Newswise — When Aaron Lindenberg was introduced to ultrafast science as a first-year grad student at UC Berkeley, he was immediately hooked. He knew he wanted to be part of a hot research field that explores nature’s speediest processes and lets us see the world with different eyes.

Ultrafast science, he says, offers young researchers unique opportunities to make a real impact on research that has never been done before. For him, it’s a scientific adventure that is both highly rewarding and lots of fun.

Over the past 14 years, Lindenberg has built a research team at Stanford and SLAC that uses extremely powerful beams of X-rays and electrons to look at femtosecond phenomena in a broad range of important materials. The scientists want to understand how materials work, and their insights are helping them design technologies of the future.

What excites you most about your research?

When microscopes were invented, they let us see bacteria for the first time. Telescopes allowed us to glimpse moons orbiting faraway planets. Now the modern tools of femtosecond science provide a completely new way of seeing what’s really going on in materials and devices around us.

These tools are basically advanced cameras that take very sharp images of individual atoms. We then string these images together into movies of ultrafast atomic motions. This information not only helps us understand how materials get their unique properties; it also gives us clues for making them better, because in many cases these very fast processes determine how materials function.

In solar cells, for instance, rapid motions of atoms and electrons affect how efficiently sunlight is converted into electricity. In two-dimensional materials, which are only a few atoms thick, ultrafast motions are closely linked to unique properties that make these materials interesting for high-performance chemical catalysts, fast and flexible electronics, photonic devices such as solar cells, and other applications.

How do these advanced cameras work?

The principle behind them is very similar to high-speed flash photography, in which you take a series of snapshots of an object with a fast strobe light. This allows you to capture things you normally don’t see, such as a hummingbird flapping its wings. The faster the flashes, the faster the motions you can see.

In our work we use flashes of X-rays coming from the Linac Coherent Light Source (LCLS) X-ray laser as well as “flashes” of electrons produced in an apparatus for ultrafast electron diffraction, or UED. These pulses are very bright and last only femtoseconds. They open a new window into the atomic world.

What exactly is “ultrafast electron diffraction?”

In UED, we cram very energetic electrons into very short pulses and send them through our samples. The electrons get deflected into a detector, where they produce a characteristic pattern that encodes the precise positions of all the atoms in the sample. Repeating the experiment at different points in time after the sample was stimulated and observing how the pattern changes tells us exactly how the atoms are moving. Experiments at LCLS basically work the same way, using X-rays instead of electrons.

So why do you combine X-ray and electron techniques?

Because the techniques are very complementary. Each has certain technical advantages when looking at particular kinds of samples, and they also teach us different things about a material.

Let me give you an example. My group is very interested in the possibility of manipulating two-dimensional materials with light. With UED, we were able to see that femtosecond light pulses lead to large, ultrafast rippling of single atomic layers of these materials. At LCLS, looking at samples consisting of many 2-D layers, we discovered that light can be used to manipulate the bonding between the layers and, surprisingly, push the layers together at the atomic scale. Both studies uncovered totally different responses and suggest different ways of modifying the optical and electronic properties of 2-D materials.

What do you hope to achieve in the future?

For me, the near future is about really grasping what determines how materials and devices function. The fact that we’re getting better at understanding more and more complex systems and are able to visualize the very first microscopic, ultrafast steps that determine the functionality of materials can really have a huge impact on how we engineer new materials. It’ll allow us to go further than just look at what happens on the atomic scale; it could help us find useful ways of using light or other stimuli to direct materials into states in which they have useful and novel properties.

I’m also excited about the upgrade of LCLS and potential developments in UED, which in a few years will make it possible to study ultrafast atomic motions in materials in their natural environments. At the moment, we need to blast materials with extremely powerful laser, electron and X-ray beams to generate large enough signals that we can analyze. However, we don’t always fully understand the effects of these intense beams. When we study solar cell materials, for example, we would really like to be able to shine only as much light on our sample as the sun would. This would give us results that are potentially closer to real-world applications.