post-exfoliation separation techniques are needed to achieve 2D nanomaterial dispersions with monodispersity in lateral size, thickness, and properties. In this Account, we survey the latest developments in solution-based separation methods that aim to produce monodisperse dispersions and thin films of emerging 2D nanomaterials such as graphene, boron nitride, transition metal dichalcogenides, and black phosphorus. First, we motivate the need for precise thickness control in 2D nanomaterials by reviewing thickness-dependent physical properties. Then we present a succinct survey of solution-based exfoliation methods that yield 2D nanomaterial dispersions in organic solvents and aqueous media. The Account subsequently focuses on separation methods, including a critical analysis of their relative strengths and weaknesses for 2D nanomaterials with different buoyant densities, van der Waals interactions, and chemical reactivities. Specifically, we evaluate sedimentation-based density gradient ultracentrifugation (sDGU) and isopycnic DGU (iDGU) for post-exfoliation 2D nanomaterial dispersion separation. The comparative advantages of sedimentation and isopycnic methods are presented in both aqueous and nonaqueous media for 2D nanomaterials with varying degrees of chemical reactivity. Finally, we survey methods for forming homogeneous thin films from 2D nanomaterial dispersions and emerging technologies that are likely to benefit from these structures. Overall, this Account provides not only an overview of the present state-of-the-art but also a forward-looking vision for the field of solution-processed monodisperse 2D nanomaterials.

19.
Nano Lett ; 16(12): 7370-7375, 2016 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-27960516

RESUMO

The decreasing cost of silicon-based photovoltaics has enabled significant increases in solar electricity generation worldwide. Silicon photoanodes could also play an important role in the cost-effective generation of solar fuels, but the most successful methods of photoelectrode passivation and performance enhancement rely on a combination of precious metals and sophisticated processing methods that offset the economic arguments for silicon. Here we show that metal-free carbon-based nanomaterial coatings deposited from solution can protect silicon photoanodes carrying out the oxygen evolution reaction in a range of working environments. Purified semiconducting carbon nanotubes (CNTs) act as a hole extraction layer, and a graphene (Gr) capping layer both protects the CNT film and acts as a hole exchange layer with the electrolyte. The performance of semiconducting CNTs is found to be superior to that of metallic or unsorted CNTs in this context. Furthermore, the insertion of graphene oxide (GO) between the n-Si and CNTs reduces the overpotential relative to photoanodes with CNTs deposited on hydrogen-passivated silicon. The composite photoanode structure of n-Si/GO/CNT/Gr shows promising performance for oxygen evolution and excellent potential for improvement by optimizing the catalytic properties and stability of the graphene protective layer.

20.
Nano Lett ; 16(11): 7216-7223, 2016 11 09.
Artigo em Inglês | MEDLINE | ID: mdl-27700101

RESUMO

Isopycnic density gradient ultracentrifugation (iDGU) has been widely applied to sort nanomaterials by their physical and electronic structure. However, the commonly used density-gradient medium iodixanol has a finite maximum buoyant density that prevents the use of iDGU for high-density nanomaterials. Here, we overcome this limit by adding cesium chloride (CsCl) to iodixanol, thus increasing its maximum buoyant density to the point where the high-density two-dimensional nanomaterial rhenium disulfide (ReS2) can be sorted in a layer-by-layer manner with iDGU. The resulting aqueous ReS2 dispersions show photoluminescence at ∼1.5 eV, which is consistent with its direct bandgap semiconductor electronic structure. Furthermore, photocurrent measurements on thin films formed from solution-processed ReS2 show a spectral response that is consistent with optical absorbance and photoluminescence data. In addition to providing a pathway for effective solution processing of ReS2, this work establishes a general methodology for sorting high-density nanomaterials via iDGU.

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