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Review Article

Mechanics of Crystalline Nanowires: An Experimental Perspective

[+] Author and Article Information
Yong Zhu

Department of Mechanical
and Aerospace Engineering,
North Carolina State University,
Raleigh, NC 27502
e-mail: yong_zhu@ncsu.edu

Manuscript received June 24, 2016; final manuscript received December 11, 2016; published online January 12, 2017. Assoc. Editor: Xiaodong Li.

Appl. Mech. Rev 69(1), 010802 (Jan 12, 2017) (24 pages) Paper No: AMR-16-1054; doi: 10.1115/1.4035511 History: Received June 24, 2016; Revised December 11, 2016

A wide variety of crystalline nanowires (NWs) with outstanding mechanical properties have recently emerged. Measuring their mechanical properties and understanding their deformation mechanisms are of important relevance to many of their device applications. On the other hand, such crystalline NWs can provide an unprecedented platform for probing mechanics at the nanoscale. While challenging, the field of experimental mechanics of crystalline nanowires has emerged and seen exciting progress in the past decade. This review summarizes recent advances in this field, focusing on major experimental methods using atomic force microscope (AFM) and electron microscopes and key results on mechanics of crystalline nanowires learned from such experimental studies. Advances in several selected topics are discussed including elasticity, fracture, plasticity, and anelasticity. Finally, this review surveys some applications of crystalline nanowires such as flexible and stretchable electronics, nanocomposites, nanoelectromechanical systems (NEMS), energy harvesting and storage, and strain engineering, where mechanics plays a key role.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Key developments in the experimental methods for measuring mechanical properties of 1D nanostructures including CNTs and crystalline NWs in the last two decades. 1: AFM lateral bending [38], 2: AFM normal bending [39], 3: nanoindentation [40], 4: AFM contact resonance [41], 5: AFM lateral bending [42], 6: AFM normal bending [43], 7: AFM nanoindentation [44], 8: thermal resonance in TEM [45], 9: electrostatic resonance in TEM [46], 10: tension in SEM [47], 11: mechanical resonance in SEM [48], 12: MEMS tension in SEM [49], 13: resonance in SEM [50], 14: MEMS tension in TEM [98], 15: tension in SEM [51,52], 16: tension and bending in SEM [53], 17: MEMS tension in SEM at high temperature [54], 18: MEMS tension (relaxation) in SEM [55], and 19: MEMS tension in SEM at high strain rate [56]

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Fig. 2

Overview of the major experimental methods for testing 1D nanostructures based on AFM: (a) contact mode, (b) lateral force mode, (c) AFM nanoindentation mode, and (d) contact resonance mode

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Fig. 3

AFM contact mode. (a) (Top) AFM cantilever deflection versus piezo-actuator position and (bottom) NW deflection at a fixed position along the NW length as a function of the applied force. Note that the NW deflection equals the piezo-actuator displacement subtracted by the AFM cantilever deflection. In the case of AFM tip directly on top of the substrate (line A), the piezo-actuator displacement equals the AFM cantilever deflection, neglecting the indentation into the substrate. (b) Deflection profile along the NW length at a constant applied force for a cantilever NW (top) and a double-clamped NW (bottom). (Reprinted with permission from Paulo et al. [43]. Copyright 2005 by American Institute of Physics).

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Fig. 4

AFM lateral force mode. Force–displacement curves during a sequence of repeated loading and unloading cycles of a Au NW. (Reprinted with permission from Wu et al. [42]. Copyright 2005 by Nature Publishing Group).

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Fig. 5

(a) Bending test. An NW clamped on a nanomanipulator probe is bent in an MEMS device. (Reprinted with permission from Cheng et al. [101]. Copyright 2015 by Nature Publishing Group.) (b) Buckling test. An NW is compressed to buckling between a nanomanipulator probe (actuator) and an AFM cantilever (load sensor) (from Ref. [53]). (c) Tension test. An NW is pulled between a nanomanipulator probe (actuator) and an AFM cantilever (load sensor). (Reprinted with permission from Zhu et al. [51]. Copyright 2009 by American Chemical Society.) (d) Resonance test. An NW clamped on a nanomanipulator probe is excited to resonance by mechanical vibration. (Reproduced with permission from Qin et al. [61]. Copyright 2012 by Wiley).

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Fig. 6

(a) Force–displacement curve in a buckling test. (Reprinted with permission from Cheng et al. [101]. Copyright 2015 by Nature Publishing Group.) (b) Stress–strain curve in a tension test. (Reprinted with permission from Zhu et al. [51]. Copyright 2009 by American Chemical Society.) (c) Amplitude–frequency curve showing a resonance peak in a resonance test. (Reprinted with permission from Chang et al. [102]. Copyright 2016 by Elsevier).

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Fig. 7

(a) An integrated MEMS testing stage for mechanical testing of single NWs (from Ref. [49]). The stage includes a thermal actuator and a capacitive load sensor with a gap in between, across which the NW sample is mounted. (b) An MEMS stage for fatigue testing. (Reprinted with permission from Hosseinian and Pierron [124]. Copyright 2013 by Royal Society of Chemistry.) Compared to the one in (a), one more capacitive sensor is included to measure sample displacement digitally. (c) An MEMS stage including an on-chip heater based on Joule heating (the boxed region in the center). (Reprinted with permission from Chang and Zhu [54]. Copyright 2013 by American Institute of Physics.) This stage features a symmetric actuator and load sensor design to ensure the same temperature at both ends of the sample.

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Fig. 8

(a) The deflection profiles along the NW sample length under AFM contact mode. (Left) For an NW with diameter of 65.9 nm (small diameter), the deflection profile was fitted best with doubly clamped boundary condition; (right) for an NW with diameter of 125.5 nm (large diameter), the deflection profile was fitted better with simply supported boundary condition. (Reprinted with permission from Chen et al. [59]. Copyright 2006 American Institute of Physics.) (b) The resonance frequency as a function of the clamp size for a ZnO NW under resonance in SEM. (Left) The resonance peaks for different clamp sizes, and (right) the resonance frequency increases with the increasing clamp size. (Reproduced with permission from Qin et al. [61]. Copyright 2012 by Wiley).

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Fig. 9

The Young's modulus of ZnO NWs as a function of the NW diameter. The stiffening size effect is more pronounced under bending (buckling) than under tension (from Ref. [53]).

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Fig. 10

(a) Elasticity size effect of Si NWs [51,67,153,161, 162165]. The data are normalized by the bulk value in the 〈111〉 orientation. (b) Elasticity size effect of ZnO NWs [50,68,95, 98,166,167]. The data are normalized by the bulk value in the [0001] orientation. (c) Elasticity size effect of Ag NWs [41,60, 102,168171]. The data are normalized by the bulk value in the 〈110〉 orientation.

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Fig. 11

Fracture strength as a function of NW diameter for (a) Si [51,88,127,189194], (b) ZnO [53,68,92,94,195], and (c) SiC. (Reprinted with permission from Cheng et al. [196]. Copyright 2014 by American Chemical Society.) (d) Ag [102,168170,197,198] and (e) Cu. (Reprinted with permission from Richter et al. [52]. Copyright 2009 by American Chemical Society).

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Fig. 12

(a) Fracture strength of Si NWs and thin films as a function of side surface area. (Reprinted with permission from Zhu et al. [51]. Copyright 2009 by American Chemical Society.) (b) Weibull statistics applied to fracture strength data of ZnO NWs correlating to surface area (left) and point defects (right). (Reprinted with permission from He et al. [210]. Copyright 2011 by American Institute of Physics).

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Fig. 13

(a) Stress–strain curve (left) and TEM image of the fracture surface (right) of a Pd NW. (Reprinted with permission from Chen et al. [218]. Copyright 2015 by Nature Publishing Group.) (b) TEM image showing two partial dislocations. (Reprinted with permission from Narayanan et al. [197]. Copyright 2015 by American Chemical Society.) (c) Stress–strain curve (left) and a sequence of SEM images showing the twin propagation and superplasticity (right) of a Au NW. (Reprinted with permission from Seo et al. [179]. Copyright 2011 by American Chemical Society).

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Fig. 14

(a) Recoverable plasticity (from Ref. [55]) and (b) Bauschinger effect (Reprinted with permission from Bernal et al. [187]. Copyright 2015 by American Chemical Society.) for pentatwinned Ag NWs.

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Fig. 15

(a) Anelastic strain as a function of recovery time for six different durations of holding time. The NW diameter was 54 nm and the initial bending strain was 1.94%. (b) A sequence of SEM images showing the recovery process of a ZnO NW after the bending load was removed. Scale bar: 2 μm. (Reprinted with permission from Cheng et al. [101]. Copyright 2015 by Nature Publishing Group).

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Fig. 16

(a) Field-effect transistors based on Ge/Si NW arrays with different channel widths that can be printed on flexible substrates. (Reprinted with permission from Fan et al. [261]. Copyright 2009 by Wiley.) (b) A 3D coiled Si NW (due to buckling) under stretching. (Reprinted with permission from Xu et al. [245]. Copyright 2011 by American Chemical Society.) (c) Resistance as a function of applied strain during loading, unloading, and reloading (left) and the schematic of the corresponding mechanism. (Reprinted with permission from Xu and Zhu [12]. Copyright 2012 by Wiley.) (d) A pressure sensor array. (Reprinted with permission from Yao and Zhu [246]. Copyright 2014 by Royal Society of Chemistry).

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Fig. 17

(a) Piezoelectric energy harvesting based on an array of ZnO NWs. (Reprinted with permission from Wang and Song [5]. Copyright 2006 by American Association for the Advancement of Science). (b) Si NW anodes exhibited near theoretical specific capacity. (Reprinted with permission from Chan et al. [8]. Copyright 2008 by Nature Publishing Group).

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Fig. 18

(a) Optical image of a buckled CdS NW (left) and the corresponding PL mapping (right). (Reprinted with permission from Sun et al. [315]. Copyright 2013 by American Chemical Society.) (b) A single ZnO NW under tension in SEM (top) and the CL signal as a function of the applied strain. (Reprinted with permission from Wei et al. [314]. Copyright 2012 by American Chemical Society).

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