Observation of Plasmoelectric Effect in Plasmonic Zirconium Nitride

Abstract

silicon-gold (Si-Au) interface can harvest near-infrared light longer than 1100 nm, [1] allowing near-infrared photodetection using Si-based structures with improved efficiencies. Sub-bandgap excitation is not limited to Si; other semiconductors such as germanium, [2] III-V semiconductors, [3] and oxide semiconductors [4] have also demonstrated subbandgap hot-carrier excitations when they form heterojunctions with metals. What is common among these demonstrations is that hot carrier excitations are drastically enhanced at surface plasmon resonance wavelengths [5] where plasmon resonances are responsible for increasing optical absorption and local electric fields. As hot carrier excitations take place at the nanoscale, scanning probe techniques [6] including Kelvin probe force microscope (KPFM) [7] and conductive atomic force microscope [8] turned out to be powerful tools to directly image hot carriers at the nanoscale.If a metallic nanostructure is in contact with a metal, but not with a semiconductor, charge separation typically does not occur through optical excitation such that photo-induced voltage due to hot carriers will not be generated. However, recent studies have proposed a mechanism to generate voltage in such a structure, that is, the plasmoelectric effect. [9] Consider a nanostructure under optical irradiation in a steady state and a derivative of the thermodynamic free energy of the system. The chemical potential µ can be expressed as follows:A plasmonic nanostructure forming a metal-semiconductor interface generates electric potential by optical illumination. Grounded plasmonic nanostructures can also generate electric potentials based on the recently demonstrated plasmoelectric effect that allows all metallic photoelectric devices to be fabricated and is capable of generating negative and positive potentials at offresonance by merely tuning the illumination wavelength. However, to date, the plasmoelectric effect has been observed only with gold and silver. In this study, the generation of plasmoelectric effect by zirconium nitride (ZrN) is experimentally demonstrated, which is a nonmetallic plasmonic material. The Kelvin probe force microscope measurements demonstrate that ZrN nanodisk arrays fabricated through e-beam lithography and dry etching exhibit characteristic potential sign changes of the plasmoelectric potential. The features of the wavelength-dependent potential shifts in the experiments agree with the numerical calculations. It is anticipated that the plasmoelectric effect can be observed in other non-metallic plasmonic materials and these studies may lead to robust photoelectric devices working at off-resonances.

Innovative Process to Obtain Thin Films and Micro-Nanostructured Zrn Films from a Photo-Structurable Zro2 Sol-Gel Using Rapid Thermal Nitridation

“…Indeed, few authors have reported processes to pattern ZrN films. E-beam lithography and dry etching [25] or scanning probe microscopy oxidation and hydrofluoric acid etching [26] were used for this purpose, but these techniques are time consuming, use toxic products, and are expensive. Conversely, sol-gel ZrO 2 can be easily structured by UV exposure [27], thereby making it possible to create ZrN micro-nanostructured thin films with complex shapes after nitridation.…”