Anomalies in thickness measurements of graphene and few layer graphite crystals by tapping mode atomic force microscopy

Carbon (Impact Factor: 6.2). 12/2008; 46:1435-1442. DOI: 10.1016/j.carbon.2008.06.022
Source: arXiv


Atomic Force Microscopy (AFM) in the tapping (intermittent contact) mode is a commonly
used tool to measure the thickness of graphene and few layer graphene (FLG) flakes on silicon oxide surfaces. It is a convenient tool to quickly determine the thickness of individual FLG films. However, reports from literature show a large variation of the measured thickness of graphene layers. This paper is focused on the imaging mechanism of tapping mode AFM (TAFM) when measuring graphene and FLG thickness, and we show that at certain measurement parameters significant deviations can be introduced in the measured thickness of FLG flakes. An increase of as much as 1 nm can be observed in the measured height of FLG crystallites, when using an improperly chosen range of free amplitude values of the tapping cantilever.We present comparative Raman spectroscopy and TAFM measurements on selected single and multilayer graphene films, based on which we suggest ways to correctly measure graphene and FLG thickness using TAFM.

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    • "It was reported that large variations in the GN thickness values for similar substrates determined by different groups are result of exact setting of the scanning parameters. Error in determination of the GN thickness for the SiO2 substrate was reported as 1 nm [58]. Hence we assigned the flat GN parts as delaminated from the substrate for dGN_substrate > 2.6 nm (the GN_5, GN_6, GN_8, GN_10 samples, Table 1). "
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    ABSTRACT: Wrinkles in monolayer graphene (GN) affect the GN electronic and transport properties. Defined network of wrinkles can be reached by placing the GN on a substrate decorated with nanoparticles (NPs). In order to explain mechanism behind the topographically induced changes of the electronic structure of the GN and to correlate it with the wrinkling, correct description of the GN morphology is of high demand. We propose a methodology based on advanced analysis of atomic force microscopy (AFM) images, which enables determination of the contact/delamination of the GN from the substrate and correlation of the NP density with the character of the wrinkling. Also the relevance of detection of the NPs hidden beneath the GN layer is discussed. The study was carried out on the samples of the GN transferred on the top of SiO2/Si substrate decorated with metal-oxide NPs with nominal diameter of 6 and 10 nm. The NP density varied in the range of ∼20–450 NPs/μm2. The projected area of wrinkles increased linearly with the increasing NP density, independently on the NP diameter.
    Carbon 12/2015; 95:573-579. DOI:10.1016/j.carbon.2015.08.043 · 6.20 Impact Factor
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    • "While investigating properties and phenomena related to MLG, an accurate, easy and preferably nondestructive method that can characterize its thickness (or number of layers) is very much required. The currently available techniques are accompanied by certain drawbacks and limitations [2] [3]. In general, optical techniques offer faster and simpler avenues to tackle this problem. "
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    ABSTRACT: Abstract A simple method based on relative luminance is proposed for the rapid counting of layers in multilayer graphene. The number of graphene layers can be immediately identified by processing the acquired standard RGB images, once the one-time calibration of the entire optical system has been performed. The estimated number of layers was corroborated using the common counting methods of Raman spectroscopy and atomic force microscopy. The relative luminance method was successfully applied on both pristine and chemical vapor deposited graphene, regardless of the microscopes or even the substrates utilized, as long as there are some noticeable contrast differences.
    Carbon 11/2015; 94:646 - 649. DOI:10.1016/j.carbon.2015.07.050 · 6.20 Impact Factor
    • "Considering that AFM measurements of thickness for both pristine and oxidized forms of graphene supported onto SiO 2 /Si generally include an artifactual contribution amounting to $1 nm [53] [54], we conclude that the actual thickness of the sheets obtained from HOPG and graphite foil is not greater than about 1 nm, i.e., the sheets comprise no more than three or four monolayers . We note that such a high extent of exfoliation was attained "
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    ABSTRACT: Anodic exfoliation of graphite has emerged as an attractive method to access graphene nanosheets in large quantities, but oxidation reactions associated to this process compromise the structural quality of the resulting materials. Here, we demonstrate that the type of starting graphite material impacts the oxygen and defect content of anodically exfoliated graphenes obtained thereof. We investigated highly oriented pyrolytic graphite (HOPG) as well as graphite foil, flakes and powder as electrode in the anodic process. Importantly, materials with low levels of oxidation and disorder (similar to those typically achieved with cathodic exfoliation approaches) could be attained through proper choice of the graphite electrode. Specifically, using graphite foil afforded nanosheets of higher quality than that of HOPG-derived nanosheets. This discrepancy was interpreted to arise from the structural peculiarities of the former, where the presence of folds, voids and wrinkles would make its exfoliation process to be less reliant on oxidation reactions. Furthermore, cell viability tests carried out with murine fibroblasts on thin graphene films suggested that the anodically exfoliated graphenes investigated here (possessing low or high oxidation levels) are highly biocompatible. Overall, control upon the extent of oxidation and disorder should expand the scope of anodically exfoliated graphenes in prospective applications.
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