Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Author: search.filters.author.Kang, Jun

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  • Article
    Molecular Engineering of Exchange Bias in Fe3GeTe2/Molecule Heterostructures
    (Amer Chemical Soc, 2025) Sharma, Mayank; Jo, Junhyeon; Avedissian, Garen; Bayindir, Bertug; Kang, Jun; Sahin, Hasan; Hueso, Luis E.
    Molecules offer a versatile route to tailor magnetism through chemical design and spin-state control. When integrated with surface-sensitive layered magnets, molecules can not only exhibit tunable magnetic properties or even activate distinct magnetic phases but can also interact with the layered magnets to manipulate their magnetic dynamics. Here, we demonstrate tunable exchange bias in hybrid heterostructures composed of the layered ferromagnet Fe3GeTe2 (FGT) and metallophthalocyanine (MPc) molecules having different central transition ions: MnPc, ZnPc, and H2Pc. The MnPc/FGT system exhibits a robust exchange bias of 1000 Oe at 10 K, with a record-high exchange bias-to-coercivity ratio of 0.37, attributed to the antiferromagnetic nature of MnPc. Surprisingly, the diamagnetic ZnPc induces a finite exchange bias of 200 Oe, highlighting the contribution of the emerging spinterface effect. In contrast, the metal-free H2Pc yields no exchange bias, underscoring the essential role of designed molecules for magnetic interaction. First-principles calculations reveal energetically favorable stacking configurations and spin alignments, in agreement with experimental observations. These results highlight the potential of molecular functionalization on magnetism, enabling the on-demand engineering of layered magnetic systems.
  • Article
    Citation - WoS: 17
    Citation - Scopus: 18
    Origin of Anomalous Band-Gap Bowing in Two-Dimensional Tin-Lead Mixed Perovskite Alloys
    (American Physical Society, 2021) Gao, Qiang; Şahin, Hasan; Kang, Jun; Wei, Su-Huai
    The origin of the pronounced and composition-dependent band-gap bowing in Sn/Pb mixed perovskite alloys has been under debate for a long time. Previous studies reported conflicting results on whether the chemical or structural effect is the dominant mechanism. In this paper, the band-gap bowing effect and its possible origins in recently synthesized two-dimensional (2D) Cs2PbxSn1-xI2Cl2 alloys are investigated from first-principles calculations. In agreement with experiments, a large and composition-dependent bowing coefficient is observed. By analyzing the contribution from volume deformation, charge exchange, structural relaxation, and short-range order, it is found that the dominant mechanism causing the anomalous gap bowing is the structural relaxation-induced wave-function localization, forming isovalent-defect-like states, despite the negligible octahedral distortion and small lattice mismatch between the two end compounds. This is understood by the s-p repulsion-induced strong antibonding character of the valence-band maximum which leads to a large deformation potential, thus even a small atomic displacement can result in a large shift of the energy level. These results thus highlight the critical role of strong deformation potential and structural relaxation effect in unusual band evolution of 2D Sn/Pb perovskite alloys, and can be helpful to the modulation of their band gap for optoelectronic applications.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Electronic Properties of Intrinsic Vacancies in Single-Layer Caf2 and Its Heterostructure With Monolayer Mos2
    (AIP Publishing LLC, 2021) Li, Zhenzhen; Başkurt, Mehmet; Şahin, Hasan; Gao, Shiwu; Kang, Jun
    Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF2 single layer and its heterostructures with monolayer MoS2 are investigated from first-principles calculations. V-Ca introduces a shallow defect level close to the VBM, whereas VF introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, VF has a relatively lower formation energy than VCa, except for the extreme Ca-rich case. Thus, VF should be dominant in CaF2. The band offset between CaF2 and MoS2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF2, the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF2 to MoS2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS2, and the electronic properties of MoS2 are almost intact. Compared with h-BN that has a small valence band offset with MoS2 and could introduce in-gap defect states, CaF2 can be a good candidate to serve as the dielectric layer of MoS2-based transistors. Published under an exclusive license by AIP Publishing.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Strain Tunable Band Structure of a New 2d Carbon Allotrope C-568
    (IOS Press, 2020) Gao, Qiang; Kang, Jun; Şahin, Hasan
    Recently, C(568)has emerged as a new carbon allotrope, which shows semiconducting properties with a band gap around 1 eV and has attracted much attention. In this work, the external strain effects on the electronic properties of C(568)have been studied theoretically through first-principle calculations. The numerical results show that while in-plane uniaxial and biaxial strains both reduces the band gap of C(568)in case of tensile strain, their effects are quite different in the case of compressive strain. With increasing compressive uniaxial strain, the band gap of C(568)first increases, and then dramatically decreases. In contrast, the application of compressive biaxial strain up to -10% only leads to a slight increase of band gap. Moreover, an indirect-to-direct gap transition can be realized under both types of compressive strain. The results also show that the optical anisotropy of C(568)can be induced under uniaxial strain, while biaxial strain does not cause such an effect. These results indicate good strain tunability of the band structure of C-568, which could be helpful for the design and optimization of C-568-based nanodevices.
  • Article
    Citation - WoS: 14
    Citation - Scopus: 12
    Octahedrally Coordinated Single Layered Caf2: Robust Insulating Behaviour
    (Royal Society of Chemistry, 2020) Başkurt, Mehmet; Kang, Jun; Şahin, Hasan
    Using first-principles calculations, the structural, vibrational, and electronic properties of single-layered calcium fluoride (CaF2) are investigated. The dynamical stability of 1T-CaF2 is confirmed by the phonon dispersions. Raman active vibrational modes of 1T-CaF2 enable its characterization via Raman spectroscopy. In addition, the calculated electronic properties of 1T-CaF2 confirmed insulating behavior with an indirect wide band gap which is larger than that of a well-known single-layered insulator, h-BN. Moreover, one-dimensional nanoribbons of CaF2 are investigated for two main edge orientations, namely zigzag and armchair, and it is revealed that both structures maintain the 1T nature of CaF2 without any structural edge reconstructions. Electronically, both types of CaF2 nanoribbons display robust insulating behavior with respect to the nanoribbon width. The results show that both the 2D and 1D forms of 1T-CaF2 show potential in nanoelectronics as an alternative to the widely-used insulator h-BN with its similar properties and wider electronic band gap.
  • Article
    Citation - WoS: 67
    Citation - Scopus: 66
    Tis3 Nanoribbons: Width-Independent Band Gap and Strain-Tunable Electronic Properties
    (American Physical Society, 2015) Kang, Jun; Şahin, Hasan; Özaydın, H. Duygu; Senger, Ramazan Tuğrul; Peeters, François M.
    The electronic properties, carrier mobility, and strain response of TiS3 nanoribbons (TiS3 NRs) are investigated by first-principles calculations. We found that the electronic properties of TiS3 NRs strongly depend on the edge type (a or b). All a-TiS3 NRs are metallic with a magnetic ground state, while b-TiS3 NRs are direct band gap semiconductors. Interestingly, the size of the band gap and the band edge position are almost independent of the ribbon width. This feature promises a constant band gap in a b-TiS3 NR with rough edges, where the ribbon width differs in different regions. The maximum carrier mobility of b-TiS3 NRs is calculated by using the deformation potential theory combined with the effective mass approximation and is found to be of the order 103cm2V-1s-1. The hole mobility of the b-TiS3 NRs is one order of magnitude lower, but it is enhanced compared to the monolayer case due to the reduction in hole effective mass. The band gap and the band edge position of b-TiS3 NRs are quite sensitive to applied strain. In addition we investigate the termination of ribbon edges by hydrogen atoms. Upon edge passivation, the metallic and magnetic features of a-TiS3 NRs remain unchanged, while the band gap of b-TiS3 NRs is increased significantly. The robust metallic and ferromagnetic nature of a-TiS3 NRs is an essential feature for spintronic device applications. The direct, width-independent, and strain-tunable band gap, as well as the high carrier mobility, of b-TiS3 NRs is of potential importance in many fields of nanoelectronics, such as field-effect devices, optoelectronic applications, and strain sensors.