@article{cheng_miao_qin_li_xu_haftbaradaran_dickey_gao_zhu_2015, title={Large anelasticity and associated energy dissipation in single-crystalline nanowires}, volume={10}, ISSN={1748-3387 1748-3395}, url={http://dx.doi.org/10.1038/NNANO.2015.135}, DOI={10.1038/nnano.2015.135}, abstractNote={Anelastic materials exhibit gradual full recovery of deformation once a load is removed, leading to dissipation of internal mechanical energy. As a consequence, anelastic materials are being investigated for mechanical damping applications. At the macroscopic scale, however, anelasticity is usually very small or negligible, especially in single-crystalline materials. Here, we show that single-crystalline ZnO and p-doped Si nanowires can exhibit anelastic behaviour that is up to four orders of magnitude larger than the largest anelasticity observed in bulk materials, with a timescale on the order of minutes. In situ scanning electron microscope tests of individual nanowires showed that, on removal of the bending load and instantaneous recovery of the elastic strain, a substantial portion of the total strain gradually recovers with time. We attribute this large anelasticity to stress-gradient-induced migration of point defects, as supported by electron energy loss spectroscopy measurements and also by the fact that no anelastic behaviour could be observed under tension. We model this behaviour through a theoretical framework by point defect diffusion under a high strain gradient and short diffusion distance, expanding the classic Gorsky theory. Finally, we show that ZnO single-crystalline nanowires exhibit a high damping merit index, suggesting that crystalline nanowires with point defects are promising materials for energy damping applications.}, number={8}, journal={Nature Nanotechnology}, publisher={Springer Science and Business Media LLC}, author={Cheng, Guangming and Miao, Chunyang and Qin, Qingquan and Li, Jing and Xu, Feng and Haftbaradaran, Hamed and Dickey, Elizabeth C. and Gao, Huajian and Zhu, Yong}, year={2015}, month={Jul}, pages={687–691} }
 @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={There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices. Here we report a dislocation-mediated, time-dependent and fully reversible plastic behaviour in penta-twinned silver nanowires. In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour. Molecular dynamics simulations reveal that the observed behaviour in penta-twinned nanowires originates from the surface nucleation, propagation and retraction of partial dislocations. More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.}, 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{qin_zhu_2013, title={Temperature control in thermal microactuators with applications to in-situ nanomechanical testing}, volume={102}, ISSN={["1077-3118"]}, DOI={10.1063/1.4773359}, abstractNote={Thermal microactuators are used in many micro/nano-technologies. To circumvent undesired heating of the end effector, heat sink beams are co-fabricated with the thermal actuator and connected to the substrate. This paper reports a combined experimental and modeling study on the effect of such heat sink beams. Temperature distribution is measured and simulated using Raman scattering and multiphysics finite element method, respectively. Our results show that heat sink beams are effective in controlling the temperature of the thermal actuator. Insights on how to achieve both low temperature and large actuator displacement for in-situ mechanical testing of nanoscale specimens are provided.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Qin, Qingquan and Zhu, Yong}, year={2013}, month={Jan} }
 @article{qin_xu_cao_ro_zhu_2012, title={Measuring True Young's Modulus of a Cantilevered Nanowire: Effect of Clamping on Resonance Frequency}, volume={8}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/smll.201200314}, DOI={10.1002/smll.201200314}, abstractNote={The effect of clamping on resonance frequency and thus measured Young's modulus of nanowires (NWs) is systematically investigated via a combined experimental and simulation approach. ZnO NWs are used in this work as an example. The resonance tests are performed in situ inside a scanning electron microscope and the NWs are cantilevered on a tungsten probe by electron-beam-induced deposition (EBID) of hydrocarbon. EBID is repeated several times to deposit more hydrocarbons at the same location. The resonance frequency increases with the increasing clamp size until approaching that under the "fixed" boundary condition. The critical clamp size is identified as a function of NW diameter and NW Young's modulus. This work: 1) exemplifies the importance of considering the effect of clamping in measurements of Young's modulus using the resonance method, and 2) demonstrates that the true Young's modulus can be measured if the critical clamp size is reached. Design guidelines on the critical clamp size are provided. Such design guidelines can be extended to other one-dimensional nanostructures such as carbon nanotubes.}, number={16}, journal={Small}, publisher={Wiley}, author={Qin, Qingquan and Xu, Feng and Cao, Yongqing and Ro, Paul I. and Zhu, Yong}, year={2012}, month={May}, pages={2571–2576} }
 @article{zhu_qin_xu_fan_ding_zhang_wiley_wang_2012, title={Size effects on elasticity, yielding, and fracture of silver nanowires: In situ experiments}, volume={85}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.85.045443}, abstractNote={Thispaperreportsthequantitativemeasurementofafullspectrumofmechanicalpropertiesoffivefoldtwinned silver (Ag) nanowires (NWs), including Young’s modulus, yield strength, and ultimate tensile strength. In-situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a scanning electron microscope (SEM). Young’s modulus, yield strength, and ultimate tensile strength all increased as the NW diameter decreased. The maximum yield strength in our tests was found to be 2.64 GPa, which is about 50 times the bulk value and close to the theoretical value of Ag in the � 110� orientation. The size effect in the yield strength is mainly due to the stiffening size effect in the Young’s modulus. Yield strain scales reasonably well with the NW surface area, which reveals that yielding of Ag NWs is due to dislocation nucleation from surface sources. Pronounced strain hardening was observed for most NWs in our study. The strain hardening, which has not previously been reported for NWs, is mainly attributed to the presence of internal twin boundaries.}, number={4}, journal={PHYSICAL REVIEW B}, author={Zhu, Yong and Qin, Qingquan and Xu, Feng and Fan, Fengru and Ding, Yong and Zhang, Tim and Wiley, Benjamin J. and Wang, Zhong Lin}, year={2012}, month={Jan} }
 @article{qin_zhu_2011, title={Static Friction between Silicon Nanowires and Elastomeric Substrates}, volume={5}, ISSN={["1936-086X"]}, DOI={10.1021/nn202343w}, abstractNote={This paper reports the first direct measurements of static friction force and interfacial shear strength between silicon (Si) nanowires (NWs) and poly(dimethylsiloxane) (PDMS). A micromanipulator is used to manipulate and deform the NWs under a high-magnification optical microscope in real time. The static friction force is measured based on "the most-bent state" of the NWs. The static friction and interface shear strength are found to depend on the ultraviolet/ozone (UVO) treatment of PDMS. The shear strength starts at 0.30 MPa without UVO treatment, increases rapidly up to 10.57 MPa at 60 min of treatment and decreases for longer treatment. Water contact angle measurements suggest that the UVO-induced hydrophobic-to-hydrophilic conversion of PDMS surface is responsible for the increase in the static friction, while the hydrophobic recovery effect contributes to the decrease. The static friction between NWs and PDMS is of critical relevance to many device applications of NWs including NW-based flexible/stretchable electronics, NW assembly and nanocomposites (e.g., supercapacitors). Our results will enable quantitative interface design and control for such applications.}, number={9}, journal={ACS NANO}, author={Qin, Qingquan and Zhu, Yong}, year={2011}, month={Sep}, pages={7404–7410} }
 @article{zhu_qin_gu_wang_2010, title={Friction and Shear Strength at the Nanowire-Substrate Interfaces}, volume={5}, ISSN={["1931-7573"]}, DOI={10.1007/s11671-009-9478-4}, abstractNote={Abstract}, number={2}, journal={NANOSCALE RESEARCH LETTERS}, author={Zhu, Yong and Qin, Qingquan and Gu, Yi and Wang, Zhong Lin}, year={2010}, month={Feb}, pages={291–295} }
 @article{xu_qin_mishra_gu_zhu_2010, title={Mechanical Properties of ZnO Nanowires Under Different Loading Modes}, volume={3}, ISSN={["1998-0124"]}, DOI={10.1007/s12274-010-1030-4}, abstractNote={A systematic experimental and theoretical investigation of the elastic and failure properties of ZnO nanowires (NWs) under different loading modes has been carried out. In situ scanning electron microscopy (SEM) tension and buckling tests on single ZnO NWs along the polar direction [0001] were conducted. Both tensile modulus (from tension) and bending modulus (from buckling) were found to increase as the NW diameter decreased from 80 to 20 nm. The bending modulus increased more rapidly than the tensile modulus, which demonstrates that the elasticity size effects in ZnO NWs are mainly due to surface stiffening. Two models based on continuum mechanics were able to fit the experimental data very well. The tension experiments showed that fracture strain and strength of ZnO NWs increased as the NW diameter decreased. The excellent resilience of ZnO NWs is advantageous for their applications in nanoscale actuation, sensing, and energy conversion.}, number={4}, journal={NANO RESEARCH}, author={Xu, Feng and Qin, Qingqun and Mishra, Ashish and Gu, Yi and Zhu, Yong}, year={2010}, month={Apr}, pages={271–280} }
 @article{zhu_xu_qin_fung_lu_2009, title={Mechanical Properties of Vapor-Liquid-Solid Synthesized Silicon Nanowires}, volume={9}, ISSN={["1530-6984"]}, DOI={10.1021/nl902132w}, abstractNote={The Young's modulus and fracture strength of silicon nanowires with diameters between 15 and 60 nm and lengths between 1.5 and 4.3 mum were measured. The nanowires, grown by the vapor-liquid-solid process, were subjected to tensile tests in situ inside a scanning electron microscope. The Young's modulus decreased while the fracture strength increased up to 12.2 GPa, as the nanowire diameter decreased. The fracture strength also increased with the decrease of the side surface area; the increase rate for the chemically synthesized silicon nanowires was found to be much higher than that for the microfabricated silicon thin films. Repeated loading and unloading during tensile tests demonstrated that the nanowires are linear elastic until fracture without appreciable plasticity.}, number={11}, journal={NANO LETTERS}, author={Zhu, Yong and Xu, Feng and Qin, Qingquan and Fung, Wayne Y. and Lu, Wei}, year={2009}, month={Nov}, pages={3934–3939} }