(45d) Au-Pd Alloys for Near-Infrared Hot Carrier Devices: Structural, Electronic and Optical Properties

Noble metals are the most common materials for plasmonic-based devices due to their chemical stability, small ohmic losses and high DC conductivity. However, the band structure of noble metals limits their performance in hot carrier (e.g. carriers that are not in equilibrium) devices that operate at near-infrared frequencies. This is due to fact that the majority of the electronic states in noble metals cannot be excited at these low energy wavelengths. One possible route to improve the near-infrared hot carrier response is to modify the electronic density of states (EDOS) of the noble metal via alloying with a transition metal.

Here, we present a simple low-cost method to fabricate single-phase Au-Pd alloy thin films at room temperature with tunable optical and electronic properties. We characterized the structural properties of the alloy thin films at different compositions by grazing incidence x-ray diffraction (GIXRD). The electronic and optical properties were evaluated by taking ultraviolet photoelectron spectroscopy (UPS) measurements and ellipsometry measurements, respectively. While UPS represents the EDOS, the ellipsometry data shows the complex dielectric function.

Our GIRXD results show that all Au-Pd alloythin films are true alloys (single phase) with face centered cubic crystal structure. UPS data supports our initial hypothesis that adding Pd to Au considerably increases the EDOS in the near-infrared region which could imply an improvement in hot carrier generation from devices made with Au-Pd alloys instead of noble metals. The ellipsometry measurements show that adding Au to Pd modifies the dielectric constants of the metals which results in an improvement for the optical performance compared with pure Pd in the near-infrared region.