New research infrastructure enables the study of materials in the atomic scale at the University of Oulu

The new equipment at the University of Oulu, namely the APXPS (Ambient Pressure X-ray Photoelectron Spectroscopy) and the APT (Atom Probe Tomography) instruments provide researchers capabilities to study materials and processes at small scale down to atomic level. Down the line, this type of research can and will be applied in fields like materials engineering, metallurgy, energy production and consumption, battery technology and so on.

The equipment is a part of a major collaboration involving the European Union, Research Council of Finland, University of Oulu, VTT, and Tampere University. There are two infrastructure initiatives, Hub for Hydrogen-Materials Interactions Research Infrastructures – H2MIRI and Operando Research Infrastructure for Energy Materials and Systems – OperaRI, which are a coordinated effort to create a shared research environment in Finland.

High quality equipment paves the way for high quality research

Both the APXPS and the APT are unique to the University of Oulu in Finland: the closest machines are in Sweden and elsewhere in Europe. This is a significant benefit, as researchers in the university can collect datasets from both equipment under one roof without having to resort to measurements and datasets conducted in another research facility in another country. Both measurement devices provide information at a very high resolution, and state-of-the-art capabilities lead to world-class research, says Assistant professor Vahid Javaheri, leader of the Microstructure and Mechanisms research group.

“In empirical sciences like material sciences, the quality of research naturally starts with the researchers, but it is also related to the devices you have at your disposal. You cannot get good results with bad tools. This equipment sets the stage for very high-quality research that can be published in the world’s top journals”, Javaheri explains.

The APXPS device offers a way to study matter in situ and operando, or in typical actual work environment and during processes. APXPS can study samples for example in the pressure of one atmosphere, which is the condition that all of us are on Earth. Other methods typically require placing samples in (ultra) high-vacuum conditions, which is not typical of real-world applications. Operando means that it is possible for instance to study chemical reactions as they happen, like when a battery is charged or discharged.

From theory to practical environments

Put simply, APXPS is a method where solid matter, for example a metal like nickel, is bombarded with light, X-rays in this case. Hitting a material with large enough energy will knock off electrons from its surface and measuring the kinetic energy of these electrons will yield information on the sample.

“This technique is based on the photoelectric effect which was already explained by Albert Einstein. We are able to find out all the elements and their chemical environments which are present in the sample with this technique. It is a way of confirming theoretical quantum mechanical models in practice as well as changes in the chemical composition of materials under close to realistic operation conditions”, says Senior research fellow Samuli Urpelainen of the Nano and Molecular Systems Research Unit.

As APXPS has become more available to scientists, the number of publications has risen rapidly since the early 2000’s. There are a few dozen such machines in existence, and Urpelainen says that Oulu’s device is the northernmost APXPS equipment in the world. There is a lot of research being done at the University of Oulu that will directly benefit from having access to this technique, such as metallurgy and hydrogen energy research.

“The steel industry is looking for ways to prevent corrosion in applications like hydrogen fuel cells, which are a very aggressive environment. When you have hydrogen and water in very high temperatures, many chemical reactions may happen that will oxidize and corrode steel. Things like this would be very difficult, if not impossible, to study with other methods”, says Urpelainen.

Another example is the semiconductor industry and their use of atomic layer deposition (ALD) in manufacturing microchips. The theory is that it is possible to create a metal oxide for a semiconductor component by absorbing vapor on a sample on a silicon disc. The vapor will oxidize the metal by knocking off organic material and leaving electrodes behind.

“In theory, you can create a metal oxide that is the thickness of a single atomic layer. If you need a layer that has the thickness of five atomic layers, then you just repeat the process five times. In practice, though, things are different because other reactions happen during the deposition. This is where APXPS becomes an incredibly powerful tool”, Urpelainen says.

The closer you look, the more difficult things get

This kind of atomic level scrutiny is key to things like creating more durable steel, as we have seen. As professor and the Head of the Materials and Mechanical Engineering unit Jukka Kömi puts it, the steel industry is looking closer and closer at metals to understand them better.

“They–and we–need to understand a lot of things. The atomic layer is very challenging, and the steel industry is trying to understand what the role of an atom or a handful of atoms is in a 100-ton steel cache. Steel is mainly an alloy of carbon and iron and for different applications we may need to add different other alloys. For example, stainless steel is an alloy of them plus nickel and chromium. We need to understand and map every alloy”, Kömi says.

APT is a mass spectrometer, but a unique one. APT is a method to create a 3D model of atom distributions in solid materials by applying very high, several kilovolt voltages to a nanoscale sample and extracting ions from the surface of the sample. The resolution of the equipment is very high which enables researchers to see almost to a single atom.

While the APXPS and the APT are both powerful techniques in the study of materials, the ability to use both methods in tandem opens new possibilities for researchers.

"Power comes from knowing what to use," says Vahid Javaheri.

Javaheri compares choosing the right research tools to an everyday-life situation of needing to go to the grocery store and choosing the right vehicle for the trip.

“While an airplane is a powerful mode of transport, it is probably too much for such a short trip. The same principle applies here: we can use light microscopy to study things on the millimeter scale like we did as school children. Then we can go to scanning electron microscopy and transmission electron microscopy (TEM) to magnify things a hundred thousand or a million times. APT is on the atom scale, but it comes with its own challenges, for example sample preparation, as the samples are typically 1,000 times thinner than human hair”, Javaheri explains.

To have a full picture of material behavior, researchers can now combine APT with other instruments like TEM and APXPS when the situation calls for it. Having all these modern facilities in one research centre is unique and highly attractive to researchers, says Javaheri.

“It is important for them to know what this equipment is good for. We now have several instruments which are quite unique and in the long run we should see a major uptick in the scientific output of the University of Oulu.”