chaired by Gertjan Koster / Michel de Jong and Floris Zwanenburg
Advances in exotic materials: chalcogenides, topological insulators, ruthenium and graphene
Edges and boundaries of transition-metal di-chalcogenides
Sridevi Krishnamurthi (CMS)
Interaction between counter-propagating quantum Hall edge channels in the 3D topological insulator BiSbTeSe2
Bob de Ronde (ICE)
Charge Induced Dynamics of Water in a Graphene-Mica Slit Pore
Edwin Dollekamp (PIN)
Single-shot damage of Ru thin film induced by XUV FEL fs pulses
Igor Milov (XUV)
Edges and boundaries of transition-metal di-chalcogenides, Sridevi Krishnamurthi (CMS)
Single layers of transition-metal-di-chalcogenides (TMDCs) MX2, M=Mo,W, X=S,Se,Te, are two-dimensional direct band gap semiconductors. Many edges and grain boundaries of TMDC layers have a remarkably robust one-dimensional (1D) metallic character and form the catalytically active sites. We study the electronic structures of TMDC edges and boundaries using first-principles DFT+U calculations. The metallicity of the edge states, we show is of topological origin. Emerging 1D spin- and charge-density waves, which break the symmetry at the edges or boundaries, open up band gaps.
Interaction between counter-propagating quantum Hall edge channels in the 3D topological insulator BiSbTeSe2, Bob de Ronde (ICE)
The quantum Hall effect is studied in the topological insulator BiSbTeSe2. By employing top- and back-gate electric fields at high magnetic field, the Landau levels of the Dirac cones in the top and bottom topological surface states can be tuned independently. When one surface is tuned to the electron-doped side of the Dirac cone and the other surface to the hole-doped side, the quantum Hall edge channels are counter-propagating. The opposite edge mode direction, combined with the opposite helicities of top and bottom surfaces, allows for scattering between these counter-propagating edge modes. The total Hall conductance is integer valued only when the scattering is strong. For weaker interaction, a non-integer quantum Hall effect is expected and measured.
Charge Induced Dynamics of Water in a Graphene-Mica Slit Pore, Edwin Dollekamp (PIN)
We use atomic force microscopy to in situ investigate the dynamic behavior of confined water at the interface between graphene and mica. The graphene is either uncharged, negatively charged or positively charged. At high humidity, a third water layer will intercalate between graphene and mica. When graphene is negatively charged, the interface fills faster with a complete three layer water film, compared to uncharged graphene. At positive voltages, the third water layer dewets the interface, either by evaporation into the ambient or by the formation of 3D droplets on top of the remaining double water layer. Our experimental findings reveal novel phenomena of water at the nanoscale, which are interesting from a fundamental point of view and demonstrate the direct control over the wetting properties of the graphene/water interface.
Single-shot damage of Ru thin film induced by XUV FEL fs pulses, Igor Milov (XUV)
In this work we present experimental and theoretical studies of single-shot damage of ruthenium films induced by fs extreme ultraviolet (EUV) free-electron laser (FEL) pulses with 13.5 nm wavelength at FLASH in Hamburg. Ex-situ analysis of the damaged spots by means of SEM, TEM and AFM revealed the nature of the induced damage to be melting and spallation. The two-temperature model is used to simulate the interaction of the EUV fs FEL pulse with the Ru film. Simulations show that heating of Ru by the FEL EUV pulse occurs in the stress confinement regime which means that the lattice temperature increase is faster than the time needed for the system to mechanically react to that ultrafast heating. Large stresses develop inside the material leading to spallation of the top Ru layer, which is in agreement with the mentioned experimental observations.