Browsing by Author "Pohjavirta, Ilona"

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2D metal-organic framework of dicyanoanthracene on Au(111)
(2019-03-12) Pohjavirta, Ilona
Perustieteiden korkeakoulu | Master's thesis
Two-dimensional metal-organic frameworks (2D MOFs) are single-atom-thick porous lattices comprising coordinating metal atoms and molecular ligands on an atomistically flat surface. Every component in the system can be varied, resulting in diverse structures exhibiting numerous different lattice symmetries as well as a rich variety of physics. 2D MOFs have been predicted to host exotic quantum-mechanical phenomena, perhaps most interestingly topological phases which make them especially appealing for applications in e.g. spintronics and quantum computing. However, despite numerous theoretical predictions, the realization of topological electronic states in 2D MOFs remains elusive. This thesis focuses on a 2D MOF of gold centers and 9,10-dicyanoanthracene (DCA) molecules in a kagome lattice symmetry - a structure predicted to be a topological insulator. The synthesis of the Au-DCA lattice onto a Au(111) surface was demonstrated and the structure was characterized by scanning tunneling microsopy (STM) and scanning tunneling spectrosopy (STS). The results obtained point towards an extensive electronic system throughout the lattice, perhaps even band formation. However, challenges in synthesis resulting in limited sample size as well as the metal substrate used prevent from drawing further conclusions. After this first step, the future research towards realizing the topological phase in the Au-DCA lattice is outlined by enhancing the lattice growth as well as synthesis onto a weakly interacting substrate.
Characterization of graphene on silicon dioxide and hexagonal boron-nitride
(2014-12-18) Pohjavirta, Ilona
Perustieteiden korkeakoulu | Bachelor's thesis
On‐Surface Assembly of Au‐Dicyanoanthracene Coordination Structures on Au(111)
(2019-09-17) Yan, Linghao; Pohjavirta, Ilona; Alldritt, Benjamin; Liljeroth, Peter
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
On‐surface metal‐organic coordination provides a promising way for synthesizing different two‐dimensional lattice structures that have been predicted to possess exotic electronic properties. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we studied the supramolecular self‐assembly of 9,10‐dicyanoanthracene (DCA) molecules on the Au(111) surface. Close‐packed islands of DCA molecules and Au‐DCA metal‐organic coordination structures coexist on the Au(111) surface. Ordered DCA3Au2 metal‐organic networks have a structure combining a honeycomb lattice of Au atoms with a kagome lattice of DCA molecules. Low‐temperature STS experiments demonstrate the presence of a delocalized electronic state containing contributions from both the gold atom states and the lowest unoccupied molecular orbital of the DCA molecules. These findings are important for the future search of topological phases in metal‐organic networks combining honeycomb and kagome lattices with strong spin‐orbit coupling in heavy metal atoms.