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 Universität München, Germany

Image by: University of British Columbia, Canada

Extreme Science

Why do we care about ultra, micro, high and fast?
Science is trying to push human knowledge a bit further every day. In science you can find people working with extreme conditions to push these limits and gain an even deeper knowledge about fundamental science. To be able to know what happens in fundamental processes, you have to push these limits. Here, I want to walk you through some of the main extreme sides of research in physics and try to explain why we care about them.

Nano 
As this blog focuses mostly on nanotechnology, let’s start with that extreme. Trying to work on smaller and smaller length scales opens up a whole new dimension and possible discoveries. Why? If you want to study or manipulate single atoms or molecules, you have to work in the nano scale, which is a hundred thousand times smaller than the width of a hair.

One of the four huge detectors at CERN. In the centre
is the actual beamline (image: CERN). 

High-energy
One of the most famous example of high-energy physics is the large hadron collider (LHC) established in 2008 at Cern in Geneva, Switzerland. This massive huge ring underneath the surface is accelerating protons, the positive charged particles in an atom, to energies up to 7 Teraelectronvolt. The energy is so high that two protons are accelerated in the ring to almost near the speed of light, to be precise it's 99.9999991% of the speed of light. The protons travel in opposite directions in this ring and at some point they collide. Detectors like the one in the left image are recording these collisions. Why? The purpose of the LHC is to discover new particles. Once the two protons collide, they will break into smaller particles  One specific particle, the Higgs-Boson is of special interest, as this is supposed to be the particle giving mass to all other particles.

Low-Temperature

Many experiments on single atoms are performed at low temperatures. Temperature is a measure of how fast atoms move. If the temperature of e.g. water is above 100°C it will boil, the movement of water molecules is so strong that it will become a gas. If the temperature is below 0°C, the atoms do not move that much anymore and ice is formed. The absolute zero for the temperature is -273.15°C (or 0 Kelvin, the temperature unit system used most commonly in science). At this temperature, atoms do not move any more. However, it is really difficult to reach this zero value. Most low-temperature experiments usually run at the milli Kelvin scale, which is 1000 times colder than 1 Kelvin (-272.15°C), so already pretty cold. Why? Because the atoms almost do not move anymore, you can measure them very precisely. It's like taking a picture of moving object, it's so much easier to take a sharp image of still objects. You can study quantum mechanical effects e.g. to better understand how to improve quantum computers. 

Typical UHV set-up

Ultra High Vacuum (UHV)

In my last blog, I talked about cleanrooms. An UHV system is like an even better cleanroom on smaller scale. However, you can not enter a UHV system, as there is almost no air in there, only the samples are inside. For a vacuum in the range of 10^-11 mBar, one atom has to travel for about 7000 km to collide with another particle. In practice, one atom is hitting the wall of the chamber much earlier than any other particle. It’s amazing how few atoms are in the whole system. It is also amazing to see how these UHV systems look like. Usually, you'll find a UHV system covered with a huge amount of aluminium foil and cables hanging everywhere. ;-) Why? In a UHV system, one can study atomic structures without ANY other unwanted particles. As explained before, it's like the ultimate cleanroom. 

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