Moiré Nanolithography Based on Ultrathin Anodized Aluminium Oxide Membranes

A new nanofabrication method for construction of complex superlattice structure with versatile super-periodicity is developed using the moiré fringe of anodized aluminium oxide (AAO) membranes. Two ultrathin AAO membranes with long-range order holes are stacked to form 2D moiré nanopatterns. Both rotational symmetry and the periodicity of the holes are modified by the relative spatial displacement between the superimposing layers. Using the membranes as metal evaporation masks, a wide assortment of complex Al nanostructures are fabricated by varying the misorientation angle of the two ultrathin AAO membranes. Highly ordered Al nanoparticles with different sizes, shapes, orientations, and arrangements on substrates are achieved, which are expected to give abundant surface plasmon mode.

Interband, Surface Plasmon and Fano Resonances in Titanium Carbide (MXene) Nanoparticles in the Visible to Infrared Range

Since the discovery of the optical properties of two-dimensional (2D) titanium carbide (MXene) conductive material, an ever increasing interest has been devoted towards understanding it as a plasmonic substrate or nanoparticle. This noble metal-free alternative holds promise not only due to its lower cost but also its 2D nature, hydrophilicity and apparent bio-compatibility. Herein, the optical properties of the most widely studied Ti3C2Tx MXene nanosheets are theoretically analyzed and absorption cross-sections are calculated exploiting available experimental data on its dielectric function. The occurrence of quadrupole surface plasmon mode in the optical absorption spectra of large MXene nanoparticles is demonstrated for the first time. The resonance wavelengths corresponding to interband transitions, longitudinal and transversal dipole oscillations and quadrupole longitudinal surface plasmon mode are identified for single and coupled nanoparticles by modeling their shapes as ellipsoids, disks and cylinders. A new mechanism of excitation of longwave transversal surface plasmon oscillations by an external electric field perpendicular to the direction of charge oscillations is presented. Excitingly enough, a new effect in coupled MXene nanoparticles—Fano resonance—is unveiled. The results of calculations are compared to known experimental data on electron absorption spectroscopy, and good agreement is demonstrated.