Scanning tunneling microscopy of single polyalkylthiophene molecules adsorbed on graphite (original) (raw)
Related papers
… Materials for Optics …, 1993
The self-assembly technique experimented for the deposition of alkanes and alkyl derivatives on layered compounds at the liquid/solid interface has been successfully extended to the adsorption of poly(3-decyl-thiophene) on graphite. The molecular films so obtained have been investigated using scanning tunnelling microscopy (STM). Images taken in both the constantcurrent and constant-height modes show highly packed arrays of molecules characterised by an average length and an average spacing that are in good agreement with results obtained by X-ray diffraction investigations. Constant-current images allow one to observe domain formations in preferential directions coincident with the main axes of the graphite lattice, while constant-height imaging, performed on small areas, allows one to resolve atomic structures within the polymer backbone. In particular, periodic, 0.71 nm spaced features have been identified along the side of the polymer backbone; they can be associated with the length of two monomer units and are attributable to imaging of sulphur atoms in the backbone. KEYWORDS Scanning tunnelling microscopy Self-assembly Monolayer Poly(alky1-thiophene)
Journal of Applied Physics, 2011
Polythiophene molecules adsorbed on a highly oriented pyrolytic graphite surface were studied by combined dynamic scanning tunneling microscopy (STM) and frequency modulation atomic force microscopy (FM-AFM) with a quartz tuning fork sensor operating in Qplus mode and equipped with a Pt/Ir tip. Upon completing a careful sub-angström oscillation amplitude calibration of the probe, experiments were conducted in an ultra high vacuum at room temperature. By selecting the tip/surface distance regulation parameter, one can select the type of simultaneous information obtained in an area. For distance regulation based on the mean tunneling current, dynamic STM images together with maps of tip/surface force gradient were obtained. FM-AFM images with maps of the tunneling current were also acquired when the distance regulation was based on the frequency shift. Comparison between these images reveals interesting features. For example the tip which operates in STM mode with ultra low current (<10 pA) generates different interaction forces above molecules or graphite. Changes in energy dissipation processes as small as tens of millielectronvolts per cycle were recorded when the tip oscillates above the polymer or on the graphite surface. Hence data demonstrates that a stiff piezoelectric tuning fork of several kilonewtons/meters working as an AFM/STM probe with sub-angström amplitude can characterize weakly adsorbed molecules.
Imaging and modification of polymers by scanning tunneling and atomic force microscopy
Journal of Applied Physics, 1988
Direct imaging of ultrathin organic films on solid surfaces is important for a variety of reasons; in particular, the use of such films as ultrathin resists for nanometer scale fabrication and information recording requires that we understand their microstrucure. We have used the Langmuir–Blodgett technique to prepare monolayer and submonolayer films of poly(octadecylacrylate) (PODA) and poly(methylmethacrylate) (PMMA) on graphite substrates. Atomic scale images obtained with the scanning tunneling microscope (STM) and the atomic force microscope of the PODA films showed a variety of structures, including isolated narrow fibrils, parallel groups of fibrils, and an ordered structure consistent with the side chain crystallization expected with that material. The fibrils observed are interpreted as individual polymer chains or small bundles of parallel chains. Images of the PMMA samples show no ordered regions. By applying voltage pulses on the STM tip, we were able to locally modify a...
2006
Regioregular poly(3-dodecylthiophene) films self-organized on highly oriented pyrolytic graphite have been investigated by scanning tunneling microscopy and two-dimensional scanning tunneling spectroscopy (STS). Simulated spectra in very good agreement with the experimental data have been obtained by a method combining ab initio and semiempirical approaches, which allows a careful discussion of the polymer electronic states. From the experimental data, with the support of modeling, it is shown that the STS spectra give a direct access to the polymer semiconducting band gap without noticeable charge-transfer effects from the substrate. Spectroscopic images are achieved at the single chain scale, which allows scrutinizing the electronic consequences of chain folds and π-stacking effects through spectroscopic contrasts. While chain folds do not locally increase the polymer band gap more than a few tens of millielectonvolt, a striking widening of the STS conductance gap is observed in the case of electronic tunneling through two interacting polymer layers. Scenarios based on nonplanar configuration of thiophene cycles within the second layer or variations of the charge screening effects are proposed to explain this phenomenon.
Langmuir, 1996
Experimental evidence that STM tips can induce grafting of N-vinyl-2-pyrrolidone (NVP) molecules on a graphite surface from a solution of NVP is presented. Such a process depends mainly on the bias voltage (Vt) applied to graphite. For Vt < 2.9 V, the graphite surface remains unchanged while, at Vt ) 3 V, NVP islands are detected. When Vt > 3.4 V and applied for 100 s, islands are formed together with holes in the graphite surface. For Vt ) 3 V, islands with a diameter which varies from 0.3 to 4.5 nm are formed. They exhibit a similar thickness (∼0.4 nm). High-resolution STM images show that the electronic structure of the graphite is perturbed around these islands. Some islands appear made of units which have a diameter of 0.5-0.6 nm, in agreement with the known diameter of a single NVP molecule. A mechanism for the grafting is proposed.
Nanoscale Pattern Formation with the Scanning Tunneling Microscope on Polymer Thin Films
Japanese Journal of Applied Physics, 1994
Nanometer-scale structures can be routinely fabricated with voltage pulses applied through the sharp tip of the scanning tunneling microscope (STM) on thin (<2000 Å) films of hydroxypropylcellulose. Structures were 20–30 Å in diameter in ambient atmosphere, and ∼200 Å in diameter in ultrahigh vacuum. Thermally induced structures can also be created with a modest power input (0.1–3 V tip bias voltages, 6 nA current, 10's of seconds duration for a ∼100 Å thick film). The structure formation mechanism appeared to include thermal effects from the current and its implications will be discussed.
Thin Solid Films, 2006
Conformations of one of the variations of k-conjugated poly-alkylthiophene, poly(3-dodecylthiophene)s (P3DDT)s on the surface in ultra high vacuum (UHV) were investigated by non-contact atomic force microscopy (NC-AFM) operated by frequency-modulation mode (FMmode). From individual molecules to several multi-layered ones, polymer chains on the surface were clearly resolved on conducting highly oriented pyrolytic graphite (HOPG) substrates and insulating mica ones, respectively. Solvent evaporation was found to have two stages, which influenced the diffusion, ordering, and adhesion processes of polymer chains on the substrate. To keep the ordered conformations of deposited polymer chains when they are transferred from ambient condition to UHV, these evaporation processes should be carefully considered. The initial conformation of polymers on the substrate was found to depend strongly on the lattice matching conditions and interactions between polymers and substrates. Formations of stripe-like structures of P3DDT polymers were found on the mica substrates, which is promising for device application.
Macromolecular Rapid Communications, 2008
A solution processible polymer-poly(3,3 000 -didodecylquaterthiophene) (PQT-12) is investigated at the liquid/solid interface using the scanning tunneling microscopy (STM). Twodimensional ordered films made up of self-assembled domains, with dimensions of 100 nm  50 nm adsorbed on highly oriented pyrolytic graphite (HOPG) were formed. These domains consist of parallel lamellar polymer chains, with the alkyl chains forming interdigitated structures, along with U-shaped and closed ring segments of the polymer chains. A polymer chain packing model is proposed herein, which attempts to propose a correlation between the packing of long chains and charge mobilities. These STM results could help in understanding the relationship between the extended conjugation and molecular organization of the PQT-12 chains.