55 research outputs found
Metal hierarchical patterning by direct nanoimprint lithography
Three-dimensional hierarchical patterning of metals is of paramount importance in diverse fields involving photonics, controlling surface wettability and wearable electronics. Conventionally, this type of structuring is tedious and usually involves layer-by-layer lithographic patterning. Here, we describe a simple process of direct nanoimprint lithography using palladium benzylthiolate, a versatile metal-organic ink, which not only leads to the formation of hierarchical patterns but also is amenable to layer-by-layer stacking of the metal over large areas. The key to achieving such multi-faceted patterning is hysteretic melting of ink, enabling its shaping. It undergoes transformation to metallic palladium under gentle thermal conditions without affecting the integrity of the hierarchical patterns on micro- as well as nanoscale. A metallic rice leaf structure showing anisotropic wetting behavior and woodpile-like structures were thus fabricated. Furthermore, this method is extendable for transferring imprinted structures to a flexible substrate to make them robust enough to sustain numerous bending cycles
Angstrofluidics:walking to the limit
Angstrom-scale fluidic channels are ubiquitous in nature, and play an
important role in regulating cellular traffic, signaling, and responding to
stimuli. Synthetic channels are now a reality with the emergence of several
cutting-edge bottom-up and top-down fabrication methods. In particular, the use
of atomically thin two dimensional (2D) materials and nanotubes as components
to build fluidic conduits has pushed the limits of fabrication to the
Angstrom-scale. Here, we provide an overview of the recent developments in the
fabrication methods for nano- and angstrofluidic channels while categorizing
them on the basis of dimensionality (0D pores, 1D tubes, 2D slits), along with
the latest advances in measurement techniques. We discuss the ionic transport
governed by various stimuli in these channels and draw comparison of ionic
mobility, streaming and osmotic power, with varying pore sizes across all the
dimensionalities. Towards the end of the review, we highlight the unique future
opportunities in the development of smart ionic devices.Comment: Keywords: Angstrofluidics, nanofluidics, confinement, ion transport,
2D materials, molecular transport 6 figures, review articl
Highly tapered pentagonal bipyramidal Au microcrystals with high index faceted corrugation: synthesis and optical properties
Focusing light at sub-wavelength region opens up interesting applications in optical sensing and imaging beyond the diffraction limit. In the past, tapered Au wires with carved gratings have been employed to achieve nanofocusing. The fabrication process however, is expensive and the obtained wires are polycrystalline with high surface roughness. A chemical synthetic method overcoming these hurdles should be an attractive alternative. Here, we report a method to chemically synthesize Au microcrystals (∼10 μm) bearing pentagonal bipyramidal morphology with surface corrugations assignable to high index planes. The method is a single step solid state synthesis at a temperature amenable to common substrates. The microcrystals are tapered at both ends forming sharp tips (∼55 nm). Individual microcrystals have been used as pick and probe SERS substrates for a dye embedded in a polymer matrix. The unique geometry of the microcrystal also enables light propagation across its length
Water friction in nanofluidic channels made from two-dimensional crystals.
From Europe PMC via Jisc Publications RouterHistory: ppub 2021-05-01, epub 2021-05-25Publication status: PublishedFunder: European Research Council; Grant(s): 852674Membrane-based applications such as osmotic power generation, desalination and molecular separation would benefit from decreasing water friction in nanoscale channels. However, mechanisms that allow fast water flows are not fully understood yet. Here we report angstrom-scale capillaries made from atomically flat crystals and study the effect of confining walls' material on water friction. A massive difference is observed between channels made from isostructural graphite and hexagonal boron nitride, which is attributed to different electrostatic and chemical interactions at the solid-liquid interface. Using precision microgravimetry and ion streaming measurements, we evaluate the slip length, a measure of water friction, and investigate its possible links with electrical conductivity, wettability, surface charge and polarity of the confining walls. We also show that water friction can be controlled using hybrid capillaries with different slip lengths at opposing walls. The reported advances extend nanofluidics' toolkit for designing smart membranes and mimicking manifold machinery of biological channels
Stray magnetic field imaging of thin exfoliated iron halides flakes
Magnetic van der Waals materials are often proposed for use in future
spintronic devices, aiming to leverage the combination of long-range magnetic
order and near-atomic thinness to produce energy-efficient components. One
class of material that has been discussed in this context are the iron halides
FeCl and FeBr, which are A-type antiferromagnets with strong uniaxial
magnetocrystalline anisotropy. However, despite characterization of the bulk
materials, the possibility for sustaining the magnetic behaviors that would
underpin such applications in thin flakes has not been investigated. In this
work, we use nitrogen-vacancy (NV) center microscopy to quantitatively image
magnetism in individual exfoliated flakes of these iron halides, revealing the
absence of magnetic remanence, a weak induced magnetization under bias field
and variable behavior versus temperature. We show that our results are
consistent with the antiferromagnetic behavior of the bulk material with a soft
ferromagnetic uncompensated layer, indicating that extended (m)
ferromagnetic domains are not sustained even at low temperatures (down to 4 K).
Finally, we find that the magnetic order is strongly affected by the sample
preparation, with a surprising diamagnetic order observed in a thin, hydrated
sample.Comment: 15 pages, 13 figure
Anomalously low dielectric constant of confined water
The dielectric constant ε of interfacial water has been predicted to be smaller than that of bulk water (ε ≈ 80) because the rotational freedom of water dipoles is expected to decrease near surfaces, yet experimental evidence is lacking. We report local capacitance measurements for water confined between two atomically flat walls separated by various distances down to 1 nanometer. Our experiments reveal the presence of an interfacial layer with vanishingly small polarization such that its out-of-plane ε is only ~2. The electrically dead layer is found to be two to three molecules thick. These results provide much-needed feedback for theories describing water-mediated surface interactions and the behavior of interfacial water, and show a way to investigate the dielectric properties of other fluids and solids under extreme confinement
Stray magnetic field imaging of thin exfoliated iron halides flakes
Magnetic van der Waals materials are often proposed for use in future spintronic devices, aiming to leverage the combination of long-range magnetic order and near-atomic thinness to produce energy-efficient components. One class of material that has been discussed in this context are the iron halides FeCl2 and FeBr2, which are A-type antiferromagnets with strong uniaxial magnetocrystalline anisotropy. However, despite characterization of the bulk materials, the possibility for sustaining the magnetic behaviors that would underpin such applications in thin flakes has not been investigated. In this work, we use nitrogen-vacancy center microscopy to quantitatively image magnetism in individual exfoliated flakes of these iron halides, revealing the absence of magnetic remanence, a weak induced magnetization under bias field, and variable behavior versus temperature. We show that our results are consistent with the antiferromagnetic behavior of the bulk material with a soft ferromagnetic uncompensated layer, indicating that extended (>1µm) ferromagnetic domains are not sustained even at low temperatures (down to 4 K). Finally, we find that the magnetic order is strongly affected by the sample preparation, with a surprising diamagnetic behavior observed in a thin, hydrated sample.<br/
Liquid-activated quantum emission from native hBN defects for nanofluidic sensing
Nanostructures made of two-dimensional (2D) materials have become the
flagship of nanofluidic discoveries in recent years. By confining liquids down
to a few atomic layers, anomalies in molecular transport and structure have
been revealed. Currently, only indirect and ensemble averaged techniques have
been able to operate in such extreme confinements, as even the smallest
molecular fluorophores are too bulky to penetrate state-of-the-art single-digit
nanofluidic systems. This strong limitation calls for the development of novel
optical approaches allowing for the direct molecular imaging of liquids
confined at the nanoscale. Here, we show that native defects present at the
surface of hexagonal boron nitride (hBN) - a widely used 2D material - can
serve as probes for molecular sensing in liquid, without compromising the
atomic smoothness of their host material. We first demonstrate that native
surface defects are readily activated through interactions with organic
solvents and confirm their quantum emission properties. Vibrational spectra of
the emitters suggest that their activation occurs through the chemisorption of
carbon-bearing liquid molecules onto native hBN defects. The correlated
activation of neighboring defects reveals single-molecule dynamics at the
interface, while defect emission spectra offer a direct readout of the local
dielectric properties of the liquid medium. We then harvest these effects in
atomically smooth slit-shaped van der Waals channels, revealing molecular
dynamics and increasing dielectric order under nanometre-scale confinement.
Liquid-activated native defects in pristine hBN bridge the gap between
solid-state nanophotonics and nanofluidics and open up new avenues for
nanoscale sensing and optofluidics.Comment: 16 pages, 5 figure
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