L. Jiang

In situ AFM study of the electrochemical deposition of polybithiophene from propylene carbonate solution

Abstract Early stages of galvanostatic deposition of polybithiophene onto highly oriented pyrolytic graphite (HOPG) from propylene carbonate solution were investigated using electrochemical atomic force microscopy (ECAFM). The polymer film thickness was evaluated in situ using surface modification with the AFM tip and was found to be proportional to the grafting charge Q and independent of the deposition current density i in the current density range from 0.1 mA/cm 2 to 2 mA/cm 2 . The first stage of the deposition was the formation of polymer nuclei with an average height of ca. 1 nm; continuous film was formed at Q ≥0.5 mC/cm 2 . Even at the earliest stages, the polymer featured grain structure with the average grain size of ca. 50 nm. The presence of the crystalline phase in the films was demonstrated by the X-ray diffraction data.

Kelvin probe force microscopic study of anodically and cathodically doped poly-3-methylthiophene

The doping-level distribution and surface morphology of thin films of p- and n-doped poly-3-methylthiophene (P3MT) deposited onto highly oriented pyrolytic graphite (HOPG) were characterized on a microscopic scale by using Kelvin probe force microscopy (KFM) and in situ atomic force microscopy (ECAFM) techniques. Two different types of surface structures were found on different sites of the polymer surface, one of them representing relatively amorphous polymer globules, and the other highly crystalline polymer grains. For the two structures, in both the p- and n-doping processes, the doping-level distribution was again found to be directly related to the polymer surface morphology, as was the case for p-doped polybithiophene (PBT) [O.A. Semenikhin, L. Jiang, T. Iyoda, K. Hashimoto, A. Fujishima, J. Phys. Chem. 100 (1996) 18603; O.A. Semenikhin, L. Jiang, T. Iyoda, K. Hashimoto, A. Fujishima, Electrochim. Acta 42 (1997) 3321]. At the same time, the relatively amorphous structure featured a higher degree of microheterogeneity: the observed polymer granules featured both oxidized and reduced regions. The crystalline grains of the second structure were more uniformly doped. However, in the cathodic doping, some of these grains remained undoped or even p-doped.

Self-Assembly of Hierarchical Chiral Nanostructures Based on Metal–Benzimidazole Interactions: Chiral Nanofibers, Nanotubes, and Microtubular Flowers

Controlled hierarchical self-assembly of synthetic molecules into chiral nanoarchitectures to mimic those biological chiral structures is of great importance. Here, a low-molecular-weight organogelator containing a benzimidazole moiety conjugated with an amphiphilic l-glutamic amide has been designed and its self-assembly into various hierarchical chiral nanostructures is investigated. Upon gel formation in organic solvents, 1D chiral nanostructure such as nanofiber and nanotube are obtained depending on the solvents. In the presence of transition and rare earth metal ions, hierarchical chiral nanostructures are formed. Specifically, the addition of TbCl3 , EuCl3 , and AgNO3 leads to nanofiber structures, while the addition of Cu(NO3 )2 , Tb(NO3 )3 , or Eu(NO3 )3 provides the microflower structures and microtubular flower structures, respectively. While Eu(III) and Tb(III)-containing microtubular flowers keep the chirality, the Cu(II)-coordinated microflowers lose chirality. More interestingly, the nanofibers formed by the gelator coordinated with Eu(III) or Tb(III) ions show not only the supramolecular chirality but also the circularly polarized luminescence.

Molecularly resolved observation of surface reconstruction of C60 epitaxial films by atomic force microscopy

Abstract Reconstructed surfaces of C 60 epitaxial films on KBr(001) substrates were directly observed by atomic force microscopy (AFM). AFM images showed ridge-like fringes running along the three equivalent [110] directions on the face-centered cubic (fcc) (111) face on the surfaces of C 60 thick (> 500 nm) films. Molecular-resolution images revealed that the raised fringe region is contracted by ca 3% in the [112] direction and that the vertical displacement of the fringe is 0.30±0.02 nm. The observations suggest a stacking-fault-domain model involving periodic transitions between fcc (ABCABC… stacking) and hexagonal close-packed (hcp, ABAB… stacking) structures. Fcc surface domains were proposed to exist on the wider areas between fringes on the C 60 film surface based on the fact that the fcc bulk structure is energetically slightly more favorable than that of hcp.