Photonics / Fotonik

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

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Author: search.filters.author.Akbalı, BarışInstitution Author: search.filters.institutionAuthor.Senger, Ramazan Tuğrul

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  • Article
    Citation - WoS: 54
    Citation - Scopus: 54
    Strain Mapping in Single-Layer Two-Dimensional Crystals Via Raman Activity
    (American Physical Society, 2018) Yağmurcukardeş, Mehmet; Bacaksız, Cihan; Yağmurcukardeş, Mehmet; Akbalı, Barış; Senger, Ramazan Tuğrul; Senger, Ramazan Tuğrul; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    By performing density functional theory-based ab initio calculations, Raman-active phonon modes of single-layer two-dimensional (2D) materials and the effect of in-plane biaxial strain on the peak frequencies and corresponding activities of the Raman-active modes are calculated. Our findings confirm the Raman spectrum of the unstrained 2D crystals and provide expected variations in the Raman-active modes of the crystals under in-plane biaxial strain. The results are summarized as follows: (i) frequencies of the phonon modes soften (harden) under applied tensile (compressive) strains; (ii) the response of the Raman activities to applied strain for the in-plane and out-of-plane vibrational modes have opposite trends, thus, the built-in strains in the materials can be monitored by tracking the relative activities of those modes; (iii) in particular, the A peak in single-layer Si and Ge disappears under a critical tensile strain; (iv) especially in mono- and diatomic single layers, the shift of the peak frequencies is a stronger indication of the strain rather than the change in Raman activities; (v) Raman-active modes of single-layer ReX2 (X=S, Se) are almost irresponsive to the applied strain. Strain-induced modifications in the Raman spectrum of 2D materials in terms of the peak positions and the relative Raman activities of the modes could be a convenient tool for characterization.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Stable Ultra-Thin Cdte Crystal: a Robust Direct Gap Semiconductor
    (IOP Publishing Ltd., 2017) İyikanat, Fadıl; Akbalı, Barış; Selamet, Yusuf; Senger, Ramazan Tuğrul; Selamet, Yusuf; Senger, Ramazan Tuğrul; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Employing density functional theory based calculations, we investigate structural, vibrational and strain-dependent electronic properties of an ultra-thin CdTe crystal structure that can be derived from its bulk counterpart. It is found that this ultra-thin crystal has an 8-atom primitive unit cell with considerable surface reconstructions. Dynamic stability of the structure is predicted based on its calculated vibrational spectrum. Electronic band structure calculations reveal that both electrons and holes in single layer CdTe possess anisotropic in-plane masses and mobilities. Moreover, we show that the ultra-thin CdTe has some interesting electromechanical features, such as strain-dependent anisotropic variation of the band gap value, and its rapid increase under perpendicular compression. The direct band gap semiconducting nature of the ultra-thin CdTe crystal remains unchanged under all types of applied strain. With a robust and moderate direct band gap, single-layer CdTe is a promising material for nanoscale strain dependent device applications.