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European Microscopy Congress 2020 Abstract Database

Mechanical properties of Au nano-contacts measured by TEM combined with quartz resonator force sensor

Mechanical properties of Au nano-contacts measured by TEM combined with quartz resonator force sensor

Session

PSA.1 - 1D & 2D Materials

Authors

Dr. Keisuke Ishizuka (1), Prof. Masahiko Tomitori (1), Prof. Toyoko Arai (2), Prof. Yoshifumi Oshima (1)

Affiliations

1. JAIST
2. Kanazawa Univ.

Keywords

TEM

nanocontact

AFM

Young's modulus

mechanical property

in-situ TEM

Abstract text

Mechanical properties of nano-contacts (NCs) have attracted much interest, which are expected to depend on size, shape and crystal orientation due to surface effect and/or quantum confinement. In molecular dynamical calculation, Au NCs have been suggested to show various deformation processes (plastic property) depending on the orientation of the axis. Also, the Young’s modulus (elastic property) depended on the orientation of the axis. However, such size dependence have been rarely investigated experimentally. Because it is difficult to measure structure and mechanical response of metal NC at the same time, which is necessary to evaluate the mechanical properties. 

In this study, we developed a TEM holder equipped with a quartz length extension resonator (LER) as a force sensor (Fig.1) [1,2]. LER has high spring constant (7×10⁵ N/m) and high Q-factor so that it can ignore the deformation of LER due to the interaction with the NC. The spring constant of the NC (k_NC) is precisely obtained from the resonance frequency shift (Δf) in frequency modulation method as the following formula, , where is a resonant frequency of LER. For measurement of the mechanical response, LER must be oscillated, but its amplitude can be set to less than100 pm, which enable us to avoid plastic deformation of Au NC or distortion of TEM image when measuring the spring constant.

Figure 2 shows a typical time evolution of electrical conductance and spring constant during stretching Au NC and a series of TEM images taken at 150, 75, 50 and 30 G₀ (=2e²/h, quantized unit of condutance; e is elemental charge and h is plank constant) in conductance. Structural information such as shape, crystal orientation and contact length was obtained in the TEM image. The cross-sectional area of the thinnest part of Au NC was determined from the measured conductance value. The measured spring constant, k_m, can be regarded as a series coupling of a spring of the Au NC, k_NC, and the springs of two Au bases, k_b, as follows,

1/k_m=1/k_NC+1/k_b,             (1)

Thus, the spring constant of the thinning Au NC was extracted by subtracting the spring constant of Au wire (base), measured just before the formation of Au NC, from the measured spring constant. From the extracted spring constants of the Au NCs as a function of radius r of the minimum cross section, the Young’s moduli of the Au NC having the axis of the [110] direction could be estimated to be 85 GPa. [2].

References

[1] J. Zhang et al., Nanotechnology (2020) doi.org/10.1088/1361-6528/ab71b9

[2] K. Ishizuka et al., APEX 13 (2020) 025001.