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1.
Nano Lett ; 2020 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-33283521

RESUMO

The global COVID-19 pandemic has changed many aspects of daily lives. Wearing personal protective equipment, especially respirators (face masks), has become common for both the public and medical professionals, proving to be effective in preventing spread of the virus. Nevertheless, a detailed understanding of respirator filtration-layer internal structures and their physical configurations is lacking. Here, we report three-dimensional (3D) internal analysis of N95 filtration layers via X-ray tomography. Using deep learning methods, we uncover how the distribution and diameters of fibers within these layers directly affect contaminant particle filtration. The average porosity of the filter layers is found to be 89.1%. Contaminants are more efficiently captured by denser fiber regions, with fibers <1.8 µm in diameter being particularly effective, presumably because of the stronger electric field gradient on smaller diameter fibers. This study provides critical information for further development of N95-type respirators that combine high efficiency with good breathability.

2.
Science ; 368(6486): 71-76, 2020 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-32241944

RESUMO

A defining feature of emergent phenomena in complex oxides is the competition and cooperation between ground states. In manganites, the balance between metallic and insulating phases can be tuned by the lattice; extending the range of lattice control would enhance the ability to access other phases. We stabilized uniform extreme tensile strain in nanoscale La0.7Ca0.3MnO3 membranes, exceeding 8% uniaxially and 5% biaxially. Uniaxial and biaxial strain suppresses the ferromagnetic metal at distinctly different strain values, inducing an insulator that can be extinguished by a magnetic field. Electronic structure calculations indicate that the insulator consists of charge-ordered Mn4+ and Mn3+ with staggered strain-enhanced Jahn-Teller distortions within the plane. This highly tunable strained membrane approach provides a broad opportunity to design and manipulate correlated electron states.

3.
Beilstein J Nanotechnol ; 10: 922-929, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31165019

RESUMO

The nanoscale composition of silk defining its unique properties via a hierarchial structural anisotropy needs to be analysed at the highest spatial resolution of tens of nanometers corresponding to the size of fibrils made of ß-sheets, which are the crystalline building blocks of silk. Nanoscale optical and structural properties of silk have been measured from 100 nm thick longitudinal slices of silk fibers with ca. 10 nm resolution, the highest so far. Optical sub-wavelength resolution in hyperspectral mapping of absorbance and molecular orientation were carried out for comparison at IR wavelengths of 2-10 µm using synchrotron radiation. A reliable distinction of transmission changes by only 1-2% as the anisotropy of amide bands was obtained from nanometer-thin slices of silk.

4.
ACS Cent Sci ; 4(1): 97-104, 2018 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-29392181

RESUMO

Lithium metal is the ultimate anode choice for high energy density rechargeable lithium batteries. However, it suffers from inferior electrochemical performance and safety issues due to its high reactivity and the growth of lithium dendrites. It has long been desired to develop a materials coating on Li metal, which is pinhole-free, mechanically robust without fracture during Li metal deposition and stripping, and chemically stable against Li metal and liquid electrolytes, all while maintaining adequate ionic conductivity. However, such an ideal material coating has yet to be found. Here we report a novel synthesis method by reacting clean molten lithium foil directly with pure nitrogen gas to generate instantaneously a pinhole-free and ionically conductive α-Li3N film directly bonded onto Li metal foil. The film consists of highly textured large Li3N grains (tens of µm) with (001) crystalline planes parallel to the Li metal surface. The bonding between textured grains is strong, resulting in a mechanically robust film which does not crack even when bent to a 0.8 cm curvature radius and is found to maintain pinhole-free coverage during Li metal deposition and stripping. The measured ionic conductivity is up to 5.2 × 10-4 S cm-1, sufficient for maintaining regular current densities for controllable film thicknesses ranging from 2 to 30 µm. This Li3N coating is chemically stable, isolating the reactive metallic lithium from liquid electrolyte, prevents continuous electrolyte consumption during battery cycling, and promotes dendrite-free uniform lithium plating/stripping underneath. We demonstrated Li|Li4Ti5O12 cells with stable and flat potential profiles for 500 cycles without capacity decay or an increase in potential hysteresis.

5.
Proc Natl Acad Sci U S A ; 114(46): 12138-12143, 2017 11 14.
Artigo em Inglês | MEDLINE | ID: mdl-29087316

RESUMO

Lithium, with its high theoretical specific capacity and lowest electrochemical potential, has been recognized as the ultimate negative electrode material for next-generation lithium-based high-energy-density batteries. However, a key challenge that has yet to be overcome is the inferior reversibility of Li plating and stripping, typically thought to be related to the uncontrollable morphology evolution of the Li anode during cycling. Here we show that Li-metal texturing (preferential crystallographic orientation) occurs during electrochemical deposition, which governs the morphological change of the Li anode. X-ray diffraction pole-figure analysis demonstrates that the texture of Li deposits is primarily dependent on the type of additive or cross-over molecule from the cathode side. With adsorbed additives, like LiNO3 and polysulfide, the lithium deposits are strongly textured, with Li (110) planes parallel to the substrate, and thus exhibit uniform, rounded morphology. A growth diagram of lithium deposits is given to connect various texture and morphology scenarios for different battery electrolytes. This understanding of lithium electrocrystallization from the crystallographic point of view provides significant insight for future lithium anode materials design in high-energy-density batteries.

6.
Phys Rev Lett ; 119(7): 077201, 2017 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-28949659

RESUMO

Perpendicular magnetic anisotropy (PMA) plays a critical role in the development of spintronics, thereby demanding new strategies to control PMA. Here we demonstrate a conceptually new type of interface induced PMA that is controlled by oxygen octahedral rotation. In superlattices comprised of La_{1-x}Sr_{x}MnO_{3} and SrIrO_{3}, we find that all superlattices (0≤x≤1) exhibit ferromagnetism despite the fact that La_{1-x}Sr_{x}MnO_{3} is antiferromagnetic for x>0.5. PMA as high as 4×10^{6} erg/cm^{3} is observed by increasing x and attributed to a decrease of oxygen octahedral rotation at interfaces. We also demonstrate that oxygen octahedral deformation cannot explain the trend in PMA. These results reveal a new degree of freedom to control PMA, enabling discovery of emergent magnetic textures and topological phenomena.

7.
Proc Natl Acad Sci U S A ; 114(23): 5918-5923, 2017 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-28533377

RESUMO

In this study we control the surface structure of Cu thin-film catalysts to probe the relationship between active sites and catalytic activity for the electroreduction of CO2 to fuels and chemicals. Here, we report physical vapor deposition of Cu thin films on large-format (∼6 cm2) single-crystal substrates, and confirm epitaxial growth in the <100>, <111>, and <751> orientations using X-ray pole figures. To understand the relationship between the bulk and surface structures, in situ electrochemical scanning tunneling microscopy was conducted on Cu(100), (111), and (751) thin films. The studies revealed that Cu(100) and (111) have surface adlattices that are identical to the bulk structure, and that Cu(751) has a heterogeneous kinked surface with (110) terraces that is closely related to the bulk structure. Electrochemical CO2 reduction testing showed that whereas both Cu(100) and (751) thin films are more active and selective for C-C coupling than Cu(111), Cu(751) is the most selective for >2e- oxygenate formation at low overpotentials. Our results demonstrate that epitaxy can be used to grow single-crystal analogous materials as large-format electrodes that provide insights on controlling electrocatalytic activity and selectivity for this reaction.

8.
Nat Mater ; 16(3): 349-355, 2017 03.
Artigo em Inglês | MEDLINE | ID: mdl-28024157

RESUMO

Controlling inorganic structure and dimensionality through structure-directing agents is a versatile approach for new materials synthesis that has been used extensively for metal-organic frameworks and coordination polymers. However, the lack of 'solid' inorganic cores requires charge transport through single-atom chains and/or organic groups, limiting their electronic properties. Here, we report that strongly interacting diamondoid structure-directing agents guide the growth of hybrid metal-organic chalcogenide nanowires with solid inorganic cores having three-atom cross-sections, representing the smallest possible nanowires. The strong van der Waals attraction between diamondoids overcomes steric repulsion leading to a cis configuration at the active growth front, enabling face-on addition of precursors for nanowire elongation. These nanowires have band-like electronic properties, low effective carrier masses and three orders-of-magnitude conductivity modulation by hole doping. This discovery highlights a previously unexplored regime of structure-directing agents compared with traditional surfactant, block copolymer or metal-organic framework linkers.


Assuntos
Calcogênios/química , Diamante/química , Condutividade Elétrica , Estruturas Metalorgânicas/química , Nanodiamantes/química , Nanotecnologia/métodos , Nanofios/química , Modelos Moleculares , Conformação Molecular
9.
Phys Rev Lett ; 109(15): 157207, 2012 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-23102365

RESUMO

We present a study of the thickness dependence of magnetism and electrical conductivity in ultrathin La0.67Sr0.33MnO3 films grown on SrTiO3 (110) substrates. We found a critical thickness of 10 unit cells below which the conductivity of the films disappeared and simultaneously the Curie temperature increased, indicating a magnetic insulating phase at room temperature. These samples have a Curie temperature of about 560 K with a significant saturation magnetization of 1.2±0.2µ(B)/Mn. The canted antiferromagnetic insulating phase in ultra thin films of n<10 coincides with the occurrence of a higher symmetry structural phase with a different oxygen octahedra rotation pattern. Such a strain engineered phase is an interesting candidate for an insulating tunneling barrier in room temperature spin polarized tunneling devices.

10.
Adv Mater ; 24(24): 3269-74, 2012 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-22605625

RESUMO

Strongly textured organic semiconductor micropatterns made of the small molecule dioctylbenzothienobenzothiophene (C(8)-BTBT) are fabricated by using a method based on capillary force lithography (CFL). This technique provides the C(8)-BTBT solution with nucleation sites for directional growth, and can be used as a scalable way to produce high quality crystalline arrays in desired regions of a substrate for OFET applications.


Assuntos
Microtecnologia/métodos , Compostos Orgânicos/química , Impressão/métodos , Semicondutores , Condutividade Elétrica
11.
Nat Commun ; 2: 445, 2011 Aug 23.
Artigo em Inglês | MEDLINE | ID: mdl-21863012

RESUMO

At extreme pressures and temperatures, such as those inside planets and stars, common materials form new dense phases with compacted atomic arrangements and unusual physical properties. The synthesis and study of new phases of matter at pressures above 100 GPa and temperatures above 10(4) K--warm dense matter--may reveal the functional details of planet and star interiors, and may lead to materials with extraordinary properties. Many phases have been predicted theoretically that may be realized once appropriate formation conditions are found. Here we report the synthesis of a superdense stable phase of body-centred-cubic aluminium, predicted by first-principles theories to exist at pressures above 380 GPa. The superdense Al phase was synthesized in the non-equilibrium conditions of an ultrafast laser-induced microexplosion confined inside sapphire (α-Al(2)O(3)). Confined microexplosions offer a strategy to create and recover high-density polymorphs, and a simple method for tabletop study of warm dense matter.

12.
J Nanosci Nanotechnol ; 11(4): 2931-6, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21776656

RESUMO

We report on structural characterization of sapphire photomodified by voids of sub-wavelength diameter surrounded by amorphised regions formed after exposure by tightly-focused femtosecond laser pulses of 800 nm wavelength and 150 fs duration at the single and double-pulse irradiation inside crystalline sapphire. Regrowth of a crystalline phase near the edge between the amorphous and crystalline phases was observed by transmission electron microscopy (TEM) in the case of double-pulse-irradiated locations. Regions patterned by single-pulse-induced voids inside sapphire were characterized by synchrotron X-ray diffraction (XRD) technique. The XRD patterns indicate presence of an expanded phase of the host crystal. The origin of structural changes observed in TEM and XRD is discussed and is consistent with fast thermal quenching.


Assuntos
Óxido de Alumínio/química , Óxido de Alumínio/efeitos da radiação , Lasers , Nanoestruturas/efeitos da radiação , Nanoestruturas/ultraestrutura , Teste de Materiais , Nanoestruturas/química , Tamanho da Partícula , Doses de Radiação , Propriedades de Superfície/efeitos da radiação
13.
Nano Lett ; 11(3): 1161-5, 2011 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-21323381

RESUMO

We present a new method to manipulate the channel charge density of field-effect transistors using dipole-generating self-assembled monolayers (SAMs) with different anchor groups. Our approach maintains an ideal interface between the dipole layers and the semiconductor while changing the built-in electric potential by 0.41-0.50 V. This potential difference can be used to change effectively the electrical properties of nanoelectronic devices. We further demonstrate the application of the SAM dipoles to enable air-stable operation of n-channel organic transistors.

14.
J Colloid Interface Sci ; 289(1): 1-13, 2005 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-16009212

RESUMO

In this paper we present results that describe the speciation of Cu sorbed to the clay mineral vermiculite, with special attention to the effects of reduction on Cu sorption complexes. Sorption complexes were studied using powdered extended X-ray absorption fine structure (EXAFS) spectroscopy, polarized EXAFS spectroscopy, and X-ray diffraction (XRD). Ionic strength (I), background ion, and clay reduction (structural iron) were varied in the sorption samples. At low I EXAFS results indicate that Cu was surrounded by up to six water molecules sorbed in the interlayer of reduced vermiculite. EXAFS results from Cu-equilibrated reduced vermiculite with high I Ca background electrolyte revealed that Cu was surrounded by 4 O atoms at 1.95 Angatroms and 8 second shell O atoms at 3.14 Angstroms. Angular dependence of the second shell O atoms interpreted from the polarized-EXAFS spectra indicated that the atoms are out of plane from the basal plane of the vermiculite (inclined approximately 25 degrees from the ab plane). The local atomic environment and angular dependence of the EXAFS spectra suggest that the Cu atoms are adsorbed above the hexagonal cavities of the reduced clay mineral and form a Cu dimer in the interlayer. This adsorption mechanism was not observed in the non-reduced vermiculite under identical equilibration conditions. Our results provide molecular level evidence that Cu sorption mechanisms on vermiculite are dependent on solution conditions, such as redox potential and background electrolyte. These results can be used to develop better models of Cu sorption mechanisms on clay mineral surfaces.


Assuntos
Silicatos de Alumínio/química , Cobre/química , Ferro/química , Adsorção , Cálcio/química , Oxirredução , Potássio/química , Propriedades de Superfície
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