Molecular Self-Assembly on Graphene on SiO2 and h‑BN Substrates

• Published in: Nano letters Vol. 13; no. 7; pp. 3199 - 3204
• Main Authors: Järvinen, Päivi, Hämäläinen, Sampsa K, Banerjee, Kaustuv, Häkkinen, Pasi, Ijäs, Mari, Harju, Ari, Liljeroth, Peter
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.07.2013
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electron states and collective excitations in thin films, multilayers, quantum wells, mesoscopic and nanoscale systems; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Materials science; Methods of nanofabrication; Physics; Self-assembly; Specific materials; Supramolecular and biochemical assembly; cobalt phthalocyanine (CoPc); scanning tunneling spectroscopy (STS); Molecular self-assembly; hexagonal boron nitride (h-BN); graphene; scanning tunneling microscopy (STM); Electronic properties; Doping; Boron nitride; Cobalt; CVD; Scanning tunneling microscopy; Self-assembly; Hexagonal crystals; Molecular assembly; Graphene; Silicon oxides; Square lattices; Scanning tunneling spectroscopy; Phthalocyanines
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl401265f

One of the suggested ways of controlling the electronic properties of graphene is to establish a periodic potential modulation on it, which could be achieved by self-assembly of ordered molecular lattices. We have studied the self-assembly of cobalt phthalocyanines (CoPc) on chemical vapor deposition (CVD) grown graphene transferred onto silicon dioxide (SiO2) and hexagonal boron nitride (h-BN) substrates. Our scanning tunneling microscopy (STM) experiments show that, on both substrates, CoPc forms a square lattice. However, on SiO2, the domain size is limited by the corrugation of graphene, whereas on h-BN, single domain extends over entire terraces of the underlying h-BN. Additionally, scanning tunneling spectroscopy (STS) measurements suggest that CoPc molecules are doped by the substrate and that the level of doping varies from molecule to molecule. This variation is larger on graphene on SiO2 than on h-BN. These results suggest that graphene on h-BN is an ideal substrate for the study of molecular self-assembly toward controlling the electronic properties of graphene by engineered potential landscapes.