Imagine what it would be like to watch how the individual atoms of molecules rearrange during a chemical reaction to form a new substance, or to see the compounds of DNA move, rearrange and replicate. The simple idea of watching how molecules break, or transform, during chemical reactions has, until now, been unfathomable since it requires tracking all of the atoms, which constitute a molecule, with sub-atomic spatial and few-femtosecond temporal resolution. Hence, taking such “snapshots” with a combined spatio-temporal resolution to witness a molecular reaction was considered fodder for science fiction.

In their recent study, reported in Science, the team led by ICREA Prof. Dr. Jens Biegert head of the Attoscience and Ultrafast Optics Group at ICFO in collaboration with researchers from the USA, the Netherlands, Denmark and Germany, have reported the first real time and space imaging of molecular bond breakup in acetylene (C₂H₂) nine femtoseconds (1 femtosecond = 1 millionth of a billionth of a second) after its ionization. The team was able to track the individual atoms of one isolated acetylene molecule with a spatial resolution as small as 0.05 Ångström – less than the width of an individual atom – and with a temporal resolution of 0.6 femtoseconds. What’s more, they were able to trigger the breakup of only one of the bonds of the molecule and see how one proton leaves the molecule.

The team took a single electron, steered it along a specific path with the laser and scattered it off an isolated molecule to record its diffraction pattern. It is mind-boggling to imagine the length and time scales of the experiment. The fantastic cooperation between experimentalists and theorists, atomic physicists and quantum chemists from ICFO, Kansas State University, Max-Planck-Institut für Kernphysik, Physikalisch Technische Bundesanstalt, Center for Free Electron Laser Science/DESY/CUI, Aarhus University, Friedrich-Schiller University Jena, Leiden University, and Universität Kassel made it possible to achieve such feat.

Flexoelectricity is a property of all insulating materials whereby they generate a voltage when they are bent. Flexoelectricity is however a tiny, almost inmeasurable, effect at the macroscale, hence it remains relatively unknown. This year, however, there have been a couple of notable advances may change the status of flexoelectricity. The first has been the demonstration that, at the nanoscale, electromechanical actuators can be made that bend in response to voltage¹. The key to their big performance is that things are much easier to bend when they are nanoscopically thin. In addition to being competitive in terms of performance, flexoelectric actuators also have other advantages over competing piezoelectric technology: their architecture is simpler, their performance is more linear and less temperature-dependent, and the range of available flexoelectric materials is enormous. Last, but not least, our flexoelectric actuators are made on silicon substrates, meaning that they are compatible with the key material and fabrication processes already used by microelectronics industry, which should facilitate their industrial uptake.

In parallel with the effort to make devices that exploit the large magnitude of flexoelectricity at the nanoscale, there is also a very active search for ways to make it meaningful also at the macroscale. Here we have made a major breakthrough discovery: by bending semiconductors it is possible to achieve effective flexoelectric coefficients that are hundreds and even thousands of times larger than for insulators². An important additional aspect of semiconductor flexoelectricity is that it grows with thickness. This means that, unlike insulators, semiconductor flexoelectrics remain as potent at the macroscale as they are at the nanoscale.