With a nanometer being just a billionth of a meter, the nanoscale indeed is very small. So, what is technology at the nanoscale? We talked to Prof. Bengt Kasemo to learn more about what is so special about nanotechnology and how the area originated.
The nanoscale is in between the atomic scale and the microscale. Putting a nm in perspective and comparing it to the dimensions of things that are familiar to us, a water molecule is ~0.3 nm and the diameter of a typical strand of hair is ~75 000 nm.
- In a broad sense, nanoscience and nanotechnology deals with matter, and constructions of matter, in the size range that we are talking about, says Prof. Kasemo.
A water molecule is a little too small to be nanotechnology, it is rather molecular physics, but if we go up three times in linear size, to ~1 nm, we could have many tens of water molecules, or other molecules, in some construct. Then, if we go up two orders of magnitude in size, up to 100 nm, the volume actually goes up 106 times. So, then we are talking about millions or tens of millions of molecules and we're still in the size range of say 100 nm, prof Kasemo continues.
To put that into perspective, this is about where an optical microscope stops to see things – the wavelength of visible light is a few hundred nanometers. So, in this size range we can build things with a few tens of atoms or molecules, or we can build things with millions of atoms, or molecules, that have special functional properties, says Prof Kasemo. The upper dimension of where nanotechnology ends and microtechnology begins is somewhat floating and depends on the (functional) properties and behavior of the actual system, but usually the limit is set to a few hundred nanometers.
- ‘Functional’ is a key word for nanotechnology. When we scale down from the macroscopic scale to micrometers and down to nanometers, at some point matter very often changes its properties and behavior dramatically, Prof Kasemo says.
This change of properties, for example electrical or optical properties, is a challenge for researchers who are just interested in finding out what happens, for example what can you do and what can you construct. But it is also of extreme importance to make new functional units in electronics, in materials science, and so on. Often these new first order properties are related to quantum effects. And researchers and engineers want to exploit these new properties.
- One could claim that it started with the discovery at the Bell telephone Laboratory, that one can build a unit that resembles the functional properties of radio tubes (triodes) by making a so-called transistor. It was a solid-state device, and this happened around 1947, says Prof Kasemo. It was yet far from the nanoscale but it initiated decades of development eventually entering the nanoscale.
This discovery started to revolutionize the building of electrical circuits at the end of the 1950s and through the 1960’ies. Then started a development where every transistor and every other component, diodes and so on, shrunk for every year. The reason for this was that you get more functional units in the micro circuits the more transistors you had per unit area, so by close packing you could gain in both performance, speed and cost, Prof. Kasemo explains. So, this started on the macro scale around 1960. But then as the components continued to shrink over about 40 years, the smallest part of an integrated circuit, a transistor, would eventually pass the size of a hundred nanometers. This happened around the last switch of the century.
At this point, they found that there were some limits that they started to run into on how to make things that small, Prof Kasemo continues. Also new phenomena started to appear. So, the perspective of microelectronics shrinking below 100 nm put a lot of effort and attention to making things smaller and smaller. Making things that small required two special things; first it required fabrication and production instruments that could make things that small, using for example photolithography, and later on electron beam lithography. So, making things small was very important, but at the same time seeing things that small was important. Since optical microscopes couldn't see the smallest components, analytical instruments that could see things that small were also very important, like for example electron microscopes and scanning electron microscopes. This put an enormous drive on technological development of producing and analyzing at the nanoscale. And this spilled over from the area of microelectronics to essentially every other area of technology, but also into science, i.e. pure science, to make things small and study properties in this size range of matter.
In my view, this (microelectronics) was the strongest driving force for nanoscience and nanotechnology development, says Prof. Kasemo. But there was another parallel development in chemistry. That was to make functional molecules that were larger than what we normally call molecules, nano-objects, nanoparticles. To make these nanoparticles from very few atoms/molecules, around 1 nm in size, to many, up to 100 nm in size, was a parallel development that complemented the one in microelectronics. Today, fabrication and studies of nano-systems that show new behavior and properties are a wide scientific field affecting almost every area of science and technology, from basic materials science to medicine.
Listen to the full interview with Prof. Kasemo in this pod episode where we talk about the history of nanotechnology, the risks and opportunities with nanosized entities, as well as the future of this area.
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