Investigating new materials plays an important role for advancing the field of nanoplasmonics. In this work, we fabricate nanodisks from magnesium and demonstrate tuning of their plasmon resonance throughout the whole visible wavelength range by changing the disk diameter. Furthermore, we employ a catalytic palladium cap layer to transform the metallic Mg particles into dielectric MgH2 particles when exposed to hydrogen gas. We prove that this transition can be reversed in the presence of oxygen. This yields plasmonic nanostructures with an extinction spectrum that can be repeatedly switched on or off or kept at any intermediate state, offering new perspectives for active plasmonic metamaterials.

Palladium-hydrogen is a prototypical metal-hydrogen system. It is therefore not at all surprising that a lot of attention has been devoted to the absorption and desorption of hydrogen in nanosized palladium particles. Several seminal articles on the interaction of H with Pd nanocubes and nanoparticles have recently been published. Although each article provides for the first time detailed data on specific aspects of hydrogen in nanoparticles, they individually do not contain enough information to draw firm conclusions about the involved mechanisms. Here, we show that the large body of data available so far in literature exhibits general patterns that lead to unambiguous conclusions about the processes involved in H absorption and desorption in Pd nanoparticles. On the basis of a remarkably robust scaling law for the hysteresis in absorption-desorption isotherms, we show that hydrogen absorption in palladium nanoparticles is consistent with a coherent interface model and is thus clearly different from bulk Pd behaviour. However, H desorption occurs fully coherently only for small nanoparticles (typically smaller than 50 nm) at temperatures sufficiently close to the critical temperature. For larger particles it is partially incoherent, as in bulk, where dilute α-PdHx and high concentration β-PdHx phases coexist.

Titanium nitride (TiN) is a novel refractory plasmonic material which can sustain high temperatures and exhibits large optical nonlinearities, potentially opening the door for high-power nonlinear plasmonic applications. We fabricate TiN nanoantenna arrays with plasmonic resonances tunable in the range of about 950-1050 nm by changing the antenna length. We present second-harmonic (SH) spectroscopy of TiN nanoantenna arrays, which is analyzed using a nonlinear oscillator model with a wavelength-dependent second-order response from the material itself. Furthermore, characterization of the robustness upon strong laser illumination confirms that the TiN antennas are able to endure laser irradiation with high peak intensity up to 15 GW/cm(2) without changing their optical properties and their physical appearance. They outperform gold antennas by one order of magnitude regarding laser power sustainability. Thus, TiN nanoantennas could serve as promising candidates for high-power/high-temperature applications such as coherent nonlinear converters and local heat sources on the nanoscale.

We employ laser interference lithography as a reliable and low-cost fabrication method to create nanowire and nanosquare arrays in photopolymers for manufacturing plasmonic perfect absorber sensors over homogeneous areas as large as 5.7 cm 2 . Subsequently, we transfer the fabricated patterns into a palladium layer by using argon ion beam etching. Geometry and periodicity of our large-area metallic nanostructures are precisely controlled by adjusting the interference conditions during single-and double-exposure processes, resulting in active nanostructures over large areas with spectrally selective perfect absorption of light from the visible to the near-infrared wavelength range. In addition, we demonstrate the method's applicability for hydrogen detection schemes by measuring the hydrogen sensing performance of our polarization independent palladium-based perfect absorbers. Since palladium changes its optical and structural properties reversibly upon hydrogenation, exposure of the sample to hydrogen causes distinct and reversible changes within seconds in the absorption of light, which are easily measured by standard microscopic tools. The fabricated large-area perfect absorber sensors provide nearly perfect absorption of light at 730 and 950 nm, respectively, and absolute reflectance changes from below 1% to above 4% in the presence of hydrogen. This translates to a relative signal change of almost 400%. The large-area and fast manufacturing process makes our approach highly attractive for simple and low-cost sensor fabrication, and therefore, suitable for industrial production of plasmonic devices in the near future.

dispersion. In general, these two quantities are Kramers-Kronig related. [3] Both effects can be utilized to study chiral molecules, with circular dichroism spectroscopy being the most commonly used. Chirality is a powerful method to analyze the 3D conformation of molecules as it is an intrinsically 3D property. CD spectra can help to unravel the secondary structure of proteins, which is ultimately responsible for the interaction of proteins and for the biologically and physiologically relevant processes. [4] That said, it is obvious that the exact conformation of a molecule and the differences between the molecules of an ensemble are of paramount interest. However, in chemistry and biology the CD of many molecules is measured in a solution with a CD spectrometer, as the CD response of a single molecule appears to be too small to be determined. This measurement scheme obstructs the contribution of the individual molecule and thus does not allow for single molecule based secondary structure investigations. In recent years, researchers have been intensely studying chiral plasmonic systems. [5][6][7][8][9][10][11][12] A plasmon is the collective oscillation of the quasi-free conduction electrons in a metallic nanoparticle. Such plasmon resonances have large resonant light interaction cross sections which allow for the detection and measurement of single nanostructures. What is more, the locally enhanced near-fields associated with the plasmon resonance allow to couple adjacent nanoparticles and create plasmonic molecules of nearly arbitrary complexity. Due to advances in the top-down techniques related to micro-and nanofabrication, we are able to structure such systems in two and three dimensions nearly at will. [13][14][15] Additionally, bottomup techniques, such as DNA-mediated self-assembly, [16][17][18][19][20] even allow for switchable chiral structures. [21][22][23][24][25][26][27][28] Two aspects are of particular importance here: On the one hand, the tunability of these systems allows studying the properties of chirality in great detail while having full control over the chiral plasmonic structures, [29,30] which is in stark contrast to molecular systems whose structures cannot be manipulated easily. On the other hand, researchers are searching for interactions between chiral (bio)-molecules and chiral plasmonic molecules which could lead to decreased detection limits. [31][32][33][34][35][36] In all the mentioned cases, it is of large interest to study single structures and unravel the influence of even minute conformational differences or to track changes in time on a single structure level. Dark-field scattering spectroscopy has been widely used to measure the (chiral) optical response of single Chirality plays a crucial role in our everyday lives. Many biomolecules are handed and the associated biological processes rely on their handedness. Thus, chirality is investigated intensely, also because of the fundamental and inherent interest in the concept of chirality. However, virtually all studies are perfo...