Berkeley Builds Shape-shifting <span style='color:red'>Molecular</span> Memory
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Berkeley Builds Shape-shifting Molecular Memory

　　As CMOS approaches the atomic scale, a molecular-sized shape-changing memory technology is being perfected that reversibly changes the crystalline-lattice structure of molybdenum ditelluride. The approach, which requires only a few atoms to store ones and zeroes as shapes, could enable solid-state memories that store mechanical qualities and match the scale of future atomic-level processors, according to professor Xiang Zhangat the University of California, Berkeley, where he is director of materials science at Lawrence Berkeley National Laboratory.　　The technology uses electron injection — not to encode the memory as charge, spin, or any ephemeral quantity, but rather to change the crystalline lattice structure of MoTe2 in a reversible process. Rearranging the atomic structure via electrical stimulation changes the material’s properties, thus allowing ones and zeroes to be formed and sensed using far less energy than is required for shifting chemical properties or for thermally induced transitions, as in phase-change memories, according to Zhang.　　The key to the process is the use of a transition-metal dichalcogenide (TMD) — in this case, MoTe2 — whose atomically thin monolayer films allow its internal lattice structure to be altered with electronic pulses that shift the structure between two stable states. In the example MoTe2 film used by Zhang and his co-researchers at UC-Berkeley and Berkeley National Lab, the two stable lattice structures are the symmetric 2H arrangement and its slanted counterpart, 1T.　　The Berkeley researchers are experimenting with various TMDs as target materials for their electron-injection method of shape-changing crystalline lattice structures, but MoTe2 is favored because it has both electronic and photonic properties that can be changed. Their goal is to create a library of “designer films” that can be used in both computer and optical applications, including solar panels.　　The electronic and optical properties that can be electronically changed in the 2-D, monolayer TMD films include electrical resistance, spin transport, and the phase-related shape \changes used in the Berkeley approach.　　The researchers’ proof of concept used “electrostatic doping,” with electrons, instead of atoms, serving as the dopant, according to Zhang. After coating the MoTe2 monolayer with an ionic liquid, they used the injected-electron dopant to change the crystalline lattice’s shape, reportedly without creating defects in the material. The resultant 1T structure is slanted and metallic, allowing it to be easily differentiated from the semi-metallic 2H atomic lattice arrangement. Removing the dopant electrons by applying a lower voltage reinstates the original, 2H structure.　　The U.S. Department of Energy funded the project. The DoE’s Office of Basic Energy Sciences performed the transport studies, and its Light-Material Interactions in Energy Conversion Frontier Research Center performed the optical measurements. The DOE Energy Frontier Research Centers and the National Science Foundation (NSF) supported the project through device design and fabrication. China’s Tsinghua University provided reference materials. Researchers at Stanford University also contributed, with funding from the Army Research Office, the Office of Naval Research, NSF, and a Stanford Graduate Fellowship.
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Release time：2017-12-27 00:00 reading：1455 Continue reading>>
<span style='color:red'>Molecular</span> magnetism packs power with 'messenger electron'
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Molecular magnetism packs power with 'messenger electron'

　　Atoms on adjacent molecules like this could be linked to form a long, magnetic chain, creating a new type of magnetic structure, says John Berry, a professor of chemistry at the University of Wisconsin-Madison　　The spins of unpaired electrons are crucial to permanent magnetism, and after 10 years of design and re-design, research conducted by John Berry at the University of Wisconsin-Madison, has resulted in a molecule that gains magnetic strength through an unusual way of controlling those spins.　　According to Berry the new structure, created by graduate student Jill Chipman could lead to a breakthrough in quantum computing.　　The presence and activity, or "spin," of unpaired electrons sets the strength of a permanent magnet, so molecules with a high degree of spin are crucial. The unusually large spin in the new magnetic molecule, Berry explains, results from a "messenger electron" that shuttles between an unpaired electron at each end of the rod-shaped molecule and persuades all three of them to adopt the same spin.　　That agreement of spin, termed "orthogonality", adds strength to a permanent magnet.　　Berry, a UW-Madison professor of chemistry, notes that in other materials, a traveling electron tends to oppose the spins of magnetic centres, reducing the magnetic strength. In Chipman's work, however, the messenger electron causes the two remote unpaired electrons to take the same spin, adding strength and/or durability.　　The new molecule, described in the journal Chemistry, contains carbon, nickel, chlorine, nitrogen, and molybdenum, but lacks the costly rare earth elements that have impacted on efforts to commercialise super-strong new magnets.　　Its structure suggests that the molecule could be formed into a polymer - a repeating chain of units like those found in plastics - raising the possibility of cheaper, but much stronger magnets.　　"We tried to remove electrons from this molecule 10 years ago so it had an unpaired electron at each end, but did not get far," Berry says. "We since learned that this made a chemical that is really temperature-sensitive, so we had to develop a low-temperature process that relies on dry ice to cool it to -780C."　　The electron establishes "a design principle that could be used to create many new magnetic molecules that behave as little bar magnets," Berry says.　　Much of the focus of magnet innovation concerns greater strength, Berry says, "but there are all sorts of things people look for. We need both permanent magnets and those with ephemeral magnetization for different technical reasons. Magnets are widespread in ultra-cold refrigeration, motors, computer hard drives and electronic circuits."　　By going the next step, and miniaturising magnets to a single molecule, quantum computing could be enabled, Berry says.
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Release time：2017-11-15 00:00 reading：1472 Continue reading>>

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