Nano-structure and optical properties (plasmonic) of graded helical square tower-like (terraced) Mn sculptured thin films

• Published in: Applied surface science 2017-01, Vol.393, p.234-255
• Main Authors: Savaloni, Hadi, Fakharpour, Mahsa, Siabi-Garjan, Araz, Placido, Frank, Babaei, Ferydon
• Format: Article
• Language: English
• Subjects: Blue shift; Electric near-field distribution; Extinction spectra; Graded helical; Manganese; Nanostructure; Optical properties; Scanning electron microscopy; Shadows; Square sculptured thin films; Substrates; Terraced; Thin films; Wavelengths
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2016.10.012

[Display omitted] •Graded helical square tower-like terraced sculptured Mn thin films are produced with different number of arms.•XRD, AFM, FESEM and optical analyses as well as theoretical calculations are carried out.•Intensity of Plasmon peaks depend on the polarization, the incident angle, and the distance from the shadowing block.•The presence of defects in these sculptured structures can be predicted by theoretical investigation.•Experimental and theoretical investigations show consistent results. Graded helical square tower-like terraced sculptured Mn thin films (GHSTTS) are produced in three stages with different number of arms using oblique angle deposition together with rotation of substrate holder about its surface normal, plus a shadowing block fixed at the centre of the substrate holder. The structural characterization of the produced samples was obtained using field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). Results showed a structural gradient with distance from the edge of the shadowing block, which in turn is responsible for the decrease in the volume of void fraction and increase of grain size. Plasmon absorption peaks observed in the optical analysis of these nano-structures showed that their wavelength region and intensity depend on the polarization and the incident angle of light, as well as the distance from the edge of the shadowing block. According to our model and discrete dipole approximation (DDA) calculations, when the number of parallel nano-rods of different lengths and radii are increased the peak in the spectrum shifts to shorter wavelengths (blue shift). Also when the diameters of the nano-rods increases (a situation that occurs with increasing film thickness) the results is again a blue shift in the spectrum. The presence of defects in these sculptured structures caused by the shadowing effect is predicted by the theoretical DDA investigation of their optical spectra. Good agreement is obtained between our theoretical results and the experimental observations in this work.