Browsing by Author "Drost, R."

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Epitaxial hexagonal boron nitride on Ir(111): A work function template
(2014) Schulz, F.; Drost, R.; Hämäläinen, Sampsa; Demonchaux, T.; Seitsonen, A.P.; Liljeroth, P.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Hexagonal boron nitride (h-BN) is a prominent member in the growing family of two-dimensional materials with potential applications ranging from being an atomically smooth support for other two-dimensional materials to templating growth of molecular layers. We have studied the structure of monolayer h-BN grown by chemical vapor deposition on Ir(111) by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments and state-of-the-art density functional theory (DFT) calculations. The lattice mismatch between the h-BN and Ir(111) surface results in the formation of a moiré superstructure with a periodicity of ∼29 Å and a corrugation of ∼0.4 Å. By measuring the field emission resonances above the h-BN layer, we find a modulation of the work function within the moiré unit cell of ∼0.5 eV. DFT simulations for a 13-on-12 h-BN/Ir(111) unit cell confirm our experimental findings and allow us to relate the change in the work function to the subtle changes in the interaction between boron and nitrogen atoms and the underlying substrate atoms within the moiré unit cell. Hexagonal boron nitride on Ir(111) combines weak topographic corrugation with a strong work function modulation over the moiré unit cell. This makes h-BN/Ir(111) a potential substrate for electronically modulated thin film and heterosandwich structures.
Synthesis of Extended Atomically Perfect Zigzag Graphene - Boron Nitride Interfaces
(2015) Drost, R.; Shawulienu, Kezilebieke; Ervasti, Mikko; Hämäläinen, Sampsa; Schulz, F.; Harju, A.; Liljeroth, P.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The combination of several materials into heterostructures is a powerful method for controlling material properties. The integration of graphene (G) with hexagonal boron nitride (BN) in particular has been heralded as a way to engineer the graphene band structure and implement spin- and valleytronics in 2D materials. Despite recent efforts, fabrication methods for well-defined G-BN structures on a large scale are still lacking. We report on a new method for producing atomically well-defined G-BN structures on an unprecedented length scale by exploiting the interaction of G and BN edges with a Ni(111) surface as well as each other.
Ultra-narrow metallic armchair graphene nanoribbons
(2015) Kimouche, A.; Ervasti, Mikko; Drost, R.; Halonen, S.; Harju, A.; Joensuu, Pekka; Sainio, J.; Liljeroth, P.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Graphene nanoribbons (GNRs)—narrow stripes of graphene—have emerged as promising building blocks for nanoelectronic devices. Recent advances in bottom-up synthesis have allowed production of atomically well-defined armchair GNRs with different widths and doping. While all experimentally studied GNRs have exhibited wide bandgaps, theory predicts that every third armchair GNR (widths of N=3m+2, where m is an integer) should be nearly metallic with a very small bandgap. Here, we synthesize the narrowest possible GNR belonging to this family (five carbon atoms wide, N=5). We study the evolution of the electronic bandgap and orbital structure of GNR segments as a function of their length using low-temperature scanning tunnelling microscopy and density-functional theory calculations. Already GNRs with lengths of 5 nm reach almost metallic behaviour with ~100 meV bandgap. Finally, we show that defects (kinks) in the GNRs do not strongly modify their electronic structure.