Scanning tunneling microscopy of various graphitic surfaces (original) (raw)
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Scanning tunnelling microscopy of oxidized graphite
Journal of Microscopy, 1988
Scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM) have been used to investigate the surface of a pyrolitic graphite oxidized in liquid phase by NaClO. Two main features of the oxidized HOPG are revealed by STM. First, a large number of steps of different heights have developed on the graphite surface. These steps can be observed by TEM on another kind of graphite, HSAG 12, but this technique cannot give any information on their heights. Another kind of defect on the previously flat surface of HOPG consists in patches where the surface is rough and perturbed. These domains are very difficult to observe by TEM due to a poor contrast. Thus for the study of surface heterogeneities intentionally created on graphite, STM, providing information along three directions, appears to be complementary of TEM which gives only images of project area.
Surface structure of donor graphite intercalation compounds by scanning tunneling microscopy
Physical review. B, Condensed matter, 1989
Scanning tunneling microscopy (STM) has been used to study the surface of C6Li as a stage-1 donor graphite intercalation compound from a submicrometer down to the atomic scale. Ordered superlattices commensurate as well as incommensurate with the graphite lattice have been observed. The measured STM corrugation at small bias voltage (&200 mV) has been found to be similar to graphite whereas at larger bias voltage a strong decrease of the corrugation was observed. This experimental result is compared with recent theoretical predictions.
Journal of Analytical Atomic Spectrometry, 1997
The interaction between solid or liquid samples on the one injection hole area and was explained by graphite redeposition. Habicht et al.12 used atomic force microscopy (AFM) for the hand and pyrolytically coated graphite or highly oriented pyrolytic graphite (HOPG) sample holders on the other hand first time to study the change of topography of PCG tube surfaces at the sub-micrometre level. A continuous roughening during electrothermal vaporization was studied. For the characterisation of the micrometer scale topographical changes of the surface was observed with the number of firings done and the size of dominant protrusions shifted towards 500 nm. occurring on these graphite surfaces as a result of solid sample evaporation, atomic force microscopy (AFM ) was used. The
A new interpretation of the scanning tunneling microscope image of graphite
Chemical Physics, 2008
In this work, highly-resolved scanning tunneling microscopy images of graphite basal plane are obtained and theoretical computations are performed to explain the resolution of only half the atoms in STM images of graphite. Our experimental and computational findings indicate that the bright elliptical spots observed in trigonal STM images of graphite may not correspond to carbon positions but to π-states localized above alternate carbon–carbon bonds. This interpretation is based on STM experiments that suggest that the elliptical shape of the bright spots may not be a tip artifact and on simulated STM images of a graphite using orthorhombic unit cells that are in excellent agreement with experimentally obtained images.
The effect of acid treatment on the surface chemistry and topography of graphite
Carbon, 2013
Highly oriented pyrolytic graphite (HOPG) samples were investigated as model catalyst supports. The surfaces were treated with dilute HCl and HNO 3 under ambient conditions and examined with atomic force microscopy and scanning tunnelling microscopy (STM) and Xray photoelectron spectroscopy (XPS). Raised features were formed on the HOPG surface after acid treatment. These protrusions were typically 4-6 nm in height and between 10 to 100 nm in width, covering 5% to 20% of the substrate for acid concentrations between 0.01 and 0.2 M. Both width and surface density of the features increases with acid concentration but the heights are not affected. STM images show that the graphite lattice extends over the protrusions indicating that the features are "blisters" on the surface rather than deposited material, a view that is supported by the XPS which shows no other significant adsorbates except for oxygen in the case of the nitric acid. We propose that penetration of the acid at defective sites leads to a decrease in the interplanar van der Waals forces and a local delamination similar to the "bubbles" reported between exfoliated graphene sheets and a substrate. These findings are important in the context of understanding how carbon supports stabilise active components in heterogeneous catalysts.
The Structure of Graphite Oxide: Investigation of Its Surface Chemical Groups
Journal of Physical Chemistry B, 2010
The structure of graphite oxide (GO) has been systematically studied using various tools such as SEM, TEM, XRD, Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), 13 C solidstate NMR, and O K-edge X-ray absorption near edge structure (XANES). The TEM data reveal that GO consists of amorphous and crystalline phases. The XPS data show that some carbon atoms have sp 3 orbitals and others have sp 2 orbitals. The ratio of sp 2 to sp 3 bonded carbon atoms decreases as sample preparation times increase. The 13 C solid-state NMR spectra of GO indicate the existence of sOH and sOs groups for which peaks appear at 60 and 70 ppm, respectively. FT-IR results corroborate these findings. The existence of ketone groups is also implied by FT-IR, which is verified by O K-edge XANES and 13 C solid-state NMR. We propose a new model for GO based on the results; sOs, sOH, and sCdO groups are on the surface.
Langmuir, 1994
Adsorption was examined on STM-characterized graphite and glassy carbon surfaces, in order to relate adsorption behavior to specific surface structures. The adsorption of four electroactive quinones was determined voltammetrically on highly ordered pyrolytic graphite (HOPG) and fractured glassy carbon (GC). The average surface coverage on HOPG was 0.25-0.50, while that on GC was 2.7-4.0, consistent with GC surface roughness. STM of a large number of defects on HOPG yielded an average defect coverage of 0.01 f 0.004, much too low to account for the observed adsorption by a simple geometric model. STM and adsorption measurements on identical HOPG surfaces showed that adsorption tracks observed defect area, but with the adsorption about 30 times higher than expected. High-resolution STM ofHOPG revealed an electronic perturbation near the step defects which was larger than the defect itself by a factor of about 8. The results are consistent with quinone adsorption to the entire electronically perturbed region rather than to only the physical defect. The results are inconsistent with an adsorption mechanism based on specific chemical sites such as oxides or surface radicals. The results imply that adsorption of quinones on GC and defective HOPG depends on an electronic effect such as an electrostatic attraction between the adsorbate and partial surface charges, rather than a specific chemical effect. (27) (a) Schlogl, R. Suq. Sci. 1987,189,861. (b) Atamny, F.; Blocker, J.; Henschke, B.; Schlogl, R.; Schedel-Niedrig, T.; Bradshaw, A. M. J. (31) Brown andYou30breported an atomic arrangement for a polished GC surface which corresponds to a x f i graphitic structure. However, because of their surface preparation and material synthesis, direct comparison to this work is questionable.
The surface energies of graphite
Carbon, 1973
A discussion is presented describing the possible influence of the internal surface energy of polycrystalline and pyrolytic graphites on three phenomena: (a) the thermodynamic "standard" state of carbon, (b) the graphitization process, and (c) the structural stability of graphites at high temperatures. In order to do this, the surface enthalpies and free energies of the basal surface and edge faces have been calculated from a number of sources, and their temperature dependence up to .WOOK discussed. Suggestions have been made for methods to measure both basal surface and "edge" surface energies more directly.
Mesoscopic structure features in synthetic graphite
Materials & Design, 2018
The mesocopic structure features in the coke fillers and binding carbon regions of a synthetic graphite grade have been examined by high resolution transmission electron microscopy (TEM) and Raman spectroscopy. Within the fillers, the three-dimensional structure is composed of crystal laminae with the basal plane dimensions (La) of hundreds nanometres, and thicknesses (Lc) of tens of nanometres. These laminae have a nearly perfect graphite structure with almost parallel c-axes, but their a–b planes are orientated randomly to form a “crazy paving” structure. A similar structure exists in the binding carbon regions, with a smaller La. Significantly bent laminae are widely seen in quinoline insoluble inclusions and the graphite regions developed around them. The La values measured by TEM are consistent with estimates from the intensity ratios of the D to G Raman peak in these regions. Atomistic modelling finds that the lowest energy interfaces in the crazy paving structure comprise 5, 6 and 7 member carbon rings. The bent laminae tend to maintain the 6 member rings, but are strained elastically. We suggest that a 7 member carbon ring leaves a cavity representing an arm-chair graphite edge contributing to the Raman spectra D peak.
Chemistry of Materials
Historically, reported values for the surface energy of graphite have covered a very wide range. Here we use finite-dilution inverse gas chromatography (FD-IGC) to show that the dispersive component of the surface energy of graphite has contributions from edge and basal plane defects as well as from the hexagonal carbon lattice. The surface energy associated with the defect-free hexagonal lattice is measured at high probe-coverage to be 63±7 mJ/m 2 , independent of graphite type. However, the surface energy measured at low probe coverage varied from 125-175 mJ/m 2 depending on the graphite type. Simulation of the FD-IGC output for different binding site distributions allows us to associate this low-coverage surface energy with the binding of probe molecules to high energy defect sites. Importantly, we find the rate of decay of surface energy with probe coverage to carry information about the defect density. By analysing the dependence of these properties on flake size, it is possible to separate out the contributions of edge and basal plane defects, estimating the basal plane defect content to be ~10 15 m-2 for all graphite samples. Comparison with simulation gives some insights to the basal plane and defect binding energy distributions.