Identifying engineering materials with Dr. Edwin B. Fohtung

Rensselaer campus is home to a variety of academic research projects led by professors and students alike. One of these innovative facilities is the lab of Dr. Edwin B. Fohtung, Associate Professor of Materials Science and Engineering, who works in developing techniques for studying materials on the nanoscale and discovering new materials for use in all engineering and science disciplines.

Fohtung leads a physics group mainly working in materials science. After studying applied physics in his earlier education, Fohtung branched into X-ray physics for his PhD, working with synchrotrons and free electron lasers which produce X-ray photons which are 10 billion times brighter than sunlight. Fohtung labels them as a unique source, producing X-rays that can move on a time scale as small as picoseconds (10 trillionth of a second). By taking advantage of X-rays’ extremely short wavelength, scientists are able to use diffraction to examine the structures of crystalline materials.

Fohtung’s laboratory specifically focuses on developing new scattering imaging and spectroscopy techniques for studying materials on the nanoscale. They aim to not only capture static images of internal structures, but also observe systems while they’re operating. Fohtung’s group has developed a lensless microscopic imaging approach, which captures diffraction scattering from very small objects—on the scale of nanometers. By reconstructing the observed pattern created from the scattering, they are able to recreate an image of what the object looks like. This technique also allows them to create an internal image, enabling them to spatially resolve distributions of how atoms are displayed and how molecules are moved. In comparison to microscopy, which limited to the quality and numerical aperture of the lenses within, this lensless technique is only limited by diffraction and wavelength.

Recently, Fohtung’s group has been imaging cancer cells and tissues. Another advantage of his lensless microscopic imaging technique is that it is a label-free imaging approach, meaning that materials can be observed in their natural environments. When using other methods such as cryomicroscopy, optical or fluorescent microscopy, specimens must be taken from the environment and stained with dyes to be seen under the lens of a microscope. In comparison, Fohtung’s technique shoots X-rays through devices while they are operating, enabling them to see how things evolve and deteriorate over time, allowing the development of machines with longer lifespans.

In differentiating between other imaging techniques and his own, Fohtung gave the example of brain imaging, pointing out how CT scans only produce an image of the brain at a certain moment in time. Comparatively, MRIs image the brain over a span of time, showing how it is changing and developing as the person performs certain tasks. Fohtung’s imaging technique is similar to an MRI and is used to image machines, magnetic devices, cellphones, and other devices to observe their internal functioning and better understand how they work. They also look at battery materials as well, observing the changes in the cathode system as it is recycled. Again, they are able to observe these materials in a non-destructive manner. In summary, these unique approaches allow scientists to study any materials with a crystalline structure, and even some amorphous materials, depending on the use of diffraction or spectroscopy imaging.

When Fohtung refers to diffraction imaging, he refers to the process of allowing X-ray photons to scatter across an object. Then, the scattered diffraction is collected and inverted with numerical lenses to reveal images of the objects. With the development of new materials, these techniques are useful for determining where they can be used throughout the engineering disciplines.

Recently, Fohtung’s team identified a class of materials called heamanganites. These are multiferroic substances with controllable magnetization vectors when an electric field is applied and controllable electric polarization when an external magnetic field is applied. The versatile uses of these materials leads Fohtung to believe that they will be very useful in future engineering studies. Fohtung then related these magnetic materials to uses in computing. Currently, hard drives are made of metal and contain a coil which produces a magnetic field. Therefore, to increase the strength of the system, engineers either have to increase the current or the number of coils. In order to keep reducing the size of computing devices while increasing the strength, scientists need new materials to work with. Multiferroic materials both have ferroelectric and ferromagnetic degrees of freedom within them, making them useful for miniaturizing storage and computing devices.

Later, Fohtung pointed out how this relates to a unique property of particle physics and cosmology. Particle physics, in terms of the Big Bang, is a completely different school of thought: it is a single event when the universe went through a rapid cooling process. Fohtung noted that physicists have data indicating that prior to the Big Bang, the universe was full of radiation. Therefore, matter which evolved from the Big Bang came to be from nucleations known as topological defects. In order to fully understand the Big Bang, the obvious but completely impractical method would be to recreate the event in the lab. Another possibility would be to design experiments which emulate a similar level of extremely high energy release, which is also quite impractical. Scientists could also work to simulate the quantum fuels produced in the Big Bang with computing methods. Overall, there are many different theories and approaches that scientists may attempt to understand the Big Bang. What Fohtung and his colleagues are doing differently is that they found classes of materials which obey the types of symmetry that the original universe had. They even found that if these materials are cooled down to a certain phase transition, they nucleate similar topological defects and features to that of the theory of the early universe. The benefit of using these materials to understand the Big Bang is that they do not have to go through the processes described previously, where an enormous amount of energy is required. In contrast, the materials only need to go through their phase transition in order to study the topological defects. Fohtung labels these discoveries as some he finds extremely fascinating, as there are startling similarities between the atomic and cosmic levels. He emphasizes that these similarities allowed him to inform himself on how things are interconnected, and how it also brings cosmology into the lab without the destructive nature of creating an entire Big Bang.

Expanding on these topics, Fohtung pointed out the unique nature of temperature. Whereas in everyday life this seems like a normal concept, it relies on the baseline assumption that, for example, atoms exist. By definition, temperature relates to the mean velocity of all atoms in a given space, as temperature has to do with both the speed and collision of those atoms. In these engineering processes where people are working at the nanoscale, or with fewer atoms, it would potentially be plausible to create a vacuum with few or no atoms—so then what is the notion of temperature? This returns back to Fohtung’s discussion of the Big Bang; there was only radiation before the event, so what was the notion of temperature before there was any matter in the universe? Overall, there are new concepts to be learned about the physics of scenarios which exist outside the normal physical assumptions of our world. Similarly, as engineers move towards working on a smaller and smaller scale, the understanding of thermodynamics and the laws of physics also have to be experimentally redefined.

Another factor that must be considered when working on the nanoscale in engineering is the notion of density: mass divided by volume. As the volume of an object approaches zero, its density approaches infinity. This idea of infinite density returns once again to Fohtung’s discussion of cosmology, as black holes are something which scientists believe are a point in space and time with an infinite density. So what are the physics in these areas? Is there a limit to how small of a scale engineers can work with, or can things be reduced to the level of a single atom? There are already 2D and 1D materials being discovered currently. An example is graphene: a single atomic layer of carbon atoms. Through experimental evidence, scientists are learning how these 2D and 1D materials create unexpected properties. In essence, as Fohtung stated, “You kind of see how… nature is very, very fascinating when you’re playing with thermodynamic parameters: pressure, temperature, and volume.”

As exciting as all these topics are, Fohtung always aims to bring his work back to the applications and new imaging approaches he is developing in his lab. That, as Fohtung shared, is how he grounds himself as an engineer.