Temperature stability of thin film refractory plasmonic materials

Abstract

Materials such as W, TiN, and SrRuO (SRO) have been suggested as promising alternatives to Au and Ag in plasmonic applications owing to their stability at high operational temperatures. However, investigation of the reproducibility of the optical properties after thermal cycling between room and elevated temperatures is so far lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, SrRuO and SrNbO are investigated to assess their viability for robust refractory plasmonic applications. These results are further compared to the performance of SrMoO reported in literature. Films ranging in thickness from 50 to 105 nm are deposited on MgO, SrTiO and Si substrates by e-beam evaporation, RF magnetron sputtering and pulsed laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic ellipsometry, and DC resistivity. Measurements are conducted before and after annealing in air at temperatures ranging from 300 to 1000° C for one hour, to establish the maximum cycling temperature and potential longevity at elevated temperatures for each material. It is found that SrRuO retains metallic behaviour after annealing at 800° C, while SrNbO undergoes a phase transition resulting in a loss of metallic behaviour after annealing at 400° C. Importantly, the optical properties of TiN and TiON are degraded as a result of oxidation and show a loss of metallic behaviour after annealing at 500° C, while the same is not observed in Au until annealing at 600° C. Nevertheless, both TiN and TiON may be better suited than Au or SRO for high temperature applications operating under vacuum conditions.

Hot carrier optoelectronics with titanium nitride

“…Additionally, titanium nitride has been shown to achieve enhanced hot electron harvesting relative to gold, [7,8] and indeed is reported to have long-lived hot carriers [9], although the physical origin of this phenomenon is poorly understood. TiN is also expected to be resilient to high operating temperatures [10]. The physical properties of TiN are extremely sensitive to the substitution of oxygen within its lattice, enabling also the tuning of its optical response.…”

3D Hybrid Plasmonic Framework with Au Nanopillars Embedded in Nitride Multilayers Integrated on Si

“…[26] It is noted that previous study has suggested that Au might be more thermally stable in air than TiN. [27] TiN grown under low temperature is CMOS compatible. [28,29] Furthermore, epitaxial TiN thin film has been previously reported grown on Si substrate by domain epitaxial matching, that is, 4 of TiN (002) match with 3 of Si (004) to overcome the very large lattice mismatch (f ≈ 24%).…”

Metamaterial emitter for thermophotovoltaics stable up to 1400 °C

“…Such refractory metals need to be structured to provide spectral selectivity 19–22 . There are two major mechanisms that lead to degradation of these structures: surface diffusion 23–26 and oxidation 22,27–30 . The 2D and 3D structured materials contain edges on the nano scale which are subject to strong surface diffusion at temperatures below 1200 °C 25,26,31–33 .…”