Abstract: Erbium oxide (Er₂O₃) coatings were deposited using filtered vacuum arc deposition (FVAD) and their structure and thermal stability were studied as a function of fabrication parameters. The coatings were deposited on silicon wafer and tantalum substrates with an arc current of 50 A and a deposition rate of 1.6 ± 0.4 nm/s. The arc was sustained on truncated cone Er cathodes. The influence of oxygen pressure (P= 0.40-0.93 Pa), bias voltage (V_b= -20, -40 or grounded) and substrate temperature (room temperature (RT) or 673K) on film properties was studied before and after post deposition annealing (1273K for 1 hour, at P~ 1.33 Pa). The coatings were characterized using X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Knoop Hardness.

Optical microscope images indicated that the coatings had very low macroparticle concentration on their surface. The macroparticle diameters were less than 2.5 μm. The coatings were composed of only Er₂O₃ without any metallic phase under all deposition parameters tested. The coatings deposited on RT substrates were XRD amorphous and had a featureless cross-section microstructure. However, the coatings deposited on 673K heated substrates had a C-Er₂O₃ structure with (222) preferred orientation and weak columnar microstructure. The coating hardness varied with deposition pressure and substrate bias, and reached a maximum value of 10 GPa at P = 0.4 Pa and V_b = -40 V. The post-deposition annealing caused crystallization, and the coatings hardness dropped to 4 GPa with thermal treatment. However, after post-deposition annealing, no peeling or cracking appeared at the coating surface or the interface with the substrate.

Keywords: Erbium oxide, Filtered vacuum arc deposition, thin films, thermal stability, crystallinity.

Abstract: Topography and composition of Cr-free, titanium-based pretreatment layers on hot dip galvanized steel were studied with scanning electron microscopy, atomic force microscopy, time of flight secondary ion mass spectrometry and Auger electron spectroscopy. A layer within the target coating weight range (4-10 mg Ti/m²) for industrial coil coating processes contained a micro-structure with hillocks and valleys, showing significant topographical variations. A local maximum film thickness of about 50 nm was detected for a sample containing 5.0 mg Ti/m². The hillocks were composed of metal complexes and phosphates, formed as a result of rapid zinc dissolution and metal hydroxide/phosphate precipitation reactions. During the layer formation also the polymer component of the pretreatment chemical becomes embedded within the structure. The structure composed of hillocks and valleys may be highly beneficial for paint adhesion, increasing the surface contact area for primary and secondary chemical bonding.

Keywords: Atomic force microscopy, time of flight secondary ion mass spectrometry, Auger electron spectroscopy, coil coating, Cr-free pretreatment, topography.