Self-organization of two-dimensional poly(3-hexylthiophene) crystals on Au(111) surfaces

Abstract

A novel approach to construct organized structures and tunable electronic properties of poly(3-hexylthiophene) (P3HT) monolayers on Au(111) surfaces was developed based on a self-assembly process in a liquid phase. On a bare Au(111) surface, P3HT adsorbs as a monolayer with a randomly oriented and curvy-wire morphology. When the gold surface was pre-modified by an iodine adlayer (I-Au(111)), the passivation effect of iodine decreases the substrate-adsorbate interaction. As a result, P3HT adsorbs as linear chains, stacking and folding into regular arrays of a polymer bundle. By controlling the electrode at more negative potentials, it is able to desorb the iodine adlayer from the substrate. The remaining P3HT adsorbs onto the Au(111) surface directly, retaining a linear and regular arrangement. However, a different electronic structure is imaged by scanning tunneling microscopy (STM). The scanning tunneling spectroscopy (STS) analysis reveals that this molecular image is associated with a 0.16 eV shift of the Fermi level toward HOMO position, indicating a stronger p-doping characteristic of the adlayer. The phenomenon is ascribed to an iodine-induced p-doping reaction which occurs during the desorption of iodine. This work demonstrates that electrode potential and pre-adsorbed halide adlayers can be effectively used to regulate the arrangement and electronic properties of adsorbed molecules on metallic substrates.

Semiconducting Polymer Thin Films Used in Organic Solar Cells: A Scanning Tunneling Microscopy Study

“…Figure 3 shows P3HT monolayers, prepared by drop casting from a dilute solution on HOPG surface, measured under the STM liquid/solid interface technique. [35] These STM images reveal that chain conformations and packing are similar to those previously reported, in UHV conditions with STM, with a chain average length in the range 13-26 nm; [20][21][22][23] however, the average length of the polymer chain in this work: ≈41 nm (images treated with the gwyddion software), is almost twice larger than the two previous commented P3HT, [21,23] it is possibly due to the bigger molecular weight, also, perhaps due to the extraction of short chains in the purification process. [35] These STM images reveal that chain conformations and packing are similar to those previously reported, in UHV conditions with STM, with a chain average length in the range 13-26 nm; [20][21][22][23] however, the average length of the polymer chain in this work: ≈41 nm (images treated with the gwyddion software), is almost twice larger than the two previous commented P3HT, [21,23] it is possibly due to the bigger molecular weight, also, perhaps due to the extraction of short chains in the purification process.…”

“…It is worth to mention that previous STM studies of P3HT films were usually performed by using the UHV STM, [21,22] our results totally correlate with these earlier analyses through this mentioned easier and more economical STM technique. STM film research was carried out by using the easy and more economical liquid/solid interface approach.…”

“…If a conductive tip (tungsten or Pt-Ir, typically) is brought within a close range of the sample surface (≈1 nm) and a voltage U is applied between the tip and the electrically conducting sample, an exponentially dependent tunneling current I t is detected, which may be used as a feedback signal for regulating the tip-sample distance to a constant. For instance, direct measurements from STM images of P3HT films, [21][22][23] revealed that the interchain distances are around 1.3-1.4 nm and form crystalline domains of 20 nm in width with different alkyl side chain arrangements and orientation in monolayers. [19] For instance, Osteritz et al [20] studied the properties of a series of self-assembled functionalized regioregular oligo(3-alkylthiophene) and the self-organization of the polymer chain.…”

Gold nanorods with conjugated polymer ligands: sintering-free conductive inks for printed electronics

“…This is in accordance with results previously reported for poly-(3-hexylthiophene) (P3HT), a polymer with the same backbone, that adsorbs face-on on Au (111) surface. 33 According to the TGA data, each AuNR is surrounded by an average of three polymer layers that bind to the gold and to each other through π-stacking interactions.…”

Polymer adsorption on reconstructed Au(001): A statistical description of P3HT by scanning tunneling microscopy and coarse-grained Monte Carlo simulations

“…Hence a number of experimental studies addressed for example the influence of structure formation by polymer self-assembly on ideal surfaces on the electronic properties of oligo-and polythiophenes. 8,9 Due to the complexity of these macromolecules, the experimental findings have not been supported with simulations so far, which in contrast is well-established for studies of small organic molecules. This study reports on an approach to combine the experimental observation of polymer chain conformations adsorbed on a metal surface with coarse-grained Monte Carlo simulations.…”