With the progress of modern transmission elec- tron microscopy （TEM） and development of dedicated func- tional TEM specimen holders, people can now manipulate a nano-object with nanometer-range precision and simulta- neously acquire mechanical data together with atomic-scale structural information. This advanced methodology is play- ing an increasingly important role in nanomechanics. The present review summarizes relevant studies on the in situ in- vestigation of mechanical properties of various nanomateri- als over the past decades. These works enrich our knowledge not only on nanomaterials （such as carbon nanotubes, car- bon onions, boron nitride nanotubes, silicon nanowires and graphene, etc.） but also on mechanics at the nanoscate.
Because of its high compatibility with conventional microfabrication processing technology, epitaxial graphene （EG） grown on SiC shows exceptional promise for graphene-based electronics. However, to date, a detailed understanding of the transformation from three-layer SiC to monolayer graphene is still lacking. Here, we demonstrate the direct atomic-scale observation of EG growth on a SiC （11^-00） surface at 1,000℃ by in situ transmission electron microscopy in combination with ab initio molecular dynamics （AIMD） simulations. Our detailed analysis of the growth dynamics of monolayer graphene reveals that three SiC （11^-00） layers decompose successively to form one graphene layer. Sublimation of the first layer causes the formation of carbon clusters containing short chains and hexagonal rings, which can be considered as the nuclei for graphene growth. Decomposition of the second layer results in the appearance of new chains connecting to the as-formed clusters and the formation of a network with large pores. Finally, the carbon atoms released from the third layer lead to the disappearance of the chains and large pores in the network, resulting in a whole graphene layer. Our study presents a clear picture of the epitaxial growth of the monolayer graphene from SiC and provides valuable information for future developments in SiC-derived EG technology.
The transmission electron microscope(TEM)is now one of the most powerful tools for structural characterization due to its high spatial resolution,especially with the advent of the spherical aberration corrector.The interaction between electrons and specimens allows tailoring surface structures by electron irradiation.Furthermore,along with the development of special holders and specimen preparation techniques,the structural evolution of surfaces/interfaces can be dynamically monitored under external fields or reaction environments at the nanoscale,which promotes not only the establishment of the relationship between atomic structures and novel properties,but also potential applications in nanodevices.In this report,we review some of our recent results obtained by TEM,including dynamical observation of surface-mediated novel phenomena,controllable fabrication of nanostructures,and some potential applications in nanodevices.
