Indentation size effects in graphene oxide under suspended nanoindentation. (July 2021)

• Record Type: Journal Article
• Authors: Alejandra Huitrón Segovia, E.; Torres- Torres, D.; Raúl Pérez Higareda, J.; García-García, A.
• Is Part Of: Mechanics of materials. Volume 158(2021)
• Publication Date: 2021-07
• Subjects: Two-dimensional materials -- Graphene oxide -- Nanoindentation -- Atomic force microscopy -- Roughness -- Finite element simulation; Strength of materials -- Periodicals; Mechanics, Applied -- Periodicals; Résistance des matériaux -- Périodiques; Mécanique appliquée -- Périodiques; Mechanics, Applied; Strength of materials; Periodicals; Electronic journals; 620.11
• DOI: 10.1016/j.mechmat.2021.103875
• Languages: English
• ISSNs: 0167-6636

Abstract

Abstract: In this study, measurements of the elastic properties and the pre-stress of free-standing multilayers graphene oxide (GO) sheets were performed by suspended nanoindentation tests, using two indenter radius with values of approximately 50 nm and 636 nm, in an atomic force microscope and a triboindenter system respectively. The GO sheets were obtained by a modified Hummers' method and deposited by drop-casting method over a specialized transmission electronic microscopy (TEM) grid. The GO sheets had about 3 layers, an average area of 3 μm 2, and a roughness average, r a, of approximately 3 nm. The results showed that the GO sheets had differences in the magnitude of the mechanical properties, according to the number of layers. However, once the measurements were normalized based on their thickness, the bulk elastic modulus from both types of nanoindentation systems had a different value of approximately 130 GPa. Thus, it can be argued that also the mechanical behavior was influenced by the roughness as well as by magnitude of contact depth according to the tip radius size used. Besides, finite element (FE) simulations of both nanoindentations performed on a representative GO sheet, were carried out to verify the elastic modulus obtained experimentally, and then to approximate the pre-stresses involved in the regarding suspended nanoindentations. It was demonstrated that GO sheet roughness, as the tip radius, were also fundamental factors that played a significant role in the different mechanical properties obtained by the considered experimental and computational procedures. Graphical abstract: BRIEFS . The highest quality nanomechanical characterization of 2D-materials requires the exhaustive characterization of the samples as well as of the testing conditions. For example, test results can only be as good as the indenter and the sample surface characteristics are well known. Two kinds of indenters, an AFM cantilever, and a Berkovich indenter, were considered in the present work to quantify the effects in the mechanical properties measurement of GO samples, analyzing the combination of sample roughness and thickness with the indenter tip radius, to establish the main differences in the results that can be produced by these factors. Image 1 Highlights: The challenge of characterizing the 2D-materials mechanical performances, was treated. It was analyzed the role of the sample morphology, and the indenter conditions, for mechanical measurements of a 2D-material. The main differences during suspended nanoindentations, were produced by sample roughness and the indenter size used. The consistencies of the experimental mechanical properties were analyzed approaching the nanoindentation by FE simulation.