Tunneling Voltage Polarity Dependent Submolecular Contrast of Naphthalocyanine on Graphite. A STM Study of Close-Packed Monolayers under Ultrahigh-Vacuum Conditions

Abstract

Self-assembled monolayers of free-base naphthalocyanine are examined in the context of analogous phthalocyanine films, revealing the influence of the more extended π-electron system on monolayer properties. Naphthalocyanine was vapor-deposited on a graphite substrate in ultrahigh vacuum and investigated in situ at low temperature (50 K) using scanning tunneling microscopy (STM). The crystallographic monolayer parameters of the deposited films were determined by means of submolecularly resolved STM images. In addition, vacancies in the monolayer have allowed for an accurate measurement of single molecule azimuthal angles. In STM topographs with submolecular resolution, a clear difference is evident between tunneling images corresponding to occupied and unoccupied sample states. The intramolecular structure exhibited by the STM images can be understood qualitatively by considering frontier orbitals calculated for isolated molecules. Moreover, single point tunneling spectra show a distinct signature of the organic adlayer as expected for resonant tunneling.

Anisotropic Crystalline Organic Step-Flow Growth on Deactivated Si Surfaces

“…The Si spectrum reveals that the surface has been deactivated with the unoccupied state at about 1.5 eV above the Fermi level and an occupied back-bond state at about 1.5 eV below the Fermi level, consistent with the previous study [31]. Spectrum on ZnPc shows the available density of states near +2.5 V, corresponding to the resonant tunneling through the lowest unoccupied molecular orbital (LUMO) [33,34].…”

Surface chemistry of porphyrins and phthalocyanines

“…Ref. [293] provides a detailed comparison of the different structures and packing densities of 2HNc on Au(1 0 0) [292], Au (1 1 1) [293] and graphite (HOPG) [295][296][297]. 4 1.…”

Metallophthalocyanine-based molecular materials as catalysts for electrochemical reactions

“…The use of self-assembled monolayers (SAMs) of alkylthio-, arylthio-and thiol-derivatized phthalocyanines [57,82,102,109,[195][196][197][198][199][200][201][202][203][204][205][206][207][208] is a rather new and convenient method for immobilizing these macrocyclic complexes on gold surfaces. Indeed, thiol derivatized macrocyclic bound to a gold substrate via their thiol arms lead to the formation of reproducible and stable films of SAMs.…”