Highly Oriented Pyrolytic Graphite Surface Research Articles

Observation of Liquid Crystal Molecule on Graphite by Scanning Tunneling Microscopy

Abstract Molecules of liquid crystals(LCs) adsorbed on highly-oriented pyrolytic graphite(HOPG) were imaged by scanning tunneling microscopy(STM). Planar layer structures induced by the HOPG surface were obtained. Molecular packing models for the STM images are introduced with the aid of a molecular orbital calculation. Also we discuss the rearrangement of the LC alignment during the continuous STM measurement.

Scanning tunneling microscopy of actin filament

We present a scanning tunneling microscopy (STM) image of a supramolecular structure of biological importance, fibrous actin (F-actin) polymers from muscle. F-actin is one of the major components in biological contractile machinery such as muscle. A drop of a solution containing F-actin was put on a highly oriented pyrolytic graphite (HOPG) surface and dried in air at room temperature. F-actin deposited on an HOPG surface was imaged by using a commercially available STM operated in air without metal coating. A sheet type of F-actin paracrystal from sample preparation in the presence of 12 mM MgCl2 has been observed. The STM images showed corrugations consistent with the geometry expected from the known configuration of the sheet type paracrystal. We discuss the STM image and compare it with a conventional transmission electron microscope image.

Scanning tunneling microscopy of the annealing of a thin platinum film on highly oriented pyrolytic graphite

Scanning tunneling microscopy (STM) was used to study morphological changes of a Pt thin film deposited on highly oriented pyrolytic graphite (HOPG) during an annealing process. In air, it was possible to image the morphology of the thin film with a vertical resolution of 0.5 Å and a lateral resolution of 20 Å. Surface structural change was observed after the annealing processes. When the annealing temperature was below 573 K, surface morphology changed only slightly. Between 573 and 873 K, the originally uniformly distributed rolling hills of Pt coagulated into larger clumps. Above 873 K, Pt crystal facets started to form on the surface. At 1123 K, a large portion of the surface turned into well defined Pt crystal facets. Above 1123 K, the Pt film started to crack and formed scattered crystals on the HOPG surface. A complementary X-ray diffraction measurement showed that the crystallized Pt film was preferentially oriented with the (111) plane parallel to the substrate graphite (0001) basal plane, indicating epitaxy of the Pt overlayer with the graphite substrate underneath.

Scanning tunneling microscopic images of an azobenzene derivative differently deposited on highly oriented pyrolytic graphite surfaces

Ordered molecular structures have been observed by scanning tunneling microscopy (STM) in 4-octyl-4'-(5-carboxypentamethy-lene oxy)-azobenzene (ABD) films deposited on highly oriented pyrolytic graphite (HOPG) surfaces by the Langmuir-Blodgett (LB) method and by a simple deposition process. The simple deposition is achieved by depositing a known amount of ABD directly onto the HOPG surface, and in contrast to the LB method, a disordered film was formed initially. The observed ordered molecular arrangement in the disordered film was effected through the action of the scanning tip. The STM images indicate that the molecular arrangement in the LB film was more compact than the tip-induced one.

Scanning Tunneling Microscopy with Atomic Resolution in Aqueous Solutions

Abstract A scanning tunneling microscope was constructed for in-situ electrochemical studies. The apparatus could provide atomic resolution of a highly oriented pyrolytic graphite (HOPG) surface in both air and aqueous solutions. The electrodeposition of platinum (Pt) on the surface of HOPG was investigated.

Ion channeling studies of regrowth kinetics of disordered surface layers on graphite

The crystallization of disordered surface layers on highly oriented pyrolytic graphite (HOPG) has been studied by Rutherford backscattering spectrometry and channeling techniques. Disordered layers (∼1000–3000 Å thick) are produced on the surface of HOPG by the implantation of various ions. The disordered layers are regrown by thermal annealing of the samples in an inert environment. Isochronal anneals reveal two distinct regrowth processes: one, a rapid process of low activation energy (Ea∼0.15 eV) which is observed primarily in regions where the disorder is sufficient to prevent the channeling of the ions, but insufficient to totally destroy the graphitic structure. This low activation energy may indicate annealing of the damage by migration of interstitials where the interstitials are the knock-on carbon atoms produced by the primary ions. A regrowth process with higher activation energy (Ea∼1.2 eV) occurs primarily in regions where the disorder is close to the saturation disorder produced by ion implantation. Both regrowth processes are epitaxial in nature and the epitaxial nature of the process may explain the much lower activation energy for three-dimensional AB layer stacking as measured in ion-implanted graphite when compared with results on the bulk graphitization of pyrocarbons. The time dependence of the annealing process shows a depth dependence and thus the regrowth cannot be uniquely interface or diffusion limited. In the case of the damaged layer produced by As ion implantation, the ability of the lattice to retain As atoms after high-temperature anneals increases with the extent of damage in the lattice. With the advent of three-dimensional ordering, most of the As is squeezed out of the lattice.

Channeling Studies of Thermal Regrowth in Ion Damaged Graphite

ABSTRACTThe crystallization of disordered surface layers on highly oriented pyrolytic graphite (HOPG) have been studied by Rutherford backscattering spectrometry (RBS) and channeling techniques. Disordered layers (~1000–3000Å thick) are produced on the surface of HOPG by the implantation of various ions. The disordered layers are regrown by thermal annealing of the samples in an inert environment. Isochronal anneals reveal two distinct regrowth processes: one, a rapid process of low activation energy (Ea ~ 0.15 eV) which is observed primarily in regions where the disorder is sufficient to prevent the channeling of the ions but insufficient to totally destroy the graphitic structure. This low activation energy may indicate annealing of the damage by migration of interstitials where the interstitials are the knock-on carbon atoms produced by the primary ions. A regrowth process with higher activation energy (Ea ~ 2.0 eV) occurs primarily in regions where the disorder is close to the saturation-disorder produced by ion implantation. Both the regrowth processes are epitaxial in nature and the epitaxial nature of the process may explain the much lower activation energy for 3D AB stacking as measured in ion implanted graphite when compared with results on the bulk graphitization of pyrocarbons.

X-ray photoelectron spectroscopy of graphite intercalated withH2SO4

A study of the electrical and chemical structure of highly-oriented-pyrolytic graphite (HOPG) electrochemically intercalated with ${\mathrm{H}}_{2}$S${\mathrm{O}}_{4}$ to stage-1 level has been carried out using x-ray photoelectron spectroscopy (XPS). The interpretation of the XPS spectra in terms of the electrical and chemical structure of the intercalated samples are enabled through a comparison with the corresponding spectra for ${\mathrm{H}}_{2}$S${\mathrm{O}}_{4}$ adsorbed on the surface of HOPG, and with the spectra of several model compounds. No evidence for the existence of isolated ${(\mathrm{S}{\mathrm{O}}_{4})}^{2\ensuremath{-}}$ ions is found. Instead, the spectroscopic data indicate that the intercalant consists of species containing a variety of ${\mathrm{S}}_{n}{{\mathrm{O}}_{4n}}^{2\ensuremath{-}}$ ions (with $ng~1$), hydrogen bonded together.