Science Concentrates Benzonitrile has been identified in the Taurus Molecular Cloud.
ASTROCHEMISTRY
Radio telescope spots aromatic molecule for first time Detecting benzonitrile in space could help astronomers zero in on what else is out there too similar to parse, and many PAHs lack Astronomers have identified an aromatic strong polarity, making signatures in their molecule in space using a radio telescope rotational spectra—typically collected for the first time, spotting benzonitrile in with radio telescopes—difficult to detect. an interstellar dust cloud 430 light-years Although benzonitrile isn’t strictly a away. Brett A. McGuire, a Hubble fellow at PAH because of the nitrogen it contains, the National Radio Astronomy ObservatoMcGuire’s group set its sights on ry, and colleagues plan to use the N the molecule because of its strong spectroscopic data they collected C dipole moment. Benzonitrile is to figure out how this and other thought to form from a reaction complex chemicals arise in outer between benzene and cyanide, so space (Science 2018, DOI: 10.1126/ Benzonitrile measuring benzonitrile may be science.aao4890). one way to estimate how much Astrochemists have known that benzene, a PAH, exists in space, as well as polycyclic aromatic hydrocarbons (PAHs) other molecules. make up an estimated 10% of all interstelUsing the Robert C. Byrd Green Bank lar carbon in the universe, but it has been Telescope, in West Virginia, the researchers challenging for them to distinguish one could make high-resolution measurements PAH from another. Bond-stretching motions in the molecules’ infrared spectra are at specific radio frequencies. The team
observed eight of benzonitrile’s nine predicted rotational transitions, the frequencies of which had been confirmed via lab experiments. The discovery is good news for astronomers searching for molecules in space, according to Christine Joblin, an astrophysicist at the University of Toulouse. In an accompanying perspective article in Science, she and José Cernicharo of the Institute of Materials Science of Madrid explain that until now, most compounds in space have been detected by telescopes that scanned different wavelengths. “Since most of the environments are out of reach for a direct chemical analysis, we are gathering all the information we can from photons over the different frequency ranges,” Joblin says.—SAM LEMONICK
2-D MATERIALS
A new class of electronic devices could be used for memory cells and telecommunications switches Two-dimensional materials can be exploited to make a new kind of electronic device that researchers have dubbed an atomristor. In early-stage studies, the researchers demonstrated a possible application for the atomristor in low-power communications circuits (Nano Lett. 2017, DOI: 10.1021/acs.nanolett.7b04342). The device’s name comes from “atomically thin memristor.” Memristors are capable of acting in ways similar to memory cells and transistors, meaning they can both store and process information. They’re promising for use in computer memory because they are nonvolatile: Even when the power is turned off, they hold on to their data. Deji Akinwande of the University of Texas, Austin, and his group made memristors by sandwiching a variety of atomically thin transition-metal dichalco-
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C&EN | CEN.ACS.ORG | JANUARY 15, 2018
genides, such as molybdenum disulfide, between metal electrodes. By applying different voltages, they could change the material’s electrical resistance along a continuum, an essential characteristic of a memristor. And when the power was switched off, the resistance stayed steady. Atomristors could be used to store data, but Akinwande and coworkers explored a new application for the devices as telecommunications switches. Their
A layer of molybdenum disulfide between two gold electrodes forms a new type of electronic device called an atomristor.
atomristors can switch on and off at a 50 gigahertz frequency. Such devices could support low-power communications networks because they consume energy only when sending signals, Akinwande says. He believes that defects in the materials, such as missing sulfur atoms in MoS2, are the key to how the devices work. In an applied electric field, atoms from the metal electrodes may move into the 2-D material’s vacancies, allowing current to flow directly between the electrodes and changing the sandwiched material’s resistance, he says. When the power is turned off, the atoms stay where they are, explaining why the atomristors are nonvolatile. Mark C. Hersam of Northwestern University, who works on memristors made from 2-D materials, agrees that defects are likely important and says that Akinwande’s atomristors show characteristics that are desirable in such devices.—KATHERINE
BOURZAC, special to C&EN
C R E D I T: ES O ( C LO UD ) ; N A NO LE T T. ( ATO MR I STO R )
‘Atomristors’ made from 2-D materials
