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1.
Nat Mater ; 19(5): 528-533, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32094495

RESUMO

Developing a precise and reproducible bandgap tuning method that enables tailored design of materials is of crucial importance for optoelectronic devices. Towards this end, we report a sphere diameter engineering (SDE) technique to manipulate the bandgap of two-dimensional (2D) materials. A one-to-one correspondence with an ideal linear working curve is established between the bandgap of MoS2 and the sphere diameter in a continuous range as large as 360 meV. Fully uniform bandgap tuning of all the as-grown MoS2 crystals is realized due to the isotropic characteristic of the sphere. More intriguingly, both a decrease and an increase of the bandgap can be achieved by constructing a positive or negative curvature. By fusing individual spheres in the melted state, post-synthesis bandgap adjustment of the supported 2D materials can be realized. This SDE technique, showing good precision, uniformity and reproducibility with high efficiency, may further accelerate the potential applications of 2D materials.

2.
Rev Sci Instrum ; 90(8): 083701, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31472643

RESUMO

Motivated by the advanced photon source upgrade, a new hard X-ray microscope called "Velociprobe" has been recently designed and built for fast ptychographic imaging with high spatial resolution. We are addressing the challenges of high-resolution and fast scanning with novel hardware designs, advanced motion controls, and new data acquisition strategies, including the use of high-bandwidth interferometric measurements. The use of granite, air-bearing-supported stages provides the necessary long travel ranges for coarse motion to accommodate real samples and variable energy operation while remaining highly stable during fine scanning. Scanning the low-mass zone plate enables high-speed and high-precision motion of the probe over the sample. With an advanced control algorithm implemented in a closed-loop feedback system, the setup achieves a position resolution (3σ) of 2 nm. The instrument performance is evaluated by 2D fly-scan ptychography with our developed data acquisition strategies. A spatial resolution of 8.8 nm has been demonstrated on a Au test sample with a detector continuous frame rate of 200 Hz. Using a higher flux X-ray source provided by double-multilayer monochromator, we achieve 10 nm resolution for an integrated circuit sample in an ultrafast scan with a detector's full continuous frame rate of 3000 Hz (0.33 ms per exposure), resulting in an outstanding imaging rate of 9 × 104 resolution elements per second.

3.
Science ; 363(6427): 627-631, 2019 02 08.
Artigo em Inglês | MEDLINE | ID: mdl-30733417

RESUMO

The role of the alkali metal cations in halide perovskite solar cells is not well understood. Using synchrotron-based nano-x-ray fluorescence and complementary measurements, we found that the halide distribution becomes homogenized upon addition of cesium iodide, either alone or with rubidium iodide, for substoichiometric, stoichiometric, and overstoichiometric preparations, where the lead halide is varied with respect to organic halide precursors. Halide homogenization coincides with long-lived charge carrier decays, spatially homogeneous carrier dynamics (as visualized by ultrafast microscopy), and improved photovoltaic device performance. We found that rubidium and potassium phase-segregate in highly concentrated clusters. Alkali metals are beneficial at low concentrations, where they homogenize the halide distribution, but at higher concentrations, they form recombination-active second-phase clusters.

4.
J Phys Chem Lett ; 9(15): 4182-4188, 2018 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-29979596

RESUMO

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212, with δ = 0.1). The morphology of the ribbon-like phase evolves simultaneously with the dome-shaped TC behavior under pressure. X-ray absorption studies show that the increasing of TC is associated with oxygen-hole redistribution in the CuO2 plan, while TC starts to decrease with pressure when oxygen holes become immobile. Additional X-ray irradiation experiments reveal that nanoscaled short-range ordering of oxygen vacancies could further lower TC, which indicates that the optimal TC is affected not only by an optimal morphology of the ribbon phase, but also an optimal distribution of oxygen vacancies. Our studies thereby provide for the first time compelling experimental evidence correlating the TC with micron to nanoscale inhomogeneity.

5.
ACS Nano ; 12(5): 4938-4945, 2018 05 22.
Artigo em Inglês | MEDLINE | ID: mdl-29715007

RESUMO

Memristive devices are an emerging technology that enables both rich interdisciplinary science and novel device functionalities, such as nonvolatile memories and nanoionics-based synaptic electronics. Recent work has shown that the reproducibility and variability of the devices depend sensitively on the defect structures created during electroforming as well as their continued evolution under dynamic electric fields. However, a fundamental principle guiding the material design of defect structures is still lacking due to the difficulty in understanding dynamic defect behavior under different resistance states. Here, we unravel the existence of threshold behavior by studying model, single-crystal devices: resistive switching requires that the pristine oxygen vacancy concentration reside near a critical value. Theoretical calculations show that the threshold oxygen vacancy concentration lies at the boundary for both electronic and atomic phase transitions. Through operando, multimodal X-ray imaging, we show that field tuning of the local oxygen vacancy concentration below or above the threshold value is responsible for switching between different electrical states. These results provide a general strategy for designing functional defect structures around threshold concentrations to create dynamic, field-controlled phases for memristive devices.

6.
Sci Adv ; 4(5): eaar3679, 2018 05.
Artigo em Inglês | MEDLINE | ID: mdl-29806024

RESUMO

The success of strain engineering has made a step further for the enhancement of material properties and the introduction of new physics, especially with the discovery of the critical roles of strain in the heterogeneous interface between two dissimilar materials (for example, FeSe/SrTiO3). On the other hand, the strain manipulation has been limited to chemical epitaxy and nanocomposites that, to a large extent, limit the possible material systems that can be explored. By defect engineering, we obtained, for the first time, dense three-dimensional strongly correlated VO2±Î´ epitaxial nanoforest arrays that can be used as a novel "substrate" for dynamic strain engineering, due to its metal-insulator transition. The highly dense nanoforest is promising for the possible realization of bulk strain similar to the effect of nanocomposites. By growing single-crystalline halide perovskite CsPbBr3, a mechanically soft and emerging semiconducting material, onto the VO2±Î´, a heterogeneous interface is created that can entail a ~1% strain transfer upon the metal-insulator transition of VO2±Î´. This strain is large enough to trigger a structural phase transition featured by PbX6 octahedral tilting along with a modification of the photoluminescence energy landscape in halide perovskite. Our findings suggest a promising strategy of dynamic strain engineering in a heterogeneous interface carrying soft and strain-sensitive semiconductors that can happen at a larger volumetric value surpassing the conventional critical thickness limit.

7.
J Phys Chem Lett ; 9(9): 2388-2393, 2018 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-29669204

RESUMO

Understanding how the structures of a crystal behave under compression is a fundamental issue both for condensed matter physics and for geoscience. Traditional description of a crystal as the stacking of a unit cell with special symmetry has gained much success on the analysis of physical properties. Unfortunately, it is hard to reveal the relationship between the compressed phases. Taking the family of metal dioxides (MO2) as an example, the structural evolution, subject to fixed chemical formula and highly confined space, often appears as a set of random and uncorrelated events. Here we provide an alternative way to treat the crystal as the stacking of the coordination polyhedron and then discover a unified structure transition pattern, in our case VO2. X-ray diffraction (XRD) experiments and first-principles calculations show that the coordination increase happens only at one apex of the V-centered octahedron in an orderly fashion, leaving the base plane and the other apex topologically intact. The polyhedron evolves toward increasing their sharing, indicating a general rule for the chemical bonds of MO2 to give away the ionicity in exchange for covalency under pressure.

8.
Proc Natl Acad Sci U S A ; 115(8): 1713-1717, 2018 02 20.
Artigo em Inglês | MEDLINE | ID: mdl-29432145

RESUMO

The diamond anvil cell (DAC) is considered one of the dominant devices to generate ultrahigh static pressure. The development of the DAC technique has enabled researchers to explore rich high-pressure science in the multimegabar pressure range. Here, we investigated the behavior of the DAC up to 400 GPa, which is the accepted pressure limit of a conventional DAC. By using a submicrometer synchrotron X-ray beam, double cuppings of the beveled diamond anvils were observed experimentally. Details of pressure loading, distribution, gasket-thickness variation, and diamond anvil deformation were studied to understand the generation of ultrahigh pressures, which may improve the conventional DAC techniques.

9.
Phys Rev Lett ; 118(9): 097601, 2017 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-28306309

RESUMO

Ferroelectric-dielectric superlattices consisting of alternating layers of ferroelectric PbTiO_{3} and dielectric SrTiO_{3} exhibit a disordered striped nanodomain pattern, with characteristic length scales of 6 nm for the domain periodicity and 30 nm for the in-plane coherence of the domain pattern. Spatial disorder in the domain pattern gives rise to coherent hard x-ray scattering patterns exhibiting intensity speckles. We show here using variable-temperature Bragg-geometry x-ray photon correlation spectroscopy that x-ray scattering patterns from the disordered domains exhibit a continuous temporal decorrelation due to spontaneous domain fluctuations. The temporal decorrelation can be described using a compressed exponential function, consistent with what has been observed in other systems with arrested dynamics. The fluctuation speeds up at higher temperatures and the thermal activation energy estimated from the Arrhenius model is 0.35±0.21 eV. The magnitude of the energy barrier implies that the complicated energy landscape of the domain structures is induced by pinning mechanisms and domain patterns fluctuate via the generation and annihilation of topological defects similar to soft materials such as block copolymers.

10.
Nano Lett ; 16(12): 7974-7981, 2016 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-27960450

RESUMO

One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX3 (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensurate epitaxy, paving a way for a universally applicable method to grow a broad family of halide perovskite materials. The unique photon transport in the one-dimensional structure has been studied in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.

11.
Mol Genet Genomic Med ; 4(6): 641-661, 2016 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-27896287

RESUMO

BACKGROUND: Amelogenin is required for normal enamel formation and is the most abundant protein in developing enamel. METHODS: Amelx+/+, Amelx+/- , and Amelx-/- molars and incisors from C57BL/6 mice were characterized using RT-PCR, Western blotting, dissecting and light microscopy, immunohistochemistry (IHC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), backscattered SEM (bSEM), nanohardness testing, and X-ray diffraction. RESULTS: No amelogenin protein was detected by Western blot analyses of enamel extracts from Amelx-/- mice. Amelx-/- incisor enamel averaged 20.3 ± 3.3 µm in thickness, or only 1/6th that of the wild type (122.3 ± 7.9 µm). Amelx-/- incisor enamel nanohardness was 1.6 Gpa, less than half that of wild-type enamel (3.6 Gpa). Amelx+/- incisors and molars showed vertical banding patterns unique to each tooth. IHC detected no amelogenin in Amelx-/- enamel and varied levels of amelogenin in Amelx+/- incisors, which correlated positively with enamel thickness, strongly supporting lyonization as the cause of the variations in enamel thickness. TEM analyses showed characteristic mineral ribbons in Amelx+/+ and Amelx-/- enamel extending from mineralized dentin collagen to the ameloblast. The Amelx-/- enamel ribbons were not well separated by matrix and appeared to fuse together, forming plates. X-ray diffraction determined that the predominant mineral in Amelx-/- enamel is octacalcium phosphate (not calcium hydroxyapatite). Amelx-/- ameloblasts were similar to wild-type ameloblasts except no Tomes' processes extended into the thin enamel. Amelx-/- and Amelx+/- molars both showed calcified nodules on their occlusal surfaces. Histology of D5 and D11 developing molars showed nodules forming during the maturation stage. CONCLUSION: Amelogenin forms a resorbable matrix that separates and supports, but does not shape early secretory-stage enamel ribbons. Amelogenin may facilitate the conversion of enamel ribbons into hydroxyapatite by inhibiting the formation of octacalcium phosphate. Amelogenin is necessary for thickening the enamel layer, which helps maintain ribbon organization and development and maintenance of the Tomes' process.

12.
Nano Lett ; 16(10): 6555-6559, 2016 10 12.
Artigo em Inglês | MEDLINE | ID: mdl-27680948

RESUMO

We report the in situ investigation of the morphological evolution of silver nanowires to hollow silver oxide nanotubes using transmission X-ray microscopy (TXM). Complex silver diffusion kinetics and hollowing process via the Kirkendall effect have been captured in real time. Further quantitative X-ray absorption analysis reveals the difference between the longitudinal and radial diffusions. The diffusion coefficient of silver in its oxide nanoshell is, for the first time, calculated to be 1.2 × 10-13 cm2/s from the geometrical parameters extracted from the TXM images.

13.
Sci Rep ; 6: 21999, 2016 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-26915398

RESUMO

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

14.
Angew Chem Int Ed Engl ; 55(5): 1742-5, 2016 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-26696553

RESUMO

Chromium(III) nutritional supplements are widely consumed for their purported antidiabetic activities. X-ray fluorescence microscopy (XFM) and X-ray absorption near-edge structure (XANES) studies have now shown that non-toxic doses of [Cr3 O(OCOEt)6 (OH2 )3 ](+) (A), a prospective antidiabetic drug that undergoes similar H2 O2 induced oxidation reactions in the blood as other Cr supplements, was also oxidized to carcinogenic Cr(VI) and Cr(V) in living cells. Single adipocytes treated with A had approximately 1 µm large Cr hotspots containing Cr(III) , Cr(V) , and Cr(VI) (primarily Cr(VI) thiolates) species. These results strongly support the hypothesis that the antidiabetic activity of Cr(III) and the carcinogenicity of Cr(VI) compounds arise from similar mechanisms involving highly reactive Cr(VI) and Cr(V) intermediates, and highlight concerns over the safety of Cr(III) nutritional supplements.


Assuntos
Adipócitos/metabolismo , Carcinógenos/síntese química , Cromo/metabolismo , Suplementos Nutricionais , Carcinógenos/química , Microscopia de Fluorescência , Oxirredução
15.
Chem Sci ; 6(1): 152-157, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-28553464

RESUMO

As the third-generation rigid macrocycles evolved from progenitor 1, cyclic aromatic oligoamides 3, with a backbone of reduced constraint, exhibit extremely strong stacking with an astoundingly high affinity (estimated lower limit of Kdimer > 1013 M-1 in CHCl3), which leads to dispersed tubular stacks that undergo further assembly in solution. Computational study reveals a very large binding energy (-49.77 kcal mol-1) and indicates highly cooperative local dipole interactions that account for the observed strength and directionality for the stacking of 3. In the solid-state, X-ray diffraction (XRD) confirms that the aggregation of 3 results in well-aligned tubular stacks. The persistent tubular assemblies of 3, with their non-deformable sub-nm pore, are expected to possess many interesting functions. One such function, transmembrane ion transport, is observed for 3.

16.
J Synchrotron Radiat ; 19(Pt 5): 814-20, 2012 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-22898962

RESUMO

New aspects of synchrotron Mössbauer microscopy are presented. A 5 µm spatial resolution is achieved, and sub-micrometer resolution is envisioned. Two distinct and unique methods, synchrotron Mössbauer imaging and nuclear resonant incoherent X-ray imaging, are used to resolve spatial distribution of species that are chemically and magnetically distinct from one another. Proof-of-principle experiments were performed on enriched (57)Fe phantoms, and on samples with natural isotopic abundance, such as meteorites.


Assuntos
Meteoroides , Espectroscopia de Mossbauer/métodos , Microscopia , Imagens de Fantasmas , Síncrotrons
17.
Nat Commun ; 3: 949, 2012 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-22805556

RESUMO

A long-standing aim in molecular self-assembly is the development of synthetic nanopores capable of mimicking the mass-transport characteristics of biological channels and pores. Here we report a strategy for enforcing the nanotubular assembly of rigid macrocycles in both the solid state and solution based on the interplay of multiple hydrogen-bonding and aromatic π-π stacking interactions. The resultant nanotubes have modifiable surfaces and inner pores of a uniform diameter defined by the constituent macrocycles. The self-assembling hydrophobic nanopores can mediate not only highly selective transmembrane ion transport, unprecedented for a synthetic nanopore, but also highly efficient transmembrane water permeability. These results establish a solid foundation for developing synthetically accessible, robust nanostructured systems with broad applications such as reconstituted mimicry of defined functions solely achieved by biological nanostructures, molecular sensing, and the fabrication of porous materials required for water purification and molecular separations.

18.
J Am Chem Soc ; 133(46): 18590-3, 2011 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-22023016

RESUMO

Aromatic oligoamide macrocycles exhibit strong preference for highly directional association. Aggregation happens in both nonpolar and polar solvents but is weakened as solvent polarity increases. The strong, directional assembly is rationalized by the cooperative action of dipole-dipole and π-π stacking interactions, leading to long nanotubular assemblies that are confirmed by SEM, TEM, AFM, and XRD. The persistent nanotubular assemblies contain non-collapsible hydrophilic internal pores that mediate highly efficient ion transport observed with these macrocycles and serve as cylindrical sites for accommodating guests such as metal ions.

19.
Rev Sci Instrum ; 82(4): 043903, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-21529021

RESUMO

In this report, we demonstrate the feasibility of applying a 250-nm focused x-ray beam to study a single crystalline NbSe(3) nanobelt under high-pressure conditions in a diamond anvil cell. With such a small probe, we not only resolved the distribution and morphology of each individual nanobelt in the x-ray fluorescence maps but also obtained the diffraction patterns from individual crystalline nanobelts with thicknesses of less than 50 nm. Single crystalline diffraction measurements on NbSe(3) nanobelts were performed at pressures up to 20 GPa.

20.
Mol Biosyst ; 6(7): 1316-22, 2010 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-20445927

RESUMO

Herein is described a general sampling protocol that includes culture, differentiation and fixing of cells in their preferred morphology on the one sample substrate (Si(3)N(4)) to enable subsequent diverse modern microspectroscopic analyses. The protocol enables unprecedented correlated and complementary information on the intracellular biochemistry of metabolic processes, diseases and their treatment, which offers the opportunity to revolutionize our understanding of cell and tissue biology at a molecular level. The culture of adherent cells onto inexpensive Si(3)N(4) membranes allows microspectroscopic analyses across the electromagnetic spectrum, from hard X-ray fluorescence (both XRF and XANES), through to visible and fluorescence light microscopies, and infrared microspectroscopy without substrate interference. Adherent mammalian cell lines (3T3-L1 adipocytes and H9c2 cardiac myocytes) illustrate the in vitro application of these protocols. The cells adhered strongly to Si(3)N(4) membranes and visually displayed normal proliferative and phenotypic growth; more importantly, rapid alcohol fixation of cells did not affect their structural integrity for subsequent analyses.


Assuntos
Adipócitos/citologia , Proliferação de Células , Microscopia de Fluorescência/métodos , Miócitos Cardíacos/citologia , Compostos de Silício/metabolismo , Células 3T3-L1 , Animais , Adesão Celular , Técnicas de Cultura de Células , Diferenciação Celular , Linhagem Celular , Camundongos , Microscopia/instrumentação , Microscopia/métodos , Compostos de Silício/química , Espectrometria por Raios X , Espectroscopia de Infravermelho com Transformada de Fourier/instrumentação , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Síncrotrons
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