Ultrathin and Smooth Pheomelanin-like Photoconductive Film.

This study introduces a facile method for the substrate-independent deposition of pheomelanin-like films, revealing unique and promising electrical characteristics. The conventional darkening of a dopamine solution at a basic pH was significantly delayed by the addition of l-cysteine, resulting in a distinctive temporal pattern: an initial quiescent period without apparent color change followed by an abrupt and explosive burst. Surprisingly, within the quiescent period, the deposition of ultrathin and smooth pheomelanin-like films was observed, in addition to rough and thick films formed after the burst. Regardless of thickness or texture, these films exhibited common chemical properties, including moisture-capturing capability and dark- and bright-state conductivities. Particularly noteworthy were consistent photocurrent responses under bias voltage across various pheomelanin-like films, which were not observed in polydopamine films, highlighting the influential role of l-cysteine addition. These findings present a novel avenue for the potential application of pheomelanin-like films in bioelectronics, emphasizing their distinct electrical characteristics and prompting further exploration into their intricate conductive mechanisms. The study contributes to advancing our understanding of melanin-based materials and their potential in diverse scientific and technological domains.

Morphology-Controlled ZnO@ZnWO4 Hetero-Nanostructures for Efficient Photooxidation of Water in Near-Neutral pH.

One-dimensional ZnO nanorods (NRs) have been extensively studied as photoanodes because of their unique optical properties, high electron mobility, and suitable band positions for water oxidation. However, their practical efficiency is often compromised by chemical instability during water oxidation and high carrier recombination rates. To overcome this issue, precise morphological control of ZnO@ZnWO4 core-shell structured photoanodes, featuring a ZnO core and a ZnWO4 shell was used. This was accomplished by depositing WO3 onto hydrothermally grown ZnO NRs using the thermal chemical vapor deposition process. The photoelectrochemical performance of ZnO@ZnWO4 with an optimized morphology outperforms that of pristine ZnO NRs. Systematic optical and electrochemical analyses of ZnO@ZnWO4 demonstrated that the enhancement is attributed to the enhanced charge transfer efficiency facilitated by the optimized ZnWO4 shells.

Enantioselective sensing by collective circular dichroism.

Quantitative determination and in situ monitoring of molecular chirality at extremely low concentrations is still challenging with simple optics because of the molecular-scale mismatch with the incident light wavelength. Advances in spectroscopy1-4 and nanophotonics have successfully lowered the detection limit in enantioselective sensing, as it can bring the microscopic chiral characteristics of molecules into the macroscopic scale5-7 or squeeze the chiral light into the subwavelength scale8-17. Conventional nanophotonic approaches depend mainly on the optical helicity density8,9 by localized resonances within an individual structure, such as localized surface plasmon resonances (LSPRs)10-16 or dielectric Mie resonances17. These approaches use the local chiral hotspots in the immediate vicinity of the structure, whereas the handedness of these hotspots varies spatially. As such, these localized resonance modes tend to be error-prone to the stochasticity of the target molecular orientations, vibrations and local concentrations18,19. Here we identified enantioselective characteristics of collective resonances (CRs)20 arising from assembled 2D crystals of isotropic, 432-symmetric chiral gold nanoparticles (helicoids)21,22. The CRs exhibit a strong and uniform chiral near field over a large volume above the 2D crystal plane, resulting from the collectively spinning, optically induced dipoles at each helicoid. Thus, energy redistribution by molecular back action on the chiral near field shifts the CRs in opposite directions, depending on the handedness of the analyte, maximizing the modulation of the collective circular dichroism (CD).

Enhanced Electrochemical Performance of Micro-Supercapacitors Via Laser-Scribed Cobalt/Reduced Graphene Oxide Hybrids.

The evolution of "smart life," which connects all internet-of-things (IoT) microdevices and microsensors under wireless communication grids, requires microscale energy storage devices with high power and energy density and long-term cyclability to integrate them with sustainable power generators. Instead of Li-ion batteries with a short lifetime, pseudocapacitors with longer or infinite cyclability and high-power density have been considered as efficient energy storage devices for IoT. However, the design and fabrication of microscale pseudocapacitors have difficulties in patterning microscale electrodes when loading active materials at specific points of the electrodes using conventional microfabrication methods. Here, we developed a facile, one-step fabrication method of micro-supercapacitors (MSCs) through the in situ formation of Co metals and the reduced graphene oxides (rGOs) in a one-pot laser scribing process. The prepared Co/rGO MSC thus exhibited four times higher capacitance than the rGO MSC, due to the Faradaic charge capacitance behavior of the Co/rGO composites.

Self-emitting blue and red EuOX (X = F, Cl, Br, I) materials: band structure, charge transfer energy, and emission energy.

Self-emitting blue and red EuOX (X = F, Cl, Br, and I) were successfully synthesized and characterized. Far-infrared and Raman measurements revealed that the vibration modes prominently reflected the Eu-O and Eu-X bond characters of these materials. X-ray photoelectron spectroscopy (XPS) of the red-emitting EuOX compounds showed that Eu exclusively existed as Eu3+, while in the blue-emitting EuOX, a mixed Eu3+/Eu2+ state was observed. For the red-emitting EuOX (X = F, Cl, and Br), the maximum wavelengths of the charge-transfer (CT) bands were red-shifted: F → Cl → Br (282, 320, and 330 nm for F, Cl, and Br, respectively). Using one-electron spin-polarized band structure calculations, it was verified that the red-shift of the CT energy from F to Br in EuOX was mainly due to the relative positions of the halogen orbital energies being gradually increased, following the trend in their electronegativity. For the blue-emitting EuOX (X = Cl, Br, and I), the emission band maxima were red-shifted from Cl to I (409, 414, and 432 nm for Cl, Br, and I, respectively), which was quite opposite to the trend predicted based on the spectrochemical series in crystal field theory, which was in good agreement with the previous results of the calculated 5d → 4f transition energies of the Eu2+ activator based on the crystal field theory. Through photoluminescence, UV-visible absorbance, and XPS, it was elucidated that the red emission due to Eu3+ was strongly masked by the intensified blue emission associated with the small amount of Eu2+ in the blue-emitting EuOX (X = Cl, Br, and I). These materials may provide a platform for modeling new phosphors for application in solid-state lighting.

Neurite Guidance on Laser-Scribed Reduced Graphene Oxide.

This paper describes a one-step, chemical-free method to generate micropatterned in vitro neuronal networks on chemically unmodified reduced graphene oxide. The suggested method relies on infrared-based photothermal reduction of graphene oxide, which concurrently leads to the formation of submicrometer-scale surface roughness that promotes neuronal adhesion and guides neurite outgrowth. A commercially available laser source (LightScribe DVD drive) controlled by a computer software can be used to reduce graphene oxide (GO), and its repetitive scribing to a GO film brings about gradual increase and decrease in electrical conductivity and neurite guiding ability of the scribed regions, respectively. Our results also indicate that the observed adhesion-promoting and neurite guiding effect originate from the contrast in surface nanotopography, but not that in conductivity. This method is readily applicable to diverse graphene-based biomedical devices.