Ultra-thin metallic films are widely applied in optics and microelectronics. However, their properties differ significantly from the bulk material and depend on the substrate material. The nucleation, film growth, and layer properties of atomic layer deposited (ALD) iridium thin films are evaluated on silicon wafers, BK7, fused silica, SiO₂, TiO₂, Ta₂O₅, Al₂O₃, HfO₂, Ru, Cr, Mo, and graphite to understand the influence of various substrate materials. This comprehensive study was carried out using scanning electron and atomic force microscopy, X-ray reflectivity and diffraction, four-point probe resistivity and contact angle measurements, tape tests, and Auger electron spectroscopy. Within few ALD cycles, iridium islands occur on all substrates. Nevertheless, their size, shape, and distribution depend on the substrate. Ultra-thin (almost) closed Ir layers grow on a Ta₂O₅ seed layer after 100 cycles corresponding to about 5 nm film thickness. In contrast, the growth on Al₂O₃ and HfO₂ is strongly inhibited. The iridium growth on silicon wafers is overall linear. On BK7, fused silica, SiO₂, TiO₂, Ta₂O₅, Ru, Cr, and graphite, three different growth regimes are distinguishable. The surface free energy of the substrates correlates with their iridium nucleation delay. Our work, therefore, demonstrates that substrates can significantly tailor the properties of ultra-thin films.

The structural, optical, and mechanical properties of TiO₂ nanolaminate films grown by plasma-enhanced atomic layer deposition are discussed. Several TiO₂/Al₂O₃ and TiO₂/SiO₂ compositions have been investigated to study the effect of the relative number of ALD oxide cycles on the film properties to obtain a high refractive index coating with low optical losses, low roughness, and low mechanical stress. The formation of crystalline TiO₂ observed at high deposition temperature, or film thickness was inhibited by periodically introducing ultra-thin amorphous layers into the film. Only 4 ALD cycles of Al₂O₃ (corresponding to ca. 0.5 nm) between 335 ALD cycles of TiO₂ (ca. 11 nm) form a closed, distinct layer suppressing the crystallization in TiO₂ film. Consequently, the roughness of the pure TiO₂ film is reduced from ca. 20 nm rms to 1 nm rms in the 335/4 nanolaminate, with only a slight decrease of the refractive index from 2.46 to 2.44 in 100 nm pure TiO₂ and the nanolaminate, respectively. The refractive indices of the nanolaminates in various compositions vary between 2.38 and 2.50 at 632 nm, and the corresponding optical losses from the films are low. The mechanical stress was reduced to about 140 MPa in several TiO₂/Al₂O₃ nanolaminates; however, lower mechanical stress has not been obtained with the studied compositions. The nanolaminate structure is preserved up to 600 °C annealing temperature. After annealing at 800 °C, the individual layers interdiffuse into each other so that no distinct nanolaminate structure is detected. By using TiO₂/Al₂O₃ nanolaminates with reduced mechanical stress, a narrow bandpass filter was realized on various substrates, including half-ball and aspherical lenses.

HfO₂ has promising applications in semiconductors and optics due to its high dielectric constant and high refractive index. In this work, HfO₂ thin films were deposited by plasma enhanced atomic layer deposition (PEALD) using tetrakis-dimethylamino hafnium (TDMAH) and oxygen plasma. The process optimization to obtain high quality HfO₂ thin films with excellent uniformity over a 200 mm diameter is thoroughly discussed. The effects of deposition temperature and plasma parameters on the structural, mechanical, and optical properties, and the chemical composition of the films were investigated. Optimized process parameters yielding a high refractive index, high density, low impurities, low OH incorporation, low absorption in the UV spectral range, and high laser-induced damage threshold (LIDT) were selected for antireflection coatings. The HfO₂ thin films were incorporated into antireflection coatings designed for the fundamental wavelength at 1064 nm and its higher harmonics up to the 4^th order.

Absorption losses and laser-induced damage threshold (LIDT) are considered to be the major constraints for development of optical coatings for high-power laser optics. Such coatings require paramount properties, such as low losses due to optical absorption, high mechanical stability, and enhanced damage resistance, to withstand high-intensity laser pulses. In this work, heterostructures were developed by sub-nanometer thin films of SiO₂ and HfO₂ using the plasma-enhanced atomic layer deposition (PEALD) technique. Thin-film characterization techniques, such as spectroscopic ellipsometry, spectrophotometry, substrate curvature measurements, X-ray reflectivity, and Fourier transform infrared spectroscopy, were employed for extracting optical constants, residual stress, layer formation, and functional groups present in the heterostructures, respectively. These heterostructures demonstrate tunable refractive index, bandgap, and improved optical losses and LIDT properties. The films were incorporated into antireflection coatings (multilayer stacks and graded-index coatings) and the LIDT was determined at 355 nm wavelength by the R-on-1 method. Optical absorptions at the reported wavelengths were characterized using photothermal common-path interferometry and laser-induced deflection techniques.

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.