Thickness-dependent growth of Ni vertical columns deposited by GLAD method: Study on the microstructural and optical properties

The paper presents a study on the structural and optical properties of nickel (Ni) thin films in the shape of vertical columns obtained by using the glancing angle deposition method. The films are deposited onto glass substrates at a fixed deposition angle of 85° to the different thicknesses of 50 nm, 80 nm, 110 nm, and 140 nm. Field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and high resolution transmission electron microscopy (HR-TEM) were utilized to analyze the morphological, chemical, and microstructural properties of the films. SEM and TEM analyses are showing well-defined columnar structures, where the increase in thickness leads to more porous films and larger column diameters. The results of the surface examination of the XPS confirm that metallic Ni is a major phase in the deposited structures, but all samples also exhibit a certain amount of oxide phases. The optical measurements of the effective dielectric function reveal that both real and imaginary parts are strongly influenced by the changes in the film thickness. The surface plasmon resonance (SPR) peak is significantly shifted from 585.6 nm, as obtained for a 50 nm thick film, to 1291.8 nm in the case of a thickness of 140 nm. The variation in SPR peak position can be related to the differences in the film's morphology, and it is attributed to the changes in the size of the formed Ni nanoparticles. Finally, the experimental results show that with increasing film thickness, the electrical resistivity decreases. Both optical and electrical properties are found to be determined by the growth mechanism, and they are discussed on the basis of the defect concentration of the films.