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The mechanical properties of black phosphorus (BP) nanoribbons suspended on narrow grooves are quantitatively investigated with the nanoindentation method on the basis of atomic force microscopy. The elastic moduli of BP nanoribbons are strongly related to the included angle between the lattice orientation and the groove. A theoretical model based on classical elasticity theory is established to explain the directional elastic modulus and matches well with the experimental results. The ideal elastic modulus of zigzag and armchair BP nanoribbons are about 65 and 27 GPa, respectively, and this agrees with the simulation results obtained by theoretical calculations. The obtained results in the present investigations strengthen the understanding of the fascinating anisotropic properties of BP, which would be of great help for future application of BP in flexible electronics, nanoelectromechanical systems, etc.

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Here, we propose a method to determine the thickness of the most common transition metal dichalcogenides (TMDCs) placed on the surface of transparent stamps, used for the deterministic placement of two-dimensional materials, by analyzing the red, green and blue channels of transmission-mode optical microscopy images of the samples. In particular, the blue channel transmittance shows a large and monotonic thickness dependence, making it a very convenient probe of the flake thickness. The method proved to be robust given the small flake-to-flake variation and the insensitivity to doping changes of MoS2. We also tested the method for MoSe2, WS2 and WSe2. These results provide a reference guide to identify the number of layers of this family of materials on transparent substrates only using optical microscopy. MANUSCRIPT TEXT.Since the isolation of graphene in 2004[1], the mechanical exfoliation method (also called Scotch tape method) has established itself as one of the most used techniques to produce 2D materials [2][3][4][5]. Its facile implementation combined with the high quality of the produced samples are most likely the reasons behind the success of this technique. Mechanical exfoliation, nonetheless, yields randomly distributed flakes of various thicknesses and sizes on the surface of the substrate. This limitation has been overcome to a great extent through the development of rapid methods to find and identify thin flakes based on the observation of the apparent color when they are transferred onto a SiO2/Si surface [6][7][8][9][10][11][12]. On this substrate, there is a dependency of the apparent color of the flake with its thickness due to thin-film interference effects and many