Acta Mechanica Sinica (2012) 28(6):1513–1527 DOI 10.1007/s10409-012-0167-7 REVIEW In situ investigation of the mechanical properties of nanomaterials by transmission electron microscopy Jun Sun Δ · Feng Xu Δ · Li-Tao Sun Δ These authors contribute to the article equally Received: 7 November 2012 / Revised: 14 November 2012 / Accepted: 8 December 2012 ©The Chinese Society of Theoretical and Applied Mechanics and Springer-Verlag Berlin Heidelberg 2012 Abstract 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 nanoscale. Keywords Nanomaterials · Transmission electron mi- croscopy · In situ · Nanoscale mechanics 1 Introduction Understanding the deformation mechanism of structures at small scales, from the micrometer to nanometer and even- tually to the atomic scales, seems to be a permanent pursuit of mankind. Historically, this reductionism gave rise to new phenomena and scientific laws, such as the dislocation The project was supported by the National Basic Research Pro- gram of China (973) (2011CB707601 and 2009CB623702), the Na- tional Natural Science Foundation of China (51071044, 61274114, 61106055 and 21243011), and Gatan Scholarship for Excellence in Science. J. Sun · F. Xu · L.-T. Sun ( ) SEU-FEI Nano-Pico Center, Key Laboratory of MEMS of Ministry of Education, Southeast University, 210096 Nanjing, China e-mail: slt@seu.edu.cn theory in metals, the crack tips in fracture mechanics, and the entropic elasticity of polymer chains [1]. In recent years, nanoscale objects have attracted increasing interest. Numer- ous studies indicate that when the characteristic structure di- mension shrinks below 100 nm, the materials display many excellent mechanical properties, which is the so-called size effect. The large number of surface atoms leads to the fre- quent occurrence of defect annealing in the internal inter- face (e.g., crystal grain boundaries) or on the specimen sur- face. Thus, the deformation mechanism differs from those of macroscopic materials. In situ microscopy, a new branch of electron microscopy, is playing an increasingly impor- tant role in investigating deformation mechanisms at the mi- croscale and mechanics in nanomaterials. A conventional textbook may indicate that electron mi- croscopy enables visual observation of the morphology and structure of nanomaterials. However, in situ electron mi- croscopy introduces the time parameter and allows us to study structural changes in real time under an external field. To apply an external field such as strain, electrical, or thermal fields, special experimental setups in the specimen cham- ber of a transmission electron microscope should be de- signed. However, the space between the pole pieces in the object lens of a commercial transmission electron micro- scope is usually less than 5 mm, which limits the dimensions of in situ test instruments. To solve this problem, special types of dedicated functional transmission electron micro- scope (TEM) specimen holders (hereafter denoted as TEM holders) with built-in integrated micro-electro-mechanical systems (MEMS) have been developed. These TEM hold- ers are now commercially available for several applications such as heating, electrical probing, straining, or mechani- cal testing. In contrast with in situ scanning electron mi- croscope (SEM), in situ TEM has a higher spatial resolu- tion and can enable the acquisition of complete informa- tion on a specimen, not only surface information. Contin-