The interband π plasmon of graphene has energy corresponding to the ultraviolet (UV) wave band, and hence is promising for UV nanophotonics and nanooptoelectronics. However, its special size effect and electric field-enhancement effect have not been well understood. Here, we have investigated the far-field optical extinction and near-field enhancement features of the interband π plasmon in a graphene nanodisk using discrete dipole approximation and finite-difference time-domain methods. Very interestingly, it has been found that the in-plane (transverse mode) optical extinction peak of monolayer graphene firstly significantly red shifts with increasing diameter, but then tends to a saturation value when the diameter is above 20 nm, showing a strong small-size-sensitive effect. Furthermore, the transverse mode optical extinction peak obviously blue shifts with increasing thickness when the thickness is relatively small. Significantly, the corresponding local electric field enhancement factor produced by the plasmon, which can be found to be as large as several tens, firstly increases with the increase of the size and then reaches a maximum value at only several nanometers in size. Such an ultrasmall-size-sensitive plasmon in the UV region endows graphene dots with new promising potential uses in ultrasmall photo-electric devices and nanoantennas, and in UV enhancers.

The surface plasmon resonance (SPR) of periodic hexagonal lattice arrays of silver nano‐disks positioned on glass slides is studied using finite‐difference time domain (FDTD) simulations. We investigate numerically the influence of diameter of nano‐disks and the gap between nano‐disks on SPR transmission spectra and electric field enhancement. We find a strong dependence of resonance wavelength on diameter of the nanodisks. With increasing the gap, electric field enhancement factor could significantly increase and reach a maximum value, which indicates that a special long‐range interaction plays an important role. This study is useful for optical modulation applied in near or far field optics, sensing and data storage, and solar cell.

Ultraviolet (UV) surface plasmon (SP) has distinct applications in UV filters, high-density optical storage, spectral enhancement, optical detectors, and nanolithography, which are closely related to plasmon-induced extraordinary optical transmission (EOT). However, such EOT in the UV region has not been the subject of detailed research. We report UV transmission based on theoretical research using the finite-difference time-domain method, by modulating the Al thickness, hole size, array periodicity, and SiO ₂ overlayer thickness. It is notable that we can obtain dual-channel UV transmission peaks with excellent qualities such as high transmissivity, zero cross-talk, narrow bandwidth, and perfect symmetry, by optimizing the parameters. The UV transmission peaks have been discovered to non-monotonously shift with increasing hole size. Although array periodicity has great influence on the transmission peak position, the peak energy in the UV region is much less than the value predicted by the well-known periodicity-related surface plasmon polariton (SPP) wavelength equation; the energy discrepancy in the UV region can reach above 20%, which is much larger than the value (typically 4%) in the visible-infrared region. Furthermore, the SiO ₂ overlayer may significantly modify the transmission properties. The Al nanohole arrays have also been found to exhibit distinct multi-band UV electric field enhancement properties with special interface effect and size effect. Such extraordinary dual-channel UV transmission with zero cross-talk, based on a very simple Al nanohole array, has promising application in dual-channel UV filters, high-density optical storage, and plasmon-enhanced fluorescence/Raman spectroscopy, which generally involves two wavebands (writing/reading storage or exciting/emission wavelengths). This study is expected to broaden our fundamental understanding of the UV EOT phenomenon, and provide references for experimental research and application of deep-UV and near-UV-related dual-band plasmonic devices.

The effects of RF plasma treatments using different gases (Ar, O₂, and N₂) and processing parameters on the surface wettability of polyethylene terephthalate (PET) films were systematically investigated. Atomic force microscopy (AFM) and X–ray photoelectron spectroscopy (XPS) were employed to characterize the evolution of surface topography and chemical composition. While all treatments enhanced hydrophilicity, the magnitude of improvement and the governing mechanisms were gas-dependent. Among them, O₂ plasma treatment exhibited the most pronounced effect: under optimal conditions (20 W, 80 s), the water contact angle (WCA) was reduced to 3.7°, indicating a superhydrophilic surface. This enhancement was primarily attributed to a substantial increase in surface oxygen content (O/C ratio) and the incorporation of strongly polar oxygen-containing functional groups, such as C=O and COOH. N₂ plasma offered moderate improvement via nitrogen-containing groups, while non-reactive Ar plasma relied primarily on physical etching, yielding the smallest enhancement. Analysis revealed that wettability evolution was dominated by increased polar surface energy from chemical functionalization, with surface roughness playing a synergistic role. These results demonstrate that optimizing plasma gas and parameters effectively controls PET wettability through the coupled regulation of surface chemistry and topography.