Flexible electronic systems such as roll-up displays and wearable devices promise exciting possibilities that could change the way humans interact with the environment. However, they suffer from poor reliability of interconnects and devices. Interconnects on flex are prone to open-circuit failures due to mechanical stress, electrostatic discharge, and environmental degradation. Passive approaches such as the use of stretchable conductors and novel geometries improve their response to mechanical stress but cannot salvage the interconnect if a fault were to occur. Active approaches using self-healing techniques can repair a fault and have been demonstrated with use of methods that use relatively rare materials, change conventional interconnect-fabrication processes, address only faults due to mechanical stress, or do not permit stretching. In this work we discuss a self-healing technique that overcomes these limitations and demonstrate heals having metallic conductivity and nearly plastic stretchability. This is achieved by dispersion of conductive particles in an insulating fluid encapsulated over the interconnect. Healing is automatically triggered by the electric field appearing in the open gap of a failed interconnect, irrespective of the cause of failure. The field polarizes the conductive particles, causing them aggregate and chain up to bridge the gap and repair the fault. Using dispersions of copper microspheres in silicone oil, we show self-healing interconnects with the stretchable heal having conductivity of about $5\times {10}^5$ S/m and allowing strains from 12 to 60. Previously, stretchable interconnects used materials other than copper. Here we effectively show self-healing, stretchable copper. This work promises high-speed, self-healing, and stretchable interconnects on flex, thereby improving system reliability.

Label-free biosensors enable the monitoring of biomolecular interactions in real time, which is key to the analysis of the binding characteristics of biomolecules. While refractometric optical biosensors such as surface plasmon resonance (SPR) are sensitive and well-established, they are susceptible to any change of the refractive index in the sensing volume caused by minute variations in composition of the sample buffer, temperature drifts, and most importantly nonspecific binding to the sensor surface in complex fluids such as blood. The limitations arise because refractometric sensors measure the refractive index of the entire sensing volume. Conversely, diffractometric biosensors–for example, focal molography–only detect the diffracted light from a coherent assembly of analyte molecules. Thus any refractive index distribution that is noncoherent with respect to this molecular assembly does not add to the coherent signal. This makes diffractometric biosensors inherently robust and enables sensitive measurements without reference channels or temperature stabilization. The coherent assembly is generated by selective binding of the analyte molecules to a synthetic binding pattern–the mologram. Focal molography has been introduced theoretically [C. Fattinger, Phys. Rev. X 4, 031024 (2014)] and verified experimentally [V. Gatterdam, A. Frutiger, K.-P. Stengele, D. Heindl, T. Lübbes, J. Vörös, and C. Fattinger, Nat. Nanotechnol. 12, 1089 (2017)] in previous papers. However, further understanding of the underlying physics and a diffraction-limited readout is needed to unveil its full potential. This paper introduces refined theoretical models, which can accurately quantify the amount of biological matter bound to the mologram from the diffracted intensity. In addition, it presents measurements of diffraction-limited molographic foci, i.e., Airy discs. These improvements enable us to demonstrate a resolution in real-time binding experiments comparable to the best SPR sensors without the need for temperature stabilization or drift correction and to detect low-molecular-weight compounds label free in an endpoint format. The presented experiments exemplify the robustness and sensitivity of the diffractometric sensor principle.

We seek stable tractor beams that not only axially pull objects but also transversely trap the object. Transverse force acting on a spherical particle centered on the axis of acoustic Bessel beams is examined using the Gor’kov potential and partial wave expansion. The results suggest flexibility of trapping both relatively dense and stiff particles and relatively light and soft particles at the pressure maximum of the axisymmetric Bessel beam in the Rayleigh regime. This trapping is more flexible than trapping by standing waves and focused beams used in acoustic tweezers. The flexibility is interpreted by the contribution of axial velocity to the force potential and by momentum projection. We then reveal parameters (paraxiality, density ratio, and bulk modulus ratio) for simultaneous trapping and pulling of an elastic object and droplet in and beyond the Rayleigh regime. The results reveal the capability and conditions to simultaneously trap and pull a Rayleigh particle even in the situation when losses are accounted for. Our study guides designs of stable tractor beams and drives development of acoustic tweezers.

Strain engineering is a powerful technology that exploits the stationary external or internal stress of specific spatial distribution for controlling the fundamental properties of condensed materials and nanostructures. This advanced technique modulates in space the carrier density and mobility, the optical absorption, and in strongly correlated systems, the phase, e.g., insulator-metal or ferromagnetic-paramagnetic. However, while successfully accessing nanometer-length scales, strain engineering is yet to be brought down to ultrafast time scales allowing strain-assisted control of the state of matter at THz frequencies. We demonstrate control of an optically-driven insulator-to-metal phase transition by a picosecond strain pulse, which paves the way to ultrafast strain engineering in nanostructures with phase transitions. This is realized by simultaneous excitation of ${\mathrm{VO}}_2$ nanohillocks by a 170-fs laser and picosecond strain pulses finely timed with each other. By monitoring the transient optical reflectivity of the ${\mathrm{VO}}_2$, we show that strain pulses, depending on the sign of the strain at the moment of optical excitation, increase or decrease the fraction of ${\mathrm{VO}}_2$ that undergoes an ultrafast phase transition. A transient strain of moderate amplitude of approximately 0.1% applied during ultrafast photo-induced nonthermal transition changes the fraction of ${\mathrm{VO}}_2$ in the laser-induced phase by approximately 1%. In contrast, if applied after the photoexcitation when the phase transformations of the material are governed by thermal processes, a transient strain of the same amplitude produces no measurable effect on the phase state.

Physical systems in the time domain may exhibit analogous phenomena in real space, such as time crystals, time-domain Fresnel lenses, and modulational interference in a qubit. Here, we report the experimental realization of time-domain grating using a superconducting qutrit in periodically modulated probe and control fields via two schemes: simultaneous modulation and complementary modulation. Both experimental and numerical results exhibit modulated Autler-Townes (AT) and modulation-induced diffraction (MID) effects. Theoretical results also confirm that the peak positions of the interference fringes of AT and MID effects are determined by the usual two-level relative phases, while the observed diffraction fringes, appearing only in the complementary modulation, are, however, related to the three-level relative phase. Further analysis indicates that such a single-atom time-domain diffraction originates from the correlation effect between the two time-domain gratings. Moreover, we find that the widths of the diffraction fringes are independent of the control-field power. Our results shed light on the experimental exploration of quantum coherence for modulated multilevel systems and may find promising applications in fast all-microwave switches and quantum-gate operations in the strong-driving regime.

To reduce material and processing costs of commercial permanent magnets and to attempt to fill the empty niche of energy products, 10–20 MGOe, between low-flux (ferrites, alnico) and high-flux (${\mathrm{Nd}}_2{\mathrm{Fe}}_{14}\mathrm{B}$- and ${\mathrm{Sm}\mathrm{Co}}_5$-type) magnets, we report the synthesis, structure, magnetic properties, and modeling of $\mathrm{Ta}$-, $\mathrm{Cu}$-, and $\mathrm{Fe}$-substituted ${\mathrm{Ce}\mathrm{Co}}_5$. Using a self-flux technique, we grow single crystals of ${\mathrm{Ce}}_{15.1}{\mathrm{Ta}}_{1.0}{\mathrm{Co}}_{74.4}{\mathrm{Cu}}_{9.5}$, ${\mathrm{Ce}}_{16.3}{\mathrm{Ta}}_{0.6}{\mathrm{Co}}_{68.9}{\mathrm{Cu}}_{14.2}$, ${\mathrm{Ce}}_{15.7}{\mathrm{Ta}}_{0.6}{\mathrm{Co}}_{67.8}{\mathrm{Cu}}_{15.9}$, ${\mathrm{Ce}}_{16.3}{\mathrm{Ta}}_{0.3}{\mathrm{Co}}_{61.7}{\mathrm{Cu}}_{21.7}$, and ${\mathrm{Ce}}_{14.3}{\mathrm{Ta}}_{1.0}{\mathrm{Co}}_{62.0}{\mathrm{Fe}}_{12.3}{\mathrm{Cu}}_{10.4}$. X-ray-diffraction analysis shows that these materials retain a ${\mathrm{Ca}\mathrm{Cu}}_5$ substructure and incorporate small amounts of $\mathrm{Ta}$ in the form of “dumbbells,” filling the $2e$ crystallographic sites within the one-dimensional hexagonal channel with the $1a$ $\mathrm{Ce}$ site, whereas $\mathrm{Co}$, $\mathrm{Cu}$, and $\mathrm{Fe}$ are statistically distributed among the $2c$ and $3g$ crystallographic sites. Scanning-electron-microscopy, energy-dispersive-x-ray-spectroscopy, and scanning-transmission-electron-microscopy examinations provide strong evidence of the single-phase nature of the as-grown crystals, even though they readily exhibit significant magnetic coercivities of approximately 1.6 kOe to approximately 1.8 kOe caused by $\mathrm{Co}$-enriched, nanosized structural defects and faults that can serve as pinning sites. Heat treatments at $1040{}^{\circ }\mathrm{C}$ for 10 h and hardening at $400{}^{\circ }\mathrm{C}$ for 4 h lead to the formation of a so-called composite crystal with a bimodal microstructure that consists of a $\mathrm{Ta}$-poor matrix and $\mathrm{Ta}$-rich laminal precipitates. Formation of the composite crystal during the heat treatment creates a three-dimensional array of extended defects within a primarily single-grain single crystal, which greatly improves its magnetic characteristics. Possible causes for the formation of the composite crystal may be associated with $\mathrm{Ta}$ atoms leaving matrix interstices at lower temperatures and/or matrix degradation induced by decreased miscibility at lower temperatures. $\mathrm{Fe}$ strongly increases both the Curie temperature and magnetization of the system resulting, in $(BH{)}_{max}\approx 13$ MGOe at room temperature.

Testing the limits in performance of device setups with respect to sizes and oscillation frequencies by trying every single combination of the available media can give a set of superior designs with novel properties. This approach is followed for the absorption and scattering of visible light by core-shell nanowires, whose optical thickness is simultaneously large enough to individually perturb the background field and small enough to support coherent collective operation. Numerous maximally performing particles are reported, one for each pair of the bulk materials used, providing a set of limits for the absorbed and scattered power in the presence of realistic losses. This procedure detects the supported resonances at core-shell nanorods, finds the best designs for such a simple geometry, and thus offers additional degrees of freedom in particle or metasurface modeling.

We experimentally study the thermoelectric properties of an ${\mathrm{Au}}_x{\mathrm{Ge}}_{1-x}$ thin-film alloy close to the metal-insulator transition ($x=19.5\mathrm{\%}$). The thermoelectric characterization of the thin-film alloy shows a Seebeck coefficient comparable to that of $\mathrm{Au}$ thin film while preserving good thermal sensor properties, revealing the potential interest in its use in nanoscale thermoelectric systems. In particular, we demonstrate the ability to directly evaporate an ${\mathrm{Au}}_x{\mathrm{Ge}}_{1-x}$ thin film on different nanometric-thick molecular layers. A device engineering is proposed paving the way for investigation of the thermoelectricity of large-area nanometric-thick molecular layers, where the alloy is integrated as a contact electrode, fulfilling the double role of an in situ local heater and a high-resolution thermometer.

We show that engineered diffraction gratings can considerably simplify the design of acoustic ground cloaking devices. Acoustic reflecting gratings are designed in such a way that all the incident energy is channeled toward the diffracted mode traveling in the direction opposite the direction of the incident field (retroreflection effect), and this effect is used to cloak an object placed over an acoustically rigid surface. Axisymmetric gratings consisting of rigid surfaces with just one groove per unit cell are used to design thin acoustic carpet cloaks. Finally, full-wave numerical simulations are performed and a conical carpet cloak is experimentally tested, showing an excellent scattering-cancellation effect.

Strong nonlinear optical effects generally require giant optical fields interacting with the nonlinear media. Doped graphene hosts electrically tunable plasmons with long lifetimes that interact strongly with light. We investigate a graphene plasmonic coupler and explore two mechanisms to pursue highly efficient third-harmonic generation (THG): (1) phase matching of graphene plasmons at fundamental- and third-harmonic frequencies and (2) peak third-order nonlinear susceptibility of doped graphene. The third-harmonic wave is mainly converted from the evanescent mode of the incident light and the THG efficiency is found to be enhanced by over 10 orders of magnitude compared with a bare monolayer graphene. The significantly enhanced nonlinear optical responses in the graphene plasmonic coupler make this configuration an ideal platform for the development of alternative frequency generators and for signal processing at midinfrared and terahertz frequencies.

We demonstrate that interfaces can play a significant role in overcoming the diffusive and subdiffusive nature of exciton transport in organic semiconductors. By designing interfaces with an imbalance between the forward and reverse rates of energy transfer, the interface can act as a gate, thereby directing exciton transport. While previous work has examined from a theoretical perspective the function of multiple exciton gates arranged in series, we provide a combined theory-experiment treatment that permits an assessment of the utility of exciton-permeable gating interfaces in optoelectronic devices. The required asymmetry in interfacial-exciton-transfer rates is realized by engineering a molecular site imbalance. The impact of interfaces on exciton transport is considered by optically injecting excitons into the gating architecture, and detecting those that migrate through the structure using a luminescent sensitizer. For exciton transport in the archetypical organic fluorescent dye 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10(2-benzothiazolyl) quinolizino-[9,9a,1gh] coumarin (C545T) diluted in the wide-gap organic semiconductor p-bis(triphenylsilyl)benzene (UGH2), a more than 200% improvement in transport efficiency is found in an architecture with properly optimized gates compared to a neat film of C545T.

We investigate the impact of the combined diamond heat-spreading layer and microfluidic convection on the performance of a model electronic chip heated locally. Experiments are carried out and a finite element method is used to simulate the thermal response of the device under transient step-wise (without flow) and steady-state (with flow) operation conditions up to heat flux values of 38 and $190\mathrm{W}/{\mathrm{cm}}^2$, respectively. In all cases, the temperature on the heated outer silicon surface did not exceed 100°C. The temperature field contour has an oval shape for transient heating without flow and a funnel shape for steady-state heating with flow. For a step-wise heat flux of $38\mathrm{W}/{\mathrm{cm}}^2$, the differences between temperatures at the center of the resistor and at the outer surface edge after a time interval of 8 s are 5, 3, and 1°C for the chips without a diamond layer, with a 100-µm diamond layer, and only a 400-µm diamond, respectively, which proves the enhanced spreading due to the diamond layer. Under steady-state conditions at a heat flux of $190\mathrm{W}/{\mathrm{cm}}^2$ and volumetric flow rates of water between 2 and 5 ml/min, the surface temperature decreases by approximately15% for silicon wafer with a 100-µm diamond layer and by approximately 22% for a 400-µm diamond as compared to heating without the addition of diamond. Of crucial importance is the proximity of the diamond layer to the heat source, which makes this method advantageous over other thermal management procedures, especially for pulsed operating conditions and hot spots.

Many hydrogen-bonded organic ferroelectrics exhibit low-field switching of large spontaneous polarizations. Although the switchable electric dipoles of π-conjugated organic molecules account for the large spontaneous polarizations, their relevant optoelectronic processes have not been used to probe the ferroelectricity. We show that the variation in electro-optic response enables visualization of the ferroelectric domains and domain walls in single-crystal films of a hydrogen-bonded molecular cocrystal. Highly sensitive and rapid visualization is realized by difference optical image sensing between the forward and reverse field applications. We call this technique “ferroelectrics field modulation imaging (FFMI).” The unique optical-probe nature reveals the existence of two types of domain walls showing different three-dimensional orientations within the films; one is roughly perpendicular to the film plane, whereas the other is considerably tilted from the normal to the plane. We explain that both of the domain walls are stabilized to generate substantial neutrality by being directed parallel to the direction of polarization. This study opens a route for exploring the three-dimensional topological nature of domain walls in ferroelectric materials.

Surface acoustic waves (SAWs) propagating on magnetostrictive ferromagnets can induce magnetization reversal: their weak damping and mature technology make them ideal for remote wave control of magnetic bits. Experimental demonstrations of this spectacular coupling have so far required the simultaneous application of a static magnetic field. We show here SAW-driven all-acoustic switching (AAS) over millimetric distances. It relies on the triggering of magnetization precession of a uniaxial in-plane magnetized film by acoustic ferromagnetic resonance at zero field. Moreover, the absence of a biasing field enables toggling between the two equilibrium magnetic states for over 20 consecutive acoustic pulses. This proof-of-concept opens up an alternative path to magnetic-bit manipulation.

The interfacing of quantum platforms via photonic links is a precursor for establishing scalable quantum networks. The connection of different types of quantum memories for hybrid networking requires the overcoming of the disparate photon wavelengths emitted by each quantum memory. Given achievements in quantum information processing with trapped-ion and neutral-atom architectures, a hybrid system with modular interconnectivity is advantageous. Here, we use a trapped ${}^{138}{\mathrm{Ba}}^{+}$ ion and a periodically poled lithium-niobate (PPLN) waveguide, with a fiber-coupled output, to demonstrate 19% end-to-end efficient quantum frequency conversion (QFC) of single photons from 493 to 780 nm and use fluorescence of the ion to produce light at the ${}^{87}\mathrm{Rb}{D}_2$ transition wavelength. To demonstrate the quantum nature of both the unconverted 493 nm photons and the converted photons near 780 nm, we observe strong quantum statics in their respective second-order intensity correlations. This work extends the range of intralaboratory networking between ions and networking between disparate quantum memories.

Achieving simultaneous control of the amplitude and phase of a metasurface, especially in transmission geometry, is very essential in modern photonic research. An alternative strategy for manipulating the transmissive amplitude and phase is proposed by using a three-layered element. Two outer orthogonal gratings of the element can determine the transmissive polarization while the center modified I-shaped particle achieves a high-efficiency linear polarization conversion. We can control the transmissive phase by modulating the gap size of the modified I-shaped structure, and manipulate the transmissive amplitude by rotating the structure. As a proof of concept, we design a fan-shaped beam metasurface by using a genetic algorithm to obtain the optimal phase and amplitude distributions. The results show that the metasurface can generate a flat top (azimuthal angle range is −40° to 40°) beam under rectangular coordinates within 9.1–10.9 GHz. Our findings offer possibilities to realize arbitrary beam shapes, which not only widen the areas for shaping a wavefront by metasurfaces, but also offer an economical and simple alternative for a beam-forming array antenna.

Three-dimensional (3D) confocal imaging of multiphase flows in a network of microcapillaries is used to conceptualize and quantify the mobilization process of an oleic wetting viscous phase by aqueous nanofluids and surfactant solutions. This microscale visualization reveals that nanoparticles decrease the thickness of wetting-phase film. The efficiency of surfactants in oil mobilization results from their capability to break the wetting phase into smaller ganglia. The type of injectant significantly influences the size of the clusters and the distribution of the wetting phase. We show that the mean size of the wetting phase clusters is a decreasing function of the displacement efficiency for each solution. Incorporation of silica nanoparticles with surfactant solutions hinders the wetting phase break up and decreases the number of clusters. The most frequently occurring cluster size (mode) decreases in the presence of surfactants, but remains unchanged in the presence of silica nanoparticles. Unlike the average cluster size, which is a decreasing function of the nonwetting phase saturation, it is interesting that the mode remains almost unchanged during the displacement process. The reduction of wetting film thickness and the fragmentation of wetting phase have numerous applications in natural and engineering sciences.

We investigate new phenomena in elastic wave propagation in metamaterials characterized by long-range interactions. The kind of waves in this context reveal wave-stopping, negative group velocity, instability, and hypersonic or superluminal effects both for instantaneous and for nonlocal retarded actions. Closed-form results are presented and a universal propagation map synthesizes the expected properties of these materials. Perspectives in physics, engineering, and social dynamics are discussed.

This paper presents experimental evidence for the existence of acoustic valley Hall edge (AVHE) states in topological elastic waveguides. The fundamental lattice is assembled on the basis of a nonresonant unit where space-inversion symmetry (SIS) is broken by our simply perturbing the underlying lattice geometry. This aspect is in contrast with existing elastic AVHE designs that exploit locally resonant units and require the addition of masses to break SIS. The experimental results presented in this study validate findings so far presented only at the theoretical and numerical level. In particular, it is found that edge modes can effectively propagate along domain walls between topologically dissimilar domains and that disorder-induced backscattering is substantially suppressed due to the weak coupling between oppositely-valley-polarized modes. The coupling between valley modes is further investigated and linked to an evident chiral flux of the mechanical energy. Finally, we show that the weak coupling between the valleys can be exploited to achieve selective mode injection at the domain wall, hence realizing a very effective excitation strategy for the chiral edge states.

Digital holographic tomography (DHT) can measure the 3D refractive-index map of a microscopic specimen. To obtain the 3D map using a 2D camera, existing methods scan the angle of illumination, rotate the sample, scan the objective-lens focus, or change the wavelength. Here, we present a snapshot DHT technique that does not rely on a scanning mechanism. Using a technique named snapshot holographic optical tomography (SHOT), we acquire the 3D refractive-index maps of a polystyrene bead and a single Henrietta Lacks (HeLa) cell.