Archived Highlights

We discover that landing macromolecules on an one-atom-thick membrane, like graphene, preserves the gas-phase 3D-structure of the molecules at the surface. By exploiting this dynamics for proteins landing on graphene, we are able to land folded proteins on surface and see them one-at-a-time by low-energy electron holography technique. Our approach opens new opportunities to visualize 3D-structures of many proteins, nucleic acids, and carbohydrates at the single molecule level.

Interference requires coherence, which is usually hard to come by in condensed matter environments. However, sometimes even short coherence times are suffcient to reveal most peculiar phenomena such as making it look like a supercurrent reverses its flow, which can be exploited for quantum sensing. An international collaboration of scientists between the Max Planck Institute for Solid State Research in Stuttgart, Ulm University, the Autonomous University of Madrid, and the University of Uppsala has now used such a supercurrent reversal to detect the ground state of a magnetic impurity coupled to a superconductor. Using a scanning tunneling microscope, they detect the interference in the Josephson current thereby creating a rudimentary phase sensitivity like in a superconducting quantum interference device (SQUID).

To better understand and possibly control fast chemical reactions, it is necessary to study the behavior of electrons as precisely as possible - at their intrinsic length and time scales. Until now, however, microscopy techniques have only provided sharp images in either space or time. Using a unique combination of tunneling microscopy and attosecond technology, we have managed to overcome these difficulties. Our atomic quantum microscope can visualize the movement of electrons in individual molecules, simultaneously at picometer length and attosecond time scales.

Molecular imaging at the single-molecule level of large and flexible proteins such as monoclonal IgG antibodies is possible by low-energy electron holography after chemically selective sample preparation by native electrospray ion beam deposition (ES-IBD) from native solution conditions. The single-molecule nature of the measurement with a spatial resolution down to 5 Å allows the mapping of the structural variability of the protein molecules that originates from their intrinsic flexibility and from different adsorption geometries.

Molecules colliding with surfaces at energies relevant to chemistry (0 – 50 eV) undergo selective conformation changes and mechanochemical reactions. The origin of these phenomena is the compression of the molecules when the fast-approaching molecules are brought to sudden halt upon their impact at the surface. Our novel approach offers a general pathway to explore the conformation space and the mechanochemistry of any molecule that can be electrosprayed.

Despite plenty of room at the bottom, there is a limit to the miniaturization of every process. Using scanning tunneling microscopy, we have exploited a magnetic impurity at a superconducting tip and one on a superconducting sample to demonstrate tunneling between two energy levels as a minimal configuration of a tunneling current. The underlying theory, which was developed together with colleagues from Ulm and Madrid, becomes surprisingly simple and allow us to extract the rather long lifetime of the Yu-Shiba-Rusinov states.

There is a new perspective on sugar. In collaboration with colleagues from the Max Planck Institute for Colloids and Interfaces we have used scanning tunnelling microscopy to image how individual polysaccharide molecules are folded for the first time. Using electrospray ion beam deposition we could isolate single sugar molecules at a cold surface and image them with submolecular resolution. Our landmark experiments make it possible to investigate the relationship between the spatial structure of polysaccharides such as those found on pathogens and their biological effect.

The operation of components for future computers can now be filmed in HD quality, so to speak. Manish Garg and Klaus Kern, researchers at the Max Planck Institute for Solid State Research in Stuttgart, have developed a microscope for the extremely fast processes that take place on the quantum scale. This microscope – a sort of HD camera for the quantum world – allows the precise tracking of electron movements down to the individual atom. It should therefore provide useful insights when it comes to developing extremely fast and extremely small electronic components, for example.

When a single electron is made to tunnel across a vacuum gap, it may occasionally produce not just one, but two photons at a time. When these very rare events are produced in excess, the result is a phenomenon known as photon superbunching. With this finding, we have expanded the range of fundamental processes that can be controlled in a tunnel junction environment.

The strong spin-orbit coupling in three-dimensional topological insulators imparts a transversal spin Hall effect supported by their bulk states. It is demonstrated that the resulting spin accumulation at the lateral edges of Bi₂Te₂Se nanoplatelets can be effectively read out at room temperature through the local detection of a helical, bias-dependent photoconductance. The spin accumulation is further supported by the observation of a finite bias-dependent Kerr angle at the nanoplatelet edges.

A wide range of device applications of graphene rely upon suitable methods for tailoring its electronic properties. Along these lines, band gap opening in graphene has been achieved via covalent chemical modification of its basal plane. We have developed a novel approach to chemically functionalize graphene in covalent manner, involving the use of hyperthermal molecular cation beams of 4,4’-azobis(pyridine) in electrospray ion beam deposition (ES-IBD). The one-step, room temperature ion-surface reaction process takes place in high vacuum (10-7 mbar) above a threshold kinetic energy of 165 eV of the molecular ions. Covalently linked azopyridine moieties are obtained with a functionalization degree of 3% of the carbon atoms of graphene after 3-5 hours of ion exposure of 2⋅1014 azopyridinium/cm 2 of which 50% bind covalently. This method is highly promising for the patterned functionalization of extended graphene areas under conditions compatible with state-of-the-art device fabrication technologies

Dye-sensitized solar cells constitute a promising approach to sustainable and low-cost solar energy conversion. Our work provides for the first time atomic-scale insights into the relevant N3 dye - TiO2 anatase (101) interface revealing multi-conformational adsorption and energy level alignment of the photosensitizers as well as supramolecular interaction. Most importantly, the findings show that optimization strategies based solely on the electrochemical properties of the dye molecules should be replaced by a more comprehensive approach considering kinetic aspects in the dye-substrate coupling, possible strain in the molecular chromophore, and the atomic-scale structure of the dye−semiconductor interface.