Browsing by Author "Boneschanscher, M.P."
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- Quantitative Atomic Force Microscopy with Carbon Monoxide Terminated Tips
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2011) Sun, Z.; Boneschanscher, M.P.; Swart, I.; Vanmaekelbergh, D.; Liljeroth, PeterNoncontact atomic force microscopy (AFM) has recently progressed tremendously in achieving atomic resolution imaging through the use of small oscillation amplitudes and well-defined modification of the tip apex. In particular, it has been shown that picking up simple inorganic molecules (such as CO) by the AFM tip leads to a well-defined tip apex and to enhanced image resolution. Here, we use the same approach to study the three-dimensional intermolecular interaction potential between two molecules and focus on the implications of using molecule-modified AFM tips for microscopy and force spectroscopy experiments. The flexibility of the CO at the tip apex complicates the measurement of the intermolecular interaction energy between two CO molecules. Our work establishes the physical limits of measuring intermolecular interactions with scanning probes. - Quantum confined electronic states in atomically well-defined graphene nanostructures
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2011) Hämäläinen, Sampsa; Sun, Z.; Boneschanscher, M.P.; Uppstu, Christer; Ijäs, M.; Harju, A.; Vanmaekelbergh, D.; Liljeroth, PeterDespite the enormous interest in the properties of graphene and the potential of graphene nanostructures in electronic applications, the study of quantum-confined states in atomically well-defined graphene nanostructures remains an experimental challenge. Here, we study graphene quantum dots (GQDs) with well-defined edges in the zigzag direction, grown by chemical vapor deposition on an Ir(111) substrate by low-temperature scanning tunneling microscopy and spectroscopy. We measure the atomic structure and local density of states of individual GQDs as a function of their size and shape in the range from a couple of nanometers up to ca. 20 nm. The results can be quantitatively modeled by a relativistic wave equation and atomistic tight-binding calculations. The observed states are analogous to the solutions of the textbook “particle-in-a-box” problem applied to relativistic massless fermions. - Structure and Local Variations of the Graphene Moiré on Ir(111)
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2013) Hämäläinen, Sampsa; Boneschanscher, M.P.; Jacobse, P.H.; Swart, I.; Pussi, Katariina; Moritz, W.; Lahtinen, J.; Liljeroth, P.; Sainio, J.We have studied the incommensurate moiré structure of epitaxial graphene grown on iridium(111) by dynamic low-energy electron diffraction [LEED I(V)] and noncontact atomic force microscopy (AFM) with a CO-terminated tip. Our LEED I(V) results yield the average positions of all the atoms in the surface unit cell and are in qualitative agreement with the structure obtained from density functional theory. The AFM experiments reveal local variations of the moiré structure: The corrugation varies smoothly over several moiré unit cells between 42 and 56 pm. We attribute these variations to the varying registry between the moiré symmetry sites and the underlying substrate. We also observe isolated outliers, where the moiré top sites can be offset by an additional 10 pm. This study demonstrates that AFM imaging can be used to directly yield the local surface topography with pm accuracy even on incommensurate two-dimensional structures with varying chemical reactivity. - Suppression of electron-vibron coupling in graphene nanoribbons contacted via a single atom
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2013) van der Lit, J.; Boneschanscher, M.P.; Vanmaekelbergh, D.; Ijäs, M.; Uppstu, Christer; Ervasti, M.; Harju, A.; Liljeroth, P.; Swart, I.Graphene nanostructures, where quantum confinement opens an energy gap in the band structure, hold promise for future electronic devices. To realize the full potential of these materials, atomic-scale control over the contacts to graphene and the graphene nanostructure forming the active part of the device is required. The contacts should have a high transmission and yet not modify the electronic properties of the active region significantly to maintain the potentially exciting physics offered by the nanoscale honeycomb lattice. Here we show how contacting an atomically well-defined graphene nanoribbon to a metallic lead by a chemical bond via only one atom significantly influences the charge transport through the graphene nanoribbon but does not affect its electronic structure. Specifically, we find that creating well-defined contacts can suppress inelastic transport channels.