masonlw

How molecules interact and transfer energy between each other dictates the performance in molecular electronics, organic light emitting diodes, photovoltaics, or in many biological processes. However, imaging the controlling underlying molecular order and associated wavefunction delocalization on the molecular scale has long remained a major challenge in imaging science.

A STROBE team from CU Boulder, UC Berkeley and LBNL, has overcome this challenge developing a new technique of nanoimaging in the infrared probing the delicate low-energy landscape of molecular interactions. Measuring coupled molecular vibrations with high precision provides for a new molecular ruler to resolve the effect of disorder with sub-nanometer resolution. In a representative organic electronic material of metal-porphyrin nano-crystals the researchers learned about the relationship between structure and function of energy transfer on molecular length scales. The new insights gained advance our understanding of light harvesting in photosynthesis and improve the design of next generation organic electronic and photonic devices.

The next generation of semiconducting materials that will facilitate energy transport and storage in the technologies around us is becoming increasingly complex. The ability of energy carriers to move between atoms and molecules underlies biochemical and material function. Understanding and controlling energy flow, however, requires observing it on ultrasmall and ultrafast spatio-temporal scales, where energetic and structural roadblocks dictate the fate of energy carriers.

A STROBE team led by Naomi Ginsberg (UCB) developed a novel time-resolved interferometric scattering microscope to visualize how energy navigates the intrinsically disordered landscapes in these materials on the nanoscale. With this high-throughput technique, they collected non-invasive stroboscopic movies in a variety of organic, inorganic, and hybrid materials to demonstrate its powerful versatility. Applied to other cutting-edge materials, we hope to inform the design of new functional devices for the semiconductor industry of tomorrow.

Due to the reduced dimensionality, the properties and functionality of 2D materials and van der Waals heterostructures are strongly influenced by atomic defects such as dopants, vacancies, dislocations, grain boundaries, strains, ripples and interfaces. Although x-ray diffraction can determine the 3D crystal structure of 2D materials at atomic resolution, it is blind to crystal defects. Aberration corrected electron microscopy and scanning probe microscopy allow us to see individual atoms without the constraint of crystal averaging. But, seeing atoms is not the same as knowing their 3D coordinates with high precision, which is required for an accurate prediction of properties using quantum mechanics. No ab initio calculations can take a 2D image of atoms as direct input to determine material properties.

A STROBE team led by John Miao (UCLA) in collaboration with scientists from Harvard University, ORNL and Rice University recently developed scanning atomic electron tomography (sAET) to determine the atomic positions and crystal defects in Re-doped MoS2 with a 3D precision down to 4 picometers. They observed dopants, vacancies and ripples, measured the full 3D strain tensor and quantified local strains induced by single dopants. By directly providing experimental 3D atomic coordinates to density functional theory (DFT), they obtained more truthful electronic band structures than those derived from conventional DFT calculations relying on relaxed 3D atomic models, which was confirmed by photoluminescence spectra measurements. Furthermore, they observed that the local strain induced by atomic defects along the z-axis is larger than that along the x- and y-axis and thus more strongly affects the electronic property of the 2D material. It is anticipated that sAET is not only generally applicable to the determination of the 3D atomic coordinates of 2D materials and heterostructures, but also could transform ab initio calculations by using experimental atomic coordinates as direct input to reveal more realistic physical, material, chemical and electronic properties.

Bacteriocins are contractile molecular syringes — nanomachines produced by one bacterium that can puncture the cell membrane of another bacterium to deliver a lethal punch. In this week’s issue of Nature and featured on the cover, STROBE UCLA scientist Hong Zhou and his colleagues present high-resolution structures of the bacteriocin pyocin R2 from P. aeruginosa – in both its preand post-contraction states. The results allow the researchers to suggest in detail how the molecular syringe works, offering insight into how R-type bacteriocins might be developed into a new class of antimicrobials. This work was featured in the April 2020 cover of Nature.