2024-04-13 09:35:13
Researchers have used neutron spectroscopy to reveal the unique moonlike motion of triphenylphosphine on graphite, advancing our understanding of molecular motion and its applications in materials science. Credit: TU Graz
Nanoscale insight into molecular motion on surfaces.
Researchers have used neutron spectroscopy data from the ILL to gain ground-breaking insights into molecular motion at the nanoscale, offering new perspectives that could influence future materials and technology development. The study was recently published in the journal Chemistry of communication.
For years, scientists have been intrigued by how molecules move across surfaces. The process is critical for many applications, including catalysis and fabrication of nanoscale devices.
Now, using neutron spectroscopy experiments performed at the Institut Laue-Langevin (ILL) and advanced theoretical modeling and computer simulations, a team led by Anton Tematgel, from the Graz University of Technology, has revealed the unique motion of triphenylphosphine (PPh3) molecules on graphite surfaces, a behavior similar to the undermoon nanoscopic.
In fact, PPh3 molecules exhibit an unusual form of motion, rolling and translating in ways that challenge previous understandings. This Moonland-like motion appears to be facilitated by their unique geometry and three-point tethering with the surface.
“The delving into the complex world of molecular movement on graphite surfaces was an exciting journey,” reveals Anton Tematgel, and adds: “Measurements and simulation revealed a sophisticated movement and ‘dance’ of the molecules, and provided us with a deeper understanding of surface dynamics. And opening new horizons for materials science and nanotechnology “.
Video illustrating the motion of a single triphenylphosphine molecule across graphite in top view, as produced from a molecular dynamics simulation at 300 K. Credit: TU Graz
The role of triphenylphosphine in industry
Triphenylphosphine is an important molecule for the synthesis of organic compounds and nanoparticles with many industrial applications. The molecule exhibits a peculiar geometry: PPh3 is pyramidal with a propeller-like arrangement of its three periodic groups of atoms (see image).
Neutrons offer unique possibilities in the study of the structure and dynamics of materials. In a typical experiment, neutrons scattered from the sample are measured as a function of their change in direction and energy. Due to their low energy neutrons are an excellent probe for studying low energy excitations such as molecular rotations and diffusion. Neutron spectroscopy measurements were performed on ILL Instruments IN5 (TOF spectrometer) and IN11 (neutron spin-echo spectrometer).
Illustration showing one molecule of triphenylphosphine on the surface of graphite. Credit: TU Graz
“It is amazing to see how ILL’s powerful spectrometers allow us to follow the dynamics of these fascinating molecular systems, even if the amount of sample is tiny,” says ILL scientist Peter Fucke, explaining that “neutron beams do not destroy these sensitive samples and allow a perfect comparison with computer simulations.”
The research shows that PPh3 molecules interact with the graphite surface in a way that allows them to move with surprisingly low energy barriers. The movement is characterized by rotations and translations (jumping movements) of the molecules. While rotations and intramolecular motion dominate up to about 300 K, the molecules follow additional translational hopping motion at the surface from 350–500 K.
Understanding the detailed mechanisms of molecular movement at the nanoscale opens new avenues for the production of advanced materials with tailored properties. Besides the fundamental interest, the movement of PPh3 and related compounds on graphite surfaces is of great importance for applications.
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