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Face masks play a critical role in reducing the transmission risk of COVID-19 and other respiratory diseases. Masks made with nanofibers have drawn increasingly more attention because of their higher filtration efficiency, better comfort, and lower pressure drop. However, the interactions and consequences of the nanofibers and microwater droplets remain unclear. In this work, the evolution of fibers made of polymers with different contact angles, diameters, and mesh sizes under water aerosol exposure is systematically visualized. The images show that capillarity is very strong compared with the elasticity of the nanofiber. The nanofibers coalesce irreversibly during the droplet capture stage as well as the subsequent liquid evaporation stage. The fiber coalescence significantly reduces the effective fiber length for capturing aerosols. The nanofiber mesh that undergoes multiple droplet capture/evaporation cycles exhibits a fiber coalescing fraction of 40%–58%. The hydrophobic and orthogonally woven fibers can reduce the capillary forces and decrease the fiber coalescing fraction. This finding is expected to assist the proper design, fabrication, and use of face masks with nanofibers. It also provides direct visual evidence on the necessity to replace face masks frequently, especially in cold environments.

CsPbBr3 quantum dots (QDs) were doped into a blend of poly(3-hexylthiophene) and indene-C60 bisadduct to fabricate bulk heterojunction polymer photodetectors. The addition of the QDs significantly increased the shunt resistance of the device, thereby suppressing the reverse leakage current and improving both the signal-to-noise ratio and the specific detectivity. The photoresponse and recovery time both decreased because of the enhanced built-in electric field and improved charge carrier mobility.CsPbBr3 quantum dots (QDs) were doped into a blend of poly(3-hexylthiophene) and indene-C60 bisadduct to fabricate bulk heterojunction polymer photodetectors. The addition of the QDs significantly increased the shunt resistance of the device, thereby suppressing the reverse leakage current and improving both the signal-to-noise ratio and the specific detectivity. The photoresponse and recovery time both decreased because of the enhanced built-in electric field and improved charge carrier mobility.

We report the fabrication of polymer grid triodes (PGTs) using C60 as the semiconducting medium. The structure, a self-assembling porous conducting polyaniline network placed between two semiconducting layers of C60, and sandwiched between two metal electrodes, demonstrates the I–V characteristics of a three terminal device in which the current is controlled by the grid potential. As a result of the higher mobilities of the fullerenes compared to those of conjugated polymers, the fullerene devices offer some performance advantages; the operating voltages are less than 5 V with current densities exceeding 1 mA/cm2. By fabricating devices with different grid densities, it is shown that the grid exhibits a strong influence on the I–V characteristics for high grid densities, and a correspondingly low influence for low densities, in agreement with theory. The I–V characteristics of the C60 PGTs are well described by an effective diode model, similar to that used for vacuum triodes.

Enhanced in-field critical current densities (Jc’s) have been obtained in epitaxial superconducting (RE1,RE2)Ba2Cu3O7−x (RE1=rare‐earthion 1, and RE2=rare earth ion 2) films grown on both single crystal and buffered metallic substrates. For a constant average RE ionic radius (equal to that of yttrium), there is a systematic dependence of the in-field Jc on the RE ion size variance, with a small, but nonzero, variance being optimum. Compared to the standard YBa2Cu3O7−x composition, a factor of two improvement in Jc(75.5K) is reproducibly observed at 0.2T(‖c) for the composition Dy1∕3Ho2∕3Ba2Cu3O7−x on both single crystal and buffered-metallic substrates. Angular dependent magnetic field studies and transmission electron microscopy indicate the presence of additional pointlike random defects.

Magnetron-sputter-deposited austenitic 330 stainless steel (330 SS) films, several microns thick, were found to have a hardness ∼6.5 GPa, about an order of magnitude higher than bulk 330 SS. High-resolution transmission electron microscopy revealed that sputtered 330 SS coatings are heavily twinned on {111} with nanometer scale twin spacing. Molecular dynamics simulations show that, in the nanometer regime where plasticity is controlled by the motion of single rather than pile-ups of dislocations, twin boundaries are very strong obstacles to slip. These observations provide a new perspective to producing ultrahigh strength monolithic metals by utilizing growth twins with nanometer-scale spacing.

We report on the structural and transport properties of EuBa2Cu3O7−x (Eu123) films on SrTiO3 substrates. A substrate temperature 100 °C higher than that used to deposit YBa2Cu3O7−x (Y123) is needed to grow high-performance Eu123 films directly on SrTiO3 substrates. However, this high-temperature restriction can be circumvented by inserting a seed layer (∼12 nm) of Y123, Gd123, or Dy123 between the substrate and the Eu123. A structural analysis reveals that a transition region that promotes the growth of the a-axis is first formed on the surface of the substrate if the Eu123 is deposited directly on SrTiO3 at a temperature of less than 800 °C. On the other hand, the use of a seed layer of another superconducting material restructures the Eu123 to the right phase without forming this transition region. Eu123 films with critical temperatures of 94 K and critical current densities of 5.8×106 A/cm2 at 75.5 K have been deposited under standard deposition conditions using such an approach.

One of the most intensely researched subjects in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors is the methodology for achieving ever-sharper film texture on flexible metal substrates. This is a critical issue due to the intrinsic weak-link behavior that results in depressed critical current density (Jc) in polycrystalline YBCO. Using ion-beam-assisted deposition of magnesium oxide, we have achieved YBCO texture on superalloy substrates approaching that on single-crystal oxide substrates. This advance has allowed us to fabricate coated conductor samples with Jcs that are as high as for films on oxide crystals; for example, >2 MA/cm2 (75 K, self-field) at a YBCO thickness of ∼1.5 μm.

Most polymer electroluminescent devices to date are represented as tunnel diodes and operate under direct‐current (dc) driving field. Here we report the fabrication of symmetrically configured alternating‐current (ac) light‐emitting (SCALE) devices based on conjugated polymers. The new devices consist of an emissive polymer layer sandwiched between two redox polymer layers. This configuration enables the SCALE devices to work under both forward and reverse dc bias as well as in ac modes. The nearly ohmic electrode/redox polymer contacts improve the charge injection efficiency significantly and make the SCALE device operation insensitive to electrode work functions. Symmetric operation supports the key role of redox polymer/emissive polymer interface states.

We have fabricated unilayer electroluminescent devices from soluble poly(p‐pyridine) (PPy). The solubility of PPy in weak acids allows direct spin casting of the polymer films. The electroluminescence spectrum peaks at 2.5 eV (497 nm) corresponding to white light weighted towards the blue end of the spectrum. The photoluminescence spectrum peaks at 2.35 eV (530 nm). The operating voltages of the devices ranged from 4 to 12 V with current densities of 6 to 8 mA/mm2. We compare our devices with similar blue emitting devices based on poly(p‐phenylene).

In pulsed laser deposited YBa2Cu3O7−x thin films containing 5 mol. % Ba2YNbO6 pinning additions, we show that a growth rate of 1 nm/s (10 Hz laser repetition rate with an instant rate ∼0.1 nm/pulse) gives remarkably strong c-axis correlated pinning which is associated with the presence of Ba2YNbO6 nanocolumns. This is different to the behaviour of other well-studied pinning additions where only random nanoparticles of the pinning phase are present at high growth rates and is an important finding for industrial fabrication of coated conductors where fast growth is required.

In this paper, we report low-field magnetoresistance observed in preferentially c-axis oriented La0.67 Sr0.33MnO3:MgO composite films fabricated on (001) LaAlO3 substrates using a hybrid solution route. Addition of MgO in the composite film results in lowering of Curie temperature (∼300 K) from that of the pure film (∼360 K). The resistivity increases and temperature of highest resistivity of the composite films decrease with the addition of MgO. This behavior is attributed to a small substitution of Mg2+ in the manganite lattice and the presence of MgO near the manganite grain boundaries, thus building tunneling barriers and enhancing the spin polarized tunneling in the composite films. The values of low-field magnetoresistance increase with MgO addition and the composite film with highest amount of MgO exhibits maximum MR of −33% at 0.5 T (5000 Oe) and 10 K.

A free charge layer forms at the LaAlO3/SrTiO3 interface. We show the influence of the SrTiO3 (001) substrate miscut angle on its electronic and transport properties. Highly miscut substrates lead to a substantial mobility enhancement and a carrier density decrease at low temperature consistent with a two-carrier type model.

Thin films of Pr0.5Ca0.5MnO3 were fabricated on (001) oriented SrLaAlO4, NdGaO3, and SrTiO3 substrates using a hybrid solution route and spin coating techniques. Good crystalline and epitaxial quality of the films was confirmed with X-ray diffraction and transmission electron microscopy studies. Strain in the film grown on NdGaO3 substrate did not relax during annealing process and the film exhibited charge-ordered insulator phase at low temperatures even with magnetic fields up to 9 T. However, the films on SrLaAlO4 and SrTiO3 substrates (with partially relaxed compressive and tensile strain, respectively) displayed melting of the charge-ordered phase with applied magnetic fields of less than 5 T. The results suggest that strain-relaxation rather than only the type of strain plays an important role in lowering critical melting magnetic fields in these films.

Nanocomposite (BiFeO3)0.5:(Sm2O3)0.5 films were deposited on (001) oriented Nb-doped SrTiO3 substrates by pulsed laser deposition. The leakage current density versus electric field characteristics were investigated and compared with those of as-deposited and annealed pure BiFeO3 (BFO) thin films. The dominant leakage mechanisms of nanocomposite films were space-charge-limited current and Poole–Frenkle emission for positive and negative biases, respectively. The leakage current density of nanocomposite films was reduced three orders of magnitude in comparison with the as-deposited pure BFO films. The less oxygen vacancies in the BFO phase in the nanocomposite is believed to contribute to the leakage reduction.

The thickness dependence was studied for the critical current density (Jc) of YBa2Cu3O7−x(YBCO)+BaSnO3 (BSO) nanocomposite films. These films showed a significantly reduced decline of the Jc with thickness, especially at high magnetic fields. For example, a 2 μm thick YBCO+BSO film had a Jc∼3×105 A/cm2 at 5 T as compared to a typical Jc of 2.4×103 A/cm2 at 5 T for a 300 nm thick YBCO film. The thick YBCO+BSO films maintained high Tc (>88 K) and had a high density (2.5×1011/cm2) of continuous BSO nanocolumns that likely contributed for the observed Jc enhancements.

In this paper, we report a strong correlation between the stacking fault (SF) density and the critical current density of YBa2Cu3O7−δ (YBCO) thin films in applied field (Jcin-field). We found that the Jcin-field (H∥c) increases as a clear linear dependence of the density of SF identified in the as-grown samples deposited on both SrTiO3 (STO) and LaAlO3 substrates. Detailed microstructural studies including cross-section transmission electron microscopy (TEM) and high resolution TEM were conducted for all the films deposited on STO substrates. This work suggests that the YBCO SF density plays an important role in the YBCO in-field transport performance.

YBa2Cu3O7−x (YBCO) films with nanoparticles of BaSnO3 (BSO) were processed using pulsed laser ablation of a special target made with dual phase sectors of YBCO and BSO. Transport critical current density (Jct) of these YBCO+BSO films in applied magnetic fields and angular dependence of Jct on the applied field orientation was measured. It was observed that in the YBCO+BSO films, the Jct (H‖c orientation) increased considerably as compared to regular YBCO films and was 1.3 times higher than Jct in H‖ab orientation. Cross-sectional transmission electron microscopy images on YBCO+BSO films showed the presence of high density (3.5×1011cm−2) of nanoparticles (∼10nm size) and nanocolumns that extended throughout the thickness of the films with high density of dislocations and stacking faults (1000μm−2). The observed results of enhancements in Jct in H‖c and Jct in H‖ab orientations were discussed in the light of the observed microstructural details.

Epitaxial YXBa2Cu3O7−δ (YXBCO) thin films were deposited by pulsed laser deposition on both single crystal SrTiO3 (100) and buffered polycrystalline metal substrates, where X=0.9, 1.0, 1.1, 1.2, and 1.3. The self-field critical current density (Jc) of YXBCO exhibits the best performance at X=1.1 for the samples on both single crystal substrates and metal substrates. Epitaxial Y2O3 nanoparticles were observed in Y-rich samples (X>1.0) by X-ray diffraction and cross-sectional transmission electron microscopy. The field-dependence and angular-dependence measurements show that Y2O3 nanoparticles improve the in-field Jc performance, especially in the low field regime, without reducing self-field Jc of YBCO films.

Liquid-mediated growth of YBa2Cu3O7−x has the potential to be high rate and low cost. However, the reported critical current densities (Jc) are generally lower than for films deposited by physical vapor deposition processes. We report the deposition of thick high-Jc films (1.2MAcm−2 in self-field) on (001) SrTiO3 by high-rate hybrid liquid phase epitaxy, and show angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy.

By inserting a thin YBa2Cu3O7−δ (Y123) seed layer, high quality EuBa2Cu3O7−δ (Eu123) films can grow with epitaxial c-axis orientation on SrTiO3 (STO) substrate without increasing the growth temperature. The interfacial structures of Eu123∕STO and Eu123∕Y123∕STO were investigated using scanning transmission electron microscopy. Results show that the Eu mobility on the STO substrate is very low at the regular deposition temperature. This leads to nonuniform composition distribution at the Eu123∕STO interface and a mixture of c-axis and a-axis growth. A thin Y123 seed layer greatly improves the Eu mobility and therefore facilitates high quality c-axis growth.