Doris Humphrey: Choreographic analysis

Doris Humphrey made important contributions to American dance. Analysis of selected works in three chronological periods provides insight into her choreographic development. The first period of Humphrey's choreography to be analyzed is 1928--1934; 1928 was the year she began her own dance company with Charles Weidman. The two works analyzed are Air for the G String (1928) and The Shakers (1931). The second period is 1935--1944. It was in 1935 that Humphrey created her first evening-length work, New Dance (1935). The year 1944 was chosen to close this period, as in that year Humphrey stopped performing. The three works studied for this period are New Dance (1935); With My Red Fires (1936); and Passacagli (1938). Three works are analyzed which Humphrey created during the last period of her life, 1945--1958: Day on Earth (1947); Night Spell (1951); and Dawn in New York (1956).</p

Direct Evidence of Ion-Migration-Induced Degradation of Ultrabright Perovskite Light-Emitting Diodes

Low operational lifetime is a critical issue in perovskite light-emitting diodes. The forward-bias currents for light emission accelerate device degradation, which needs to be identified and understood to be able to improve the device stability. Here, we systematically analyze the degradation mechanism of perovskite light-emitting diodes (PeLEDs) fabricated with a sequential deposition method that produce a compact and pinhole-free perovskite film. The device exhibits an efficient green electroluminescence (peak wavelength at 533 nm and full width at half-maximum of 22 nm) with a maximum luminance of more than 67 000 cd/m2. The lifetime, however, is quite short; under the constant current bias for an initial luminance of 1000 cd/m2, the decay time to reach half of the initial luminance is approximately 13 min. Dark spots are created and enlarged as a result of perovskite film deterioration and ion migration. By investigating morphological changes in the perovskite films and the amount of ion accumulation under the Al electrode for the unoperated, T50 (luminance decay to 50% of the initial value), and T10 (luminance decay to 10% of the initial value) devices, we propose a degradation mechanism for PeLEDs. The ion migration from the perovskite layer experienced electrochemical interactions with the Al electrode, causing device degradation

Improved Efficiency of Inverted Organic Light-Emitting Diodes Using Tin Dioxide Nanoparticles as an Electron Injection Layer

We demonstrated highly efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs) using tin dioxide (SnO₂) nanoparticles (NPs) as an electron injection layer at the interface between the indium tin oxide (ITO) cathode and the organic electron transport layer. The SnO₂ NP layer can facilitate the electron injection since the conduction band energy level of SnO₂ NPs (−3.6 eV) is located between the work function of ITO (4.8 eV) and the lowest unoccupied molecular orbital (LUMO) energy level of typical electron transporting molecules (−2.5 to −3.5 eV). As a result, the IBOLEDs with the SnO₂ NPs exhibited a decrease of the driving voltage by 7 V at 1000 cd/m² compared to the device without SnO₂ NPs. They also showed a significantly enhanced luminous current efficiency of 51.1 cd/A (corresponds to the external quantum efficiency of 15.6%) at the same brightness, which is about two times higher values than that of the device without SnO₂ NPs. We also measured the angular dependence of irradiance and electroluminescence (EL) spectra in the devices with SnO₂ NPs and found that they had a nearly Lambertian emission profile and few shift in EL spectrum through the entire viewing angles, which are considered as remarkable and essential results for the application of OLEDs to display devices

<i>Operando</i> Raman Spectroscopy Insights into the Electrochemical Formation of F‑Graphite Intercalation Compounds

This study presents the first observation of the electrochemical formation of graphite-F intercalation compounds (GICs) within LiF-containing organic liquid electrolytes. As determined by operando Raman spectroscopy measurements, the peaks corresponding to the G band (i.e., in-plane mode of sp2 bonded carbon with a planar configuration) in highly oriented pyrolytic graphite (HOPG) are separated during the process of electrochemical oxidation, indicating that F-GIC is electrochemically formed in the HOPG electrodes. Furthermore, the rate of reaction and the reversibility of the electrochemical intercalation/deintercalation of F– are notably enhanced in HOPG electrodes endowed with a LiF-based surface layer. This enhancement suggests that augmenting the activity of F– ions, coupled with the suppression of side reactions, is pivotal for the successful electrochemical synthesis of F-GICs

Stabilizing the Nanosurface of LiNiO₂ Electrodes by Varying the Electrolyte Concentration: Correlation with Initial Electrochemical Behaviors for Use in Aqueous Li-Ion Batteries

This study attempted to stabilize the nanosurface of LiNiO2 (LNO) electrodes by varying the electrolyte concentration, significantly influencing its initial electrochemical behaviors for use in aqueous lithium-ion batteries. The charge/discharge capacities, reversibility, and cyclability of LNO were improved during initial cycles with an increase in the concentration of lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI). As determined by the galvanostatic intermittent titration technique, the superior diffusivity of Li+ ions in the LNO electrode is also obtained in the concentrated electrolyte. Nanoscale observation of the LNO surface revealed that its morphology is maintained relatively well in the concentrated electrolyte while it is destroyed in dilute electrolytes after the initial electrochemical cycles. These results are considered to be attributable to the variation of the interface condition in the electrical double layer with an increase in the electrolyte concentration, thus stabilizing the nanosurface of LNO by suppressing the dissolution of Ni ions from the surface. Additionally, in situ X-ray diffraction analysis demonstrated that LNO shows more stable phase transitions and volume changes as the electrolyte concentration increases, indicating that its structural changes in bulk can be directly related to the state of the nanosurface, which has a positive impact on the initial electrochemical behaviors in this system

Enhanced Light Trapping and Power Conversion Efficiency in Ultrathin Plasmonic Organic Solar Cells: A Coupled Optical-Electrical Multiphysics Study on the Effect of Nanoparticle Geometry

Plasmonic effects associated with localized surface plasmon (LSP) resonances such as strong light trapping, large scattering cross-section, and giant electric field enhancement have received much attention for the more efficient harvesting of solar energy. Notably, even as the thickness of the active layer is significantly reduced, the optical absorption capability of a solar cell could be maintained with the incorporation of plasmonic effects. This is especially important for the development of bulk heterojunction (BHJ) <i>organic</i> solar cells (OSCs), where the short exciton diffusion length, low carrier mobility, and strong charge recombination in organic materials strongly favors the use of optically thin active layers (<100 nm). However, the disappointing performance improvements obtained with plasmonic effects in the majority of BHJ OSCs realized to date suggests that plasmonic effects are yet to be fully taken advantage of; for example, in thick active layer OSCs (>100 nm), the optical absorption is already high, even in the absence of plasmonic effects, while in thin active layer OSCs (<100 nm), insufficient attention has been given to the analysis of plasmonic effects, such as the impact of plasmonic nanoparticle (NP) geometrical factors on the directional scattering efficiency. In this paper, we propose and demonstrate that the geometrical tuning of <i>spheroidal</i> plasmonic nanoparticles (NPs) could enable the full exploitation of plasmonic effects, providing dramatic improvements to the light absorption and energy harvesting capability of ultrathin film BHJ OSCs. Our theoretical analysis demonstrates a dramatic enhancement in optical absorption of ∼60% with spheroidal NPs embedded in a BHJ OSC device with ultrathin, <100 nm active layer, as compared to an NP absent reference device. These improvements are explained according to enhanced scattering of light into the active layer plane, spectral broadening of absorption resonances, in addition to an increased plasmonic modal volume, exhibited near LSP resonances of spheroidal NPs with optimal eccentricity. The result of our coupled optical-electrical device simulations also proves that the outstanding optical absorption enhancement obtained from the proposed device indeed translates into significant electrical performance gains; such as a ∼30% increase in the short-circuit current and ∼20% improvement in the power conversion efficiency (PCE)

High-Power Genuine Ultraviolet Light-Emitting Diodes Based On Colloidal Nanocrystal Quantum Dots

Thin-film ultraviolet (UV) light-emitting diodes (LEDs) with emission wavelengths below 400 nm are emerging as promising light sources for various purposes, from our daily lives to industrial applications. However, current thin-film UV-emitting devices radiate not only UV light but also visible light. Here, we introduce genuine UV-emitting colloidal nanocrystal quantum dot (NQD) LEDs (QLEDs) using precisely controlled NQDs consisting of a 2.5-nm-sized CdZnS ternary core and a ZnS shell. The effective core size is further reduced during the shell growth via the atomic diffusion of interior Cd atoms to the exterior ZnS shell, compensating for the photoluminescence red shift. This design enables us to develop CdZnS@ZnS UV QLEDs with pure UV emission and minimal parasitic peaks. The irradiance is as high as 2.0–13.9 mW cm^–2 at the peak wavelengths of 377–390 nm, several orders of magnitude higher than that of other thin-film UV LEDs

Insights into the Interlayer Water-Induced Reversible Proton Insertion and Deinsertion in Ruddlesden–Popper Layered Fe Oxides

The widespread use of two-dimensional materials in aqueous rechargeable batteries makes it essential to elucidate their electrochemical behavior in water to ensure the safety and stability of the batteries for use in grid-level energy storage systems. However, the complexity of the hydration structure of ions and the presence of protons and hydroxide ions due to water ionization hinder the discovery of new active materials and the elucidation of the reaction mechanism. This study demonstrates the feasibility of Ruddlesden–Popper layered perovskite LaSr3Fe3O10−δ as a new active material, which is capable of electrochemical reduction and oxidation and the introduction of interlayer water. The operando X-ray diffraction and X-ray absorption results revealed that the Fe redox couple and the consequent introduction of protons and the interlayer water are responsible for the charge and discharge capacities. In addition, the capacity decreased in highly concentrated aqueous solutions with a few free water molecules. Furthermore, LaSr3Fe3O8(OH)2·mH2O synthesized via a two-step process involving chemical reduction and the introduction of interlayer water showed a clear decrease in capacity although the Fe valence was as low as that obtained by the electrochemical method. This study presents novel active materials for aqueous batteries and provides insights into the role of interlayer water frequently present in layered materials

Quantum Dot−Block Copolymer Hybrids with Improved Properties and Their Application to Quantum Dot Light-Emitting Devices

To combine the optical properties of CdSe@ZnS quantum dots (QDs) with the electrical properties of semiconducting polymers, we prepared QD/polymer hybrids by grafting a block copolymer (BCP) containing thiol-anchoring moieties (poly(para-methyl triphenylamine-b-cysteamine acrylamide)) onto the surfaces of QDs through the ligand exchange procedure. The prepared QD/polymer hybrids possess improved processability such as enhanced solubility in various organic solvents as well as the film formation properties along with the improved colloidal stability derived from the grafted polymer shells. We also demonstrated light-emitting diodes based on QD/polymer hybrids, exhibiting the improved device performance (i.e., 3-fold increase in the external quantum efficiency) compared with the devices prepared by pristine (unmodified) QDs