{"id":9775,"date":"2022-02-14T11:52:20","date_gmt":"2022-02-14T10:52:20","guid":{"rendered":"http:\/\/www.cinam.univ-mrs.fr\/cinam\/?p=9775"},"modified":"2022-02-14T11:52:58","modified_gmt":"2022-02-14T10:52:58","slug":"thesis-defense-11","status":"publish","type":"post","link":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/2022\/02\/14\/thesis-defense-11\/","title":{"rendered":"Thesis defense"},"content":{"rendered":"

Title<\/strong> : Growth and ferroelectricity of GeTe on Si(111)<\/p>\n

Language : french<\/p>\n

Members of the jury<\/strong> :<\/p>\n

Antoine Barbier<\/span> (CEA) : <\/span>Rapporteur<\/span>
Alain Marty<\/span> (CEA) : Rapporteur<\/span>
Salia Cherifi-Hertel<\/span> (IPCMS) : <\/span>Examinatrice<\/span>
Yannick Fagot-Revurat<\/span> (IJL) : <\/span>Examinateur<\/span>
Vincent Garcia<\/span> (CNRS-Thal\u00e8s) : <\/span>Examinateur<\/span>
Olivier Thomas<\/span> (IM2NP) <\/span>: Examinateur<\/span>
Fabien Cheynis<\/span> (CINaM) : <\/span>Co-directeur de th\u00e8se<\/span>
Fr\u00e9d\u00e9ric Leroy<\/span> (CINaM) : Directeur de th\u00e8se<\/span><\/span><\/p>\n

Abstract :<\/strong><\/p>\n

The recently measured giant Rashba effect in GeTe has shown the potential for <\/span>spintronics of ferroelectric materials with large spin-orbit coupling. In order to elec<\/span>trically control the electrical polarization of the material and thus the spin structure <\/span> of the valence and conduction bands, it is essential to characterize the structure of <\/span>the ferroelectric domains and their spatial organization. In this thesis we have grown <\/span>GeTe thin films on Si(111)-Sb by molecular beam epitaxy in a wide range of thick<\/span>ness. At 270\u00b0C, we observe a layer-by-layer growth and a main epitaxial relationship <\/span> GeTe(111)<\/span> \u2225<\/span>Si(111) and GeTe[110]<\/span> \u2225<\/span>Si[110]. The growth of GeTe thin films shows that <\/span>initially about 40% of the grains are rotated in-plane by 180\u00b0. This proportion decreases <\/span>rapidly and reaches about 4% for a thickness of 200 nm. In addition, ferroelastic nan<\/span>odomains appear which volume fraction and size can be controlled by fine tuning the <\/span> thickness and the deposition temperature. These domains have an elongated needle <\/span>shape in the <110> direction. Their unit cell is identical to that of the main domain <\/span>(rhombohedral with<\/span> a<\/span>r<\/span> =<\/span> 4.29 \u030a<\/span>A and<\/span> \u03b8<\/span> =<\/span> 58.3\u00b0). The [111] axis of their unit cell and <\/span>their electrical polarization are tilted by about 72\u00b0 with respect to the [111] axis of the <\/span>main domain. While the majority domain has a pure tellurium surface termination Te <\/span>(1<\/span> \u00d7<\/span> 1), we show by scanning tunneling microscopy that the surface of the ferroelastic <\/span>nanodomains have three different surface structures, including a pure germanium <\/span>termination associated with a (2<\/span> \u00d7<\/span> 2) reconstruction, a missing row structure of Te, <\/span>and a more complexe scale structure that is the most stable. In situ measurements <\/span>by low energy\u00a0 electron microscopy and X-ray diffraction during thermal cycling show <\/span>the appearance and disappearance of the ferroelectric nanodomains at a temperature <\/span>around 220\u00b0C. By a detailed analysis of the GeTe\/Si interface by transmission electron <\/span>microscopy, we demonstrate that misfit dislocations localized at the interface formed <\/span>during growth play a key role in the stability of ferroelectric nanodomains. Finally, <\/span>we have characterized the electronic band structure of the GeTe majority domains <\/span>and measured a Rashba constant<\/span> \u03b1<\/span>r<\/span> =<\/span> 4.9 eV. \u030a<\/span>A that decreases with film thickness. <\/span>First measurements to characterize the Berry curvature are performed by circular <\/span>dichroism in angle-resolved photoemission spectroscopy.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

Boris CROES on Thursday February 24, 2022 at 14pm via zoom<\/p>\n","protected":false},"author":16,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[5],"tags":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/posts\/9775"}],"collection":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/users\/16"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/comments?post=9775"}],"version-history":[{"count":1,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/posts\/9775\/revisions"}],"predecessor-version":[{"id":9776,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/posts\/9775\/revisions\/9776"}],"wp:attachment":[{"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/media?parent=9775"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/categories?post=9775"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cinam.univ-mrs.fr\/cinam\/en\/wp-json\/wp\/v2\/tags?post=9775"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}