Templating effect of single-layer graphene supported by an insulating substrate on the molecular orientation of lead phthalocyanine

Abstract

The influence of single-layer graphene on top of a SiO2/Si surface on the orientation of nonplanar lead phthalocyanine (PbPc) molecules is studied using two-dimensional grazing incidence X-ray diffraction. The studies indicate the formation of a mixture of polymorphs, i.e., monoclinic and triclinic forms of PbPc with face-on (lying down) and edge-on (standing up) PbPc orientations, respectively. The formation of monoclinic fractions is attributed to the presence of the graphene layer directing the π interactions between the highly delocalized macrocycles. The competing interfacial van der Waals forces and molecule–molecule interactions lead to the formation of a small fraction of triclinic moieties. The nanoscale electrical characterization of the thin PbPc layer on graphene by means of conducting atomic force microscopy shows enhanced vertical conductance with interconnected conducting domains consisting of ordered monoclinic crystallites through which the charge transfer occurs via tunneling. These results show the importance of a templating layer to induce the formation of a required phase of PbPc suitable for specific device applications.

Comparative Study of Conduction Mechanisms in Disodium Phthalocyanine-Based Organic Diodes for Flexible Electronics

“…MPc molecules in films may attain face-on or edge-on orientation with respect to the substrate plane while forming monoclinic and triclinic forms [22]. The monoclinic form presents strong absorption in the visible range while the triclinic form exhibits intense IR absorptions bands [22,23]. These crystalline shapes and their influence on the film's electrical behavior were widely studied in M(II)Pcs.…”

Studies on the Structure, Optical, and Electrical Properties of Doped Manganese (III) Phthalocyanine Chloride Films for Optoelectronic Device Applications

“…MPcs are macrocycles made up of 18 π-electrons with exceptional properties due to delocalization, such as high chemical, thermal, and photochemical stabilities and appropriate redox properties. They also have a wide absorption region in their infrared/near-infrared spectra, as well as optical nonlinearity related to their wide range of semiconducting properties [9][10][11][12][13]. Thanks to these remarkable electronic and optical properties, MPc thin films represent an area of outstanding research for organic electronic devices [13][14][15].…”