Silver Nanoparticles-Accelerated Photopolymerization of a Diacetylene Derivative

We have investigated silver nanoparticles (AgNPs)-accelerated photopolymerization of a diacetylene derivative, 1,6-di(<i>N</i>-carbazolyl)-2,4-hexadiyne (DCHD), which undergoes a phase transformation of the crystal structure from monomer to polymer during the photopolymerization. We have successfully fabricated nanocomposites of AgNPs and DCHD monomer nanocrystals by means of the modified reprecipitation method, and we monitored its photopolymerization process with Raman spectroscopy upon 532 nm excitation. Although the localized surface plasmon resonance (LSPR) wavelength of AgNPs in an aqueous dispersion was located around 400 nm, that of AgNPs in the present nanocomposites was shifted to longer wavelength region. The extinction of the nanocomposites at 532 nm became significant because of the red-shift and broadening of the LSPR, and, thus, surface plasmon-enhanced photoelectric fields on the AgNP surfaces could generate upon 532 nm excitation. As compared to the Raman spectra of bare DCHD monomer nanocrystals, the nanocomposites exhibited strongly enhanced Raman intensities and 20–40 times faster photopolymerization. Because the excitation power used in the present experiments is considered to be insufficient for the thermal process, two- or multiphoton polymerization was assumed to be dominant. We have also observed a unique power dependence of the polymerization rate derived from the phase transformation behavior

Solution-Processed Inorganic–Organic Hybrid Electron Injection Layer for Polymer Light-Emitting Devices

A lithium quinolate complex (Liq) has high solubility in polar solvents such as alcohols and can be spin-coated onto emitting polymers, resulting in a smooth surface morphology. A polymer light-emitting device fabricated with spin-coated Liq as an electron injection layer (EIL) exhibited a lower turn-on voltage and a higher efficiency than a device with spin-coated Cs₂CO₃ and a device with thermally evaporated Ca. The mixture of ZnO nanoparticles and Liq served as an efficient EIL, resulting in a lower driving voltage even in thick films (∼10 nm), and it did not require a high-temperature annealing process

Efficient Electron Injection by Size- and Shape-Controlled Zinc Oxide Nanoparticles in Organic Light-Emitting Devices

Three different sized zinc oxide (ZnO) nanoparticles were synthesized as spherical ZnO (S-ZnO), rodlike ZnO (R-ZnO), and intermediate shape and size ZnO (I-ZnO) by controlling the reaction time. The average sizes of the ZnO nanoparticles were 4.2 nm × 3.4 nm for S-ZnO, 9.8 nm × 4.5 nm for I-ZnO, and 20.6 nm × 6.2 nm for R-ZnO. Organic light-emitting devices (OLEDs) with these ZnO nanoparticles as the electron injection layer (EIL) were fabricated. The device with I-ZnO showed lower driving voltage and higher power efficiency than those with S-ZnO and R-ZnO. The superiority of I-ZnO makes it very effective as an EIL for various types of OLEDs regardless of the deposition order or method of fabricating the organic layer, the ZnO layer, and the electrode

Facet-Dependent Diol-Induced Density of States of Anatase TiO₂ Crystal Surface

Owing to their fundamental importance and practical applications, anatase TiO₂ crystals with well-defined {001} and {101} facets attracted intensive research interests. In this study, we systematically investigated solvent dependence of the photoreaction of the different coexposed crystal facets during noble metal photodeposition. By examining the deposition position in each solvent, we revealed that solvents play a pivotal role on the facet selectivity. On the basis of density functional theory calculations, the solvent molecules were found to modify both the crystal facet electronic structure and the {001}–{001} heterojunction. These modifications are not only the origin of diverse charge-carrier pathways but are also responsible for carrier accumulation at specific facets that increase their reductive power. These findings are vital for a better understanding of photocatalytic materials and an improved design for the next-generation materials

Length-Controllable Gold-Coated Silver Nanowire Probes for High AFM-TERS Scattering Activity

Tip-enhanced Raman scattering (TERS) microscopy is an advanced technique for investigation at the nanoscale that provides topographic and chemical information simultaneously. The TERS probe plays a crucial role in the microscopic performance. In the recent past, the development of silver nanowire (AgNW) based TERS probes solved the main tip fabrication issues, such as low mechanical strength and reproducibility. However, this fabrication method still suffers from low control of the protruded length of the AgNW. In this work, a simple water–air interface electrocutting method is proposed to achieve wide controllability of the length. This water cutting method was combined with a succedent Au coating on the AgNW surface, and the probe achieved an up to 100× higher enhancement factor (EF) and a 2× smaller spatial resolution compared to pristine AgNW. Thanks to this excellent EF, the water-cut Au-coated AgNW probes were found to possess high TERS activity even in the nongap mode, enabling broad applications