Mechanical characterization of nanomaterials revealed by the microscopic nanomechanical measurement method

Mechanical properties of nanomaterials (∼10 nm or less in size) have attracted much attention for their application in nanoelectromechanical and advanced sensors. Recently, an in situ transmission electron microscope holder with a length extension resonator (LER) of quartz crystal as a force sensor, called the microscopic nanomechanical measurement (MNM) method, has been developed. It enables us to estimate not only Young's modulus but also critical shear stress for nanomaterials precisely. In this review, the principle of this novel method is introduced, and the mechanical characterization of nanomaterials revealed by this method is presented. (i) The size dependence of Young's modulus of gold nanocontacts when stretched in the [111] direction was measured, which could be explained by summing the bulk and surface Young's moduli weighted according to the ratio of internal to surface atoms. Bulk and surface Young's moduli were estimated to be 119 and 22 GPa, respectively. (ii) Young's modulus of MoS2 nanoribbons with armchair edge increased with decreasing the width, which indicated that the armchair edge bonds were stiffer than those inside the nanoribbon. (iii) By measuring the stiffness of Pt atomic chains consisting of two to five atoms, bond stiffnesses at the middle of the chain and at the connection to the base were estimated to be 25 and 23 N/m, respectively, which were higher than the bulk bond stiffness. (iv) Critical shear stress of Au nanocontacts was estimated to be 0.94 GPa by measuring the LER amplitude dependence of dissipative energy.