On the characteristics and optical properties of Mn-based (MnO 2 ) helical conical nanostructure thin films
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RESEARCH
On the characteristics and optical properties of Mn‑based (MnO2) helical conical nanostructure thin films Fahimeh Farid‑Shayegan1 · Hadi Savaloni2 Received: 11 July 2020 / Accepted: 28 October 2020 © Islamic Azad University 2020
Abstract Mn-based helical conical nano-sculptured thin films were fabricated by means of oblique angle deposition method in conjunction with the rotation of sample holder with different speeds at different pitches of each revolution. Atomic force microscopy, field emission scanning electron microscopy and X-ray diffraction (XRD) analyses were used to obtain morphology, nanostructure and crystallography of the samples. Formation of M nO2 film by the proposed method of this work is confirmed by the XRD results. Optical spectra of the films were obtained using s- and p-polarized incident lights at three different incident light angles of 0°, 20° and 30°. Bruggeman homogenization method was employed to obtain spectra for different optical parameters. The observed peaks/oscillations in these spectra are related to the different radii of the deposited sculptured structure with helical conical shape. Results show that by engineering of Mn-based ( MnO2) helical conical sculptured thin film the absorption is increased. Hence, by engineering of this type of thin films the absorption increases due to entrapment of light between the elements of the structure (rings) and results in a high broadband absorption. Keywords Mn-based helical conical · Sculptured thin films · s-polarization · p-polarization · Bruggeman homogenization
Introduction Different properties of Mn are given in detail in a review paper by Demangeat and Parlebas [1]. We used manganese in our earlier work [2] in which only simple nanorod structures were grown at different angles. Results of optical investigation on those structures did not show any particular phenomenon. The refractive index of manganese unlike noble metals does not show much variation with wavelength [3]; hence, in a normal case such as those discussed in our earlier work [2], its extinction spectra do not show pronounced plasmon peaks. The X-ray diffraction analysis of the samples in that work only showed a weak Mn (330) peak at higher deposition angles of 45° and 60°. In another work [4], in order to observe the plasmonic peaks for Mn, the geometry of the nanoparticles in the structure of Mn thin films was changed by using the oblique angle deposition (OAD) * Hadi Savaloni [email protected] 1
Plasma Physics Research Center, Faculty of Science, Science and Research Branch, Islamic Azad University, Tehran, Iran
School of Physics, College of Science, University of Tehran, North‑Kargar Street, Tehran, Iran
2
technique together with the rotation of the substrate and produced sculptured thin films of different shapes (i.e., helical rectangles and helical pentagon). These structures consisted of nanorods that are positioned at different angles relative to each other. Hence, their structure included numerous hot spots which in turn can be re
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