How stuff works: Atomic Force Microscope

Picture source: Wikimedia

Since the beginning of science itself, mankind has been driven to understand the nature of matter. During that difficult quest the building blocks of all matter in the universe was discovered - the atom. The atom was first postulated in 400BC by Democritus and later refined by Dalton in the early 1800s. As time went on, more complicated experiments actually showed that atoms were not the most fundamental building block after all. In fact atoms are made of a nucleus with sub-atomic particles called protons and neutrons, and this nucleus was surrounded by a cloud of electrons.

Mankind is now creating more and more complex technology, and as our technology gets better, it is generally getting smaller. We are now at a stage where understanding nanoscale properties of materials ("Nano" means about 1 billionth of a metre, or about 10 atoms across) is important for the future development of mankind itself. So how can we start to understand materials on this nanoscale? Well intuitively as humans we generally like to observe things, after all, seeing is believing. However, you can go to the shop today and buy the best light microscope that money can buy and I can promise you, you will not be seeing atoms anytime soon. In order to characterise materials on this nanoscale we need a new type of microscope.

Actually there are now a number of microscopes that allow use to see on the nanoscale. The one I will be talking about today is the "Atomic force microscope". The atomic microscope does not allow us to see using light or in fact any other type of electomagnetic radiation. Instead it essentially "feels" the surface. Imagine closing your eyes and using your hands to run over the back of an egg carton. You know there bumps on the surface of the egg carton because you run your hand across the surface and can feel the your hand going up and down. The atomic force microscope is doing something similar but on a much smaller scale. It consists of an atomically sharp tip which is mounted on a cantilever. The cantilever-tip system can be scanned across the surface of a material. As this occurs the tip feels features in the surface and essentially moves up and down with these features. The distance the tip moves up and down is detected using a laser which is reflected off the surface of the cantilever. As the cantilever moves up and down in response to the surface, the position of the reflected laser spot also moves and is converted into a voltage depending upon its position. This allows the mapping of features on a surface in the nanoscale, and in fact quite recently the atomic force microscope has been used to map individual atoms.

"Alien bacteria found on earth"

One of my fave topics in science is astrobiology. Which is simply the study of potential life elsewhere in the universe.

The idea that life is elsewhere in the universe seems very obvious to me, but I never cease to be surprised by human arrogance with regards to this subject. There are still many scientists out there who believe that its possible life only exists here on earth!

Our understanding of life is completely based upon our experience and observations here on earth, and its refreshing to see that new research is demonstrating that some of the previous prerequisites for life are not always valid, even here on earth. Recently NASA scientists have found a type of bacteria that is like no other found thus far. They describe it as "Alien bacteria" simply because it is so different to what our experience of life is thus far.

All life on earth contains genetic information which is encoded in DNA (Or some primitive viruses, RNA). DNA has a well known structure consisting of the elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus. NASA have now found a bacteria which was isolated from Mono Lake, California. They have found that in order to maintain growth this bacteria will replace the normally essential element Phosphorus with the element Arsenic. This is highly surprising in two ways.

Firstly, it demonstrates that the structure of DNA and hence the genetic code may be subject to change. This really opens up the possibility that the "Information of life" may be passed in different types of "DNA" - perhaps DNA is just a family of biological molecules which are capable of coding genetic information.

Secondly, Arsenic is normally toxic to life on earth and yet this new bacteria is thriving on it and using it as part of its chemical make-up.

The concept of Darwinian evolution has demonstrated the importance of the environment in the progression of life in earths history. I now think it is quite likely that this has more far reaching consequences than we previously thought and it may be possible that there is life out there in the universe in places we would no doubt class to be inhospitable, due to extreme temperatures, pressures, or lack of specific compounds such as water.

The abstract for the NASA article may be found here

Magnetic monopole defects directly imaged

Electricity and magnetism were tied together in the late 1800s by the celebrated James T. Maxwell. However it was noticed very quickly that these formulae were asymmetric. Whereas electricity allows the presence of electrical charge, such as electrons, there was no such analogue for magnetism. Everyday experience (Such as cutting a conventional bar magnet in half, leading to the generation of two new dipole magnets), tells us that magnetic charge (north and south poles) cannot normally be separated. In the 1930s a famous theoretical physicist called Dirac, predicted the existence of single magnetic poles (monopoles), which lead to a widespread search for the proof of their existence (mainly conducted in large central facilities). Recently it has been realized that arranging arrays of nano-magnets in certain geometries (known as artificial spin ice) that builds in a magnetic frustration, allow the nano-magnets to interact in such a way that excitations of this system behave much like magnetic monopoles under certain circumstances. Several research groups have now confirmed the existence of these monopole defects by direct imaging. These monopole defects may allow new devices to be made which rely on magnetic charge, and it may even be possible to realise a magnetic version of electricity - dubbed "magnetricity".

Source: Nature Physics 7, 68-74 (January 2011)