1,721,176 research outputs found
Synergism of Nanomaterials with Physical Stimuli for Biology and Medicine
No full textDeveloping innovative tools that facilitate the understanding of sophisticated biological systems has been one of the Holy Grails in the physical and biological sciences. In this Commentary, we discuss recent advances, opportunities, and challenges in the use of nanomaterials as a precision tool for biology and medicine. © 2017 American Chemical Society17101sciescopu
Chemical Transformations of Anisotropic Platelets and Spherical Nanocrystals
No full textCONSPECTUS: Inorganic nanocrystal design has been continuously evolving with a better understanding of the chemical reaction mechanisms between chemical stimuli and nanocrystals. Under certain conditions, molecular compounds can be effective as chemical stimuli to induce transformative reactions of nanocrystals toward new materials that would differ in geometric shape, composition, and crystallographic structure. To explore such evolutionary processes, two-dimensional (2D) layered transition-metal chalcogenide (TMC) nanostructures are an interesting structural platform because they not only exhibit unique transformation pathways due to their structural anisotropy but also present new opportunities for improved material properties for potential applications such as catalysis and energy conversion and storage. The high surface area/volume ratio, interlayer van der Waals (vdW) spacing, and different coordination states between the unsaturated edges and the fully saturated basal planes of the chalcogens are characteristic of 2D layered TMC nanostructures, which subsequently lead to anisotropic chemical processes during chemical transformations, such as regioselective reactions at the interfacial boundaries in the pathways for either porous or solid heteronanostructures. In this Account, we first discuss the chemical reactivity of 2D layered TMC nanostructures. By categorizing the external stimuli in terms of chemical principles, such as Lewis acid-base chemistry, a desirable regioselective chemical reaction can occur with controlled reactivity. In association with the knowledge obtained from the nanoscale chemical reactivity of 2D layered nanocrystals, similar efforts in other important morphologies such as 1D and isotropic 0D nanocrystals are introduced. For instance, for 1D and 0D metal oxide nanocrystals, the effects of molecular stimuli on the atomic-level changes in the crystal lattice are demonstrated, eventually leading to a variety of shape transformations.11Nsciescopu
Recent Advances in the Solution-Based Preparation of Two-Dimensional Layered Transition Metal Chalcogenide Nanostructures
No full textThe precise control in size/thickness, composition, crystal phases, doping, defects, and surface properties of two-dimensional (2D) layered transition metal chalcogenide (TMC) is important for the investigation of interwoven relationship between structures, functions, and practical applications. Of the multiple synthetic routes, solution-based top-down and bottom-up chemical methods have been uniquely important for their potential to control the size and composition at the molecular level in addition to their scalability, competitive production cost, and solution processability. Here, we introduce an overview of the recent advances in the solution-based preparation routes of 2D layered TMC nanostructures along with important scientific developments © 2018 American Chemical Societ
High-order synchronization of hair cell bundles
Full text linkAuditory and vestibular hair cell bundles exhibit active mechanical oscillations at natural frequencies that are typically lower than the detection range of the corresponding end organs. We explore how these noisy nonlinear oscillators mode-lock to frequencies higher than their internal clocks. A nanomagnetic technique is used to stimulate the bundles without an imposed mechanical load. The evoked response shows regimes of high-order mode-locking. Exploring a broad range of stimulus frequencies and intensities, we observe regions of high-order synchronization, analogous to Arnold Tongues in dynamical systems literature. Significant areas of overlap occur between synchronization regimes, with the bundle intermittently flickering between different winding numbers. We demonstrate how an ensemble of these noisy spontaneous oscillators could be entrained to efficiently detect signals significantly above the characteristic frequencies of the individual cells. © The Author(s) 20161
Effects of Electronic Coupling on Bright and Dark Excitons in a 2D Array of Strongly Confined CsPbBr3 Quantum Dots
No full textIn contrast to the weakly confined quantum dots dominated by bright excitons, strongly quantum confined CsPbBr3 QDs exhibit both bright and dark exciton photoluminescence (PL) at cryogenic temperatures, making them a unique source of photons and charges of two very different natures. Here, we investigate the effect of inter-QD electronic coupling on the relative energetics and dynamics of the bright and dark excitons, which dictate the PL properties of the coupled arrays of these QDs at low temperatures. For this purpose, we fabricated 2D close-packed arrays of NaBr-passivated CsPbBr3 QDs with a sub-nanomter facet-to-facet distance, which was necessary to introduce electronic coupling. In addition to the redshift of the PL due to electronic coupling, the electronically coupled array of strongly confined CsPbBr3 QDs exhibited narrowed bright-dark level splitting and an acceleration of the decay of both bright and dark exciton PL at cryogenic temperatures. These observations are qualitatively analogous to the effects of increasing the volume of noninteracting QDs, which can be explained by the delocalization of exciton wave function among the coupled QDs.11Nsciescopu
Effects of Direct Solvent-Quantum Dot Interaction on the Optical Properties of Colloidal Monolayer WS2 Quantum Dots
No full textBecause of the absence of native dangling bonds on
the surface of the layered transition metal dichalcogenides
(TMDCs), the surface of colloidal quantum dots (QDs) of
TMDCs is exposed directly to the solvent environment.
Therefore, the optical and electronic properties of TMDCS
QDs are expected to have stronger influence from the solvent than
usual surface-passivated QDs due to more direct solvent-QD
interaction. Study of such solvent effect has been difficult in
colloidal QDs of TMDC due to the large spectroscopic
heterogeneity resulting from the heterogeneity of the lateral size
or (and) thickness in ensemble. Here, we developed a new
synthesis procedure producing the highly uniform colloidal monolayer WS2 QDs exhibiting well-defined photoluminescence
(PL) spectrum free from ensemble heterogeneity. Using these newly synthesized monolayer WS2 QDs, we observed the strong
influence of the aromatic solvents on the PL energy and intensity of monolayer WS2 QD beyond the simple dielectric screening
effect, which is considered to result from the direct electronic interaction between the valence band of the QDs and molecular
orbital of the solvent. We also observed the large effect of stacking/separation equilibrium on the PL spectrum dictated by the
balance between inter QD and QD-solvent interactions. The new capability to probe the effect of the solvent molecules on the
optical properties of colloidal TMDC QDs will be valuable for their applications in various liquid surrounding environments. © 2017 American Chemical Society4
2D Crystals in Three Dimensions: Electronic Decoupling of Single‐Layered Platelets in Colloidal Nanoparticles
No full text2D crystals, single sheets of layered materials, often show distinct properties desired for optoelectronic applications, such as larger and direct band gaps, valley- and spin-orbit effects. Being atomically thin, the low amount of material is a bottleneck in photophysical and photochemical applications. Here, the formation of stacks of 2D crystals intercalated with small surfactant molecules is proposed. It is shown, using first principles calculations, that the very short surfactant methyl amine electronically decouples the layers. The indirect-direct band gap transition characteristic for Group 6 transition metal dichalcogenides is demonstrated experimentally by observing the emergence of a strong photoluminescence signal for ethoxide-intercalated WSe2 and MoSe2 multilayered nanoparticles with lateral size of about 10 nm and beyond. The proposed hybrid materials offer the highest possible density of the 2D crystals with electronic properties typical of monolayers. Variation of the surfactant's chemical potential allows fine-tuning of electronic properties and potentially elimination of trap states caused by defects © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Ultrathin Interface Regime of Core-Shell Magnetic Nanoparticles for Effective Magnetism Tailoring
No full textThe magnetic exchange coupling interaction between hard and soft magnetic phases has been important for tailoring nanoscale magnetism, but spin interactions at the core-shell interface have not been well studied. Here, we systematically investigated a new interface phenomenon termed enhanced spin canting (ESC), which is operative when the shell thickness becomes ultrathin, a few atomic layers, and exhibits a large enhancement of magnetic coercivity (HC). We found that ESC arises not from the typical hard-soft exchange coupling but rather from the large magnetic surface anisotropy (KS) of the ultrathin interface. Due to this large increase in magnetism, ultrathin core-shell nanoparticles overreach the theoretical limit of magnetic energy product ((BH)max) and exhibit one of the largest values of specific loss power (SLP), which testifies to their potential capability as an effective mediator of magnetic energy conversion. © 2017 American Chemical Society10
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