In situ tensile and fracture behavior of monolithic ultra-thin amorphous carbon in TEM

Even while being important components in day-to-day life and in advanced technology, the wider application of amorphous solids is limited by their brittle behavior. Although amorphous solids have been reported to show plasticity at the nanoscale, studies have so far been limited to metallic and oxide glasses. Here, we report on the tensile and fracture behavior of monolithic ultra-thin amorphous carbon (a-C) films during in situ nanomechanical testing inside a transmission electron microscope (TEM). Our results show that ultra-thin a-C films exhibit large plastic strain under uniaxial tension while retaining high strength. Beam-off tests confirm that the plasticity is not induced by electron-beam effects during testing. Consecutive cyclic tests and Raman spectra reveal that the plasticity results from an increased nanoporosity, and graphitic cluster size increases and bond/ cluster alignments along the tensile direction occur and likely contributes to stiffening of the a-C film. Despite the large plastic strain, catastrophic failure still occurred accompanied by the formation of multiple shear bands, which has never been reported for amorphous carbon. This study serves as a basis for our better understanding of the mechanical behavior of amorphous solids such as ultra-thin a-C, and provides new opportunities in design of flexible electronics, mechanical nanocomponents, and nanocomposites