{"id":25029,"date":"2024-07-12T09:47:48","date_gmt":"2024-07-12T04:02:48","guid":{"rendered":"https:\/\/www.revoscience.com\/en\/?p=25029"},"modified":"2024-07-12T09:47:51","modified_gmt":"2024-07-12T04:02:51","slug":"scientists-observe-record-setting-electron-mobility-in-a-new-crystal-film","status":"publish","type":"post","link":"https:\/\/www.revoscience.com\/en\/scientists-observe-record-setting-electron-mobility-in-a-new-crystal-film\/","title":{"rendered":"Scientists observe record-setting electron mobility in a new crystal film"},"content":{"rendered":"\n
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Researchers have grown thin films of ternary tetradymite (shown) that exhibit record high electron mobility. PHOTO: Courtesy of the researchers<\/em><\/figcaption><\/figure>\n\n\n\n

CAMBRIDGE, Mass. — A material with high electron mobility is like a highway without traffic. Any electrons that flow into the material experience a commuter\u2019s dream, breezing through without any obstacles or congestion to slow or scatter them off their path.\u00a0<\/p>\n\n\n\n

The higher a material\u2019s electron mobility, the more efficient its electrical conductivity, and the less energy is lost or wasted as electrons zip through. Advanced materials that exhibit high electron mobility will be essential for more efficient and sustainable electronic devices that can do more work with less power. <\/p>\n\n\n\n

Now, physicists at MIT, the Army Research Lab, and elsewhere have achieved a record-setting level of electron mobility in a thin film of ternary tetradymite \u2014 a class of mineral that is naturally found in deep hydrothermal deposits of gold and quartz. <\/p>\n\n\n\n

For this study, the scientists grew pure, ultrathin films of the material, in a way that minimized defects in its crystalline structure. They found that this nearly perfect film \u2014 much thinner than a human hair \u2014 exhibits the highest electron mobility in its class. <\/p>\n\n\n\n

The team was able to estimate the material\u2019s electron mobility by detecting quantum oscillations when electric current passes through. These oscillations are a signature of the quantum mechanical behavior of electrons in a material. The researchers detected a particular rhythm of oscillations that is characteristic of high electron mobility \u2014 higher than any ternary thin films of this class to date. <\/p>\n\n\n\n

\u201cBefore, what people had achieved in terms of electron mobility in these systems was like traffic on a road under construction \u2014 you\u2019re backed up, you can\u2019t drive, it\u2019s dusty, and it\u2019s a mess,\u201d says Jagadeesh Moodera, a senior research scientist in MIT\u2019s Department of Physics. \u201cIn this newly optimized material, it\u2019s like driving on the Mass Pike with no traffic.\u201d<\/p>\n\n\n\n

The team\u2019s results, which appear today in the journal Materials Today Physics<\/a><\/em>, point to ternary tetradymite thin films as a promising material for future electronics, such as wearable thermoelectric devices that efficiently convert waste heat into electricity. (Tetradymites are the active materials that cause the cooling effect in commercial thermoelectric coolers.) The material could also be the basis for spintronic devices, which process information using an electron\u2019s spin, using far less power than conventional silicon-based devices. <\/p>\n\n\n\n

The study also uses quantum oscillations as a highly effective tool for measuring a material\u2019s electronic performance. <\/p>\n\n\n\n

\u201cWe are using this oscillation as a rapid test kit,\u201d says study author Hang Chi, a former research scientist at MIT who is now at the University of Ottawa. \u201cBy studying this delicate quantum dance of electrons, scientists can start to understand and identify new materials for the next generation of technologies that will power our world.\u201d<\/p>\n\n\n\n

Chi and Moodera\u2019s co-authors include Patrick Taylor, formerly of MIT Lincoln Laboratory, along with Owen Vail and Harry Hier of the Army Research Lab, and Brandi Wooten and Joseph Heremans of Ohio State University.<\/p>\n\n\n\n

Beam down<\/strong><\/p>\n\n\n\n

The name \u201ctetradymite\u201d derives from the Greek \u201ctetra\u201d for \u201cfour,\u201d and \u201cdymite,\u201d meaning \u201ctwin.\u201d Both terms describe the mineral\u2019s crystal structure, which consists of rhombohedral crystals that are \u201ctwinned\u201d in groups of four \u2014 i.e. they have identical crystal structures that share a side.<\/p>\n\n\n\n

Tetradymites comprise combinations of bismuth, antimony tellurium, sulfur, and selenium. In the 1950s, scientists found that tetradymites exhibit semiconducting properties that could be ideal for thermoelectric applications: The mineral in its bulk crystal form was able to passively convert heat into electricity. <\/p>\n\n\n\n

Then, in the 1990s, the late Institute Professor Mildred Dresselhaus proposed that the mineral\u2019s thermoelectric properties might be significantly enhanced, not in its bulk form but within its microscopic, nanometer-scale surface, where the interactions of electrons is more pronounced. (Heremans happened to work in Dresselhaus\u2019 group at the time.) <\/p>\n\n\n\n

\u201cIt became clear that when you look at this material long enough and close enough, new things will happen,\u201d Chi says. \u201cThis material was identified as a topological insulator, where scientists could see very interesting phenomena on their surface. But to keep uncovering new things, we have to master the material growth.\u201d <\/p>\n\n\n\n

To grow thin films of pure crystal, the researchers employed molecular beam epitaxy \u2014 a method by which a beam of molecules is fired at a substrate, typically in a vacuum, and with precisely controlled temperatures. When the molecules deposit on the substrate, they condense and build up slowly, one atomic layer at a time. By controlling the timing and type of molecules deposited, scientists can grow ultrathin crystal films in exact configurations, with few if any defects. <\/p>\n\n\n\n

\u201cNormally, bismuth and tellurium can interchange their position, which creates defects in the crystal,\u201d co-author Taylor explains. \u201cThe system we used to grow these films came down with me from MIT Lincoln Laboratory, where we use high purity materials to minimize impurities to undetectable limits. It is the perfect tool to explore this research.\u201d <\/p>\n\n\n\n

Free flow<\/strong><\/p>\n\n\n\n

The team grew thin films of ternary tetradymite, each about 100 nanometers thin. They then tested the film\u2019s electronic properties by looking for Shubnikov-de Haas quantum oscillations \u2014 a phenomenon that was discovered by physicists Lev Shubnikov and Wander de Haas, who found that a material\u2019s electrical conductivity can oscillate when exposed to a strong magnetic field at low temperatures. This effect occurs because the material\u2019s electrons fill up specific energy levels that shift as the magnetic field changes. <\/p>\n\n\n\n

Such quantum oscillations could serve as a signature of a material\u2019s electronic structure, and the ways in which electrons behave and interact. Most notably for the MIT team, the oscillations could determine a material\u2019s electron mobility: If oscillations exist, it must mean that the material\u2019s electrical resistance is able to change, and by inference, electrons can be mobile, and made to easily flow. <\/p>\n\n\n\n

The team looked for signs of quantum oscillations in their new films, by first exposing them to ultracold temperatures and a strong magnetic field, then running an electric current through the film and measuring the voltage along its path, as they tuned the magnetic field up and down. <\/p>\n\n\n\n

\u201cIt turns out, to our great joy and excitement, that the material\u2019s electrical resistance oscillates,\u201d Chi says. \u201cImmediately, that tells you that this has very high electron mobility.\u201d<\/p>\n\n\n\n

Specifically, the team estimates that the ternary tetradymite thin film exhibits an electron mobility of 10,000 cm2<\/sup>\/V-s \u2014 the highest mobility of any ternary tetradymite film yet measured. The team suspects that the film\u2019s record mobility has something to do with its low defects and impurities, which they were able to minimize with their precise growth strategies. The fewer a material\u2019s defects, the fewer obstacles an electron encounters, and the more freely it can flow. <\/p>\n\n\n\n

\u201cThis is showing it\u2019s possible to go a giant step further, when properly controlling these complex systems,\u201d Moodera says. \u201cThis tells us we\u2019re in the right direction, and we have the right system to proceed further, to keep perfecting this material down to even much thinner films and proximity coupling<\/a> for use in future spintronics and wearable thermoelectric devices.\u201d<\/p>\n\n\n\n

This research was supported in part by the Army Research Office, National Science Foundation, Office of Naval Research, Canada Research Chairs Program and Natural Sciences and Engineering Research Council of Canada.<\/p>\n","protected":false},"excerpt":{"rendered":"

A material with high electron mobility is like a highway without traffic.<\/p>\n","protected":false},"author":2,"featured_media":25030,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[17],"tags":[],"class_list":["post-25029","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"featured_image_urls":{"full":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",900,600,false],"thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-200x200.jpg",200,200,true],"medium":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-600x400.jpg",600,400,true],"medium_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-768x512.jpg",750,500,true],"large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-675x450.jpg",675,450,true],"1536x1536":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",900,600,false],"2048x2048":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",900,600,false],"ultp_layout_landscape_large":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",900,600,false],"ultp_layout_landscape":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-870x570.jpg",870,570,true],"ultp_layout_portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-600x600.jpg",600,600,true],"ultp_layout_square":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-600x600.jpg",600,600,true],"newspaper-x-single-post":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-760x490.jpg",760,490,true],"newspaper-x-recent-post-big":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-550x360.jpg",550,360,true],"newspaper-x-recent-post-list-image":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance-95x65.jpg",95,65,true],"web-stories-poster-portrait":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",640,427,false],"web-stories-publisher-logo":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",96,64,false],"web-stories-thumbnail":["https:\/\/www.revoscience.com\/en\/wp-content\/uploads\/2024\/07\/MIT-Quantum-Dance.jpg",150,100,false]},"author_info":{"info":["By Jennifer Chu"]},"category_info":"Research<\/a>","tag_info":"Research","comment_count":"0","_links":{"self":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/25029","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/comments?post=25029"}],"version-history":[{"count":1,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/25029\/revisions"}],"predecessor-version":[{"id":25031,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/posts\/25029\/revisions\/25031"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media\/25030"}],"wp:attachment":[{"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/media?parent=25029"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/categories?post=25029"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.revoscience.com\/en\/wp-json\/wp\/v2\/tags?post=25029"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}