Bulletin of the American Physical Society
84th Annual Meeting of the APS Southeastern Section
Volume 62, Number 13
Thursday–Saturday, November 16–18, 2017; Milledgeville, Georgia
Session E1: Emerging Thin Film Materials and Interfaces |
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Chair: Ryan Comes, Auburn University Room: MSU Building University Banquet Room A |
Friday, November 17, 2017 8:30AM - 9:00AM |
E1.00001: Silicene on Silicide â a Surface Science Approach to Materials Discovery Invited Speaker: Petra Reinke Silicene like graphene is in its flat conformation a honeycomb structure with a Dirac cone at the K and Kâ points of the Brillouin zone. In other respects, graphene and silicene are surprisingly different, which can be traced back to the relative stability of sp3 versus sp2 type bonding and leads to a wide range of geometries defined by buckling z and conformation. The perfect sp2 type layer would be planar, the high buckled configuration approaches the structure of the Si(111) surface. Control of buckling and conformation is critical to the future realization of exotic quantum materials which are predicted for silicene but have so far eluded experimental realization. Our recent study of MoSi2 oxidation using scanning tunneling microscopy and spectroscopy (STM, STS) lead to the discovery of the silicene-terminated h-MoSi2 (0001) surface, which is formed via a complex high-temperature $\left( \sqrt {3}\times \sqrt {3}\right) R30^{0}$ reconstruction. This reconstruction is geometrically identical to low buckled silicene and while it differs from the armchair configuration a Dirac type behavior is expected albeit not confirmed unambiguously. The silicene layer shows characteristic defect motifs and multiples of these defect motifs, where complete hexagons are removed from the silicene layer. Silicene layers with a Dirac-type electronic structure, can only be achieved if the pertubations, which stem from buckling, conformation and bonding to the substrate, are relatively small. In silicene buckling/conformation and substrate bonding are interdependent. I will discuss this interplay in the broader context and develop rules for substrate choice for silicene layers, and illustrate that the silicene-on-silicide platform is a particularly promising material combination. In addition, the feasibility of large area growth, which is required for future integration of silicene-on-silicide in device structures, and the study of its electronic structure, will be addressed. [Preview Abstract] |
Friday, November 17, 2017 9:00AM - 9:30AM |
E1.00002: Challenges for 2D material Integration in Nanoelectronic Devices Invited Speaker: Stephen McDonnell The last decade has seen fevered interest in 2D materials for nanoelectronics. These materials, which include graphene, hexagonal boron nitride, and the plethora of transition metal dichalcogenide (TMD) combinations, have electronic structures exhibiting metallic, semiconducting, and insulating properties. This promises devices with scalability to the atomic limit combined with defect free interfaces. Realizing this promise has not proved trivial. Defects in the naturally occurring material can dominate their properties, and even synthesized materials can suffer from high impurity concentration. Process residues such as photo-resists can impact device performance. Metal depositions can result in the formation of unexpected interface compounds that can dominate the contact behavior. We study both the synthesis and integration of 2D materials for nano- and optoelectronic applications. Using an in-vacuo MBE-ARPES cluster tool, we grow TMDs from elemental sources using van der Waals epitaxy. The layer-by-layer nature of these growths can be verified in-situ using reflection high-energy electron diffraction. The composition and electronic structure of these materials can be investigated by in-vacuo XPS and ARPES. In addition to studying the synthesis of these materials, we also investigate how these materials interface with metals that are commonly used as contacts in electronic devices. Recently it has been shown that the process conditions during the electron beam deposition of metals can control interface reactions. In particular, the reactor base pressure and deposition rate can be used to tune the interface chemistry. We will present a summary of our work on the synthesis of TMDs and the interfaces formed between these materials and typical device contact metals. [Preview Abstract] |
Friday, November 17, 2017 9:30AM - 10:00AM |
E1.00003: Imaging Atomic-Scale Distortions at Buried Oxide Interfaces. Invited Speaker: Divine Kumah Electronic and magnetic interactions at the interfaces between transition metal complex oxide materials have led to the realization of a wide range of emergent properties. These properties include interfacial magnetism, superconductivity and high-mobility two dimensional electron gases and are directly linked to interfacial atomic-scale structural and chemical reconstructions. To understand and manipulate these emergent properties, we apply synchrotron-based surface diffraction and direct x-ray phase retrieval techniques to determine the atomic structures of crystalline complex oxide interfaces with picometer scale resolution. This talk will focus on how an understanding of the structure-property relationships at interfaces between doped manganites and SrTiO3 can be used to control magnetic ordering and electronic transport in manganite films with thickness on the order of a unit cell. [Preview Abstract] |
Friday, November 17, 2017 10:00AM - 10:30AM |
E1.00004: High-Temperature Interfacial Magnetic Order in Topological Insulator - Ferromagnetic Insulator Heterostructures Invited Speaker: Valeria Lauter Realization of proximity-induced magnetism on a topological insulator (TI) surface with a ferromagnetic insulator (FMI) provides a rout for device applications with novel quantum functionality. We demonstrated a fundamental step towards realization of a high temperature magnetization in a TI-FMI heterostructure. Employing strong TI-FMI exchange coupling we have induced uniform long-range ferromagnetic order onto the surface of epitaxial Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ films. Depth-sensitive polarized neutron reflectometry (PNR) discriminates the magnetism at the surface of TI from the FMI layer and directly measures proximity-induced interfacial magnetism in the top 2 QL (\textasciitilde 2 nm) layer of Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$ that is generated by the short-range exchange interaction at the interface with EuS. The interfacial spin polarized state persists up to room temperature, above the Tc of the FMI (EuS). The interfacial magnetism resulting from the large spin-orbit interaction and spin-momentum locking property of the TI surface is found to greatly enhance the magnetic ordering temperature. Due to the short-range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of the TI, while leaving its bulk states unaffected [1]. The TI ferromagnetism is observed reproducibly in a variety of bi-layer samples with different combinations of thicknesses, providing a mechanism to control this effect. The analysis of polarized neutron off-specular scattering (OSS) that arises from lateral in-plane inhomogeneities, probes correlations of lateral inhomogeneity with a length scale of \textasciitilde 0.1-10$\mu $m. These findings of locally-induced ferromagnetic order on the TI surface extending over macroscopic areas without impurity doping open the door for an energy efficient topological control mechanism for future spin-based technologies.\\ \\ [1] F. Katmis, V. Lauter, et al ``Achieving high-temperature ferromagnetic topological insulating phase by proximity coupling'', \textit{Nature 2016, }\textbf{\textit{533}}\textit{, 513} [Preview Abstract] |
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