Dropwise condensation (DWC) on non-wetting surfaces has remarkable potential to enhance heat transfer performance compared to filmwise condensation on wetting substrates. In this article, we discuss important recent developments and challenges in the field of DWC, including durability of DWC-promoting coatings, DWC of low surface tension fluids, physical mechanisms governing DWC, unconventional methods

Developing an unbreakable cryptography is a long-standing question and a global challenge in the internet era. Photonics technologies are at the frontline of research, aiming at providing the ultimate system with capability to end the cybercrime industry by changing the way information is treated and protected now and in the long run. Such a perspective discusses some of the current challenges as well

Over the past few decades, glass-ceramics doped with transition metals have become promising materials for the development of active and passive optical functional devices, including a wide variety of commercial applications due to their unique properties. In this Perspective paper, the intrinsic advantages of these composite materials are outlined, and we provide an overview of recent and on-going

If a picture tells a thousand words, then we might ask ourselves how many photons does it take to form a picture? In terms of the transmission of the picture information, then the multiple degrees of freedom (e.g., wavelength, polarization, and spatial mode) of the photon mean that high amounts of information can be encoded such that the many pixel values of an image can, in principle, be communicated

As an absorber in photovoltaic devices, Sb2Se3 has rapidly achieved impressive power conversion efficiencies despite the lack of fundamental knowledge about its electronic defects. Here, we present a deep level transient spectroscopy (DLTS) study of deep level defects in both bulk crystal and thin film device material. DLTS study of Bridgman-grown n-type bulk crystals revealed traps at 358, 447, 505

Acoustic holograms can be used to form complex distributions of pressure in 3D at MHz frequencies from simple inexpensive ultrasound sources. The generation of such fields is vital to a diverse range of applications in physical acoustics. However, at present, the application of acoustic holograms is severely hindered by the static nature of the resulting fields. In this work, it is shown that by intentionally

CH3NH3PbI3 (MAPbI3) perovskite materials hold considerable promise for future low cost, high-efficiency solar cells, and replacement materials for toxic lead have also been in demand. In this study, the optical constants, absorption coefficients, and interband electron transitions of MAPb1−xSnxI3 (x = 0, 0.4, 0.8, and 1) films have been analyzed by spectroscopic ellipsometry in the photon range of

Antimonene nanosheets are obtained by laser irradiation of antimony powder in isopropyl alcohol and the thicknesses of antimonene nanosheets are around 4–12 nm. The nonlinear optical responses of the samples are probed by a z-scan measurement employing a nanosecond laser pulse. The competition between saturable absorption and reverse saturable absorption at 532 nm is confirmed in the dispersion of

It has been established that hydrogen (H) plays a key role in p-type doping of GaN and it must be removed by dissociation of the Mg–H complex in order to achieve p-type conductivity. However, in carbon (C)-doped semi-insulating GaN, which is the core component of power electronic devices, the role of H, especially the formation and dissociation process of C–H defects, has remained to date a mystery

The evolution of surface morphology for single-crystal bulk Al-polar aluminum nitride substrates during ex situ cleaning, in situ cleaning, and subsequent homoepitaxy is investigated. Ex situ acid treatment is found to reveal atomic steps on the bulk AlN substrates. After in situ Al-assisted cleaning at high temperatures in a high vacuum environment monitored with reflection high-energy electron diffraction

We differentiate the effect of strain induced by lattice-mismatched growth from strain induced by mechanical deformation on cubic nonradiative Auger recombination in narrow-gap GaInAsSb/GaSb quantum well (QW) heterostructures. The typical reduction in the Auger coefficient observed with lattice-mismatched growth appears to be due to the concomitant compositional change rather than the addition of strain

Spectral ellipsometry is a useful technique allowing fast, nondestructive, and contactless characterization of thin films and constituent materials. In this Letter, we show that both the linear magneto-optic Kerr effect (LinMOKE, proportional to the magnetization M) and the quadratic MOKE (QMOKE, proportional to M 2) can be a useful extension of spectral ellipsometry and are able to sense the crystallographic

Topological order of magnetic films shows promise due to its unconventional electromagnetic transport effects, but the discontinuity and the miniaturization of patterned magnetic films impose a limit on research of topological properties. In this article, a technique is proposed, the application of which improves the ease of electrical measurement in sub-micrometer-sized magnetic thin film elements

The response of magnetic nanoparticles (MNPs) in a liquid to an alternating magnetic field is complicated because the rotational motions of both the magnetic moment in the MNP (internal rotation) and the MNP itself (physical rotation) affect each other. It is necessary to elucidate the mechanisms of these rotation behaviors for the success of the recent bio-applications of MNPs. However, the experimental

We perform micromagnetic simulations to investigate the propagation of spin-wave beams through spin-wave optical elements. Despite spin-wave propagation in magnetic media being strongly anisotropic, we use axicons to excite spin-wave Bessel–Gaussian beams and gradient-index lenses to focus spin waves in analogy to conventional optics with light in isotropic media. Moreover, we demonstrate spin-wave

Using bilayer films of β-Ta/Ni0.8Fe0.2, we fabricate structures consisting of two, three, and four crossing ellipses, which exhibit shape-induced bi-axial, tri-axial, and quadro-axial magnetic anisotropy in the crossing area, respectively. Structures consisting of N crossing ellipses can be stabilized in 2N remanent states by applying (and removing) an external magnetic field. However, we show that

In this combined experimental and theoretical work, we report on the evolution of the skyrmion radius and its destruction in the system Co/Ru(0001) when an out-of-plane magnetic field is applied. At low fields, skyrmions are metastable and display an elliptical instability in which along the short axis, the spin texture approaches that of the spin-spiral phase and the long axis expands in order to

Asymmetric spin relaxation induced by the residual electron spin in semiconductor quantum dots (QDs) adjacent to a superlattice (SL) was studied using spin- and time-resolved photoluminescence under the selective photoexcitation of the SL miniband states. Spin-polarized electrons were photoexcited in the SL barrier and then injected into the QDs through spin-conserving tunneling. The spin-polarized

The accurate understanding of flux dynamics is essential for the design and operation of superconducting circuits. Time evolution of flux-density distribution in an NbN strip by the transport current was observed using high-speed magneto-optical microscopy. It was determined that even for the dynamic penetration and exclusion of vortices under the transport current, the surface barrier is essential

Below its Neél temperature, the frustrated magnet CdCr2O4 exhibits an antiferromagnetic spin-spiral ground state. Such states can give rise to a sizable magnetoelectric coupling. In this report, we measure the electric polarization induced in single-crystalline CdCr2O4 by large applied magnetic field. Because the detection of a macroscopic polarization is hindered by the structural domains in the tetragonal

Quenching has been demonstrated to increase the thermal stability of the piezoelectric properties of relaxor (1−x)Na1/2Bi1/2TiO3-xBaTiO3 (NBTxBT) by 40 °C. This work establishes a correlation between the quenching temperature and salient electrical (conductivity, piezoelectric and dielectric) properties of two NBTxBT variants. The impact of quenching on the mechanical properties is quantified in terms

Conductive and electrostatic atomic force microscopy (cAFM and EFM) are used to investigate the electric conduction at nominally neutral domain walls in hexagonal manganites. The EFM measurements reveal a propensity of mobile charge carriers to accumulate at the nominally neutral domain walls in ErMnO3, which is corroborated by cAFM scans showing locally enhanced direct current conductance. Our findings

Coherent acoustic phonon dynamics in single-crystalline bismuth nanofilms transferred to a glass substrate were investigated with ultrafast pump–probe spectroscopy. Coherent phonon signals were substantially enhanced by more than four times when compared with as-grown films on Si (111) substrates. Furthermore, more than 10% reduction of the acoustic phonon velocity was observed when the film thickness

Antimonene, one of the group V elemental monolayers, has attracted intense interest due to its intriguing electronic properties. Here, we present the optical absorption properties of atomically flat antimonene for which the directional bonds between Sb atoms appear to be analogous to C–C bonds in graphene. The results, based on first-principles density functional theory calculations, predict the absorbance

High-crystalline halide perovskite nanostructures [such as nanowires and nanoplates (NPs)] provide good potential in realizing nanoscale solid light sources for on-chip optical communication, high-density storage, and life science applications. However, it remains a great challenge to fabricate nanoscale perovskite light-emitting devices using traditional fabrication methods because the perovskite

The quantum charge transport calculations at metal–molecule–metal junctions lead to various electronic properties suitable in the field of miniaturization. Finite bias-dependent conductivity is calculated through porphyrin, hexaphyrin, and hexathia[26π]annulene molecular junction devices connected to the metallic or semiconducting electrode using non-equilibrium Green's function technique based on

The cathodoluminescence (CL) of organo-lanthanide complexes is studied as a modeling of beta luminescence. It is found that complexes of Sc, La, and lanthanides with anionic ÔO, ÔN bidentate and O-monodentate ligands under excitation by fast electrons display luminescence of various intensities. In the spectra of Sc, La, Nd, Er, and Tm compounds, only broadened bands of the ligands peaked about 450 nm

Bound states in the continuum (BICs) have received increasing attention from researchers because of their potential applications in photonic crystal fibers, as well as in lasing, sensing, and surface acoustic wave devices. BICs have been experimentally observed in acoustic resonators, photonic crystal slabs, and optical waveguides. Herein, we constructed a topological inductor–capacitor (LC) circuit

The presence of instabilities in a low density, low temperature plasma expanding through an axially symmetric magnetic nozzle is investigated in the context of non-classical electron cross field transport. Electrostatic probes are used to characterize the background plasma properties and instabilities. The measurements show a primarily azimuthally propagating mode with a broad, incoherent power spectrum

The ability to achieve strong-coupling has made cavity-magnon systems an exciting platform for the development of hybrid quantum systems and the investigation of fundamental problems in physics. Unfortunately, current experimental realizations are constrained to operate at a single frequency, defined by the geometry of the microwave cavity. In this article we realize a highly tunable, cryogenic, microwave

Acoustic tweezers (ATs) have been extensively exploited in physics, biology, chemistry, and medical medicine. However, previous ATs are limited by complex designs and cumbersome configurations, and the stable manipulation of Mie particles remains challenging. Here, an AT based on acoustic focused petal beams (AFPBs) is proposed to realize 2D stable manipulations of both Rayleigh and Mie particles in

A triboelectric nanogenerator (TENG), which harvests ubiquitous ambient mechanical energy, is a promising power source for distributed energy. Recently reported new generation direct current TENG (DC-TENG) based on the air breakdown effect exhibits unique advantages over conventional modes of TENG devices, such as free-of-rectification and intrinsic switching behavior. However, owing to different working

Small scale flow energy harvesters are designed to operate at low elevations where surface effects cause significant flow velocity variations. To harness flow energy efficiently in such environments, the harvester must be very sensitive to flow fluctuations. In particular, the rise time of the harvester to the steady-state value must be short. This Letter proposes a method to reduce the rise time of

We present high-reflectivity mechanical resonators fabricated from AlGaAs heterostructures for use in free-space optical cavities operating in the telecom wavelength regime. The mechanical resonators are fabricated in slabs of GaAs and patterned with a photonic crystal to increase their out-of-plane reflectivity. Characterization of the mechanical modes reveals residual tensile stress in the GaAs device

A nanodiamond embedding a single nitrogen-vacancy (NV) center has outstanding optical properties since it is readily manipulated and coupled with nanophotonic devices. Reliable methods to identify the orientation of an NV axis on photonic platforms are important to precisely estimate the coupling efficiency between them. We report on a method to identify the orientation of an NV axis. The proposed

Frequency-angular distributions of optical signals generated via spontaneous parametric downconversion with the Stokes idler frequency shifts 0.2–5 THz are studied simultaneously with the same distributions in the anti-Stokes range while the nonlinear Mg:LiNbO3 crystal is cooled from 300 K to 4.2 K. The temperature dependencies of the angular distributions at fixed idler frequencies are analyzed using

Self-testing and semi-device independent protocols are becoming the preferred choice for quantum technologies, being able to certify their quantum nature with few assumptions and simple experimental implementations. In particular, for quantum random number generators, the possibility of monitoring, in real time, the entropy of the source only by measuring the input/output statistics is a characteristic

In this paper, we demonstrate a miniature energy harvesting wind velocity sensor of simple, low-cost construction, based on a single-degree-of-freedom galloping structure. The sensor consists of a prismatic bluff body with a triangular cross section attached to the free end of a cantilever incorporating a commercial polyvinylidene fluoride piezoelectric film. In the wind, the bluff body causes vibration

We present an experimental study of coherent high-power wakefield generation in a metamaterial (MTM) structure at 11.7 GHz by 65 MeV electron bunch trains at the Argonne Wakefield Accelerator (AWA), following a previous experiment, the Stage-I experiment, at the AWA. Both the Stage-II experiment, reported in this paper, and the Stage-I experiment were conducted using MTM structures, which are all-metal

Mid-air acoustic levitation is becoming a powerful tool to suspend and manipulate millimetric objects. Because of its unique characteristics, acoustic levitation is suitable to trap a wide variety of materials such as liquids, solids, soap bubbles, and even living creatures. Acoustic levitation can also be combined with noncontact measurement systems, allowing contactless analysis and characterization

This Perspective examines the emerging applications of photonic topological insulators (PTIs) in the microwave domain. The introduction of topological protection of light has revolutionized the traditional perspective of wave propagation through the demonstration of backscatter-free waveguides in the presence of sharp bending and strong structural defects. The pseudospin degree of freedom of light

Electric field-induced broadening and narrowing of an exciton absorption band have been observed to depend on the polarity of the applied electric field for methylammonium lead triiodide perovskite (MAPbI3) as a thin film sandwiched between a conducting film of fluorine-doped tin oxide (FTO) and an insulating film of poly(methyl methacrylate) (PMMA). The width of the absorption band increased or decreased

The Faraday rotation effect of both the La: yttrium iron garnet (YIG) film and the YIG metasurface were experimentally and numerically investigated in the terahertz (THz) region. A THz magneto-optic polarization measurement system was used to observe the transmission, resonance, and magneto-optical effect of the La:YIG film and YIG metasurface. The THz artificial chirality and resonance localization

We demonstrate electrically controlled robust state preparation of an exciton qubit by rapid adiabatic passage with Fourier-limited laser pulses. In our approach, resonant ps laser pulses are applied to generate excitonic population in a quantum dot, whereas synchronously applied ps electric transients provide a controlled sweep of the exciton transition energy. The ps electric transients applied to

Chemical etching and Al2O3 dielectric passivation were used to minimize nonradiative sidewall defects in InGaN/GaN microLEDs (mesa diameter = 2–100 μm), resulting in an increase in external quantum efficiency (EQE) as the LED size was decreased. Peak EQEs increased from 8%–10% to 12%–13.5% for mesa diameters from 100 μm to 2 μm, respectively, and no measurable leakage currents were seen in current

The voids will be formed in the physical vapor deposited (PVD)-AlN epilayer after high temperature annealing. In this work, the formation mechanism of voids and its effect on crystal quality are investigated. Based on microstructural analysis and first principles calculations, it is confirmed that (1) the dislocations mainly gather around the voids and the strain status around the voids is similar

The properties of metal/semiconductor interfaces are generally described by the metal-induced gap states (MIGS) model. However, rare-earth (RE) arsenide interfaces are found not to follow the MIGS model in having very different Schottky barrier heights (SBHs) for the Ga- or As-terminations of polar (100) or (111) RE-As/GaAs interfaces. Density function supercell calculations find this effect is due

The interfaces in oxide heterostructures that bring novel physical phenomena and functionalities have attracted great attention in fundamental research and device applications. For uncovering structure–property relationships of oxide heterostructures, direct evidence of the atomic-scale structure of heterointerfaces is highly desired. Here, we report on studying the structure of interfaces between

Liquid droplets move readily under the influence of surface tension gradients on their substrates. Substrates decorated with parallel microgrooves, or striations, presenting the advantage of homogeneous chemical properties yet varying the topological characteristics on either side of a straight-line boundary, are considered in this study. The basic type of geometry consists of hydrophobic micro-striations/rails

The growth of In2Se3/Bi2Se3 superlattices (SLs) by molecular beam epitaxy at an elevated temperature is explored. The crystalline phase structure of In2Se3 layers in the as-grown SLs is determined to be α-In2Se3. The diffusion of In from In2Se3 to Bi2Se3 is significantly promoted, while Bi diffusion into In2Se3 layers is insignificant as manifested by the in situ lattice evolution analysis, so that

Transition metal oxides exhibit an excellent photochromic property, which can be applied in optical information storage. However, the decolorization reaction hinders the formation of optical bi-stable states of the oxides. Here, we deposit WO3 nanoparticles into ZnO nanowire arrays to form a multi-site heterojunction. The heterojunction micro-interface acts as a spatially dispersed hole transport channel

Elastocaloric cooling utilizes the latent heat associated with stress-induced reversible phase transformations to achieve cooling. Currently, the key barrier to this technology is its prohibitive cost due to the high elastocaloric material cost and the large stress required to drive the cooling cycle. Vanadium (IV) oxide (VO2) is a good candidate, and it is relatively cheap. Our calorimetry study shows

Flexible transparent conductors made from networks of metallic nanowires are a potential replacement for conventional, non-flexible, and transparent conducting materials such as indium tin oxide. Cu nanowires are particularly interesting as cost-effective alternatives to Ag nanowires—the most investigated metallic nanowire to date. To optimize the conductivity of Cu nanowire networks, the resistance

Bialkali photocathodes, such as cesium potassium antimonide (CsK2Sb), can generate a high-brightness electron beam using a high-power green laser. These photocathode materials have potential applications in advanced accelerators and electron microscopes. It is known that the quantum efficiency (QE) of these photocathodes is affected severely by their substrates; however, reusability of the substrates

For the design of duct silencers, one should satisfy the essential constraints on the sound attenuation band, additional volume, and backpressure. For wideband sound attenuation, various acoustic metamaterials (AMM) using multiple resonators have been proposed. However, they often do not satisfy the spatial constraint, and the blocking of the conduit makes them impractical. This study proposes a compact

The integration of GaN on Si as large scale substrates still faces many hurdles. Besides the large difference in the lattice constant and the high thermal mismatch existing between GaN and Si, spiral hillock growth phenomena are common problems in the development of thick GaN layers. In this work, hexagonal hillocks were observed on GaN/AlGaN high-electron-mobility transistor heterostructures grown

Heterojunction band offset parameters are critical for designing and fabricating junction-based devices as these parameters play a crucial role in determining the optical and electronic properties of a device. Herein, we report the band discontinuities at the MoS2/III-nitride (InN, GaN, and AlN) heterointerfaces. Few-layer MoS2 thin films are deposited by pulsed laser deposition on III-nitrides/c-sapphire

In this study, we examined the effects of doping chlorine (Cl) into crystalline selenium (c-Se) on diminishing the tellurium-diffusion-induced shallow acceptor states associated with the dangling bonds that appear at the ends of Se chains by theoretical analysis with the first-principles calculations. In this model, the negatively charged dangling bonds can be neutralized by inserting monovalent Cl

We study the electrical and optical properties of degenerate ZnGa2O4 films grown by metalorganic chemical vapor deposition (MOCVD) on sapphire and semi-insulating films grown by pulsed laser deposition (PLD) on fused silica. After a forming-gas anneal at 700 °C, the MOCVD film is highly conducting, with a room-temperature carrier concentration of 2 × 1020 cm−3, a mobility of 20 cm2/V s, and direct

Two methods of measuring the electronic transport properties of a material are transistor DC-voltage and the Hall effect. Hall mobility measurements of normally off semiconductors can be done by electrostatic doping to lower resistance in the channel. We show that by measuring both, we can compare any value (raw measured as well as calculated data) directly to any other value along an index of FET