Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
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Article Anisotropic Tunability of Vibrational Modes in Black Phosphorus Under Uniaxial Compressive/Tensile Strain(Wiley, 2023) Li, Hao; Kutlu, Tayfun; Carrascoso, Felix; Şahin, Hasan; Munuera, Carmen; Castellanos Gomez, AndresStrain engineering is a powerful strategy for tuning the optical, electrical, vibrational properties of 2D nanomaterials. In this work, a four-point bending apparatus is constructed to apply both compressive and tensile strain on 2D anisotropic black phosphorus flake. Further polarized Raman spectroscopy is used to study the vibrational modes of black phosphorus flakes under uniaxial strain applied along various crystalline orientations. Here, a strong anisotropic blue/redshift of A1g, B2g, and A2g modes is found under compressive/tensile strain, respectively. Interestingly, mode A1g exhibits the maximum/minimum shift while mode B2g and mode A2g present the minimum/maximum shift when the strain is applied along armchair/zigzag direction. Density functional theory calculations are carried out to investigate the anisotropic strain response mechanism, finding that the strain-induced regulation of the PP bond angle, bond length, and especially interlayer interaction has a giant influence on the Raman shift. A four-point bending apparatus is constructed to study the effect of uniaxial strain on the vibrational property of anisotropic black phosphorus. Particularly, strong anisotropy on the Raman blueshift/redshift rate upon compressive/tensile strain can be observed, which results from the strain-induced regulation of the bond angle, bond length, and interlayer interactions according to density functional theory calculation analysis.imageArticle Citation - WoS: 1Citation - Scopus: 1A Multi-Layered Graphene Based Gas Sensor Platform for Discrimination of Volatile Organic Compounds Via Differential Intercalation(Royal Society of Chemistry, 2023) Özkendir İnanç, Dilce; Ng, Zhi Kai; Başkurt, Mehmet; Keleş, Berfin; Vardar, Gökay; Şahin, Hasan; Tsang, Siu Hon; Palaniappan, Alagappan; Yıldız, Ümit Hakan; Teo, EhtSelective and sensitive detection of volatile organic compounds (VOCs) is of critical importance for environmental monitoring, disease diagnosis and industrial applications. Among VOCs, assay development for primary alcohols has captured significant research attention since their toxicity causes adverse effects on gastrointestinal and central nerve systems, resulting in irreversible blindness, and coma, and can be even fatal at high exposure levels. However, selective detection of primary alcohols is extremely challenging owing to the similarity in their molecular structure and characteristic groups. Herein, we have attempted to investigate the differential methanol (MeOH)-ethanol (EtOH) discriminative properties of single-layer, bi-layer, and multi-layer graphene morphologies. Chemiresistors fabricated using the three morphologies of graphene illustrate discriminative MeOH-EtOH responses, which is attributed to the phenomenon of differential intercalation of MeOH within layered graphene morphologies as compared to that of EtOH. This hypothesis is verified by density functional theory calculations, which revealed that the adsorption of EtOH molecules on the graphene surface is more energetically favorable as compared to that of MeOH molecules, thereby inhibiting their intercalation within the layered graphene morphologies. It is further evaluated that the degree of MeOH intercalation increases with increasing layers of graphene for obtaining differential MeOH-EtOH responses. Experimental results suggest possibilities to develop selective and sensitive MeOH assays fabricated using various graphene morphologies in a combinatorial sensor array format.Article Citation - WoS: 2Citation - Scopus: 2Magnetic Single-Layer Nanoribbons of Manganese Oxide: Edge- and Width-Dependent Electronic Properties(Royal Society of Chemistry, 2022) Sözen, Yiğit; Topkıran, Uğur; Şahin, HasanIn the present work, the structural, magnetic, and electronic properties of the two- and one-dimensional honeycomb structures of recently synthesized MnO [Zhang et al., Hexagonal metal oxide monolayers derived from the metal-gas interface, Nat. Mater., 2021, 20, 1073-1078] are investigated by using first-principles calculations. Our calculations show that the single-layer 2D MnO crystal has a degenerate antiferromagnetic (AFM) ground state and a relatively less favorable ferromagnetic (FM) state. In addition, the magnetic anisotropy calculations unveil that the easy-axis direction for magnetism originating from unpaired electron states in manganese atoms is normal to the crystal plane. Electronically, while the FM MnO is a direct semiconductor with a narrow bandgap, AFM phases display large indirect bandgap semiconducting behavior. Moreover, the calculations on nanoribbons of MnO reveal that zigzag-edged ribbons display metallic behaviors, whereas armchair-edged nanoribbons are semiconductors. Magnetically, for both zigzag- or armchair-edged nanoribbons, the AFM order perpendicular to the nanoribbon growth direction is found to be favorable over the other AFM and FM orders. Moreover, depending on the edge symmetry and ribbon width, forbidden bandgap values of nanoribbons display distinct family behaviors.Article Citation - WoS: 6Citation - Scopus: 7Interface-Dependent Phononic and Optical Properties of Geo/Moso Heterostructures(Royal Society of Chemistry, 2022) Yağmurcukardeş, Mehmet; Sözen, Yiğit; Başkurt, Mehmet; Peeters, François M.; Şahin, HasanThe interface-dependent electronic, vibrational, piezoelectric, and optical properties of van der Waals heterobilayers, formed by buckled GeO (b-GeO) and Janus MoSO structures, are investigated by means of first-principles calculations. The electronic band dispersions show that O/Ge and S/O interface formations result in a type-II band alignment with direct and indirect band gaps, respectively. In contrast, O/O and S/Ge interfaces give rise to the formation of a type-I band alignment with an indirect band gap. By considering the Bethe-Salpeter equation (BSE) on top of G0W0 approximation, it is shown that different interfaces can be distinguished from each other by means of the optical absorption spectra as a consequence of the band alignments. Additionally, the low-and high-frequency regimes of the Raman spectra are also different for each interface type. The alignment of the individual dipoles, which is interface-dependent, either weakens or strengthens the net dipole of the heterobilayers and results in tunable piezoelectric coefficients. The results indicate that the possible heterobilayers of b-GeO/MoSO asymmetric structures possess various electronic, optical, and piezoelectric properties arising from the different interface formations and can be distinguished by means of various spectroscopic techniques.Article Citation - WoS: 8Citation - Scopus: 8Strain Tunable Band Structure of a New 2d Carbon Allotrope C-568(IOS Press, 2020) Gao, Qiang; Kang, Jun; Şahin, HasanRecently, 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: 6Citation - Scopus: 6Novel Ultra-Thin Two-Dimensional Structures of Strontium Chloride(Royal Society of Chemistry, 2020) Akyol, Cansu; Başkurt, Mehmet; Şahin, HasanBy performing density functional theory-based calculations, possible stable ultra-thin crystal structures of SrCl(2)are investigated. Phonon calculations reveal that, among the possible crystal structures, three different phases; namely 1H, 1T, and square, are dynamically stable. In addition,ab initiomolecular dynamics calculations show that these three phases are thermally stable up to well above room temperature. Another important stability factor of crystals, the chemical inertness against abundant molecules in the atmosphere, such as N-2, O-2, H2O, and CO2, is also investigated. The analysis shows that SrCl(2)single-layers are chemically stable against these molecules. Moreover, it is determined that in contact with H2O and CO2, ultra-thin SrCl(2)sheets display unique electronic features, allowing them to be used in sensing applications. It is also shown that single layers of SrCl(2)crystals, all having a wide electronic band gap, can form type-I and type-II vertical van der Waals heterostructures with well-known 2D materials such as MoS2, WSe2, and h-BN.Article Citation - WoS: 20Citation - Scopus: 23Kagome-Like Silicene: a Novel Exotic Form of Two-Dimensional Epitaxial Silicon(Elsevier, 2020) Sassa, Yasmine; Johansson, Fredrik O. L.; Lindblad, Andreas; Yazdi, Milad G.; Simonov, Konstantin; Weissenrieder, Jonas; Le Lay, Guy; İyikanat, Fadıl; Şahin, HasanSince the discovery of graphene, intensive efforts have been made in search of novel two-dimensional (2D) materials. Decreasing the materials dimensionality to their ultimate thinness is a promising route to unveil new physical phenomena, and potentially improve the performance of devices. Among recent 2D materials, analogs of graphene, the group IV elements have attracted much attention for their unexpected and tunable physical properties. Depending on the growth conditions and substrates, several structures of silicene, germanene, and stanene can be formed. Here, we report the synthesis of a Kagome-like lattice of silicene on aluminum (1 1 1) substrates. We provide evidence of such an exotic 2D Si allotrope through scanning tunneling microscopy (STM) observations, high-resolution core-level (CL) and angle-resolved photoelectron spectroscopy (ARPES) measurements, along with Density Functional Theory calculations.Article Citation - WoS: 5Citation - Scopus: 6Boosting Up Printability of Biomacromolecule Based Bio-Ink by Modulation of Hydrogen Bonding Pairs(Elsevier Ltd., 2020) Köksal, Büşra; Önbaş, Rabia; Başkurt, Mehmet; Şahin, Hasan; Arslan Yıldız, Ahu; Yıldız, Ümit HakanThis study describes low dose UV curable and bioprintable new bioink made of hydrogen bond donor-acceptor adaptor molecule 2-isocyanatoethyl methacrylate (NCO)modified gelatin (NCO-Gel). Our theoretical calculations demonstrate that insertion of 2-isocyanatoethyl methacrylate doubles the interaction energy (500 meV) between gelatin chains providing significant contribution in interchain condensation and self-organization as compared to methacrylic anhydride modified gelatin (GelMA). The NCO-Gel exhibits peak around 1720 cm?1 referring to bidentate hydrogen bonding between H-NCO and its counterpart O[dbnd]CN[sbnd]H. These strong interchain interactions drive chains to be packed and thereby facilitating UV crosslinking. The NCO-Gel is exhibiting a rapid, 10 s gelation process by the exposure of laser (3 W, 365 nm). The dynamic light scattering characterization also reveals that NCO-Gel has faster sol to gel transition as compared to GelMA depending on the UV curing time. The NCO-Gel was found to be more firm and mechanically strong that provides advantages in molding as well as bioprinting processes. Bioprinted NCO-Gel has shown sharp borders and stable 3D geometry as compared to GelMA ink under 10 s UV curing time. The cell viability tests confirm that NCO-Gel facilitates cell proliferation and supports cell viability. We foresee that NCO-Gel bioink formulation provides a promising opportunity when low dose UV curing and rapid printing are required. © 2020 Elsevier LtdArticle Citation - WoS: 7Citation - Scopus: 8Stable janus TaSe2 single-layers via surface functionalization(Elsevier Ltd., 2021) Kahraman, Zeynep; Başkurt, Mehmet; Yağmurcukardeş, Nesli; Chaves, A.; Şahin, HasanFirst-principles calculations are performed in order to investigate the formation of Janus structures of single-layer TaSe2. The structural optimizations and phonon band dispersions reveal that the formation and stability of hydrogenated (HTaSe2), fluorinated (FTaSe2), and the one-side hydrogenated and one-side fluorinated (Janus-HTaSe2F) single-layers are feasible in terms of their phonon band dispersions. It is shown that bare metallic single-layer TaSe2 can be turned into a semiconductor as only one of its surface is functionalized while it remains as a metal via its two surfaces functionalization. In addition, the semiconducting nature of single-layers HTaSe2 and FTaSe2 and the metallic behavior of Janus TaSe2 are found to be robust under applied uniaxal strains. Further analysis on piezoelectric properties of the predicted single-layers reveal the enhanced in-plane and out-of-plane piezoelectricity via formed Janus-HTaSe2F. Our study indicates that single-layer TaSe2 is a suitable host material for surface functionalization via fluorination and hydrogenation which exhibit distinctive electronic and vibrational properties. © 2020 Elsevier B.V.Article Citation - WoS: 4Citation - Scopus: 4Color-Tunable All-Inorganic Cspbbr3 Perovskites Nanoplatelet Films for Photovoltaic Devices(American Chemical Society, 2019) Özcan, Mehmet; Özen, Sercan; Topçu, Gökhan; Demir, Mustafa Muammer; Şahin, HasanHerein, we demonstrate a novel coating approach to fabricate CsPbBr3 perovskite nanoplatelet film with heat-free process via electrospraying from precursor solution. A detailed study is carried out to determine the effect of various parameters such as ligand concentration, electric field, flow rate, etc. on the optical properties. By controlling the volume ratios of the oleylamine (OAm) and oleic acid (OA), the coalescing and thickness of the resulting nanoplatelets can be readily tuned that results in control over emission in the range of 100 nm without any antisolvent crystallization or heating processes. The varying electrical field and flow rate was found as inefficient on the emission characteristics of the films. In addition, the crystal films were obtained under ambient conditions on the ITO coated glass surfaces as in the desired pattern. As a result, we demonstrated a facile and reproducible way of synthesizing and coating of CsPbBr3 perovskite nanoplatelets which is suitable for large-scale production. In this method, the ability of tuning the degree of quantum confinement for perovskite nanoplatelets is promising approach for the one-step fabrication of crystal films that may enable the use in optoelectronics.
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