Lateral Electrical Conduction in Organic Monolayer

Abstract

Electric conductivity of organic molecules was estimated with molecular resolution using self-assembled techniques and scanning tunneling microscopy (STM). Conjugated molecules of [1,1‘:4‘,1‘ ‘-terphenyl]-4-methanethiol (TP) were embedded in self-assembled monolayers of insulative n-alkanethiols, and when observed by STM, TP molecules appeared as protruding domains. The apparent height of the TP domains increases as the lateral size of the domains grows from 1 to 10 nm, reflecting the increase in the vertical conductance of the domains due to the lateral, intermolecular interaction. We assumed that the molecules are connected to each other with resistors for estimating the effect of intermolecular interaction on the conductance and calculated the height of conducting disks with various radii, which should roughly reproduce the size-dependent height of the TP domains observed by STM. The estimated resistance of the single TP molecule was less than 40 GΩ, and the effective lateral conductivity corresponding to the large TP domains was larger than 0.01 S/cm.

Electronic structure and polymerization of a self-assembled monolayer with multiple arene rings

“…For SAMs formed from ͓1,1Ј;4Ј, 1Љ-terphenyl͔-4-methanethiol, a commensurate ͱ 3 ϫ 2 ͱ 3 structure, with an intermolecular spacing of about 5 Å, was observed by LEED and molecular resolution STM, 69 while a ͱ 3 ϫ ͱ 3R30°, with an intermolecular spacing again of about 5 Å, has been observed in other molecular resolution STM studies. 72,73 The band structure critical points might be reconciled to such a ͱ 3 ϫ ͱ 3 R30°hexagonal packing, if the band mapping is taken along the T line of the surface hexagonal Brillouin zone, toward the Brillouin zone edge ͑K ͒, but the second Brillouin center should not be observed in this case, so this structure remains difficult to reconcile with our data.…”

Evidence for Band‐Like Transport in Graphene‐Based Organic Monolayers

“…The lateral conductivity within highly ordered islands of the HBC thiolates embedded into a (non-conducting) 2D-matrix of an COMMUNICATION www.advmat.de alkanethiolate SAM was studied using the STM-based method proposed by Ishida et al [15] Whereas for a single molecule embedded in a matrix of insulating organothiolates only the direct (through bond) path leading from the STM tip through the molecule to the substrate exists, for a HBC thiolate embedded in a structurally well-defined island consisting of alike molecules the p-p coupling between adjacent molecules will allow for intermolecular charge transfer, thus opening additional current paths. This additional current will result in a larger conductivity, i.e., the molecule will appear higher in the STM micrographs.…”

“…This additional current will result in a larger conductivity, i.e., the molecule will appear higher in the STM micrographs. [15] An analysis of the apparent height versus island size dependence allows to derive information on the charge transport between adjacent molecules. [16] The potential of this method has already been demonstrated for TP1-SAM islands embedded in a 2D-matrix of nonanethiolate or dodecanethiolate SAMs [15] and for C 11 -TTF-SAM islands embedded in a decanethiolate SAM.…”

“…[15] An analysis of the apparent height versus island size dependence allows to derive information on the charge transport between adjacent molecules. [16] The potential of this method has already been demonstrated for TP1-SAM islands embedded in a 2D-matrix of nonanethiolate or dodecanethiolate SAMs [15] and for C 11 -TTF-SAM islands embedded in a decanethiolate SAM. [17] While in previous work this method has only been used at room temperature, we demonstrate here that by additionally determining the temperature dependence, different conduction mechanisms like hopping or band-like transport can be distinguished in a rather straightforward fashion.…”

Multidimensional electrochemical imaging in materials science

“…STM and C-AFM, in conjunction with methods including use of Hg-drop electrodes, have been used as promising tools for studying the electrical conductance of molecules along the molecular axis [267,268], crossed wires [269], and break junctions [270,271]. As early as the late 90s, the conductance of single molecules embedded in insulating SAM films was discussed and evaluated by Bumm et al [237] and others [272][273][274][275][276], by use of STM. It was, however, shown that estimation of the electrical conductance of adsorbed molecules by use of STM is quite complicated compared with techniques in which the electrode is directly attached to the molecules [267][268][269][270][271].…”