NQPI Nanoforum | Properties of Mn3Sn films grown on sapphire substrates using molecular beam epitaxy, Nov. 3

The Nanoscale and Quantum Phenomena Institute (NQPI) 's Seminar Forum series features two graduate students in Physics & Astronomy on Nov. 3 at 4:10 p.m. in Walter 245.

Sneha Upadhyay will discuss “ Properties of Mn3Sn films grown on sapphire substrates using molecular beam epitaxy. ”

Abstract : The Kagome antiferromagnet Mn3Sn is a fascinating material because it’s one of the rare antiferromagnets that exhibits large anomalous Hall and Nernst effects. This opens a new area of research using functional antiferromagnets1, but for future device applications, it requires fabricating high quality thin films. There are reports of the controlled growth of Mn3Sn on substrates like m -plane sapphire,2 Pt/Al2O3 (0001)3 and others using sputtering growth, but this often can result in polycrystalline films. In this work, we investigate the growth of Mn3Sn films on c-plane sapphire substrates using molecular beam epitaxy. Effusion cells are used for Mn and Sn sources which are calibrated using a quartz crystal thickness monitor. The growth is monitored in-situ using reflection high energy electron diffraction and ex-situ measurements are carried out using X-ray diffraction, Rutherford backscattering, and cross-sectional scanning transmission electron microscopy. The samples are grown at 500 ± 9°C and 416 ± 9 °C with a Mn: Sn atomic flux ratio of 3.2: 1 on c-plane sapphire substrates for 60 mins. We observe streaky RHEED patterns at both temperatures indicating high quality crystalline growth with 2 different orientations, (0001) and (11-20), which is also backed up by the XRD spectra. STEM verifies ~3:1 Mn to Sn stoichiometry but also reveals discontiguous films. After optimizing the growth conditions, the next phase of the study is to begin in-situ scanning tunneling microscopy and spin-polarized STM studies of the structural, electronic, and magnetic properties of the as-grown Mn3Sn surfaces, and in this presentation, we plan to present initial results.

Chinonso Ugwumadu will discuss “ Atomistic Nature of Amorphous Layered Carbon Solids. ”

Abstract : Carbon’s (C) strong proclivity to form layers was observed in the disorder-order transition from random configurations of carbon atoms to layered carbon allotropes using GAP machine learning (ML) interatomic potential [1]. Three amorphous structures, graphite (a-G), fullerenes (a-F) and nanotubes (a-NT), with pentagons and heptagons in the hexagonal network, formed from NVT simulation near 3000K. The formation of these structures is strongly dependent on the type of periodic boundary condition (PBC) applied. The ring disorder in the C network was found to be combinations of Stone-Wales and (Inverse) Stone-Thrower-Wales and Stone-Wales defects. Inter-layer cohesion is partly due to interaction between delocalized π electrons into the gallery. The impact of structural disorder in electronic transport was studied. The Vibrational density of states for all the structures was computed and it is potentially an experimentally testable fingerprint of the materials.