Nanotech’s ‘small world’ inching ever closer

A breakthrough technique developed by an Israeli team could allow for the development of microscopic devices that will help millions

Dr. Ernesto Joselevich (left) and a student near carbon nanotube synthesis reactor (photo credit: Weizmann Institute)
Dr. Ernesto Joselevich (left) and a student near carbon nanotube synthesis reactor (photo credit: Weizmann Institute)

The tech universe is shrinking rapidly as companies seek to make ever-tinier devices that can do ever-more powerful things. But there’s a limit to how much you can shrink the silicon that goes into computers, cellphones, tablets, and the like; at that point you have to starting thinking about nanotech — developing components out of atom- or molecule-sized material (a nanometer is one-millionth of a millimeter).

Nanotechnology holds great promise for the future, but there are many technical challenges on the road to that future. This week, the Weizmann Institute of Science announced that it had figured out a way to overcome one of the most daunting technological issues that has been holding back nanotech development. The breakthrough, say Weizmann experts, could help jump-start a whole industry.

It’s all a function of Moore’s Law, named after Intel cofounder Gordon Moore who (accurately) predicted in the early 1960s that computer processing power would double every 18-24 months. In a semiconductor chip, the more transistors, the more powerful the chip. Manufacturers have various techniques for loading up more transistors in order to make chips more powerful (Intel, for example, has developed a multigate transistor, allowing more electronic signals to flow through a component).

While building more powerful chips — which require more “crowded” chips — manufacturers have to ensure that the chip remains small enough to fit into devices that companies like Apple and Samsung are busy dreaming up (all of which, of course, need to be small enough to fit into a pocket or purse).

Nano is about much more than computers, though; nano-sized components will, for example, allow doctors to more easily treat a wide variety of diseases, as mechanized and computerized atom-sized self-propelling devices will be able to reach and treat parts of the body that currently require major surgery — such as using nanoparticles to destroy cancer cells deep inside the body, obviating the need for chemical therapy (the technique, called Kanzius RF Therapy, is currently being researched in the US). Advanced medical devices are made up of transistors and semiconductors.

Sometime soon (probably by the end of the decade, many experts believe), straight transistors will have run out of room to grow, and manufacturers will have to start developing chips and components using nanotech techniques, manipulating atom-sized materials to build the wires that make up the transistors that create a semiconductor.

But manipulating atom-sized materials requires atom-sized tools — which do not exist (or if they do, are unsuitable for creating wires). To get around that, scientists set up a scenario to try and “guide” the nano-materials they use to develop nano-sized wires, transistors, and components. Based on the behavior of these components, scientists can, if they set the scenario properly, get the materials to form nano-wires, the first step in developing a whole component.

But things work differently in the nano-world, and getting the materials to behave properly is a challenge. With silicon, the material semiconductors are made of, you know what to expect; silicon acts as expected.

Not necessarily so in the nano-world, however; sometimes nano-materials don’t follow the rules, due to the many environmental factors that can affect them. Very often, the nano-wires curve outside of the guides they are supposed to follow, upwards and outwards, rendering them, if not useless, then far less effective as semiconductor components. This difficulty in getting the materials to do what they are expected to do has been one important reason why more progress hasn’t been made on nano-components, scientists say.

The problem has been solved — or, potentially solved — thanks to research led by Prof. Ernesto Joselevich of the Weizmann Institute’s Chemistry Faculty, who has found a way to grow semiconductor nano-wires out, not up, on a surface, providing, for the first time, fully repeatable guidance to produce relatively long, orderly, aligned structures. The team’s achievement has been published in the Proceedings of the National Academy of Sciences (PNAS), USA.

Joselevich, doctoral student David Tsivion and postdoctoral fellow Mark Schvartzman of the Materials and Interfaces Department grew nano-wires made of gallium nitride (GaN), a mix of nitrogen and gallium, using a sapphire base — a combination that appears to induce the desired behavior in the nano-wire material, said Joselevich. Another advantage of GaN nano-wires is that they are excellent conductors of electricity. The nano-wires were so well-behaved and malleable, in fact, that the team was able to build a self-assembling Address Decoder, a component that tells a processor which chip to use and when. As a result of his work in this field over the past several years, Joselevich has been awarded a European Research Council Advanced Grant.

Commenting on the findings, Joselevich said that “it was surprising to discover that the optical and electronic properties of our nano-wires were just as good, if not better, than those grown vertically, because growing semiconductors on a surface usually introduces defects that degrade their quality.”

Although gallium is a relatively rare element, the principles and methodology developed by the team will be of use with other elements and materials, so the day when nano-components start powering LEDs, lasers, information storage media, transistors, solar cells, computers, photovoltaics, medical devices, and much more may not be far off.

“Our method makes it possible, for the first time, to determine the arrangement of the nano-wires in advance to suit the desired electronic circuit,” said Joselevich. “The ability to efficiently produce circuits from self-integrating semiconductors opens the door to a variety of technological applications.”

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