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Tech Insights: Big things happen with tiny technology

Dec. 27, 2018

Nanotechnology, the branch of technology that deals with dimensions and tolerances of less than 100 nanometers, and especially the manipulation of individual atoms and molecules, is allowing 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 devices. The team has created a thermal transistor—a nanoscale switch that can conduct heat away from electronic components and insulate them against its damaging effects. In the past, researchers’ attempts at developing heat switches have met with failure, due to the transistors 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 molybdenum disulfide. To transform it into a transistor-like switch, they bathed the material in liquid rife with lithium atoms. When an electrical current is applied 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 researchers discovered that the lithium ions push apart the atoms of the crystal, making it more difficult for the heat to get through it.1

Borophene advances as 2D
materials platform

Physicists from the U.S. Department of Energy’s Brookhaven National Laboratory and Yale University have synthesized borophene (an extremely flexible, strong, and lightweight metallic semiconductor in its 2-D form, produced from boron) on copper substrates with large-area single crystal domains, ranging in size from 10 to 100 micrometers. Previous efforts had produced only nanometer-size single-crystal flakes. This further advances the production of borophene-based devices. Borophene is considered to be a promising material platform for next-generation electronic devices such as wearables, quantum computers, biomolecule sensors and light detectors.

For electronic applications, high-quality single crystals—periodic arrangements of atoms that continue throughout the entire crystal lattice without boundaries or defects—must be distributed over large areas of the surface material (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 million,” said co-author and project lead Ivan Bozovic, senior scientist and Molecular Beam Epitaxy Group Leader in Brookhaven Lab’s Condensed Matter Physics and Materials Science Department. “Large domains are required to fabricate next-generation electronic devices with high electron mobility. Electrons 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 performance 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 Nature Communications points out silicon contamination as the primary source of lackluster results, and reveals how to make superior, pure graphene—effectively doubling its performance.

An RMIT University team led by Dr. Dorna Esrafilzadeh and Dr. Rouhollah Ali Jalili inspected commercially-available graphene samples, atom by atom, with a state-of-the-art scanning transition electron microscope.

“We found high levels of silicon contamination in commercially available graphene, with massive impacts on the material’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. The testing not only identified these impurities, but also demonstrated the major influence they have on performance, with contaminated material performing up to 50% worse when tested as electrodes. The researchers were able to use pure graphene to build successful supercapacitors.3

REFERENCES
1. https://www.nanowerk.com/nanotechnology-news2/newsid=51489.php
2. https://www.sciencedaily.com/releases/2018/12/181203131102.htm
3. https://www.nanowerk.com/nanotechnology-news2/newsid=51583.php

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