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. 2021 Feb 28;12(3):248.
doi: 10.3390/mi12030248.

Mechanical/Electrical Characterization of ZnO Nanomaterial Based on AFM/Nanomanipulator Embedded in SEM

Mei Liu  1 , Weilin Su  1 , Xiangzheng Qin  1 , Kai Cheng  1 , Wei Ding  1 , Li Ma  1 , Ze Cui  1 , Jinbo Chen  1 , Jinjun Rao  1 , Hangkong Ouyang  1 , Tao Sun  1
Affiliations

Mechanical/Electrical Characterization of ZnO Nanomaterial Based on AFM/Nanomanipulator Embedded in SEM

Mei Liu et al. Micromachines (Basel). .

Abstract

ZnO nanomaterials have been widely used in micro/nano devices and structure due to special mechanical/electrical properties, and its characterization is still deficient and challenging. In this paper, ZnO nanomaterials, including nanorod and nanowire are characterized by atomic force microscope (AFM) and nanomanipulator embedded in scanning electron microscope (SEM) respectively, which can manipulate and observe simultaneously, and is efficient and cost effective. Surface morphology and mechanical properties were observed by AFM. Results showed that the average Young's modulus of ZnO nanorods is 1.40 MPa and the average spring rate is 0.08 N/m. Electrical properties were characterized with nanomanipulator, which showed that the ZnO nanomaterial have cut-off characteristics and good schottky contact with the tungsten probes. A two-probe strategy was proposed for piezoelectric property measurement, which is easy to operate and adaptable to multiple nanomaterials. Experiments showed maximum voltage of a single ZnO nanowire is around 0.74 mV. Experiment criteria for ZnO manipulation and characterization were also studied, such as acceleration voltage, operation duration, sample preparation. Our work provides useful references for nanomaterial characterization and also theoretical basis for nanomaterials application.

Keywords: ZnO; atomic force microscope; mechanical/electrical characterization; nanomanipulator; piezoelectric property.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Equivalent electric circuit of metal-semiconductor-metal structure. (a) Probe is marked in blue. When semiconductor ZnO nanorod come into contact with probe electrode, a barrier is formed at the contact point which is called depletion layer. (b) Three resistors in the circuit. RD1 and RD2 are resistance of the depletion layer, Rs is resistance of the ZnO nanorod.
Figure 2
Figure 2
Principle of piezoelectric properties characterization. Yellow rectangle represents a single ZnO nanowire. ZnO nanowire deforms when pressed by probe which is marked in blue. Two probes contact ZnO nanowire to form an electrical circuit. A digital multimeter measures voltage generated by ZnO nanowire deformation.
Figure 3
Figure 3
Force interaction between probe and nanorods with different interaction angles.
Figure 4
Figure 4
Mechanical/electrical characterization experimental apparatus. On the left is the electrical/piezoelectric characterization system (The point that a probe contacts ZnO nanorods is called irradiation point, as red dotted line marks), in the middle is the SEM, and on the right is the morphology and mechanical characterization system.
Figure 5
Figure 5
ZnO nanorods and ZnO nanowires. (a) ZnO nanorod marked by blue dotted line is suitable for operation and observation and marked by red dotted line means stacked ZnO nanorods. (b) ZnO nanowires marked by red dotted line are sample for piezoelectric properties characterization.
Figure 6
Figure 6
Release/adsorption probability vs. irradiation time between probe and nanorod. Contact strategy 3 was used. SEM acceleration voltage is 5 kV. Adsorption probability reached over 95% when contact time exceeds 4 minutes.
Figure 7
Figure 7
Morphology and mechanical properties of ZnO nanorods in the range of 2 µm × 2 µm. (a) AFM is scanning a single ZnO nanorod. (b) Morphology of an observed nanorod.
Figure 8
Figure 8
I-V curve of three groups of nanorods. Curve 1, curve 2 and curve 3 correspond to ZnO nanorods with length of 10 µm, 20 µm and 30 µm respectively, with same diameters of 2 µm. The three I-V curves are nearly symmetrical, which indicates that ZnO nanorods and probe form almost equal contact barriers between the forward bias junction and reverse bias junction.
Figure 9
Figure 9
Electrical conductivity measurement. (a–c) Lengths of ZnO nanowires are 20.9, 30.9, 40.9 µm with same diameters of 1.06 µm. (d) Blue bars represent resistance and red bars represent electrical conductivity correspond to ZnO nanowires with length of 20.9 µm, 30.9 µm and 40.9 µm.
Figure 10
Figure 10
Piezoelectric characteristic measurement. (a) ProbeⅡgets close to ZnO nanowire. (b) ProbeⅡtouches and picks up ZnO nanowire. (c) ProbeⅡtakes the nanowire away from the tape. (d) ProbeⅠdeforms the nanowire. (e) Piezoelectric voltage vs. deformation. Deformation ranges from 0 to 6 µm. Accordingly, the output voltage varies from 0 to 0.74 mV. n = 15.
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