In order to investigate the modification of the surface structure of FePS3 via Ga+ ion irradiation, we study the effect of thickness and Raman spectrum of multilayer FePS3 irradiated for 0 μs, 30 μs, and 40 μs, respectively. The results demonstrate that the intensity ratio of characteristic Raman peaks are obviously related to the thickness of FePS3. After Ga+ ion irradiation, the FePS3 sample gradually became thinner and the Eu peak and Eg(v11) peak in the Raman spectrum disappeared and the peak intensity ratio of A1g(v2) with respect to A1g(v1) weakened. This trend becomes more apparent while increasing irradiation time. The phenomenon is attributed to the damage of bipyramid structure of [P2S6]4− units and the cleavage of the P-P bands and the P-S bands during Ga+ ion irradiation. The results are of great significance for improving the two-dimensional characteristics of FePS3 by Ga+ ion beam, including structural and optical properties, which pave the way of surface engineering to improve the performance of various two-dimensional layered materials via ion beam irradiation.

We propose a plasmonic ellipse resonator possessing hybrid modes based on metalinsulator-metal (MIM) waveguide system. Specially, this nanocavity has hybrid characteristic of rectangle and disk resonator, therefore supporting both Fabry-Perot modes (FPMs) and whisperinggallery modes (WGMs). Besides, by changing the length of major and minor radius of the ellipse, the resonant wavelengths of FPMs and WGMs can be independently tuned and close to each other, thus constructing a plasmon-induced transparency (PIT) -like spectrum profile. Benefitting from this, a dual-band slow light is achieved with one single resonator. Furthermore, this component can also act as a multi-band color filter and refractive index sensor. We believe such multi-mode resonator with ultra-small footprint will play an important role in more compact on-chip optical circuits in the future.

A monolayer-graphene-based concentric-double-rings (CDR) structure is reported to achieve broadband plasmon-induced transparency (PIT) on the strength of edge mode in the mid-infrared regime. The theoretical analysis and simulation results reveal that the structure designed here has two plasmonic resonance peaks at 39.1 and 55.4 THz, and a transparency window with high transmission amplitude at the frequency of 44.1 THz. Based on the edge mode coupling between neighbor graphene ribbons, PIT phenomenon is produced through the interference between different (bright and dark) modes. The frequency and bandwidth of the transparency window and slow light time could be effectively adjusted and controlled via changing geometrical parameters of graphene or applying different gate voltages. Additionally, this structure is insensitive to the polarization and incident angle. This work has potential application on the optical switches and slow light modulators.

Pyromellitic dianhydride and oxydianiline polyimide films turn electrically conductive upon irradiation with energetic ions. Raman spectroscopy shows an initial dissociation of the molecular structure at low irradiation doses ranging from 1×1014 to 1×1015 B+/cm2, followed by the appearance, at a high dose of 1×1016 B+/cm2, of structures similar to those observed in amorphous graphite. Comparing the reduced Raman spectra of materials irradiated up to a dose as high as 1×1016 B+/cm2 with the one-phonon density of states of amorphous graphite, one finds that this structural similarity to graphite only exists within a short range. Meanwhile, an ion-beam-induced aggregation of aromatic rings in irradiated polyimide films is indicated by ultraviolet-visible spectroscopy. In view of the structural information from resonant Raman spectroscopy, the existence of structural inhomogeneity is proposed for the high-dose irradiated polyimide. From perspectives of the model of heterogeneous media, the structural similarity to graphite within a short range is attributed to the existence of the second phase composed of broken functionalities of irradiated polyimide and the sp3-bonded carbon atoms.