Photonics / Fotonik

Permanent URI for this collectionhttps://hdl.handle.net/11147/2590

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Author: search.filters.author.Bacaksız, CihanPublisher: search.filters.publisher.Royal Society of Chemistry

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  • Article
    Citation - WoS: 65
    Citation - Scopus: 67
    Angle Resolved Vibrational Properties of Anisotropic Transition Metal Trichalcogenide Nanosheets
    (Royal Society of Chemistry, 2017) Kong, Wilson; Bacaksız, Cihan; Şahin, Hasan; Wu, Kedi; Blei, Mark; Fan, Xi; Shen, Yuxia; Şahin, Hasan; Wright, David; Narang, Deepa S.; Tongay, Sefaattin; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Layered transition metal trichalcogenides (TMTCs) are a new class of anisotropic two-dimensional materials that exhibit quasi-1D behavior. This property stems from their unique highly anisotropic crystal structure where vastly different material properties can be attained from different crystal directions. Here, we employ density functional theory predictions, atomic force microscopy, and angle-resolved Raman spectroscopy to investigate their fundamental vibrational properties which differ significantly from other 2D systems and to establish a method in identifying anisotropy direction of different types of TMTCs. We find that the intensity of certain Raman peaks of TiS3, ZrS3, and HfS3 have strong polarization dependence in such a way that intensity is at its maximum when the polarization direction is parallel to the anisotropic b-axis. This allows us to readily identify the Raman peaks that are representative of the vibrations along the b-axis direction. Interestingly, similar angle resolved studies on the novel TiNbS3 TMTC alloy reveal that determination of anisotropy/crystalline direction is rather difficult possibly due to loss of anisotropy by randomization distribution of quasi-1D MX6 chains by the presence of defects which are commonly found in 2D alloys and also due to the complex Raman tensor of TMTC alloys. Overall, the experimental and theoretical results establish non-destructive methods used to identify the direction of anisotropy in TMTCs and reveal their vibrational characteristics which are necessary to gain insight into potential applications that utilize direction dependent thermal response, optical polarization, and linear dichroism.
  • Article
    Citation - WoS: 10
    Citation - Scopus: 11
    Single layer PbI2: Hydrogenation-driven reconstructions
    (Royal Society of Chemistry, 2016) Bacaksız, Cihan; Şahin, Hasan; Şahin, Hasan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of Technology
    By performing density functional theory-based calculations, we investigate how a hydrogen atom interacts with the surfaces of monolayer PbI2 and how one- and two-side hydrogenation modifies its structural, electronic, and magnetic properties. Firstly, it was shown that the T-phase of single layer PbI2 is energetically more favorable than the H-phase. It is found that hydrogenation of its surfaces is possible through the adsorption of hydrogen on the iodine sites. While H atoms do not form a particular bonding-type at low concentration, by increasing the number of hydrogenated I-sites well-ordered hydrogen patterns are formed on the PbI2 matrix. In addition, we found that for one-side hydrogenation, the structure forms a (2 × 1) Jahn-Teller type distorted structure and the bandgap is dramatically reduced compared to hydrogen-free single layer PbI2. Moreover, in the case of full hydrogenation, the structure also possesses another (2 × 2) reconstruction with a reduction in the bandgap. The easily tunable electronic and structural properties of single layer PbI2 controlled by hydrogenation reveal its potential uses in nanoscale semiconducting device applications.