New microscope reveals moiré graphene at one-nanometer resolution

Researchers at the University of Maryland have developed an imaging technique that can resolve structural details of two-dimensional materials with accuracy down to a single nanometer. The method, dubbed infrared torsional force microscopy (TFM-IR), has for the first time exposed the internal physics of moiré graphene that had remained hidden from even the most advanced optical instruments. The findings were published in Nature Communications.

The operating principle of the new device differs from conventional microscopy. Instead of tapping the probe vertically on the sample surface, the instrument's tip is set into rapid rotational motion, twisting from side to side. At the same time, the material is exposed to pulses from an infrared laser. When chemical bonds within the substance absorb this radiation, they begin to vibrate, causing a barely perceptible deformation of the surface. The device captures both vertical and horizontal displacements at a resolution of roughly one nanometer.

The technology was first tested on mica, a mineral with well-understood bonds oriented in multiple directions. The researchers registered four distinct vibrational modes and successfully separated horizontal and vertical oscillations. The collected data matched computer model predictions exactly.

The real breakthrough came with the examination of bilayer graphene, where two sheets of the material are slightly rotated relative to each other. Such moiré structures are considered among the most promising subjects in condensed matter physics, having previously revealed unusual electronic properties including superconductivity. Scientists now have a tool to observe these processes directly.