The dielectric response of two-dimensional (2D) Ti 3 C 2 stacked sheets was investigated by high-resolution transmission electron energy-loss spectroscopy and ab initio calculations in the 0.2-30-eV energy range. Intense surface plasmons (SPs), evidenced at the nanometer scale at energies as low as 0.3 eV, are shown to be the dominant screening process up to at least 45-nm-thick stacks. This domination results from a combination of efficient free-electron dynamics, begrenzungs effect, and reduced interband damping. It is shown that, in principle, the SPs energies can be tuned in the mid-infrared, from 0.2 to 0.7 eV, by controlling the sheets' functionalization and/or thickness. This point evidences a new attribute of this new class of 2D materials.

The characterization of surface plasmon resonances supported by metallic nanostructures requires high spatial and energy resolution. In the past few years, electron energy loss spectroscopy (EELS) has emerged as a very powerful tool to accomplish this task. In this work, we demonstrate the power of this technique for probing and imaging resonances of metallic nanostructures by analyzing the plasmonic response of silver nanosquares of sizes ranging from 230 nm up to 1 μm. Because of the relatively large size of these structures, we find that, despite their simple geometry, these systems can support a large variety of multipolar modes, which can only be detected and imaged thanks to the high spatial and energy resolution achieved by pushing EELS to its limits. The experimental results are supported by rigorous theoretical calculations that allow a detailed interpretation of the EELS measurements. In particular, we were able to map, with high level of detail, edge and high-order cavity modes. Furthermore, by calculating the scattering cross-section of these nanostructures, we confirm that most of the observed modes are dark and thus remain hidden in optical measurements, thus demonstrating the power of EELS as a unique tool for probing and imaging a large range and variety of plasmonic resonances of metallic nanostructures.

Energy resolution is one of the most important parameters in electron energy-loss spectroscopy. This is especially true for measurement of surface plasmon resonances, where high-energy resolution is crucial for resolving individual resonance peaks, in particular close to the zero-loss peak. In this work, we improve the energy resolution of electron energy-loss spectra of surface plasmon resonances, acquired with a monochromated beam in a scanning transmission electron microscope, by the use of the Richardson-Lucy deconvolution algorithm. We test the performance of the algorithm in a simulated spectrum and then apply it to experimental energy-loss spectra of a lithographically patterned silver nanorod. By reduction of the point spread function of the spectrum, we are able to identify low-energy surface plasmon peaks in spectra, more localized features, and higher contrast in surface plasmon energy-filtered maps. Thanks to the combination of a monochromated beam and the Richardson-Lucy algorithm, we improve the effective resolution down to 30 meV, and evidence of success up to 10 meV resolution for losses below 1 eV. We also propose, implement, and test two methods to limit the number of iterations in the algorithm. The first method is based on noise measurement and analysis, while in the second we monitor the change of slope in the deconvolved spectrum.

The controlled folding of graphene structures driven by molecular interactions with water nanodroplets is analyzed taking into account interactions with supported substrates such as silicon dioxide (SiO 2 ), hexamethyldisilazane (HMDS), and isopropyl alcohol (IPA) on SiO 2 . The interaction between unsupported graphene and a water nanodroplet is strong enough to induce folding on graphene nanostructures. However, when the graphene is supported on SiO 2 , the attraction between graphene and the substrate prevents graphene from folding but if the substrate is a hydrophobic surface such as HMDS or a solvent such as IPA, the interaction between graphene and the substrate is weak, and depending on the geometry of the graphene structure, folding is possible. The selection of an acceptable substrate and graphene geometry opens the possibility of a controlled fabrication of graphene-based capsules, scrolls, sandwiches, and rings able to carry a payload.

We investigate the plasmonic behavior of Koch snowflake fractal geometries and their possible application as broadband optical antennas. Lithographically defined planar silver Koch fractal antennas were fabricated and characterized with high spatial and spectral resolution using electron energy loss spectroscopy. The experimental data are supported by numerical calculations carried out with a surface integral equation method. Multiple surface plasmon edge modes supported by the fractal structures have been imaged and analyzed. Furthermore, by isolating and reproducing self-similar features in long silver strip antennas, the edge modes present in the Koch snowflake fractals are identified. We demonstrate that the fractal response can be obtained by the sum of basic self-similar segments called characteristic edge units. Interestingly, the plasmon edge modes follow a fractal-scaling rule that depends on these self-similar segments formed in the structure after a fractal iteration. As the size of a fractal structure is reduced, coupling of the modes in the characteristic edge units becomes relevant, and the symmetry of the fractal affects the formation of hybrid modes. This analysis can be utilized not only to understand the edge modes in other planar structures but also in the design and fabrication of fractal structures for nanophotonic applications.