Nanomechanics of few-layer materials: do individual layers slide upon folding?

Abstract

Folds naturally appear on nanometrically thin materials, also called “2D materials”, after exfoliation, eventually creating folded edges across the resulting flakes. We investigate the adhesion and flexural properties of single-layered and multilayered 2D materials upon folding in the present work. This is accomplished by measuring and modeling mechanical properties of folded edges, which allows for the experimental determination of the bending stiffness (κ) of multilayered 2D materials as a function of the number of layers (n). In the case of talc, we obtain κ ∝ n 3 for n ≥ 5, indicating no interlayer sliding upon folding, at least in this thickness range. In contrast, tip-enhanced Raman spectroscopy measurements on edges in folded graphene flakes, 14 layers thick, show no significant strain. This indicates that layers in graphene flakes, up to 5 nm thick, can still slip to relieve stress, showing the richness of the effect in 2D systems. The obtained interlayer adhesion energy for graphene (0.25 N/m) and talc (0.62 N/m) is in good agreement with recent experimental results and theoretical predictions. The obtained value for the adhesion energy of graphene on a silicon substrate is also in agreement with previous results.

Raman and Far-Infrared Synchrotron Nanospectroscopy of Layered Crystalline Talc: Vibrational Properties, Interlayer Coupling, and Symmetry Crossover

“…Monolayer (1L) and few-layer (FL) talc have recently revealed interesting magnetic, optical, − electrical, ,,, and mechanical ,− properties as a single material and when combined with other LMs in van der Waals heterostructures (vdWHs). Although the structural properties of talc have been investigated previously, ,,− ,, to the best of our knowledge, no work has fully described its Raman and far-infrared (Far-IR) active modes in the ultrathin form (Figure d) as a function of layer thickness.…”

Phyllosilicates as earth-abundant layered materials for electronics and optoelectronics: Prospects and challenges in their ultrathin limit

“…In this case, other theoretical techniques must be used. For instance, universal nanomechanical properties of suspended 113 and deposited 114 nanosheets of FL-phyllosilicates could only be theoretically analyzed through a combination of molecular dynamics and continuum-model methods. This indicates that future perspectives in this area might involve multi-scale theoretical investigations.…”

Review on infrared nanospectroscopy of natural 2D phyllosilicates

“…One of the most efficient ways to access a material structure and chemistry is to probe its natural vibrational activity [10,[19][20][21][22]. Thus, a systematical way to study the vibrational assignments of minerals in their FL form, which have a low response to excitation, is to use tip-enhanced techniques [23][24][25][26]. Since the small amount of material results in a low signal response in techniques with resolution at the microscale such as standard Fourier-transform infrared (FTIR) and Raman spectroscopy, scattering-type scanning near-field optical microscopy (s-SNOM) is a powerful alternative to overcome this diffraction limit [26][27][28] and, therefore, a tool able to characterize 2D materials composition and optical response at the nanometer scale [29].…”