Temperature-Dependent Optical Properties of Single Crystalline and Polycrystalline Silver Thin Films

Abstract

Silver holds a unique place in plasmonics compared to other noble metals owing to its low losses in the visible and near-IR wavelength ranges. With a growing interest in local heating and high temperature applications of plasmonics, it is becoming critical to characterize the dielectric function of nanometer-scale thin silver films at higher temperatures, especially near the breakdown temperature, which depends on the film thickness and crystallinity. So far, such a comprehensive study has been missing. Here we report the in situ high temperature ellipsometry measurements of ultrasmooth and epitaxial quality crystalline silver films, along with electron beam evaporated polycrystalline silver films at temperatures up to 700 °C, in the wavelength range of 330−2000 nm. Our findings show that the dielectric function of all the films changes remarkably at elevated temperatures with larger relative changes observed in polycrystalline films. In addition, low-loss epitaxial films were found to be thermally more stable at elevated temperatures. We demonstrate the importance of our findings for high temperature applications with a numerical simulation of field enhancement in a bow-tie nanoantenna, a near field transducer commonly used for heat-assisted magnetic recording. The simulated field profiles at elevated temperatures showed significant deviations compared to those at room temperature, clearly suggesting that the use of room temperature optical properties in modeling elevated temperature applications can be misleading due to the thermal deviations in the Ag dielectric function. We also provide causal analytical models describing the elevated temperature Ag dielectric functions.

Temperature-Dependent Optical Properties of Plasmonic Titanium Nitride Thin Films

“…Particularly, the real part of all the films showed a monotonic decrease in their magnitude (Fig 1(a),(c),(e)), reducing the metallicity. Contrary to the conventional understanding, the observed decrease in the magnitude of the real part is primarily because of the increase in the Drude broadening D , but not due to the decrease in the plasma frequency p 24 . In fact, p marginally increases with temperature up to 800 0 C (maximum deviation < 6%, see Drude-Lorentz oscillator models in Tables S1-S3).…”

“…In contrast to the noble metals, the temperature evolution of the dielectric function in TiN is nearly independent of the thickness. Furthermore, thin Au and Ag polycrystalline (single crystalline) films showed severe structural and surface morphological degradation upon heating to temperatures close to 400 0 C (600 0 C) 23,24 . However, no such structural or morphological degradation was observed in TiN films, even though the samples were heated to higher temperatures (AFM topographs on 50 nm TiN are shown in Fig S5).…”

Thermal effects – an alternative mechanism for plasmon-assisted photocatalysis

“…[21,22] as well as the necessary temperature-dependent permittivity data presented in Refs. [23][24][25][26] and references therein.…”

Life under Continuous Streaming: Recrystallization of Low Concentrations of Bacterial SbpA in Dynamic Flow Conditions

“…The formation of coatings expressing different crystallinity properties (mono vs. poly, semi-crystallinity, etc.) has extensively been reported in the literature for diverse starting materials such as polymers, noble metals, ionic salts, or proteins [2][3][4][5][6][7]. Regarding the particular use of peptides/proteins as film building blocks, there exist well-known examples which induce spontaneous crystal formation via cooperative self-assembly of those protein subunits into an ordered superstructure [8,9].…”