Illinois Engineers Visualize Atomic Vibrations in 2D Materials

Researchers from the University of Illinois at Urbana-Champaign, utilising electron ptychography – a technique enhancing microscope resolution – have directly observed thermal vibrations in twisted bilayer WSe2 atoms. Achieving picometer-scale resolution, and surpassing previous limits of approximately one angstrom, the team visualised atomic vibrations of roughly 0.05 angstroms, confirming the existence of phasons – low-frequency vibrational modes unique to twisted 2D materials. This direct observation of phasons, previously hypothetical, was accomplished by correlating atomic motion with image blurriness, and may contribute to the development of materials with improved thermal conductivity.

Visualising Atomic Vibration

Researchers from The Grainger College of Engineering at the University of Illinois at Urbana-Champaign have directly observed a previously hidden branch of vibrational physics in 2D materials, confirming the existence of a previously unseen class of vibrational modes. This observation was achieved through advanced imaging technology, representing the highest resolution images ever taken of a single atom. The team focused on examining 2D materials, which are considered promising candidates for next-generation electronics due to their scalability to thicknesses of just a few atoms while maintaining desirable electronic properties.

The study centred on Moire phonons, which are low-frequency vibrational modes unique to twisted 2D bilayer materials, and also investigated phasons, vibrational modes associated with atomic movement. Until this research, phasons in 2D materials had eluded direct observation, remaining purely hypothetical despite being thought to explain some of the unique properties seen in twisted 2D materials. The central goal of the investigation was to visualise heat by observing the movement of a single atom, facilitated by achieving high spatial resolution to demonstrate how atomic vibrations affect image blurriness.

To obtain these images, the team employed electron ptychography, a recently developed technique that enhances the resolution of existing microscopes. This technique enabled the researchers to achieve picometer-scale spatial resolution and directly observe thermal vibrations in twisted bilayer WSe2 atoms. The resolution achieved, as low as 0.2 angstroms, represents a significant leap from the previously thought possible limit of just under one angstrom, allowing for the visualisation of vibrations of approximately 0.05 angstroms, and fundamentally changes the capabilities of microscopes.

The research anticipates that understanding phasons may contribute to the development of electronics that function differently from current iterations. Examining single atoms and identifying defects that prevent efficient cooling is believed to be crucial for developing better thermal management techniques at the atomic scale, and the team believes that observing how individual atoms respond to thermal vibrations will provide the fundamental knowledge needed to achieve this. This approach may ultimately lead to the creation of materials with improved thermal conductivity.

The Physics of Phasons and Moire Systems

Like phonons, phasons are vibrational modes associated with atomic movement, and they are thought to explain some of the unique and desirable properties seen in twisted 2D materials. Until now, phasons in 2D materials had eluded direct observation, rendering predictions about their existence purely hypothetical.

The researchers directly observed thermal vibrations in twisted bilayer WSe2 atoms by achieving picometer-scale spatial resolution. Previously, the highest resolution thought possible was just under one angstrom, but ptychography allowed the team to achieve numbers as low as 0.2 angstroms. This leap in resolution fundamentally changes what microscopes can do, enabling the visualisation of vibrations of approximately 0.05 angstroms.

Implications for Thermal Management and Future Electronics

The research anticipates a future in which understanding phasons may contribute to the development of electronics that function differently than current iterations. One potential application of this technique is making materials that are better heat conductors, achieved by examining single atoms and identifying defects that prevent efficient cooling. The team believes that observing how individual atoms respond to thermal vibrations will provide the fundamental knowledge needed to achieve better thermal management techniques at the atomic scale.

Looking at atoms one by one and how they respond to thermal vibrations will provide the fundamental knowledge needed to achieve this improved thermal management. The team believes this approach will enable the development of materials with improved thermal conductivity by identifying defects that prevent efficient cooling at the atomic scale.