Sheng-Bin Lei

Studies of the effects of hydrogen bonding on monolayer structures of C18H37X (X=OH, SH) on HOPG

Abstract Based on Scanning tunneling microscopy (STM) observations of 1-C 18 H 37 X (X=OH, SH) adsorbed on HOPG, the hydrogen bonded complexes were studied using density functional theory (DFT) and molecular mechanics (MM). At B3LYP/6-31g and B3LYP/6-311g** levels, molecular dimers connected by hydrogen bond were obtained. The models of 1-C 18 H 37 X monolayer were optimized by consistent valence force field (CVFF), whose structures and interaction energies agree well with DFT calculations. It is noticed that due to the stronger hydrogen bond interactions between C 18 H 37 OH molecules, C 18 H 37 OH adsorbed on HOPG shows only one kind of molecular arrangement, while C 18 H 37 SH exhibits two kinds of packing induced by alkyl–alkyl and adsorbate–substrate interactions.

Self-assembled monolayer of a Schiff base on Au(111) surface: electrochemistry and electrochemical STM study

Abstract The self-assembled monolayer (SAM) of Schiff base V-ape-V molecules on Au(111) in HClO4 solution has been investigated by electrochemical techniques and electrochemical scanning tunneling microscopy (ECSTM). The adsorption of V-ape-V on Au(111) retards the oxidization of Au and reduces the double-layer capacitance. Two-dimensional ordered molecular arrays with a ( 5×2 3 ) commensurate structure are observed. The V-ape-V molecules are adsorbed on Au(111) in a flat-lying orientation. A structural model is proposed to interpret the experimental results.

Scanning Tunneling Microscopy Characterization of Aromatic Molecules Stabilized by a Buffer Layer of Alkane Derivatives

Using lamellae of 1-octadecanol and stearic acid as a buffer layer, aromatic molecules such as copper phthalocyanine (CuPc) and nitrobenzene were immobilized on the surface of highly oriented pyrolytic graphite (HOPG), and been characterized by scanning tunneling microscopy (STM). These molecules crystallized in two dimensions on top of the monolayer of alkane derivatives, and high-resolution images of these molecules were obtained. An additional advantage is that the buffer layer underneath does not change the electronic properties of the immobilized molecules. The mechanism of the immobilization of the buffer layer is considered to be the cutting down of charge transfer between the aromatic molecules and graphite. These results proved that this strategy could be used as a general method to immobilize organic species on a substrate surface.

Controlled assembly of copper phthalocyanine with 1-iodooctadecane

The binary assembly behavior of 1-iodooctadecane with substituted phthalocyanine (Pc) is studied using the scanning tunneling microscopy (STM). By altering the substituted alkyl groups attached to the phthalocyanine ring, either uniform assembly or phase separation behavior can be observed. It is suggested that the strength of intermolecular interaction between phthalocyanine molecules is the determining factor for the assembly structure.

Combined SPM investigation on the interfacial structure of a phthalocyanine/conjugated polymer composite film.

The morphology of the composite film of organic semiconductors determines the properties and performances of devices to a large extent. In this work, we present a combined AFM and STM study on the interfacial structures of CuPcOC8 and CuPcOC8/PmPV composite films on graphite surface. For CuPcOC8 thin films, the face-on epitaxial growth of CuPcOC8 could persist within 3 to 5 monolayers and the formation of π-π stacked columns will occur with edge-on configuration when the film thickness further increases. For the CuPcOC8/PmPV composite film with 1:1 weight ratio, STM results reveal a preferential adsorption of PmPV on graphite surface, while AFM results indicate the phase segregation in the upper layer. STM also reveals in the molecular scale good compatibility of CuPcOC8 with PmPV.

Two-Component Assembling of Phthalocyanine with Alkane Derivatives on Graphite Surface

Adsorption with multi-components could provide a rich range of intermolecular interactions and offer a great opportunity to chemists interested in molecular assembling. In this article, we describe the results of the coadsorption of phthalocyanine and alkane derivatives on graphite surfaces. The structural details are revealed by scanning tunneling microscopy (STM). The assembly behavior has been summarized. The possibility of controlling the assembling behavior is discussed.

2D self-assembling of 4, 5-didodecylthiolphthalonitrile on graphite surface

An important precursor 4,5-didodecylthiolphthalonitrile DCP for synthesis of phthalocyanines Pcs and subphthalocyanines SubPcs was synthesized and the assembling structure of this molecule on the basal plane of highly oriented pyrolytic graphite HOPG surface was characterized using the scanning tunneling microscopy (STM) in ambient conditions. In high-resolution images of the molecules, we found that the arrangement of the cyano groups forms a “head-to-head” configuration to keep the stability of the entire system. The mismatch of the DCP molecules with the substrate lattice has also been observed in the experiment.