Yttrium hydride nanoantennas for active plasmonics.

A key challenge for the development of active plasmonic nanodevices is the lack of materials with fully controllable plasmonic properties. In this work, we demonstrate that a plasmonic resonance in top-down nanofabricated yttrium antennas can be completely and reversibly turned on and off using hydrogen exposure. We fabricate arrays of yttrium nanorods and optically observe, in extinction spectra, the hydrogen-induced phase transition between the metallic yttrium dihydride and the insulating trihydride. Whereas the yttrium dihydride nanostructures exhibit a pronounced particle plasmon resonance, the transition to yttrium trihydride leads to a complete vanishing of the resonant behavior. The plasmonic resonance in the dihydride state can be tuned over a wide wavelength range by simply varying the size of the nanostructures. Furthermore, we develop an analytical diffusion model to explain the temporal behavior of the hydrogen loading and unloading trajectories observed in our experiments and gain information about the thermodynamics of our device. Thus, our nanorod system serves as a versatile basic building block for active plasmonic devices ranging from switchable perfect absorbers to active local heating control elements.

Silver nanowires as surface plasmon resonators.

We report on chemically prepared silver nanowires (diameters around 100 nm) sustaining surface plasmon modes with wavelengths shortened to about half the value of the exciting light. As we find by scattered light spectroscopy and near-field optical microscopy, the nonradiating character of these modes together with minimized damping due to the well developed wire crystal structure gives rise to large values of surface plasmon propagation length and nanowire end face reflectivity of about 10 microm and 25%, respectively. We demonstrate that these properties allow us to apply the nanowires as efficient surface plasmon Fabry-Perot resonators.

Wavelength-dependent optical extinction of carbonaceous particles in atmospheric aerosols and interstellar dust.

Optical extinction spectra for particles of structurally disordered carbonaceous material (carbon black, soot) are discussed in terms of the effects of size and shape and the difference between coagulated and coalesced particles. For this purpose, the orientation-averaged specific extinction for several compact and open aggregates of spherical particles is calculated and compared with the specific extincton by homogeneous particles, i.e., volume-equivalent sphere and elongated spheroids. The extinction spectra are calculated for wavelengths from 0.2 to 1000 microm by use of the optical constants for the carbonaceous materials of Jäger et al. [Astron. Astrophys. 332, 291 (1998)] and Schnaiter et al. [Astrophys. J. 498, 486 (1998)]. Comparisons with the model case of particles composed of graphite and with measurements of diesel soot aerosols are made.