Observation and characterization by scanning tunneling microscopy of structures generated by cleaving highly oriented pyrolytic graphite

Chang, Hsiangpin; Bard, Allen J.

doi:10.1021/la00054a021

Cited by 160 publications

(137 citation statements)

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“…There are some possibilities as to how a rotation of several graphite layers can be induced, of which w e are not able to favour any. I t h a s b e e n s h o wn by other groups that this can happen during the process of cleaving with adhesive tape and successive folding back o f l a yers 21,22]. A defect in the stacking sequence can also beintroduced during the graphitization of the sample and therefore bean intrinsic property, as reported by Saadaoui et al 19].…”

Section: Resultsmentioning

confidence: 93%

Bulk defects in graphite observed with a scanning tunnelling microscope

Osing

Shvets

1998

Surface Science

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Scanning tunneling microscopy (STM) has been used to observe a misorientation of a graphite layer that is buried several layers below the surface. A nanoscale periodic pattern superimposed on the atomic graphite lattice has beenobserved. The appearance of the superperiodic features in the STM image is shown to be clearly tip-sample distance dependent. We suggest that a subsurface misorientation, several layers deep, causes a nanoscale moir e pattern, which can propagate to the surface and contributes to the STMimage. This result is rather surprising as STM is thought to be unable to image bulk defects. Key words: Scanning tunneling microscopy (STM), highly oriented pyrolytic graphite (HOPG), layered materials, moir e pattern IntroductionHighly oriented pyrolytic graphite (HOPG) is commonly used as a test and calibration standard in scanning tunneling microscopy (STM) due to its unique properties: it is atomically at, easy to clean and relatively inert, even in air. These characteristics derive from the layered structure with van der Waals forces between the graphite layers and the honeycomb arrangement of the carbon atoms with strong covalent bondswithin the plane. The stacking sequence is ABAB:::, which is of signi cance for the interpretation of STM images of this material. Atoms on hollow sites (b-sites), but not the ones that have an atom directly underneath (a-sites), contribute to the STM image due to their higher density of states around the Fermi level. Therefore the atomic lattice seen with STM is a centered hexagon with a lattice constant of 2. A. This concept was rst discussed by Tom anek and Louie 1]. Superperiodic structures (SPS) of the graphite surface under di erent conditions and a wide range of periodicities have also been reported. Near defects in the surface layer or adatoms a p 3 p 3 structure was found, caused by a perturbation of the charge density in the vicinity of these defects (Friedel oscillations) 2{4]. There is another study of superstructures near grain boundaries which are caused by multiple tips scanning on di erent grains 5]. This results in an interference pattern of the signals from the multiple tip. Many groups have reported the observation of nanoscale size superperiodic features which are not caused by defects or tip e ects 6{12]. They are not topographic either but they are mostly explained by a rotation of a graphite layer with respect to the underlying crystal, resulting in a moir e pattern. The angle of this rotation should determine the periodicity S of the patterns following the suggestion of Kuwabara et al 7]: S = d 2 sin 2 , where d is the lattice constant. By resolving the orientation of the atomic graphite lattice of the top layer and the one underneath and measuring the angle of rotation between the two this theory has been shown to be valid by Rong et al 6]. Other reports indicate that superperiodic features were observed without any misorientation between the two topmost layers 13,14], but an explanation was not given. Several authors state that the superperiod...

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Section: Resultsmentioning

confidence: 93%

Bulk defects in graphite observed with a scanning tunnelling microscope

Osing

Shvets

1998

Surface Science

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“…27,37,40,41,49,50,57,[59][60][61] Fresh surfaces of AM HOPG were also revealed by mechanically cleaving with a clean razor blade, inserted perpendicular to the basal plane with a gentle rocking motion until a small piece delaminated spontaneously, as adopted elsewhere. 27,51,62 Both procedures were used for the macroscopic studies of AM grade HOPG, with samples respectively labelled as AM S and AM M . For FSCV-SECCM measurements, the AM and SPI-3 samples were prepared via Scotch tape cleavage (AM S ), while for SECCM reactive patterning studies, mechanical cleavage was used for AM (AM M ).…”

Section: Materials and Reagentsmentioning

confidence: 99%

Molecular Functionalization of Graphite Surfaces: Basal Plane versus Step Edge Electrochemical Activity

et al. 2014

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The chemical functionalization of carbon surfaces has myriad applications, from tailored sensors to electrocatalysts. Here, the adsorption and electrochemistry of anthraquinone-2,6-disulfonate (AQDS) is studied on highly oriented pyrolytic graphite (HOPG) as a model sp 2 surface. A major focus is to elucidate whether adsorbed electroactive AQDS can be used as a marker of step edges, which have generally been regarded as the main electroactive sites on graphite electrode surfaces. First, the macroscopic electrochemistry of AQDS is studied on a range of surfaces differing in step edge density by more than 2 orders of magnitude, complemented with ex-situ tapping mode atomic force microscopy (AFM) data. These measurements show that step edges have little effect on the extent of adsorbed electroactive AQDS. Second, a new fast scan cyclic voltammetry (FSCV) protocol carried out with scanning electrochemical cell microscopy (SECCM) enables the evolution of AQDS adsorption to be followed locally on a rapid timescale. Subsequent AFM imaging of the areas probed by SECCM allows a direct correlation of the electroactive adsorption coverage and the actual step edge density of the entire working area. The amount of adsorbed electroactive AQDS and the electron transfer kinetics are independent of the step edge coverage. Last, SECCM reactive patterning is carried out with complementary AFM measurements, to probe the diffusional electroactivity of AQDS. There is essentially uniform and high activity across the basal surface of HOPG. This work provides new methodology to monitor adsorption processes at surfaces and shows unambiguously that there is no correlation between the step edge density of graphite surfaces and the observed coverage of electroactive AQDS. The electroactivity is dominated by the basal surface, and studies that have used AQDS as a marker of steps need to be revised.3

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“…This is not evident based on current knowledge of step-edge density on freshly cleaved HOPG. Indeed, early scanning tunneling microscopy (STM) of the basal surface of HOPG revealed step edge densities in the range of 1-10%, 19 and this appears to be a generally accepted range, with the step edge density depending on the source of HOPG and cleavage method. 20 We provide detailed analysis of this aspect herein.…”

Section: Introductionmentioning

confidence: 99%

A New View of Electrochemistry at Highly Oriented Pyrolytic Graphite

et al. 2012

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Major new insights on electrochemical processes at graphite electrodes are reported, following extensive investigations of two of the most studied redox couples, Fe(CN) 6 4−/3− and Ru(NH 3 ) 6 3+/2+ . Experiments have been carried out on five different grades of highly oriented pyrolytic graphite (HOPG) that vary in step-edge height and surface coverage. Significantly, the same electrochemical characteristic is observed on all surfaces, independent of surface quality: initial cyclic voltammetry (CV) is close to reversible on freshly cleaved surfaces (>400 measurements for Fe(CN) 6 4−/3− and >100 for Ru(NH 3 ) 6 3+/2+ ), in marked contrast to previous studies that have found very slow electron transfer (ET) kinetics, with an interpretation that ET only occurs at step edges. Significantly, high spatial resolution electrochemical imaging with scanning electrochemical cell microscopy, on the highest quality mechanically cleaved HOPG, demonstrates definitively that the pristine basal surface supports fast ET, and that ET is not confined to step edges. However, the history of the HOPG surface strongly influences the electrochemical behavior. Thus, Fe(CN) 6 4−/3− shows markedly diminished ET kinetics with either extended exposure of the HOPG surface to the ambient environment or repeated CV measurements. In situ atomic force microscopy (AFM) reveals that the deterioration in apparent ET kinetics is coupled with the deposition of material on the HOPG electrode, while conducting-AFM highlights that, after cleaving, the local surface conductivity of HOPG deteriorates significantly with time. These observations and new insights are not only important for graphite, but have significant implications for electrochemistry at related carbon materials such as graphene and carbon nanotubes.

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Observation and characterization by scanning tunneling microscopy of structures generated by cleaving highly oriented pyrolytic graphite

Cited by 160 publications

References 0 publications

Bulk defects in graphite observed with a scanning tunnelling microscope

Bulk defects in graphite observed with a scanning tunnelling microscope

Molecular Functionalization of Graphite Surfaces: Basal Plane versus Step Edge Electrochemical Activity

A New View of Electrochemistry at Highly Oriented Pyrolytic Graphite

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