Sunday, December 9, 2012

Nano in your Daily Life

Nano became a major trending label in the beginning of the 21st century. Nowadays, you see socks, packages, food, cars, mp3 players, etc. labeled with nano. Nano sells! I want to show you what’s the science behind some of the major nano labels. For this, let me first describe to you very quickly what nanoparticles are and why they are so beneficial.

What are Nanoparticles?
Nanoparticles are small structures with a diameter of 1-100nm. At this length scale, some materials have different properties than in their bigger bulk material. Because these particles are so small, the surface area per volume is much higher. Most reactions usually happen at the surface of a material, therefore, a higher surface area means more reaction happening. Nanoparticles are actually not an invention of the modern world. These particles were around since a long time. However, nowadays these particles are trending and a good selling label.

What are Socks with Silver Nanoparticles?
There are many brands who offer socks enhanced with silver particles. But what exactly do these silver particles do? These silver nanoparticles can kill many different types of bacteria and therefore the smell from your socks. Silver nanoparticles are not only added to the fabric of socks or underwear, but also to food packaging, cosmetics, tooth brushes and even bandages.

Why add Titanium Dioxide to Sunscreen?
Most of the available sunscreens contain titanium dioxide nanoparticles (TiO2) or zinc oxide (ZnO). These specific nanoparticles are added to sunscreens as they block ultraviolet (UV) light very efficiently. Usually, the higher the blocking factor of your sunscreen, the whiter the sunscreen appears. However, if you shrink the size of titanium dioxide to the nano size, these particles are transparent and can therefore be added to light sunscreens without the thickening white effect.

Are Nanoparticles dangerous?
There is a strong debate whether particles are harmfull to your body or not. Many believe, that due to their small size they can enter into parts of your body, where you do not want to have any other materials. One can not say that nanoparticles in general are dangerous, as these properties differ very strongly among different types. There is a lot of research going on to measure the effect of nanosized particles to our bodies and environment. But don't worry, most countries have very strict regulations about putting nanoparticles into the market. 

Sunday, December 2, 2012

Writing with Atoms

How can you see single atoms?
Atoms are the building blocks of every cell and every material. An atom is only about 0.3 nm in diameter. To “see” these atoms, you have to use special microscopes. The most famous one, is the AFM (Atomic Force Microscope), which I briefly described in my first post. This technique basically feels the atoms underneath it with a very very sharp tip, ideally so sharp that there is only one atom at the tip. The tip (called cantilever) is scanning slowly over the whole surface and creates a topographical image. Below you can see salt at atomic resolution. Each "dot" is one single atom, isn't that just amazing?
Salt (NaCl) atoms under an AFM.
The frame size is 5nm.
(Image taken from: Jessica Topple)
Who wrote with atoms first?
The first amazing demonstration and milestone of modern nanotechnology, was the fact that one can write and manipulate single atoms. This was first archived by Don Eigler from IBM in 1989. He successfully managed to arrange 35 Xenon atoms to write the famous letters "IBM" (see image below). This was realized with an STM (Scanning Tunneling Microscope) tip. An STM works very similar to an AFM, the main difference is, that the tunneling current between the tip and the sample is controlled and kept constant. With an AFM, the force between the atoms are measured therefore it works on non-conducting materials as well. 

IBM logo with 35 Xenon atoms. (Image taken from IBM) 
How do you write?
Don Eigler, who was the first to ever write with atoms, used an low-temperature ulta-high vacuum (UHV) system (check out my other post on Extreme Science). This system is required in order to have a super clean environment with no other disturbing atoms and to reduce the vibration of the atoms by lowering the temperature. The trick now to move an atom across the surface is to get very close to the atom with the STM tip. At some point, a positive van der Waals attraction between the atom on the tip of the STM and the atom to be moved is created, the atom is attached to the tip. Now by keeping this distance short, the atom can be moved to a different location. Once at the correct position, the STM tip just needs to be moved away from the atom and it stays put. In only 22 hours, the first IBM logo written with single atoms was created.

Why is it important?
First of all, it's fun and amazing! Second, it was the first ever approach for nanometer scale manipulation. Third, you can now move atoms to where you want them to be to create new structures.

Since then, many more universities, institutes and companies all over the world created atomic sized versions of their logo. Here are some cool examples:

Image by: NIST, USA
Image by: Technische Universit√§t M√ľnchen, Germany
Image by: University of British Columbia, Canada