•Principle of low energy inverse photoemission spectroscopy is described.•Instruments including electron sources and photon detectors are shown.•Recent results about organic devices and fundamental ...studies are reviewed.•Electron affinities of typical organic semiconductors are compiled.
Information about the unoccupied states is crucial to both fundamental and applied physics of organic semiconductors. However, there were no available experimental methods that meet the requirement of such research. In this review, we describe a new experimental method to examine the unoccupied states, called low-energy inverse photoemission spectroscopy (LEIPS). An electron having the kinetic energy lower than the damage threshold of organic molecules is introduced to a sample film, and an emitted photon in the near-ultraviolet range is detected with high resolution and sensitivity. Unlike the previous inverse photoemission spectroscopy, the sample damage is negligible and the overall resolution is a factor of two improved to 0.25eV. Using LEIPS, electron affinity of organic semiconductor can be determined with the same precision as photoemission spectroscopy for ionization energy. The instruments including an electron source and photon detectors as well as application to organic semiconductors are presented.
When a thin layer of bathocuproine (BCP) is inserted between the metal electrode and the organic layer of the organic semiconductor device, the electron injection/collection efficiency at the ...interface is significantly improved. However, the mechanism of electron transport through the BCP layer has not been clarified yet. In this study, we directly observed the unoccupied electronic states of the Ag/BCP interface using low-energy inverse photoemission spectroscopy. The result shows that Ag strongly interacts with the BCP molecule and the lowest unoccupied molecular orbital (LUMO) level of the Ag-BCP complex aligns with the Fermi level, indicating that the electron transport occurs through the LUMO level of the complex. With the aid of DFT calculation, we identify the reaction product.
Ionization energy and electron affinity in organic solids are understood in terms of a single molecule perturbed by solid-state effects such as polarization energy, band dispersion, and molecular ...orientation as primary factors. However, no work has been done to determine the individual contributions experimentally. In this work, the electron affinities of thin films of pentacene and perfluoropentacene with different molecular orientations are determined to a precision of 0.1 eV using low-energy inverse photoemission spectroscopy. Based on the precisely determined electron affinities in the solid state together with the corresponding data of the ionization energies and other energy parameters, we quantitatively evaluate the contribution of these effects. It turns out that the bandwidth as well as the polarization energy contributes to the ionization energy and electron affinity in the solid state while the effect of the surface dipole is at most a few eV and does not vary with the molecular orientation. As a result, we conclude that the molecular orientation dependence of the ionization energy and electron affinity of organic solids originates from the orientation-dependent polarization energy in the film.
In this work, we propose a one-step subcritical methanol extraction (SCM) process for biodiesel production from Chlorella pyrenoidosa. Therefore, the present study attempts to establish and determine ...the optimum operating conditions for maximum biodiesel yield from SCM of C. pyrenoidosa. A statistical approach, i.e. response surface methodology is employed in this study. The effects of three operational factors: reaction temperature (140–220 °C), reaction time (1–15 min) and methanol to algae ratio (1–9 wt.%) were investigated using a central composite design. A maximum yield of crude biodiesel of 7.1 wt.% was obtained at 160 °C, 3 min reaction time and 7 wt.% methanol to algae ratio. The analysis of variance revealed that methanol to algae ratio is the most significant factor for maximizing biodiesel yield. Regression analysis showed a good fit of the experimental data to the second-order polynomial model. With no requirement of catalyst nor any pretreatment step, SCM process is economically feasible to scale up the commercial biodiesel production from algae.
•The one-step biodiesel extraction from C. pyrenoidosa via SCM is demonstrated.•The biodiesel yield is optimized using CCD based on response surface methodology.•Reaction temperature, reaction time and methanol to algae ratio were investigated.•A maximum biodiesel yield was about 7.1 wt.%.
This paper deals with the dehydration of fructose (F) to 5-hydroxymethylfurfural (HMF) and the rehydration of HMF to levulinic acid (LA) along with formic acid (FA) in subcritical water (sub-CW) in ...the presence of HCl as catalyst. The experimental conditions were 483−543 K, 4−15 MPa, and residence times of 0.5−300 s. The pressure (in the range of 4−15 MPa) did not affect the decomposition reactions. This differed from other operating variables. The main products were found to be HMF, 2-furaldehyde (2FA), LA, FA, and soluble polymers. The HMF, LA, and FA were also individually subjected for decomposition at the same condition. We found that, during the sub-CW reaction, byproducts (soluble polymers) were produced not only from F but also from HMF. However, we distinguished between two different polymers (i.e., produced from the decomposition of F or HMF) in a proposed reaction model. The kinetics of the sub-CW reaction was developed by considering not only F, HMF, LA, and FA but also soluble polymers. The kinetic constants obtained from the proposed reaction pathway showed good agreement with experimental results.
Photoaged skin is characterized clinically by apparent manifestations such as wrinkles and sagging, and histologically by an accumulation of abnormal elastin and a severe loss of collagen fibers in ...the dermis. Quantitative and qualitative alterations in elastin and collagens are considered to be responsible for the formation of wrinkles and sagging. However, since the integrity of elastin and collagen fibers in the dermis is maintained by their interactions with hyaluronan (HA) and a proteoglycan network structure, HA degradation may be the initial process, prior to the breakdown of the fibrillary components, leading to wrinkles and sagging in photoaged skin. We have recently discovered a new HA-degrading mechanism mediated by HYBID (hyaluronan binding protein involved in hyaluronan depolymerization), alias KIAA1199/CEMIP, in human skin fibroblasts, and examined the implication of HYBID for skin photoaging. In this review, we give an overview of the characteristics of HYBID and its prospective roles in HA turnover in normal skin and excessive HA degradation in photoaged skin. In addition, we describe our data on the inhibition of HYBID activity and expression by plant extracts in skin fibroblasts; and propose novel strategies to prevent or improve photoaging symptoms, such as skin wrinkling, by inhibition of HYBID-mediated HA degradation.
Generation of optical vortices is described in cholesteric liquid crystals with a singular point in the spatial distribution of a helix phase. The phenomenon uses the fact that a Bragg reflected ...light phase varies in proportion to the spatial phase of the helix, both at normal and oblique incidences. Our proposal enables high-efficiency, polychromatic generation of optical vortices without the need of a cumbersome fabrication process and fine-tuning.
Topological defects embedded in or combined with domain walls have been proposed in various systems, some of which are referred to as domain wall skyrmions or domain wall bimerons. However, the ...experimental observation of such topological defects remains an ongoing challenge. Here, using Lorentz transmission electron microscopy, we report the experimental discovery of domain wall bimerons in chiral magnet Co-Zn-Mn(110) thin films. By applying a magnetic field, multidomain structures develop, and simultaneously, chained or isolated bimerons arise as the localized state between the domains with the opposite in-plane components of net magnetization. The multidomain formation is attributed to magnetic anisotropy and dipolar interaction, and domain wall bimerons are stabilized by the Dzyaloshinskii-Moriya interaction. In addition, micromagnetic simulations show that domain wall bimerons appear for a wide range of conditions in chiral magnets with cubic magnetic anisotropy. Our results promote further study in various fields of physics.
A large-angle polarization volume grating (PVG) with circular-polarization selectivity is demonstrated using a three-dimensional chiral liquid crystal with simple cubic symmetry - the blue phase (BP) ...II. We confirm defect-free alignment of the BP crystal on a periodically patterned substrate down to a period of 700 nm, with Kossel diagrams and far-field diffraction patterns suggesting that the lattice becomes slanted within the cell to accommodate to the imprinted pattern. We further demonstrate a tunable PVG by exploiting the external field-responsivity of BPs, making this PVG attractive for a wide range of applications from tunable photonics to augmented reality.
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