@article{cheng_yin_li_chang_richter_gao_zhu_2020, title={In-situ TEM study of dislocation interaction with twin boundary and retraction in twinned metallic nanowires}, volume={196}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2020.06.055}, abstractNote={Metallic nanowires (NWs) with twin boundaries (TBs) running parallel to the NW length direction exhibit unusual plastic strain recovery owing to the interaction of dislocations with TBs. Here, based on in-situ transmission electron microscopy nanomechanical testing and molecular dynamics simulations, we report observation and quantification of dislocation nucleation, interaction with TBs, and retraction in bi-twinned Ag NWs with a single TB along the NW length direction. Our results show that leading partial dislocations nucleated from the free surface can be hindered by the TB, and upon unloading all or part of the leading partials can retract due to the repulsive force from the TB, leading to full or partial plastic strain recovery (Bauschinger effect), respectively. The bi-twinned Ag NWs can undergo stress relaxation, even at a stress below the yield strength, where the plastic strain also recovers upon unloading. The relaxation and recovery behaviors are compared to those of penta-twinned Ag NWs. Our results illustrate that the internal TBs in NWs can interact with surface-nucleated dislocations, leading to time-dependent plastic strain recovery and Bauschinger effect.}, journal={ACTA MATERIALIA}, author={Cheng, Guangming and Yin, Sheng and Li, Chengjun and Chang, Tzu-Hsuan and Richter, Gunther and Gao, Huajian and Zhu, Yong}, year={2020}, month={Sep}, pages={304–312} }
 @article{yin_cheng_chang_richter_zhu_gao_2019, title={Hydrogen embrittlement in metallic nanowires}, volume={10}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-019-10035-0}, abstractNote={Abstract}, journal={NATURE COMMUNICATIONS}, author={Yin, Sheng and Cheng, Guangming and Chang, Tzu-Hsuan and Richter, Gunther and Zhu, Yong and Gao, Huajian}, year={2019}, month={May} }
 @article{cheng_zhang_chang_liu_chen_lu_zhu_zhu_2019, title={In Situ Nano-thermomechanical Experiment Reveals Brittle to Ductile Transition in Silicon Nanowires}, volume={19}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.9b01789}, abstractNote={Silicon (Si) nanostructures are widely used in microelectronics and nanotechnology. Brittle to ductile transition in nanoscale Si is of great scientific and technological interest, but this phenomenon and its underlying mechanism remain elusive. By conducting in situ temperature-controlled nanomechanical testing inside a transmission electron microscope (TEM), here we show that the crystalline Si nanowires under tension are brittle at room temperature, but exhibit ductile behavior with dislocation-mediated plasticity at elevated temperatures. We find that reducing the nanowire diameter promotes the dislocation-mediated responses, as shown by 78 Si nanowires tested between room temperature and 600 K. In situ high resolution TEM imaging and atomistic reaction pathway modeling reveal that the unconventional ½〈110〉{001} dislocations become highly active with increasing temperature and thus play a critical role in the formation of deformation bands, leading to transition from brittle fracture to dislocation-mediated failure in Si nanowires at elevated temperatures. This study provides quantitative characterization and mechanistic insight for the brittle to ductile transition in Si nanostructures.}, number={8}, journal={NANO LETTERS}, author={Cheng, Guangming and Zhang, Yin and Chang, Tzu-Hsuan and Liu, Qunfeng and Chen, Lin and Lu, Wei D. and Zhu, Ting and Zhu, Yong}, year={2019}, month={Aug}, pages={5327–5334} }
 @article{cheng_yin_chang_richter_gao_zhu_2017, title={Anomalous Tensile Detwinning in Twinned Nanowires}, volume={19}, ISSN={["1079-7114"]}, DOI={10.1103/physrevlett.119.256101}, abstractNote={In spite of numerous studies on mechanical behaviors of nanowires (NWs) focusing on the surface effect, there is still a general lack of understanding on how the internal microstructure of NWs influences their deformation mechanisms. Here, using quantitative in situ transmission electron microscopy based nanomechanical testing and molecular dynamics simulations, we report a transition of the deformation mechanism from localized dislocation slip to delocalized plasticity via an anomalous tensile detwinning mechanism in bitwinned metallic NWs with a single twin boundary (TB) running parallel to the NW length. The anomalous tensile detwinning starts with the detwinning of a segment of the preexisting TB under no resolved shear stress, followed by the propagation of a pair of newly formed TB and grain boundary leading to a large plastic deformation. An energy-based criterion is proposed to describe this transition of the deformation mechanism, which depends on the volume ratio between the two twin variants and the cross-sectional aspect ratio.}, number={25}, journal={PHYSICAL REVIEW LETTERS}, author={Cheng, Guangming and Yin, Sheng and Chang, Tzu-Hsuan and Richter, Gunther and Gao, Huajian and Zhu, Yong}, year={2017}, month={Dec} }
 @article{chang_cheng_li_zhu_2016, title={On the size-dependent elasticity of penta-twinned silver nanowires}, volume={8}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2016.03.007}, abstractNote={Penta-twinned metallic NWs have recently received much attention due to their excellent mechanical properties. However, their elasticity size effect remains not well understood due to the large discrepancy in the reported experimental and simulation results. This paper reports an experimental effort to address the discrepancy about the size-dependent Young’s modulus of penta-twinned Ag NWs. Two independent experiments on the same NW, in-situ resonance test and tensile test in a scanning electron microscope, were used to measure the Young’s moduli. The cross-sectional shape of the Ag NWs was found to transit from pentagon to circle with decreasing NW diameter, which can modify the Young’s modulus as much as 8% (for resonance test) and 19% (for tensile test) for the tested diameter range. This work confirmed that the Young’s modulus of penta-twinned Ag NWs increases with decreasing NW diameter.}, journal={EXTREME MECHANICS LETTERS}, author={Chang, Tzu-Hsuan and Cheng, Guangming and Li, Chengjun and Zhu, Yong}, year={2016}, month={Sep}, pages={177–183} }
 @misc{zhu_chang_2015, title={A review of microelectromechanical systems for nanoscale mechanical characterization}, volume={25}, ISSN={["1361-6439"]}, DOI={10.1088/0960-1317/25/9/093001}, abstractNote={A plethora of nanostructures with outstanding properties have emerged over the past decades. Measuring their mechanical properties and understanding their deformation mechanisms is of paramount importance for many of their device applications. To address this need innovative experimental techniques have been developed, among which a promising one is based upon microelectromechanical systems (MEMS). This article reviews the recent advances in MEMS platforms for the mechanical characterization of one-dimensional (1D) nanostructures over the past decade. A large number of MEMS platforms and related nanomechanics studies are presented to demonstrate the unprecedented capabilities of MEMS for nanoscale mechanical characterization. Focusing on key design considerations, this article aims to provide useful guidelines for developing MEMS platforms. Finally, some of the challenges and future directions in the area of MEMS-enabled nanomechanical characterization are discussed.}, number={9}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Zhu, Yong and Chang, Tzu-Hsuan}, year={2015}, month={Sep} }
 @article{qin_yin_cheng_li_chang_richter_zhu_gao_2015, title={Recoverable plasticity in penta-twinned metallic nanowires governed by dislocation nucleation and retraction}, volume={6}, ISSN={["2041-1723"]}, DOI={10.1038/ncomms6983}, abstractNote={Abstract}, journal={NATURE COMMUNICATIONS}, author={Qin, Qingquan and Yin, Sheng and Cheng, Guangming and Li, Xiaoyan and Chang, Tzu-Hsuan and Richter, Gunther and Zhu, Yong and Gao, Huajian}, year={2015}, month={Jan} }
 @article{cheng_chang_qin_huang_zhu_2014, title={Mechanical Properties of Silicon Carbide Nanowires: Effect of Size-Dependent Defect Density}, volume={14}, ISSN={["1530-6992"]}, DOI={10.1021/nl404058r}, abstractNote={This paper reports quantitative mechanical characterization of silicon carbide (SiC) nanowires (NWs) via in situ tensile tests inside scanning electron microscopy using a microelectromechanical system. The NWs are synthesized using the vapor-liquid-solid process with growth direction of ⟨111⟩. They consist of three types of structures, pure face-centered cubic (3C) structure, 3C structure with an inclined stacking fault (SF), and highly defective structure, in a periodic fashion along the NW length. The SiC NWs are found to deform linear elastically until brittle fracture. Their fracture origin is identified in the 3C structures with inclined SFs, rather than the highly defective structures. The fracture strength increases as the NW diameter decreases from 45 to 17 nm, approaching the theoretical strength of 3C SiC. The size effect on fracture strength of SiC NWs is attributed to the size-dependent defect density rather than the surface effect that is dominant for single crystalline NWs.}, number={2}, journal={NANO LETTERS}, author={Cheng, Guangming and Chang, Tzu-Hsuan and Qin, Qingquan and Huang, Hanchen and Zhu, Yong}, year={2014}, month={Feb}, pages={754–758} }
 @article{chang_zhu_2013, title={A microelectromechanical system for thermomechanical testing of nanostructures}, volume={103}, ISSN={["1077-3118"]}, DOI={10.1063/1.4858962}, abstractNote={We report an integrated microelectromechanical system (MEMS) with an on-chip heater for in-situ mechanical testing of nanostructures from room to elevated temperatures. Multiphysics simulation is used to predict the temperature distribution in air and vacuum conditions. The temperature simulation in air agrees well with the measurement based on Raman spectroscopy. Mechanical testing of single crystalline silicon nanowires is carried out to investigate the brittle-to-ductile transition, demonstrating the efficacy of the MEMS stage. The stage reported here could be applied to investigate the temperature effect on mechanical properties at the nanoscale.}, number={26}, journal={APPLIED PHYSICS LETTERS}, author={Chang, Tzu-Hsuan and Zhu, Yong}, year={2013}, month={Dec} }