TECHNOLOGY INSIGHTS
BIG THINGS HAPPEN WITH TINY TECHNOLOGY
By Ken Cormier, Managing Editor
Nanotechnology, the branch of tech- nology that deals with dimensions
and tolerances of less than 100 nanome- ters, and especially the manipulation of individual atoms and molecules, is al- lowing scientists to make changes in the physical world that were once almost unthinkable. Manipulating materials at an atomic level is a striking advancement in human achievement, only about 120 years after the atom was discovered.
Thermal nanotransistor can conduct heat away from electronic components A Stanford-led engineering team has developed a way to manage heat, and also help route it away from delicate de- vices. The team has created a thermal transistor—a nanoscale switch that can conduct heat away from electronic com- ponents and insulate them against its damaging effects. In the past, research- ers’ attempts at developing heat switches have met with failure, due to the tran- sistors being too large, too slow and not sensitive enough. What was needed was a nanoscale technology that could toggle on and off, have a significant hot-to-cool switching contrast, and no movable parts. The Stanford team started with a
10-nanometer-thick layer of molybde- num disulfide. To transform it into a transistor-like switch, they bathed the material in liquid rife with lithium at- oms. When an electrical current is ap- plied to the system, the lithium atoms begin to infuse into the layers of the crystal, changing how it conducts heat. As the lithium infusion increases, the thermal transistor switches off. The re- searchers discovered that the lithium ions push apart the atoms of the crystal, making it more difficult for the heat to get through it.1
28 EVALUATION ENGINEERING JANUARY 2019
Borophene advances as 2D materials platform Physicists from the U.S. Department of Energy’s Brookhaven National Laboratory and Yale University have synthesized bo- rophene (an extremely flexible, strong, and lightweight metallic semiconductor in its 2-D form, produced from boron) on cop- per substrates with large-area single crystal domains, ranging in size from 10 to 100 mi- crometers. Previous efforts had produced only nanometer-size single-crystal flakes. Tis further advances the production of bo- rophene-based devices. Borophene is con- sidered to be a promising material platform for next-generation electronic devices such as wearables, quantum computers, biomol- ecule sensors and light detectors. For electronic applications, high-qual-
ity single crystals—periodic arrange- ments of atoms that continue through- out the entire crystal lattice without boundaries or defects—must be distrib- uted over large areas of the surface mate- rial (substrate) on which they are grown. Today’s microchips use single crystals of silicon and other semiconductors. “We increased the size of the single-
crystal domains by a factor of a mil- lion,” said co-author and project lead Ivan Bozovic, senior scientist and Mo- lecular Beam Epitaxy Group Leader in Brookhaven Lab’s Condensed Matter Physics and Materials Science Depart- ment. “Large domains are required to fabricate next-generation electronic de- vices with high electron mobility. Elec- trons that can easily and quickly move through a crystal structure are key to improving device performance.”2
Researchers remove silicon contamination from graphene to double its performance Graphene, research of which won the Nobel Prize for Physics in 2010, has failed
to lived up to its anticipated impact on flexible electronics, due to its mixed per- formance and sluggish adoption by the industry. The material—strong, flexible, transparent and able to conduct heat 10 times better than copper—had been expected to sweep through the industry with more powerful computer chips and solar panels, water filters, and biosensors. A study recently published in Na-
ture Communications points out silicon contamination as the primary source of lackluster results, and reveals how to make superior, pure graphene—effec- tively doubling its performance. An RMIT University team led by Dr.
Dorna Esrafilzadeh and Dr. Rouhollah Ali Jalili inspected commercially-avail- able graphene samples, atom by atom, with a state-of-the-art scanning transi- tion electron microscope. “We found high levels of silicon con-
tamination in commercially available gra- phene, with massive impacts on the ma- terial’s performance,” Esrafilzadeh said. Testing showed that silicon present in
natural graphite—the raw material used to make graphene—was not being fully removed when processed. Te testing not only identified these impurities, but also demonstrated the major influence they have on performance, with contaminat- ed material performing up to 50% worse when tested as electrodes. Te research- ers were able to use pure graphene to build successful supercapacitors.3
REFERENCES
1.
https://www.nanowerk.com/nanotech- nology-news2/newsid=
51489.php
2.
https://www.sciencedaily.com/releas- es/2018/12/
181203131102.htm
3.
https://www.nanowerk.com/nanotech- nology-news2/newsid=
51583.php
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