Nanometer Separation Research Articles

Temperature-dependent synergistic self-healing in thermoplastic-thermoset blends: Unraveling the role of thermoplastics and dynamic covalent networks

Two different self-healing approaches are studied in this work to analyze the possible contribution of each of the self-healing mechanisms at different temperatures and the possible synergetic effects between them. Thermal and mechanical properties were differently affected by the addition of each of the thermoplastic polymers. This was caused by different phase separations induced during the curing reaction in terms of size and number of the thermoplastic phase domains dispersed within the epoxy matrix and due to the different amounts of thermoplastic polymer that remain solved in the matrix. When using the vitrimeric matrix, phase separation only occurred at the nanometer scale when utilizing poly(bisphenol-A-co-epichlorohydrin) (PBAE) as a thermoplastic agent or higher contents of polycaprolactone (PCL).Self-healing capabilities showed a strong dependence on the temperature used and the type of crack. Low temperatures allowed the thermoplastic phase to flow and fill partially the cracks with moderate levels of self-healing which were only available when phases were separated. Higher temperatures allowed dynamic bonds to induce material healing reaching very high efficiencies but, more importantly, a synergic effect was observed when material was removed from the cracks. In these cases, the flow of the thermoplastic phase filled better the crack and there was an enhanced cooperation between the two healing mechanisms. At higher self-healing temperatures, materials with nanometric size phase separation enabled greater self-healing efficiencies (above 90 %) due to the vitrimeric self-healing capability while the thermoplastic phase helped fill the gaps due to material removal.

Highly Resolved and Cross‐Talk Free Multiplexed Holograms via Broadband Vectorial Interferometry

AbstractThe ever‐growing demand for ultracompact micro‐ and nano‐optics is guided by efficient applications in augmented/virtual reality, displays, and Fourier optics. The current technologies, mainly based on meta‐solutions, suffer in terms of efficiency and tunability, as well as complex and multi‐step fabrication methods that may limit their full‐scale potential. Herein, a broadband laser composed of close and highly correlated lines allows, via interference patterning, for simultaneous encoding of multiplexed, independent, and cross‐talk free holograms with nanometric separation. The reported findings show that such light, unusual for holographic recording, unlocks new features of organized collective phenomena, overcoming the usual spatial resolution limitations of the optical techniques. This approach gives promising perspectives for in situ design of reconfigurable structured optics, besides the obvious advantages of full‐scalability, easiness, cost effectiveness, and time and energy consumption.

Intermediate-Range Casimir-Polder Interaction Probed by High-Order Slow Atom Diffraction.

At nanometer separation, the dominant interaction between an atom and a material surface is the fluctuation-induced Casimir-Polder potential. We demonstrate that slow atoms crossing a silicon nitride transmission nanograting are a remarkably sensitive probe for that potential. A 15% difference between nonretarded (van der Waals) and retarded Casimir-Polder potentials is discernible at distances smaller than 51nm. We discuss the relative influence of various theoretical and experimental parameters on the potential in detail. Our work paves the way to high-precision measurement of the Casimir-Polder potential as a prerequisite for understanding fundamental physics and its relevance to applications in quantum-enhanced sensing.

The State of the Art in Constraining Axion-to-Nucleon Coupling and Non-Newtonian Gravity from Laboratory Experiments

Constraints on the Yukawa-type corrections to Newton’s gravitational law and on the coupling constant of axionlike particles to nucleons obtained from different laboratory experiments are reviewed and compared. The constraints on non-Newtonian gravity under discussion cover the wide interaction range from nanometers to millimeters and follow from the experiments on neutron scattering, measuring the Casimir force and Cavendish-type experiments. The constraints on the axion-to-nucleon coupling constant following from the magnetometer measurements, Cavendish-type experiments, Casimir physics, and experiments with beams of molecular hydrogen are considered, which refer to the region of axion masses from 10−10 to 200 eV. Particular attention is given to the recent constraints obtained from measuring the Casimir force at nanometer separation distance between the test bodies. Several proposed experiments focussed on constraining the non-Newtonian gravity, axionlike particles and other hypothetical weakly interacting particles, such as chameleons and symmetrons, are discussed.

Constraints on non-Newtonian gravity and axionlike particles from measuring the Casimir force in nanometer separation range

We obtain constraints on the Yukawa-type corrections to Newton's gravitational law and on the coupling constant of axionlike particles to nucleons following from the experiment on measuring the Casimir force between an Au-coated microsphere and a silicon carbide plate. For this purpose, both the Yukawa-type force and the force due to two-axion exchange between nucleons are calculated in the experimental configuration. In the interaction range of Yukawa force exceeding 1 nm and for axion masses above 17.8 eV, the obtained constraints are much stronger than those found previously from measuring the lateral Casimir force between sinusoidally corrugated surfaces. These results are compared with the results of other laboratory experiments on constraining non-Newtonian gravity and axionlike particles in the relevant interaction ranges.

Fabrication of uniform arrays of silver nanoparticles on silicon by electrodeposition in ethanol solution and their use in SERS detection of difenoconazole pesticide.

Surface-Enhanced Raman Scattering (SERS) is a technique currently widely used in the identification and quantification of organic and biological molecules at low concentrations, in which an important application is the detection of pesticide residues in food. To accomplish this task, SERS substrates with high Raman enhancement factor and good reproducibility are required. One of the most commonly used SERS substrates is the SERS substrate made of silver nanoparticles immobilized on a solid substrate. In this report we first present the results of electrochemical deposition of silver nanoparticles on the silicon surface using ethanol electrolyte solution. Thanks to both factors, electrochemical deposition (instead of electroless) and ethanol electrolyte (instead of aqueous), under optimal conditions, on the surface of silicon a monolayer of silver nanoparticles grew, which are uniform in shape and size and are arranged very close to each other with nanometer separation. Next we report on the use of fabricated arrays of silver nanoparticles in the role of a SERS substrate. To test the performance of the SERS substrate, the probe molecules used were molecules of difenoconazole, a well-known fungicide. Results showed that difenoconazole could be detected with a detection limit of 0.023 ppm (5.6 × 10−8 M).

Structural Forces in Mixtures of Ionic Liquids with Organic Solvents.

Using molecular dynamics simulations, we study the impact of electrode charging and addition of solvent (acetonitrile, ACN) on structural forces of the BMIM PF6 ionic liquid (IL) confined by surfaces at nanometer separations. We establish relationships between the structural forces and the microscopic structure of the confined liquid. Depending on the structural arrangements of cations and anions across the nanofilm, the load-induced squeeze-out of liquid layers occurs via one-layer or bilayer steps. The cations confined between charged plates orient with their aliphatic chain perpendicular to the surface planes and link two adjacent IL layers. These structures facilitate the squeeze-out of single layers. For both pure IL and IL-ACN mixtures, we observe a strong dependence of nanofilm structure on the surface charge density, which affects the simulated pressure-displacement curves. Addition of solvent to the IL modifies the layering in the confined film. At high electrode charges and high dilution of IL (below 10% molar fraction), the layered structure of the nanofilm is less well defined. We predict a change in the squeeze-out mechanism under pressure, from a discontinuous squeeze-out (for high IL concentrations) to an almost continuous one (for low IL concentrations). Importantly, our simulations show that charged electrodes are coated with ions even at low IL concentrations. These ion-rich layers adjacent to the charged plate surfaces are not squeezed out even under very high normal pressures of ∼5 GPa. Hence, we demonstrate the high performance of IL-solvent mixtures to protect surfaces from wear and to provide lubrication at high loads.

Interactions Between Hydrated Calcium Carbonate Surfaces at Nanoconfinement Conditions

Calcium carbonate is one of the most abundant minerals on Earth and a component of natural biogenic materials and man-made cements. The interactions between hydrated calcium carbonate surfaces at nanometer confinement are relevant in dissolution and crystallization processes as well as in adsorption of organic fluids in natural reservoirs. In this work we quantify using atomistic molecular dynamics simulations the water mediated interactions between calcium carbonate surfaces at nanometer separations. We investigate two calcium carbonate polymorphs, calcite and aragonite. We show that the adsorption behavior of water on the (1014) surface of calcite and the (001) surface of aragonite is very different. These differences are reflected in intersurface forces between the two mineral surfaces. The interactions between surfaces feature an oscillatory behavior whose origin is connected to the structuring of water at an intersurface separation <1 nm. We observe adhesion between the surfaces and demonstrate that...

Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first-order phase transition

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co substituted CaFe2As2. We use Atomic Force, Magnetic Force and Scanning Tunneling Microscopy (AFM, MFM and STM) to identify the domains and characterize their properties, finding in particular that tetragonal superconducting domains are very elongated, more than several tens of micron long and about 30 nm wide, have the same Tc than unstrained samples and hold vortices in a magnetic field. Thus, biaxial strain produces a phase separated state, where each phase is equivalent to what is found at either side of the first order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first order quantum phase transitions lead to nanometric size phase separation under the influence of strain.

Some Comments on Hydrogel and Cartilage Contact Mechanics and Friction

We discuss the origin of the low friction observed for some elastically soft materials, such as hydrogels and the human cartilage. When a soft elastic solid is squeezed against another solid in a fluid, if the nominal contact pressure is high enough, after long enough contact time the contact area percolates, resulting in islands of confined fluid. For charged surfaces, with charges of equal sign, the osmotic pressure in the area of “real contact” may be large enough to keep the surfaces separated at nanometer separation. In this case the solid contact pressure (here the osmotic pressure) in the area of “real contact” will be nearly independent of the external load. The finite surface separation in the area of “real contact” results in a very small (breakloose) friction force even after long time of stationary contact.

Shifting molecular localization by plasmonic coupling in a single-molecule mirage

Over the last decade, two fields have dominated the attention of sub-diffraction photonics research: plasmonics and fluorescence nanoscopy. Nanoscopy based on single-molecule localization offers a practical way to explore plasmonic interactions with nanometre resolution. However, this seemingly straightforward technique may retrieve false positional information. Here, we make use of the DNA origami technique to both control a nanometric separation between emitters and a gold nanoparticle, and as a platform for super-resolution imaging based on single-molecule localization. This enables a quantitative comparison between the position retrieved from single-molecule localization, the true position of the emitter and full-field simulations. We demonstrate that plasmonic coupling leads to shifted molecular localizations of up to 30 nm: a single-molecule mirage.

A Novel Electrostatic Actuator Class

Common quasi-static electrostatic micro actuators have significant limitations in deflection due to electrode separation and unstable drive regions. These actuators suffer from an operational instability, the so-called pull-in effect that limits the actuators’ travel range to one third of the electrode separation. High driving voltages and large electrode gaps are required to achieve large displacements. In our work, we present a novel electrostatic actuator class, which allows high deflections with nanometric electrode separation. The approach presented utilizes a bimorph like effective lever to transform electrostatic forces into deflection. It permits to make use of high electrostatic forces generated in small gaps and thus gives access to large actuator deflections. We demonstrate that quasi-static deflections as large as four times the gap size are possible.

Kinetic Behavior of Catalytic Active Sites Connected with a Conducting Surface through Various Electronic Coupling

Electrocatalytic model surfaces consisting of catalytically active local surface sites and conducting electrode were formed by layer-by-layer assembly of functional molecules. The strength of electronic coupling between the catalytic surface sites and the electrode was tuned by changing the length and structure of wire molecules. When cobalt(II)–tetraphenylporphyrin was employed as a model surface site, the induced activity for oxygen reduction reaction was critically dependent on the coupling strength through the wire molecules. The overall reaction kinetics was disentangled to contributions of the internal electron tunneling and the intermolecular electron transfer. In the weak coupling condition with nanometer separation between the porphyrin and electrode, the overall reaction rate was limited by coherent quantum tunneling rate inside the catalytic system. In the strong coupling condition with the closer separation, on the other hand, the activity of the catalytic sites was significantly suppressed, a...

Nanometric molecular separation measurements by single molecule photobleaching

Although considerable progress has been made in imaging distances in cells below the diffraction limit using FRET and super-resolution microscopy, methods for determining the separation of macromolecules in the 10–50nm range have been elusive. We have developed fluorophore localisation imaging with photobleaching (FLImP), based on the quantised bleaching of individual protein-bound dye molecules, to quantitate the molecular separations in oligomers and nanoscale clusters. We demonstrate the benefits of using our method in studying the nanometric organisation of the epidermal growth factor receptor in cells.

Plasmon resonance tuning using DNA origami actuation.

A strategy for an innovative, continuous and reversible LSPR tuning using DNA origami actuation to modulate the nanometric separation of two gold nanoparticles has been developed. The actuation mechanism is based on DNA hybridization, in particular three different DNA sequences were shown to induce resonance shift of up to 6 nm.

A New Physical Model for the Vacuum Field Based on Einstein’s Stimulated Emission Theory

The vacuum electromagnetic field has been a mystery ever since Hedrik Casimir [1] proposed in 1948 that it actually existed and could be measured. Many subsequent experiments [2] have confirmed that its vast field strength (over a terawatt/cm2) is real and matches quantum predictions. Radiation pressures as high as 18 psi have been measured from the reflected vacuum light between plates of 10 nanometer separation. All of this creates a mystery. The electromagnetic field strength is more than a terawatt/cm2 everywhere in the universe and yet nothing is melted, ionized or burned up by the field. This paper extracts new insight from Einstein’s famous 1917 paper, credited with the discovery of stimulated emission and still believed today. The result is a practical explanation of the vacuum field and its observed properties.

Plasmonic mode mixing in nanoparticle dimers with nm-separations via substrate-mediated coupling

We fabricate arrays of metallic nanoparticle dimers with nanometer separation using electron beam lithography and angle evaporation. These “nanogap” dimers are fabricated on thin silicon nitride membranes to enable high resolution transmission electron microscope imaging of the specific nanoparticle geometries. Plasmonic resonances of the pairs are characterized by dark-field scattering micro-spectroscopy, which enables the optical scattering from individual nanostructures to be measured by using a spatially-filtered light source to illuminate a small area. Scattering spectra from individual dimers are correlated with transmission electron microscope images and finite-difference time-domain simulations of their electromagnetic response, with excellent agreement between simulation and experiment. We observe a strong polarization dependence with two dominant scattering peaks in spectra taken with the polarization aligned along the dimer axis. This response arises from a unique Fano interference, in which the bright hybridized modes of an asymmetric dimer are able to couple to the dark higherorder hybridized modes through substrate-mediated coupling. The presence of this interference is strongly dependent on the nanoparticle geometry that defines the plasmon energy profile but also on the intense localization of charge at the dielectric surface in the nanogap region for separations smaller than 6 nm.

Lo/Ld phase coexistence modulation induced by GM1

Lipid rafts are assumed to undergo biologically important size-modulations from nanorafts to microrafts. Due to the complexity of cellular membranes, model systems become important tools, especially for the investigation of the factors affecting “raft-like” Lo domain size and the search for Lo nanodomains as precursors in Lo microdomain formation. Because lipid compositional change is the primary mechanism by which a cell can alter membrane phase behavior, we studied the effect of the ganglioside GM1 concentration on the Lo/Ld lateral phase separation in PC/SM/Chol/GM1 bilayers. GM1 above 1mol % abolishes the formation of the micrometer-scale Lo domains observed in GUVs. However, the apparently homogeneous phase observed in optical microscopy corresponds in fact, within a certain temperature range, to a Lo/Ld lateral phase separation taking place below the optical resolution. This nanoscale phase separation is revealed by fluorescence spectroscopy, including C12NBD-PC self-quenching and Laurdan GP measurements, and is supported by Gaussian spectral decomposition analysis. The temperature of formation of nanoscale Lo phase domains over an Ld phase is determined, and is shifted to higher values when the GM1 content increases. A “morphological” phase diagram could be made, and it displays three regions corresponding respectively to Lo/Ld micrometric phase separation, Lo/Ld nanometric phase separation, and a homogeneous Ld phase. We therefore show that a lipid only-based mechanism is able to control the existence and the sizes of phase-separated membrane domains. GM1 could act on the line tension, “arresting” domain growth and thereby stabilizing Lo nanodomains.

Fabrications of insulator-protected nanometer-sized electrode gaps

We developed SiO2-coated mechanically controllable break junctions for accurate tunneling current measurements in an ionic solution. By breaking the junction, we created dielectric-protected Au nanoprobes with nanometer separation. We demonstrated that the insulator protection was capable to suppress the ionic contribution to the charge transport through the electrode gap, thereby enabled reliable characterizations of liquid-mediated exponential decay of the tunneling conductance in an electrolyte solution. From this, we found distinct roles of charge points such as molecular dipoles and ion species on the tunneling decay constant, which was attributed to local structures of molecules and ions in the confined space between the sensing electrodes. The device described here would provide improved biomolecular sensing capability of tunneling current sensors.

Controlled Electroluminescence from Films Composed of Mixed Bio‐Composites and Nanotubes

Good things come in threes: A new type of light emitting bio-composites allowing for the nanometric separation of the active components is demonstrated. A protein with large host-guest capacities is used for the encapsulation of a water-soluble composite dye in a nano-sized shell, which efficiently reduces Förster resonance energy transfer and related mechanisms. Blending of this bio-composite with multi-walled nanotubes increases the charge injection efficiency, in the electro-luminescent device.