Nanovibrations: Controlling the Material Properties of Crystals

Salts and comparable structures consist of ions. In a solid state, they form ion lattices. Vibrations of ion crystals account, inter alia, for heat transfer and the diffusion of sound. Controlling vibrations may enable control of material properties of crystals. Conceivable innovative applications include thermoelectric nanoelements that could render human body heat usable as power supply of wearable electronic devices, or wafer-thin structures to create sound-proof chambers.

Now, a cooperation of Rutgers University, a center of nanobiology, and the University of Graz, Austria, relying on latest-generation electron microscopy, made ion lattice vibrations visible for the first time in ultra-high atomic and energetic resolution in both spatial and spectral dimension, compared to earlier experiments. The ion lattice of a crystal nanocube was caused to vibrate by targeting it with an electron beam. Depending on the spot on the cube hit by the electron, it can trigger different modes. The more powerful the ion trigger, the more energy is drawn from the electron beam. The individual modes of vibration can be determined from the measured loss of energy.

By causing the electron beam to cover the entire sample, vibrations of the ion lattice could be determined with topological resolution in the nanometer scale and with a very high frequency in the Terahertz range. The phenomena observed under the electron microscope were computer-simulated, which showed for the first time how ions vibrate at different locations on the cube. This may open the door to revolutionary developments in steering sound and heat with heretofore unknown precision.

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