Atomic-level 3D models show us how gadgets work

Although nanotechnology and materials science are complicated subjects for most of us, research in these fields is of great importance to almost everyone. Your digital gadgets, for example, completely depend on it.

Today, all microelectronics depends on semiconductors. These are materials that are not very good at conducting electricity. But you can add small amounts of other substances to them, a process known as doping. This improves the performance of the semiconductor so that it isn’t so bad after all.

“In the past, we’ve spiked semiconductors and found that it drastically changes the electrical properties of the material,” says PhD candidate Kasper Aas Hunnestad in NTNU’s Department of Materials Science and Engineering.

All of this is well and good. It’s good when something works. But beyond the fact that it works, we haven’t always fully understood why it works. This is especially true at the atomic level.

“Now we know much better how we can image the added individual atoms, which were previously almost impossible to find. This gives us new insight and allows us to understand how they affect the properties of this material,” says Hunnestad.

Why “knowing why” is so important

So what? Why the hell should we care about single atoms and why does anything work? Isn’t it enough to know that it works? If that were the case, physicists and chemists would certainly have fun doing the research, but the rest of us wouldn’t benefit much.

“Only when you know more about how something works can you manipulate the material and optimize it,” says Dennis Meier. He is a professor in the Department of Materials Science and Engineering at NTNU, which led the project.

In this way, for example, you can make more efficient, environmentally friendly or cheaper materials for the work to be done. Or you can assign new properties to a material you already have with much greater precision. This is also essential for the development of future materials for sustainable technology.

“Often we want to introduce new features into materials. For this, we need to know exactly what role each individual atom plays,” says Meier.

Advanced imaging techniques allow

Hunnestad and his colleagues present the results of countless hours of work using “atom probe tomography” (APT) in a recent paper by Nature Communication.

APT is an advanced state-of-the-art equipment that NTNU acquired a few years ago. The machine can provide a three-dimensional representation of what a material looks like, down to the atomic level, explains Constantinos Hatzoglou. He is a senior engineer at the APT laboratory of the Department of Materials Science and Engineering.

Hunnestad and his colleagues used this unique ability to study a new type of oxide-based semiconductor to which very small amounts of a substance were added to tailor its properties.

“Conventional microscopy techniques did not allow us to observe how small amounts of additives positioned themselves in semiconductors,” says Hunnestad. The new results show that investing in the best technical equipment, such as this APT machine, is extremely profitable and enables groundbreaking research.

Shows the huge potential

Searching is still not really easy with APT either. But by bringing together colleagues with different experimental and theoretical backgrounds – as well as hard and inspired work – the NTNU team found solutions.

“It’s not just a wonderful achievement. It also shows the huge potential of the APT technique for research areas where it has not been applied before. This shows the unique opportunities we have with the modern infrastructure available in NTNU’s NanoLab and TEM Gemini Center,” says Meier.

Hunnestad has worked with APT for about three years. He performed numerous correlated microscopy measurements, supported by Antonius van Helvoort and Per Erik Vullum. Van Helvoord is a professor in the physics department of NTNU and an expert in high-resolution electron microscopy, while Vullum is a professor II at NTNU, department of physics and a principal researcher at SINTEF Industry.

Hunnestad and Meier are excited about all the fascinating possibilities that have already emerged from their APT-based research and the new perspectives for characterizing functional materials at the atomic scale.

Imaging of Individual Titanium Atoms Mixed in a Semiconductor

For their recent paper, the research group looked at the Er(Mn,Ti)O oxide semiconductor₃. To this end, their collaborators at the Lawrence Berkeley National Laboratory in the United States added tiny amounts of the element titanium (Ti) to erbium manganate (ErMnO₃).

“With the atom probe, we can get a three-dimensional representation of how the titanium atoms are positioned in the semiconductor,” Meier explains. “This allows us to link the new electrical properties of the material down to the individual atoms.”

Dr Muhammad Zeeshan Khalid is a member of the team led by Sverre Selbach, a professor in the Department of Materials Science and Engineering at NTNU. He completed the experiments with calculations. These calculations provide insight into the effects that individual atoms can have on physical properties.

One of the benefits of what the researchers have done is that they can use the method on many other substances as well. It’s not just limited to substances that the NTNU research team has experimented with.

“The procedures and the results are of general interest. They can extend our understanding of oxide semiconductors and functional materials in general. Research opens up completely new doors,” says Meier. The cooperative approach strengthens research

Many people from different departments of NTNU contributed to make this scientific breakthrough possible. SINTEF, Research Council of Norway, Norwegian Micro- and Nano-Fabrication Facility (NorFab), Norwegian Laboratory for Minerals and Materials Characterization (MiMaC), Norwegian Center for Transmission Electron Microscopy (NORTEM) and NTNU Nano supported the work.

The researchers point out that this collaborative effort showcases the strength of interdisciplinary research. It shows what can be accomplished with a strong state-of-the-art infrastructure.

The details of how Hunnestad achieved such outstanding results are probably not easy for most of us to digest. But the link to the research article below will give you something to chew on if you want to dig.

Reference: Hunnestad, KA, Hatzoglou, C., Khalid, ZM et al. Atomic-scale 3D imaging of individual dopant atoms in an oxide semiconductor. Common Nat 13, 4783 (2022). Published August 15, 2022. https://doi.org/10.1038/s41467-022-32189-0