Scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory have discovered that nanoparticles of gold behave differently when near the edges of graphene, according to a report by foreign media. This could have big implications for the development of new sensors and quantum devices.
The discovery was made possible by a newly established ultrafast electron microscope (UEM) at Argonne National Laboratory's Center for Nanoscale Materials (CNM), a user facility of the U.S. Department of Energy's Office of Science. Ultrafast electron microscopy is capable of visualizing and investigating nanoscale phenomena on time scales of less than a trillionth of a second. The discovery could cause a stir in the growing field of plasma, which involves light shining on the surface of a material and triggering waves of electrons, known as plasma fields.
For years, scientists have pursued the development of plasma devices with a wide range of applications - from quantum information processing to optoelectronics (combining light-based and electronic components) to sensors for biological and medical applications. To do this, they have combined two-dimensional materials with atomic-level thickness, such as graphene, with nanoscale metal particles. Understanding the combined plasma behavior of these two different types of materials requires an accurate understanding of how they are coupled.
In a recent study at Argonne National Laboratory, researchers used ultrafast electron microscopy to directly observe the coupling between gold nanoparticles and graphene.
Haihua Liu, a nanoscientist at Argonne National Laboratory, said, "Surface plasmons are light-induced electronic oscillations on the surface of a nanoparticle or at the interface between a nanoparticle and another material. When we shine light on a nanoparticle, it creates a short-lived plasma field. When the two overlap, the pulsed electrons in our UEM interact with this transiently existing field and the electrons either gain or lose energy. We then collect those energized electrons with an energy filter to map the distribution of the plasma field around the nanoparticle."
While studying the gold nanoparticles, the researchers discovered an unusual phenomenon. When the nanoparticles were placed close to a flat piece of graphene, the plasma field was symmetric. But when the nanoparticles were placed close to the edge of the graphene, the plasma field was more concentrated near the edge region.
"This is a remarkable new way of thinking about how we can use light to manipulate charge and other phenomena on the nanoscale in the form of plasma fields," said Haihua Liu. With the ability to go ultrafast, there's no telling what we'll see when we tweak different materials and their properties."
This entire experiment, from stimulating the nanoparticles to detecting the plasma field, happened in less than a few trillionths of a second.
Ilke Arslan, director of CNM, said, "CNM is unique in hosting a UEM that is open to users, capable of making measurements with spatial resolution on the nanometer scale and temporal resolution on the sub-picosecond scale. Having the ability to make such measurements in such a short period of time allows for the examination of a large number of new phenomena in non-equilibrium that we have not had the ability to detect before. We are excited to make this capability available to the international user community."