Ultra-High Vacuum, Low Temperature Scanning Probe Microscope (UHV LT SPM) 7608 by EMSL
In this article, Oscar Williams surveys the fascinating evolution of surface science technologies and explains how they can transform the future of our energy systems.
Oscar is a final year PhD student at University College London and Imperial College London, working within the London Centre for Nanotechnology, where he studies how best to enhance catalytic reactions. He has a passion for science outreach and teaching, heading the UCell society for electrochemical energy devices, and writing for Physics World.
How can the behaviour of a single atom provide insights into our energy demands? How do we know that atoms actually exist? And what on Earth do the acronyms XPS, STM and UHV stand for? If you find yourself wondering about these questions (and perhaps now you are), then surface science is the yellow brick road to the answers you’re looking for.
Surface science is a broad field that encompasses physical phenomena occurring between different materials or different states of matter. It covers many different processes that allow us to develop a deeper understanding of various applications, such as the production of chemicals, the design of energy storage materials, and the particulars of photo-driven reactions in devices such as solar cells.
Gaining a fundamental understanding of these processes means that they can then be engineered and optimised to work in the best possible way, providing us with the knowledge we need to create hydrogen fuel, efficient solar cells, and green solutions for our future. In order to gain this understanding, however, surface scientists have to first simplify complex reactions and focus on the key interactions.
One way of achieving such a simplification is through the creation of an ultrahigh vacuum system with a thousand billion times less pressure than our atmosphere; this is known as UHV for short. Having such a high vacuum means that the UHV chambers have very little contamination from “extra” molecules that are irrelevant to the process being investigated. In this way, surface scientists can eliminate additional contributions from things such as the air that we breathe and thrive in, which is full of all sorts of atoms and molecules. The spotlight can then be focused on the specific reaction that is of interest to the researchers, with the option of increasing layers of complexity over time. Research facilities such as CERN (European Organization for Nuclear Research) in Geneva go one step further, building extreme high vacuum (XHV) chambers with even less pressure — around a million billion times smaller than our atmosphere! That is a seriously clean, and highly controlled, system.
The real beauty of UHV systems is the way in which the environments they create open up the potential for studying our surfaces using a wide range of techniques, some of which are not usually possible due to the high number of molecules in our normal atmosphere. One of these techniques is a method called scanning tunnelling microscopy, or STM, which allows us to directly image individual atoms on a surface and monitor their behaviour. Aside from the fact that this is incredibly cool (each atom will likely never be seen at that level by anyone ever again), being able to observe atoms and molecules at this microscopic level makes it possible for us to study and design materials one atom at a time.
The science behind STM is complex and involves mind-bending phenomena such as quantum tunnelling*, but the result is outstanding. So much so that the inventors of the technique were awarded the 1986 Nobel Prize in Physics. However, although STM gives us a brilliant look into the lives of atoms and allows us to become atomic photographers, as with any technique it has its drawbacks. Typically, STM is not chemically sensitive, which means that it can be very difficult to distinguish between, for example, an oxygen atom and a carbon atom, which is crucial to building a complete picture of a chemical or physical process.
However, all is not lost. Through collaboration and the use of other techniques within the UHV system, surface scientists are able to gain chemical sensitivity, determine dynamic behaviour and understand further properties of the materials under consideration. Thankfully, we have many of these complementary techniques available to us, such as X-ray photoelectron spectroscopy, or XPS, which provides us with valuable chemical sensitivity. Using these techniques in combination, we can begin to tell the complete story of an atomic level reaction.
This level of atomic control and understanding is unprecedented, and with it we can start to build and design materials that can, for example, harness the power of the sun to produce hydrogen for hydrogen fuel. Hydrogen fuel may sound like a futuristic and slightly scary source of energy, but it is already being implemented in London buses and a German freight train. Even commercial hydrogen cars are available now! And what better way to generate this hydrogen than through our eternal benefactor: the sun?
It is clear that the energy needs of a sustainable future will be met by innovative hybrid systems such as this, which combine the powers of different renewable sources and technologies. No single energy source will surpass the rest, but through coordination of all of these environmentally sound routes, we will give ourselves the best possible chance to prevail against global warming and impending environmental crises.
‘But if it’s so good, why aren’t hydrogen and these hybrid forms of renewable energy everywhere?’ I hear you cry. First of all, there is still more research to be done in order to improve the existing technology, otherwise surface scientists and many associated research fields would already be obsolete. Furthermore, in the same way that multiple energy sources are needed to solve our problems, we as a global community must also come together to collaborate and drive forward change. This will provide the economic and social boost needed to push research and applications such as hydrogen energy forward.
There are many beautiful, fascinating and heart-warming movements that already exist around us, which use the power of people to accomplish positive change. So although we may be able to design fantastical devices one atom at a time, on a macroscopic level we also require the necessary social drive, knowledge and passion to improve our energy infrastructures, push new research to the forefront and implement these innovations. The time is now, and the catalyst for change is you — together we can shape a brighter future, atom by atom and person by person.
*For those of you interested in delving into it, quantum tunnelling refers to the curious case of a subatomic particle transporting itself through a barrier and appearing on the other side, defying classical mechanics and common sense. In our case, an electron spontaneously transports itself from orbiting one material’s atom to another atom through a vacuum of empty space, giving rise to a tiny electric current which we record - mind-bending!
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