Newsletter, February 2014

    MIT Materials News that Matters

    February 2014
    Materials Processing Center at MIT MIT Dome
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    Faculty Highlight: Raymond C. Ashoori
    Revealing new electronic behavior - High magnetic fields and very cold temperatures reveal exotic behaviors in graphene systems.

    Physics Professor Ray C. Ashoori in the lab at MIT with a dilution refrigerator used to study electrical charges and conductivity of materials at very low temperatures. Photo: Denis Paiste, Materials Processing Center

    The process of scientific discovery often results from hard work and good luck in the lab rather than from theoretical predictions, MIT Physics Professor Ray C. Ashoori says.


    "A lot of the physics that we do arises from serendipity and luck, and we have interesting tools to bring to bear on an interesting system. Let's see what we see. Generally, the techniques that we have are pretty different from the commonly used measurements. In a lot of cases, we just don't know what we're going to see," Ashoori says. 


    One technique that took Ashoori needed more than a decade to develop is time domain capacitance spectroscopy (TDCS), a pulse tunneling method that can send on the order of a million short electrical pulses through a material to study its electronic properties. Up until recently, Ashoori's group has focused on using TDCS on semiconductor samples, but they now see an exciting possibility for work in graphene.


    Ashoori's group at MIT recently demonstrated a unique bandgap in graphene coupled to hexagonal boron nitride that could be a precursor to developing the material for functional transistors. The work was a collaboration with Pablo Jarillo-Herrero, the Mitsui Career Development Associate Professor of Physics at MIT, and other researchers in Japan and Arizona.

    "In most materials, electrons behave as though they have a mass. In graphene, it's really different," Ashoori explains. "In graphene, they look like they don't have a mass. They look like they're behaving like photons. This is good and bad. It means electronic properties of graphene are really different. For instance, it becomes hard to make barriers to impede their flow. You can't make transistors that you can actually turn off completely, because these massless electrons can get through the barriers that you try to put in their way. But if you have an energy gap and massive electrons, then you can actually create transistors that you can turn off."  Read more.  

    MIT Researchers Gear Up for Center for Integrated Quantum Materials   Eight investigators will focus on new materials, processes for quantum computing.  
    By stacking graphene on a similarly patterned layer of boron nitride, MIT researchers found interactions between carbon and boron atoms on one sublattice and carbon and nitrogen atoms on the other resulted in adequate breaking of the sublattice symmetry to give the electrons an observable mass. In the above illustration, adjacent atoms are referred to as A sites and B sites. Illustration used with permission of Michael Fuhrer, Monash University.
    Stacking graphene on similarly patterned six-sided boron nitride opens an electronic bandgap and gives carbon electrons an observable mass, MIT researchers found. lllustration used with permission of Michael Fuhrer, Monash University.

    Groundbreaking work uncovering unexpected electronic behavior in graphene is a natural segue to MIT Physics Professor Raymond C. Ashoori's new role as a co-principal investigator of the NSF-funded Center for Integrated Quantum Materials.


    "The thing that's nice about it is that we have eight people here at MIT being sponsored by it," Ashoori says. "We're all thinking about very similar kinds of problems. It's a pretty tight fit. I'm really happy to have an excuse to hang out with all these people and for us to get together more regularly. It's a group where everyone in it fits very naturally." 

    The multi-site Center for Integrated Quantum Materials, a five-year, National Science Foundation-funded project, is led by Robert M. Westervelt, Mallinckrodt Professor of Applied Physics and of Physics, at Harvard University. There are two other co-principal investigators at Howard University in Washington, D.C., and the Museum of Science in Boston.  Read more. 

    Unexpected Results in Graphene


    MIT Postdoctoral Fellow Benjamin M. Hunt part of group to show new electronic behavior in layered graphene system.

    Physics Professor Raymond C. Ashoori, left, and Postdoctoral Associate Benjamin M. Hunt in an MIT lab where a dilution refrigerator is used to study electrical charges and conductivity of materials at very low temperatures.
    Physics Professor Raymond C. Ashoori, left, and Postdoctoral Fellow Benjamin M. Hunt in an MIT lab where a dilution refrigerator is used to study electrical charges and conductivity of materials such as semiconductors at very low temperatures. Studies are conducted at 0.1 degrees (-273.05), just a fraction above absolute zero (-273.15 Celsius). Photo: Denis Paiste, Materials Processing Center

    MIT Postdoctoral Fellow Benjamin M. Hunt points to an initial finding of unexpectedly high resistivity in graphene coupled to hexagonal boron nitride as the trigger that led to new understandings of electronic behavior in graphene.

    Hunt was a key contributor and co-author of a recent paper in Science that demonstrated a unique bandgap in graphene coupled to hexagonal boron nitride that could be a precursor to developing the material for functional transistors. The researchers also showed in a paper in Nature that applying a magnetic field in the graphene plane forced electrons at the edge of graphene to move in opposite directions based on their spins. Read more.    

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    How to Create Selective Holes in Graphene
    New technique developed at MIT produces highly selective filter materials, could lead to more efficient desalination.David L. Chandler, MIT News Office 

    The MIT researchers used a four-step process to create filters from graphene (shown here): (a) a one-atom-thick sheet of graphene is placed on a supporting structure; (b) the graphene is bombarded with gallium ions; (c) wherever the gallium ions strike the graphene, they create defects in its structure; and (d) when etched with an oxidizing solution, each of those defects grows into a hole in the graphene sheet. The longer the material stays in the oxidizing bath, the larger the holes get.
    Reprinted with permission from O'Hern, S. C. et al. Nano Letters, Copyright 2014 American Chemical Society. Read more

    A Paper for Diagnostic Cancer

    Low-cost urine test developed by MIT engineers amplifies signals from growing tumors to detect disease.  

    Anne Trafton, MIT News Office


    MIT engineers have developed a simple, cheap, paper test that could improve cancer diagnosis rates and help people get treated earlier. The diagnostic, which works much like a pregnancy test, could reveal within minutes, based on a urine sample, whether a person has cancer. This approach has helped detect infectious diseases, and the new technology allows noncommunicable diseases to be detected using the same strategy. Photo: Bryce Vickmark.    Read more  

    Theorists Predict Exotic New Insulating Materials

    Topological insulators could exist in six new types not seen before.  

    David L. Chandler, MIT News Office
    Russian artist Kazimir Malevich's 1915 painting, Black Circle.MIT physics professor Senthil Todadri says the unusual electrical behavior of materials called topological insulators reminds him of the 1915 painting by Russian artist Kazimir Malevich, called "Black Circle" (above), because the only feature of interest in the painting is the boundary between the black circle and the white background. In topological insulators, all of the significant electrical activity takes place just on the surface, not the interior. Read more
    Materials Database Yields New Discoveries
    Project provides a systematic way of exploring the vast realm of unfamiliar materials.   
    David L. Chandler, MIT News Office
    Trying to find new materials, to improve the performance of anything from microchips to car bodies, has always been a process of trial and error. MIT materials scientist Gerbrand Ceder likens it to setting out from Boston for California, with neither a map nor a navigation system - and on foot. But, he says, after centuries of doing materials research the old-fashioned way, a significant revolution is underway.  Read more
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