Using continuum elasticity theory, we describe the elastic behavior of helical coils with an asymmetric double-helix structure and identify conditions under which they become very rigid. Theoretical insight gained for macrostructures including a stretched telephone cord and an unsupported helical staircase is universal and of interest for the elastic behavior of helical structures on the micrometer and nanometer scale.

A solvent-free printing process for printed electronics is successfully developed using toner-type patterning of organic semiconductor toner particles and the subsequent thin-film formation. These processes use the same principle as that used for laser printing. The organic thin-film transistors are prepared by electrically distributing the charged toner onto a Au electrode on a substrate film, followed by thermal lamination. The thermal lamination is effective for obtaining an oriented and crystalline thin film. Toner printing is environmentally friendly compared with other printing technologies because it is solvent free, saves materials, and enables easy recycling. In addition, this technology simultaneously enables both wide-area and high-resolution printing.

While antiferromagnets have been proposed as components to limit stray magnetic fields, their inability to be spin polarized inhibits their use in spintronic devices. Compensated ferrimagnets are a unique solution to this dilemma since they have zero net moment, but their nonsymmetric density of states allows the achievement of high spin polarization. Density-functional theory predicts ${\mathrm{Mn}}_3\mathrm{Al}$ in the $D{0}_3$ structure to be fully compensated and retain half-metallicity at room temperature. In this work, 50-nm ${\mathrm{Mn}}_3\mathrm{Al}$ thin films are synthesized using molecular beam epitaxy and annealed at various temperatures in order to investigate their magnetic properties. Magnetometry measurements confirm the high Curie temperature of 605 K. Polarized-neutron reflectometry (PNR) indicates a low net magnetic moment, along with depth profiles of the structure and magnetization. From the PNR data, a saturation moment of $0.11\pm 0.04{\mu }_B/\mathrm{f}.\mathrm{u}.$ is extracted, confirming the nominal zero moment present in these thin films.

The chemical and physical input signals characteristic of micro- and nanofluidic devices operating in ionic solutions should eventually be translated into output electric currents and potentials that are monitored with solid-state components. This crucial step requires the design of hybrid circuits showing robust electrical coupling between ionic solutions and electronic elements. We study experimentally and theoretically the connectivity of the nanofluidic diodes in single-pore and multipore membranes with conventional capacitor systems for the cases of constant, periodic, and white-noise input potentials. The experiments demonstrate the reliable operation of these hybrid circuits over a wide range of membrane resistances, electrical capacitances, and solution $p\mathrm{H}$ values. The model simulations are based on empirical equations that have a solid physical basis and provide a convenient description of the electrical circuit operation. The results should contribute to advance signal transduction and processing using nanopore-based biosensors and bioelectronic interfaces.

The scattering of sound by finite and infinite chains of equally spaced perforated metallic cylindrical shells in an ideal (inviscid) and viscous fluid is theoretically studied using rigorous analytical and numerical approaches. Because of perforations, a chain of thin shells is practically transparent for sound within a wide range of frequencies. It is shown that strong scattering and redirection of sound by 90° may occur only for a discrete set of frequencies (Wood’s anomalies) where the leaky eigenmodes are excited. The spectrum of eigenmodes consists of antisymmetric and symmetric branches with normal and anomalous dispersion, respectively. The antisymmetric eigenmode turns out to be a deaf mode, since it cannot be excited at normal incidence. However, at slightly oblique incidence, both modes can be resonantly excited at different but close frequencies. The symmetric mode, due to its anomalous dispersion, scatters sound in the “wrong” direction. This property may find an application for the splitting of the two resonant harmonics of the incoming signal into two beams propagating along the chain in the opposite directions. A chain of perforated cylinders may also be used as a passive antenna that detects the direction to the incoming signal by measuring the frequencies of the waves excited in the chain. Calculations are presented for aluminum shells in viscous air where the effects of anomalous scattering, redirection, and signal splitting are well manifested.

We present a polarization, spectrally, and spatially resolved near-field photoluminescence (PL) measurement technique and apply it to the study of wide $m$-plane ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}/\mathrm{GaN}$ quantum wells grown on on-axis and miscut GaN substrates. It is found that PL originates from localized states; nevertheless, its degree of linear polarization (DLP) is high with little spatial variation. This allows an unambiguous assignment of the localized states to ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ composition-related band potential fluctuations. Spatial PL variations, occurring due to morphology features of the on-axis samples, play a secondary role compared to the variations of the alloy composition. The large PL peak wavelength difference for polarizations parallel and perpendicular to the $\mathbf{c}$ axis, the weak correlation between the peak PL wavelength and the DLP, and the temperature dependence of the DLP suggest that effective potential variations and the hole mass in the second valence-band level are considerably smaller than that for the first level. DLP maps for the long wavelength PL tails have revealed well-defined regions with a small DLP, which have been attributed to a partial strain relaxation around dislocations.

Optical gratings are created by flexoelectric domains in a bent-core nematic liquid crystal. A unique feature of this structure is that its wavelength can be controlled by the amplitude of the applied voltage, as demonstrated by polarizing microscopy and light diffraction techniques. In order to understand the reaction of the system to the voltage change, the dynamics of the switching process is studied via digital processing of recorded image sequences. It is shown that the characteristics and the switching mechanisms are different if the lower voltage level is below or above the threshold of pattern onset. In both cases, the response to increasing voltage levels is much slower than the response to decreasing voltage levels.

We measure the spectra of resonant Raman scattering and doping-induced absorption of pristine films of the $\pi$-conjugated donor-acceptor ($D\text{−}A$) copolymer, namely, thieno[3,4 b]thiophene-alt-benzodithiophene (PTB7), as well as photoinduced absorption spectrum in a blend of PTB7 with fullerene phenyl–C61–butyric acid methyl ester molecules used for organic photovoltaic (OPV) applications. We find that the $D\text{−}A$ copolymer contains six strongly coupled vibrational modes having relatively strong Raman-scattering intensity, which are renormalized upon adding charge polarons onto the copolymer chains either by doping or photogeneration. Since the lower-energy charge-polaron absorption band overlaps with the renormalized vibrational modes, they appear as antiresonance lines superposed onto the induced polaron absorption band in the photoinduced absorption spectrum but less so in the doping-induced absorption spectrum. We show that the Raman-scattering, doping-, and photoinduced absorption spectra of PTB7 are well explained by the amplitude mode model, where a single vibrational propagator describes the renormalized modes and their related intensities in detail. From the relative strengths of the induced infrared activity of the polaron-related vibrations and electronic transitions, we obtain the polaron effective kinetic mass in PTB7 using the amplitude mode model to be approximately $3.8{\mathit{m}}^{*}$, where ${\mathit{m}}^{*}$ is the electron effective mass. The enhanced polaronic mass in PTB7 may limit the charge mobility, which, in turn, reduces the OPV solar-cell efficiency based on the PTB7-fullerene blend.

Degenerate band-edge (DBE) modes are known for their exceptionally high field intensity at the nearly flat dispersion-diagram profile. Because of the latter property, resonances supported by these modes are associated with a very strong field at the band edge. DBE modes and similar resonances of this class have been typically realized by introducing anisotropic dielectric slabs in volumetric photonic crystals. By contrast, in this paper, we present an analytic model of DBE modes using a simple set of nonidentical coupled transmission lines. The unequal phase velocities of the supported waves supported by these transmission lines lead to mode degeneracy, that in turn provide quartic solutions of dispersion ($\omega \text{−}\beta$) relations. The DBE mode appears as one these quartic solutions. As such, the proposed model generalizes the concept of DBE modes using the construct of nonidentical coupled transmission lines. In this paper, we also propose a propagation medium using a dual pair of nonidentical transmission lines. The medium is referred to as a “butterfly” structure and is composed of four coupled transmission lines. These four coupled transmission lines generate the ${\mathrm{TM}}_{01}$-like degenerate band-edge mode. This is done by coupling the TE modes supported on each pair of the transmission lines. Mode purity at the resonance frequency and the intense field profile on the axis are properties that can be exploited for high-power microwave sources.

W-doped ZnO films are synthesized by pulsed laser deposition on ${\mathrm{Al}}_2{\mathrm{O}}_3(11\overline{2}0)$ substrate, and their gas-sensing properties are investigated. Significantly improved sensitivity and response time to ethanol vapor are achieved. In order to study the relation between high sensing performance and local structure around the dopant W site, we carry out two-dimensional photoelectron diffraction on W-doped ZnO thin films at two different annealing temperatures (600 and $1000°\mathrm{C}$). The photoelectron-intensity angular-distribution (PIAD) patterns of Zn $3p$ and W $4f$ core levels show the presence of forward-focusing peaks of very different relative intensities in the bulk and surface. From the PIAD patterns and their circular dichroism, we find clear evidence for the substitution of a segregated W atom into a Zn site in the second atomic layer. The result shows a direct relationship between the drastic increase in gas-sensing performance via W doping and the segregation of W at the surface. It also demonstrates that this photoelectron-diffraction measurement is a powerful tool for the study of the local structure of dopant sites in gas-sensing materials.

Using frequency-modulated electrically detected magnetic resonance (EDMR), we show that signals measured from lightly doped ($1.2–5\times 10^{15}{\mathrm{cm}}^{-3}$) silicon devices vary significantly with the wavelength of the optical excitation used to generate the mobile carriers. We measure EDMR spectra at 4.2 K as a function of modulation frequency and applied microwave power using a 980-nm laser, a 405-nm laser, and a broadband white-light source. EDMR signals are observed from the phosphorus donor and two distinct defect species in all of the experiments. With near-infrared irradiation, we find that the EDMR signal primarily arises from donor-defect pairs, while, at higher photon energies, there are significant additional contributions from defect-defect pairs. The contribution of spins from different spatial regions to the EDMR signal is seen to vary as the optical penetration depth changes from about 120 nm at 405-nm illumination to $100\mu \mathrm{m}$ at 980-nm illumination. The modulation frequency dependence of the EDMR signal shows that the energy of the optical excitation strongly modulates the kinetics of the underlying spin-dependent recombination (SDR) process. Careful tuning of the optical photon energy could therefore be used to control both the subset of spin pairs contributing to the EDMR signal and the dynamics of the SDR process.

Currently, there is increasing interest from many scientific disciplines in the development of systems that are able to sort and arrange many objects in parallel at the nano- and micrometric scale. Among others, photovoltaic tweezers (PVT) are an optoelectronic technique for trapping and patterning nano- and micro-objects in accordance with an arbitrary light profile. In this work, the differential features of electro- and dielectrophoretic (EP and DEP) nanoparticle (NP) patterning using PVT are deeply investigated. The study is carried out through theory and experiments. The developed theory extends the applicability of a previously reported model to be able to compute EP potentials and to obtain numerical values for the EP and DEP potential energies. Two-dimensional patterns of charged and neutral aluminum NPs are fabricated on top of $\mathrm{Fe}:{\mathrm{LiNbO}}_3$ crystals, and different light distributions and other experimental parameters (crystal thickness and NP concentration) are compared. Patterns of charged and neutral NPs show remarkable differences in both particle density distribution and fidelity to the original light profile. The observed different features between EP and DEP trapping are satisfactorily explained by the theoretical analysis. The results provide routes for the optimization of the NP arrangements for both regimes.

Though ${\mathrm{Cu}}_2{\mathrm{ZnSnS}}_4$ (CZTS) is a promising material for thin-film solar cells, a significant challenge remains in understanding the structures being formed, particularly in nonstoichiometric materials. We use the extended x-ray absorption fine-structure technique to study the local structure and stoichiometry of as-made, Cu-deficient CZTS nanoparticles and present $K$-edge data and fits for each of the cations (Cu, Zn, and Sn). The data show that all of the metal-S ($M\text{−}\mathrm{S}$) pairs have the bond lengths of the kesterite structure within 0.02 Å, and the pair distribution function is very narrow ($\sigma \sim 0.07\AA$). These results preclude significant fractions of other phases with different $M\text{−}\mathrm{S}$ bond lengths. The data also reveal some Sn second neighbors around Sn, whereas there are none in the stoichiometric kesterite (or stannite) structure. Consequently, Sn antisite defects must be present on Cu or Zn sites; this is not surprising since there is some excess of Sn. More importantly, the second-neighbor Sn-Sn distance is significantly longer than other $M\text{−}M$ distances, and the antisite Sn defects must therefore introduce significant disorder within the Cu and Zn sublattices. The largest distortions are found around Cu and are modeled using a strongly broadened (or split) peak distribution for the $\mathrm{Cu}\text{−}\mathrm{Cu}/\mathrm{Zn}$ pairs. We also find that excess Zn does not occupy Cu sites but instead, goes onto Sn sites. The samples are best described as a kesterite structure with significant antisite disorder.

Precise measurements are the key to advances in all fields of science. Quantum entanglement shows higher sensitivity than that which is achievable by classical methods. Most physical quantities including position, displacement, distance, angle, and optical path length can be obtained by optical phase measurements. Reducing the photon wavelength of the interferometry can further enhance the optical-path-length sensitivity and imaging resolution. By quantum frequency up-conversion, we realize a short-wavelength two-photon number entangled state. Nearly perfect Hong-Ou-Mandel interference is achieved after both 1547-nm photons are up-converted to 525 nm. Optical phase measurement of the two-photon entanglement state yields a visibility greater than the threshold to surpass the standard quantum limit. A spectra change of the photon pair after being up-converted is observed and well explained. These results offer alternative ways for high-precision quantum metrology using a short-wavelength quantum entanglement number state and offer a potential all-optical spectra engineering technique for the photon pair source.

We study the spatiotemporal dynamics of a microfluidic system with a nonselective microfluidic channel gated by an ion-selective membrane which separates the ion flux paths of cations and anions. To preserve electroneutrality, the ionic concentration in the system is shown to converge to a specific inhomogeneous distribution with robust constant current fluxes. A circuit scaling theory that collapses measured asymptotic currents verifies that this is a generic and robust mechanism insensitive to channel geometry, ion selectivity, and electrolyte ionic strength. This first temporally stationary but spatially inhomogeneous depletion front can be used for modulating ionic current and for isotachophoretic isolation of low-mobility molecules and exosomes on small diagnostic chips for various medical applications that require robust high-throughput and integrated platforms.

It is demonstrated by analytical calculations and micromagnetic simulations that a microwave pumping by means of a voltage-controlled magnetic anisotropy (VCMA) could excite propagating spin waves in a ferromagnetic nanowire with in-plane static magnetization, and only the parametric excitation is possible. The efficiency of the parametric excitation is proportional to the out-of-plane component of the dynamic magnetization, and it is nonvanishing in the entire range of spin-wave wave vectors. This property ensures the excitation of spin waves in a wide frequency range (up to tens of gigahertz) using practically achievable amplitudes of the VCMA pumping. For a $\mathrm{Fe}/\mathrm{MgO}$ nanowire, the threshold of parametric excitation of spin waves lies in the range $0.5–1\mathrm{V}/\mathrm{nm}$ and only weakly depends on the nanowire width.

Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard ${\mathrm{AlO}}_x$ tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin ${\mathrm{Al}}_2{\mathrm{O}}_3$ tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial ${\mathrm{H}}_2\mathrm{O}$ pulse hydroxylated the Al surface and enabled the creation of an atomically thin ${\mathrm{Al}}_2{\mathrm{O}}_3$ tunnel barrier with a high-quality $M\text{−}I$ interface and a significantly enhanced barrier height compared to thermal ${\mathrm{AlO}}_x$. These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition ${\mathrm{Al}}_2{\mathrm{O}}_3$ is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions.

Color centers in silicon carbide have increasingly attracted attention in recent years owing to their excellent properties such as single-photon emission, good photostability, and long spin-coherence time even at room temperature. As compared to diamond, which is widely used for hosting nitrogen-vacancy centers, silicon carbide has an advantage in terms of large-scale, high-quality, and low-cost growth, as well as an advanced fabrication technique in optoelectronics, leading to prospects for large-scale quantum engineering. In this paper, we report an experimental demonstration of the generation of a single-photon-emitter array through ion implantation. $V_{\mathrm{Si}}$ defects are generated in predetermined locations with high generation efficiency (approximately $19\%\pm 4\%$). The single emitter probability reaches approximately $34\%\pm 4\%$ when the ion-implantation dose is properly set. This method serves as a critical step in integrating single $V_{\mathrm{Si}}$ defect emitters with photonic structures, which, in turn, can improve the emission and collection efficiency of $V_{\mathrm{Si}}$ defects when they are used in a spin photonic quantum network. On the other hand, the defects are shallow, and they are generated about 40 nm below the surface which can serve as a critical resource in quantum-sensing applications.

We present a theory for analyzing the phase stability of a spin-torque oscillator (STO) stabilized by a phase-locked-loop (PLL) circuit using the STO’s free-running performance and circuit parameters. We show that the linewidth measured on a spectrum analyzer, which is the most commonly used performance indicator for the phase stability of a free-running STO, is not useful for estimating the phase stability of a phase-locked STO. A more important value is the STO’s frequency-error spectral density (FESD) around the PLL bandwidth. We calculate the residual phase-error spectral density (PESD) of the phase-locked STO output signal using the actual FESD of the free-running STO and circuit parameters under three different conditions, and obtain excellent agreement with experimental results. This theoretical model allows one to predict the phase error of a STO stabilized by a PLL circuit, thus giving useful guidance for designing a PLL circuit and developing a STO. The theory indicates that a reduction of the STO’s FESD around the PLL bandwidth, which is governed by the thermal stability of the STO, is of prime importance for further improvement of the STO’s signal quality under phase-locked oscillation.