Artificial muscles may accelerate the development of robotics, haptics, and prosthetics. Although advances in polymer-based actuators have delivered unprecedented strengths, producing these devices ...at scale with tunable dimensions remains a challenge. We applied a high-throughput iterative fiber-drawing technique to create strain-programmable artificial muscles with dimensions spanning three orders of magnitude. These fiber-based actuators are thermally and optically controllable, can lift more than 650 times their own weight, and withstand strains of >1000%. Integration of conductive nanowire meshes within these fiber-based muscles offers piezoresistive strain feedback and demonstrates long-term resilience across >10
deformation cycles. The scalable dimensions of these fiber-based actuators and their strength and responsiveness may extend their impact from engineering fields to biomedical applications.
Rotational invariance strongly constrains the viscosity tensor of classical fluids. When this symmetry is broken in anisotropic materials a wide array of novel phenomena become possible. We explore ...electron fluid behaviors arising from the most general viscosity tensors in two and three dimensions, constrained only thermodynamics and crystal symmetries. We find nontrivial behaviors in both two- and three-dimensional materials, including imprints of the crystal symmetry on the large-scale flow pattern. Breaking time-reversal symmetry introduces a non-dissipative Hall component to the viscosity tensor, and while this vanishes for 3D isotropic systems we show it need not for anisotropic materials. Further, for such systems we find that the electronic fluid stress can couple to the vorticity without breaking time-reversal symmetry. Our work demonstrates the anomalous landscape for electron hydrodynamics in systems beyond graphene, and presents experimental geometries to quantify the effects of electronic viscosity.
In the presence of interactions, electrons in condensed-matter systems can behave hydrodynamically, exhibiting phenomena associated with classical fluids, such as vortices and Poiseuille flow1–3. In ...most conductors, electron–electron interactions are minimized by screening effects, hindering the search for hydrodynamic materials; however, recently, a class of semimetals has been reported to exhibit prominent interactions4,5. Here we study the current flow in the layered semimetal tungsten ditelluride by imaging the local magnetic field using a nitrogen-vacancy defect in a diamond. We image the spatial current profile within three-dimensional tungsten ditelluride and find that it exhibits non-uniform current density, indicating hydrodynamic flow. Our temperature-resolved current profile measurements reveal a non-monotonic temperature dependence, with the strongest hydrodynamic effects at approximately 20 K. We also report ab initio calculations showing that electron–electron interactions are not explained by the Coulomb interaction alone, but are predominantly mediated by phonons. This provides a promising avenue in the search for hydrodynamic flow and prominent electron interactions in high-carrier-density materials.When interactions between electrons in a material are strong, they can start to behave hydrodynamically. Spatially resolved imaging of current flow in a three-dimensional material suggests that electron–electron interactions are mediated by phonons.
The atomic structure at the interface between two-dimensional (2D) and three-dimensional (3D) materials influences properties such as contact resistance, photo-response, and high-frequency electrical ...performance. Moiré engineering is yet to be utilized for tailoring this 2D/3D interface, despite its success in enabling correlated physics at 2D/2D interfaces. Using epitaxially aligned MoS
/Au{111} as a model system, we demonstrate the use of advanced scanning transmission electron microscopy (STEM) combined with a geometric convolution technique in imaging the crystallographic 32 Å moiré pattern at the 2D/3D interface. This moiré period is often hidden in conventional electron microscopy, where the Au structure is seen in projection. We show, via ab initio electronic structure calculations, that charge density is modulated according to the moiré period, illustrating the potential for (opto-)electronic moiré engineering at the 2D/3D interface. Our work presents a general pathway to directly image periodic modulation at interfaces using this combination of emerging microscopy techniques.
Abstract
As conductors in electronic applications shrink, microscopic conduction processes lead to strong deviations from Ohm’s law. Depending on the length scales of momentum conserving (
l
MC
) and ...relaxing (
l
MR
) electron scattering, and the device size (
d
), current flows may shift from ohmic to ballistic to hydrodynamic regimes. So far, an in situ methodology to obtain these parameters within a micro/nanodevice is critically lacking. In this context, we exploit Sondheimer oscillations, semi-classical magnetoresistance oscillations due to helical electronic motion, as a method to obtain
l
MR
even when
l
MR
≫
d
. We extract
l
MR
from the Sondheimer amplitude in WP
2
, at temperatures up to
T
~ 40 K, a range most relevant for hydrodynamic transport phenomena. Our data on
μ
m-sized devices are in excellent agreement with experimental reports of the bulk
l
MR
and confirm that WP
2
can be microfabricated without degradation. These results conclusively establish Sondheimer oscillations as a quantitative probe of
l
MR
in micro-devices.
Exposure to stressful or traumatic stimuli may alter hypothalamic-pituitary-adrenal (HPA) axis and sympathoadrenal-medullary (SAM) reactivity. This altered reactivity may be a component or cause of ...mental illnesses. Dissecting these mechanisms requires tools to reliably probe HPA and SAM function, particularly the adrenal component, with temporal precision. We previously demonstrated magnetic nanoparticle (MNP) technology to remotely trigger adrenal hormone release by activating thermally sensitive ion channels. Here, we applied adrenal magnetothermal stimulation to probe stress-induced HPA axis and SAM changes. MNP and control nanoparticles were injected into the adrenal glands of outbred rats subjected to a tone-shock conditioning/extinction/recall paradigm. We measured MNP-triggered adrenal release before and after conditioning through physiologic (heart rate) and serum (epinephrine, corticosterone) markers. Aversive conditioning altered adrenal function, reducing corticosterone and blunting heart rate increases post-conditioning. MNP-based organ stimulation provides a novel approach to probing the function of SAM, HPA, and other neuro-endocrine axes and could help elucidate changes across stress and disease models.
The three-dimensional (3D) local atomic structures and crystal defects at the interfaces of heterostructures control their electronic, magnetic, optical, catalytic, and topological quantum properties ...but have thus far eluded any direct experimental determination. Here, we use atomic electron tomography to determine the 3D local atomic positions at the interface of a MoS
-WSe
heterojunction with picometer precision and correlate 3D atomic defects with localized vibrational properties at the epitaxial interface. We observe point defects, bond distortion, and atomic-scale ripples and measure the full 3D strain tensor at the heterointerface. By using the experimental 3D atomic coordinates as direct input to first-principles calculations, we reveal new phonon modes localized at the interface, which are corroborated by spatially resolved electron energy-loss spectroscopy. We expect that this work will pave the way for correlating structure-property relationships of a wide range of heterostructure interfaces at the single-atom level.
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The infiltration of a non-wetting liquid, such as molten metal, into a porous solid, such as a ceramic preform, is influenced by the wetting angle of the liquid on the solid. The link ...between local wetting and the minimum pressure required for initiation of infiltration or the pressure required for full preform infiltration can deviate strongly from what one would expect on the basis of elementary thermodynamic considerations or simple geometrical models. In this work, we explain the trends observed in experimental studies of pressure infiltration of molten metal into ceramic preforms by means of a percolation model, in which the pores themselves are given a simple geometric shape. This gives a simple yet rich and realistic treatment of the infiltration process. Specifically, the pop-through pressure necessary to traverse a throat between two neighboring circular (2D) or spherical (3D) pores can easily be calculated and incorporated in a 3D network model of many pores produced by generating a packing of slightly overlapping circles or spheres. The resulting pore structure defines a bond percolation network that agrees overall both with predictions of percolation theory and observations from experiment, and which can be extended to address a range of other aspects of multi-phase flow through porous media.
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