Development of Submicrometer Conical Surface Morphology on Nanometer-Thick Al–Fe Alloy Films under Various Conditions of Ion-Assisted Deposition onto Glass

Abstract

The morphology, topography, and wettability with distilled water of Al–1.5 at % Fe alloy films with thicknesses of 25–90 nm are investigated. These films are formed on glass by ion-assisted deposition using a resonance ion source of vacuum arc plasma. Scanning probe microscopy reveals that the longitudinal and transverse roughness parameters, as well as dimensionless complexes, vary depending on the deposition mode and time. Measurement of these dimensionless parameters yields a quantitative description of cone formation processes in the Al–Fe/glass system. The mean roughness of the films increases in the range of 20–40 nm within the duration of deposition. Under self-irradiation conditions, the transition from island growth of the films to layered growth is observed. The effect of the substrate relief on the longitudinal step parameters of the film topography is found. Scanning electron microscopy is employed to examine the size and surface density of microdroplet-fraction particles. The size-frequency distributions of the microdroplet fraction are satisfactorily approximated by a lognormal distribution. Under self-ion irradiation conditions, 60–70% of particles comprising the microdroplet fraction are up to 0.8 µm in size. For the first time, a double Gaussian function is employed to approximate histograms of the distribution of relief features in the films, improving the accuracy in the description compared to a normal distribution law. The effectiveness of this approach in analyzing the structural formation of nanoscale films at various growth stages is demonstrated. By employing a bi-Gaussian model of the surface, the role of topographic characteristics in controlling the wetting of modified coatings is determined. The mechanism of the heterogeneous wetting of hydrophilic films in the Cassie state with contact edge angles of 50°–80° is discussed. In the potential mode, with an increase in deposition duration up to 10 h, the relief distribution of the films approximates a normal distribution, and the development of a submicrometer conical morphology on the surface leads to mixed wetting.