Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
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Preprint Electronic, Magnetic and Vibrational Properties of Single Layer Aluminum Oxide(2022) Özyurt, A. Kutay; Molavali, Deniz; Şahin, HasanThe structural, magnetic, vibrational and electronic properties of single layer aluminum oxide (AlO2) are investigated by performing state-of-the-art first-principles calculations. Total energy optimization and phonon calculations reveal that aluminum oxide forms a distorted octahedral structure (1T'-AlO2) in its single layer limit. It is also shown that surfaces of 1T'-AlO2 display magnetic behavior originating from the O atoms. While the ferromagnetic (FM) state is the most favorable magnetic order for 1T'-AlO2, transformation to a dynamically stable antiferromagnetic (AFM) state upon a slight distortion in the crystal structure is also possible. It is also shown that Raman activities (350-400 cm^-1) obtained from the vibrational spectrum can be utilized to distinguish the possible magnetic phases of the crystal structure. Electronically, both FM and the AFM phases are semiconductors with an indirect band gap and they can form a type-III vdW heterojunction with graphene-like ultra-thin materials. Moreover, it is predicted that presence of oxygen defects that inevitably occur during synthesis and production do not alter the magnetic state, even at high vacancy density. Apparently, ultra-thin 1T'-AlO2 with its stable crystal structure, semiconducting nature and robust magnetic state is a quite promising material for nanoscale device applications.Article Single Layer Res2h2: Stability, Raman Activity and Electronic Properties(Eskişehir Teknik Üniversitesi, 2018) Ünsal, Elif; Şahin, HasanIn this study, the structural, vibrational and electronic properties of the hydrogenated single layer of ReS2 are investigated byperforming the first principle calculations based on density functional theory. We found that the characteristic properties ofthe monolayer ReS2 can be manipulated upon the hydrogen functionalization. As the monolayer ReS2, the ReS2H2 hasdistorted 1T phase; however, the bonding in Re slab significantly varies with the hydrogenation. Our results demonstrate thatthe full-surface hydrogenation leads to an expansion in lattice and the Re4 tetramer-chains in the monolayer ReS2 areseparated into two dimers in the hydrogenated monolayer. It is calculated that the dynamically stable monolayer of ReS2H2has 26 Raman-active vibrational modes. Constant volume specific heat calculations are also performed and the resultsindicate that at high temperature, the monolayer ReS2 approaches to limit of 3R before the monolayer ReS2H2. By performingthe electronic band structure calculations, it is shown that when the ReS2 surface is fully hydrogenated, there occurs a directto indirect band gap transition and the semiconducting hydrogen-induced monolayer has a band gap of 0.74 eV.Book Part Citation - WoS: 6Citation - Scopus: 5Strain engineering of 2D materials(Springer Verlag, 2017) Cahangirov, Seymur; Şahin, Hasan; Le Lay, Guy; Rubio, AngelWhen bulk structures are thinned down to their monolayers, degree of orbital interactions, mechanical properties and electronic band dispersion of the crystal structure become highly sensitive to the amount of applied strain. The source of strain on the ultra-thin lattice structure can be (1) an external device or a flexible substrate that can stretch or compress the structure, (2) the lattice mismatch between the layer and neighboring layers or (3) stress induced by STM or AFM tip.Book Part Citation - WoS: 7Citation - Scopus: 10Germanene, Stanene and Other 2d Materials(Springer Verlag, 2017) Cahangirov, Seymur; Şahin, Hasan; Le Lay, Guy; Rubio, AngelGermanene and stanene (also sometimes written stannene or called tinene) are 2D materials composed of germanium and tin atoms respectively arranged in a honeycomb structure similarly to graphene and silicene. The atomic structure of freestanding germanene and stanene is buckled like in the case of silicene (see Figure 2.4DFT calculations (Kresse and Joubert, Phys Rev B 59:1758-1775, 1999) performed by projector augmented wave (PAW) method (BlÖchl, Phys Rev B 50:17953-17979, 1994) and adopting PBE functional (Perdew et al. Phys Rev Lett 77:3865-3868, 1996) result in a lattice constants 4.06 and 4.67Å and buckling heights of 0.69 and 0.85Å for germanene and stanene respectively.Book Part Citation - Scopus: 1Multilayer Silicene(Springer Verlag, 2017) Cahangirov, Seymur; Şahin, Hasan; Le Lay, Guy; Rubio, AngelSilicon does not have a naturally occurring layered allotrope like graphite. However, it is possible to grow monolayer silicene on substrates, as we have seen in Chap. 3. Extending this idea further, one may wonder whether it is possible to synthesize layered silicon structures by continuing the growth started as a monolayer silicene. In this chapter we discuss the experimental and theoretical works that are based on this idea of multilayer silicene growth.Book Part Citation - WoS: 1Citation - Scopus: 2Silicene on Ag Substrate(Springer Verlag, 2017) Cahangirov, Seymur; Şahin, Hasan; Le Lay, Guy; Rubio, AngelThe isolation of graphene sheets from its parent crystal graphite has given the kick to experimental research on its prototypical 2D elemental cousin, silicene (Brumfiel 2013). Unlike graphene, silicene lacks a layered parent material from which it could be derived by exfoliation, as mentioned in Chap. 2. Hence, the efforts of making the silicene dream a reality were focused on epitaxial growth of silicene on substrates. The first synthesis of epitaxial silicene on silver (111) (Vogt et al. 2012; Lin et al. 2012) and zirconium diboride templates (Fleurence et al. 2012) and next on an iridium (111) surface (Meng et al. 2013), has boosted research on other elemental group IV graphene-like materials, namely, germanene and stanene (Matthes et al. 2013; Xu et al. 2013). The boom is motivated by several new possibilities envisaged for future electronics, typically because of the anticipated very high mobilities for silicene and germanene (Ye et al. 2014), as well as potential optical applications (Matthes et al. 2013). It is also fuelled by their predicted robust 2D topological insulator characters (Liu et al. 2011; Ezawa 2012) and potential high temperature superconductor character (Chen et al. 2013; Zhang et al. 2015). One of the most promising candidates as a substrate is Ag because from the studies of the reverse system, where Ag atoms were deposited on silicon substrate, it was known that Ag and silicon make sharp interfaces without making silicide compounds (Le Lay 1983). Indeed, studies on synthesis and characterization of silicene is mainly focused on using Ag(111) as substrates and hence we think it is important to understand this particular system. In this chapter, we present the experimental and theoretical studies investigating the atomic and electronic structure of silicene on Ag substrates.Book Part Citation - WoS: 5Citation - Scopus: 11Freestanding Silicene(Springer Verlag, 2017) Cahangirov, Seymur; Şahin, Hasan; Le Lay, Guy; Rubio, AngelObtaining a freestanding 2D graphene flake is relatively easy because it has a naturally occurring 3D layered parent material, graphite, made up of graphene layers weakly bound to each other by van der Waals interaction. In fact, graphite is energetically more favorable than diamond (which is one of the most stable and hard materials on Earth) that is the sp3 hybridized allotrope of carbon. To prepare freestanding graphene, it is enough to come up with a smart procedure for isolating the weakly bound layers of graphite. The same is also true for other layered materials like hexagonal boron nitride, black phosphorus, metal dichalcogenides and oxides. Silicene, on the other hand, doesn’t have a naturally occurring 3D parent material since silicon atoms prefer sp3 hybridization over sp2 hybridization. This makes the synthesis of freestanding silicene very hard, if not impossible. However, it is possible to epitaxially grow silicene on metal substrates and make use of its intrinsic properties by transferring it to an insulating substrate (Tao et al. 2015). In this chapter, we focus on intrinsic properties of freestanding silicene in the absence of the metallic substrate.Book Part A Brief History of Silicene(Springer Verlag, 2017) Cahangirov, Seymur; Şahin, Hasan; Le Lay, Guy; Rubio, AngelResearch on silicene shows a fast and steady growth that has increased our tool-box of novel 2D materials with exceptional potential applications in materials science. Especially after the experimental synthesis of silicene on substrates in 2012 it has attracted substantial interest from both theoretical and experimental communities. Every day, new people from various disciplines join this rapidly growing field. The aim of this book is to serve as a fast entry to the field to these newcomers and as a long-living reference to the growing community. To achieve this goal, the book is designed to emphasize the most crucial developments from both theoretical and experimental point of view since the starting of the silicene field back in 1994 with the first theoretical paper proposing the structure of silicene. We provide the general concepts and ideas such that the book is accessible to everybody from graduate students to senior researchers and we refer the reader interested in the detail to the relevant literature. We now start with a brief history of silicene where we highlight, in the chronological order, the important works that shaped our understanding of silicene.