Adsorption Dynamics of CO on Silica Supported CuO_<i>x</i> Clusters: Utilizing Electron Beam Lithography To Study Methanol Synthesis Model Systems

Electron beam lithography was used to nanofabricate 12 and 63 nm Cu clusters supported on silica (model nanoarray catalysts). The Cu clusters could reversibly be oxidized and reduced at ultrahigh vacuum conditions. The chemical activity of these clusters was probed by Auger and X-ray photoelectron spectroscopy, thermal desorption spectroscopy, and molecular beam scattering. CO was used as the probe molecule. Scanning electron microscopy was used to obtain cluster size distributions. CO adsorption is molecular and nonactivated. CO binding energies on the oxidic clusters are larger than for the metallic clusters. Adsorption transients, recorded as a function of surface temperature and CO impact energy, are consistent with precursor models, as expected from the so-called capture zone model (CZM). Cluster size effects are evident, as predicted by the CZM. However, unexpectedly, the CO saturation coverage does not simply scale with the cluster area but depends also on the rim length of the deposits. Metallic Cu clusters are more reactive than oxidic clusters, in part not only due to the cluster size effect but apparently also because of the electronic effect

Reaching the Theoretical Resonance Quality Factor Limit in Coaxial Plasmonic Nanoresonators Fabricated by Helium Ion Lithography

Optical antenna structures have revolutionized the field of nano-optics by confining light to deep subwavelength dimensions for spectroscopy and sensing. In this work, we fabricated coaxial optical antennae with sub-10-nanometer critical dimensions using helium ion lithography (HIL). Wavelength dependent transmission measurements were used to determine the wavelength-dependent optical response. The quality factor of 11 achieved with our HIL fabricated structures matched the theoretically predicted quality factor for the idealized flawless gold resonators calculated by finite-difference time-domain (FDTD). For comparison, coaxial antennae with 30 nm critical dimensions were fabricated using both HIL and the more common Ga focus ion beam lithography (Ga-FIB). The quality factor of the Ga-FIB resonators was 60% of the ideal HIL results for the same design geometry due to limitations in the Ga-FIB fabrication process