Epitaxial two-layer graphene under pressure: Diamene stiffer than Diamond

Abstract

The unprecedented ultrahigh interlayer stiffness of supported two-layer epitaxial graphene on silicon carbide (SiC) has been recently reported by our research group. We found that under localized pressure a two-layer epitaxial graphene behaves as an ultra-hard and ultrastiff coating, showing exceptional mechanical properties that far exceed those of bare SiC. Density functional theory (DFT) calculations indicate that this unique behavior stems from a sp 2-to-sp 3 reversible phase transition of carbon films under compression, leading to a single-layer diamond-like structure that we called diamene. In this paper, force versus indentation depth curves from high-resolution nanoindentation experiments of CVD diamond and sapphire are carried out and compared to those obtained from two-layer epitaxial graphene on SiC. These new measurements confirm that the stiffness of epitaxial graphene is larger than that exhibited by CVD diamond and sapphire substrates. Our measurements show that areas of the film consisting of buffer layer plus one, or at most two, additional graphene layers are the ones most likely to exhibit phasechanging behaviors and larger-than-diamond stiffness.

Fully Hydrogenated and Fluorinated Bigraphenes–Diamanes: Theoretical and Experimental Studies

“…High-pressure experiments with bi-and multilayered graphanes show the formation of 2D diamond structures [56,57]. These kinds of diamanes without adsorbents on the surfaces, named diamondenes [56], could serve as diamond seeds in nanoheterostructures and rocks subjected to high pressures.…”

Layer dependence of graphene-diamene phase transition in epitaxial and exfoliated few-layer graphene using machine learning

“…The indentation modulus measured for the 2D films is compared with the stiffness of the substrate as well as the stiffness of other ultra-stiff reference materials, namely CVD (001) diamond film obtained through a HFCVD process [65], SiC (0001), and bulk (0001) sapphire [11]. The spectral clustering algorithm discussed in the Methods section is used to isolate graphene domains in phase imaging data coupled with topographic scans in both exfoliated graphene flakes and epitaxial graphene films.…”

Å-Indentation for non-destructive elastic moduli measurements of supported ultra-hard ultra-thin films and nanostructures

“…The extremely small indentation depth utilized during MoNI/ÅI has enabled for the first time the study of the transverse elasticity of few layer thick graphene films 19 . In particular, indentation depths in the order of few tenths of an Ångstrom have been employed to probe the interlayer stiffness of epitaxial graphene and epitaxial graphene oxide, and, more recently, to demonstrate the ultra-high stiffness of 2-layer epitaxial graphene 35 , 36 . These experiments showed that Van der Waals interactions between different layers play an important role in determining the stiffness of the material when a force is applied perpendicular to the principal planes of graphene.…”

“…MoNI/ÅI has recently found applications in the characterization of the mechanical properties of the transverse mechanical stiffness of supported 2D materials, and in particular supported epitaxial graphene 19 , 35 . The enhanced resolution of MoNI/ÅI has enabled for the first time the direct measurement of the inter-layer stiffness of few layer thick graphene and graphene oxide supported films 19 and has led to the discovery of the room-temperature diamondization of epitaxial bi-layer graphene on silicon carbide 35 , 36 . These measurements have been possible only due to the extremely high spatial resolution of MoNI/ÅI.…”