Optical, structural, and functional properties of highly reflective and stable iridium mirror coatings for infrared applications

Abstract

Metallic coatings are essential for numerous optical systems due to their high and broadband reflectivity in the infrared spectral range. In contrast to well-established (protected) silver and gold mirror coatings, iridium is environmentally durable, referring to ISO 9211-3 and thermally stable up to 600 °C even without protective layers, as demonstrated. Additionally, the optical and related structural properties of atomic layer deposited (ALD) and magnetron sputtered (MS) Ir coatings were investigated using spectrophotometry, FTIR, ellipsometry, WLI, AFM, XRR, XRD, SEM, and electrical resistivity measurements. The properties of Ir ALD and Ir MS coatings differ due to their topography and microstructure.

Nonlinear polarization holography of nanoscale iridium films

“…For the second hologram, the sample is replaced by a substrate with a 5 nm-thick Ir film on the rear side produced by atomic layer deposition (ALD), see appendix. Coatings of Ir are interesting for optical applications because they do not require protective layers due to their high intrinsic stability and have a high reflectivity into x-ray frequencies [17]. In the present experiment, we found that the Ir films withstand higher laser intensities than gold films.…”

“…ALD process parameters for growing Ir are as follows: 6 s Ir(acac) 3 pulse/60 s N 2 purge/2 s O 2 pulse/6 s N 2 purge, resulting in a growth per cycle of 0.6 Å/cycle [17,38]. For the present study, relaxation mechanisms such as scattering play an important role.…”

“…The band shapes are approximated by ω k = ω0 + 1 2 b1(1 − cos(ka) − b3 (cos(3ka) − cos(ka))) with ω0 = −1.4 eV, b1 = 4 eV, b3 = 2 for the conduction band and ω0 = −1.5 eV, b1 = 1.45 eV, b3 = 2 for the valence band with the lattice constant a = 0.384 nm.The shape of the conduction band is similar as calculations on https://materialsproject.org, the shape of the valence band is chosen to enable interband transitions within the optical spectrum of the laser pulse. The real (imaginary) part of the linear refractive index of the two-band model (12) (red) and experimental reference data[17] (black dashed) are shown in (b) and (c). The blue line shows the refractive index solely due to intra-band transitions in the conduction band (calculated with(10)), the green line shows the refractive index solely due to inter-band transitions (calculated with(11)).…”

Nonlinear polarization holography of nanoscale iridium films

“…The deposition temperature was kept at 380°C. The ALD process parameters for growing Ir are as follows: 6 sec Ir(acac) 3 pulse/60 sec N 2 purge/2 sec O 2 pulse/6 sec N 2 purge, resulting in a growth per cycle (GPC) of 0.6 Å/cycle [35,37]. 6) are displayed with equilibrium decay (according to (10)) or symmetrizing decay (according to ( 9)).…”

“…The band shapes are approximated by ω k = ω 0 + 1 2 b 1 (1 − cos(ka) − b 3 (cos(3ka) − cos(ka))) with ω 0 = −1.4 eV, b 1 = 4 eV, b 3 = 2 for the conduction band and ω 0 = −1.5 eV, b 1 = 1.45 eV, b 3 = 2 for the valence band with the lattice constant a = 0.384 nm.The shape of the conduction band is similar as calculations on https://materialsproject.org, the shape of the valence band is chosen to enable interband transitions within the optical spectrum of the laser pulse. The real (imaginary) part of the linear refractive index of the two-band model (17) (red) and experimental reference data[35] (black dashed) are shown in b (c). The blue line shows the refractive index solely due to intra-band transitions in the conduction band (calculated with (15)), the green line shows the refractive index solely due to inter-band transitions (calculated with (16)).…”