With the continued miniaturization of micro/nanoelectromechanical systems and advanced interconnect devices, the structural stability and functional reliability of metallic nanomaterials under extreme conditions face increasingly severe challenges. In these micro/nanodevices, the stresses experienced by materials can easily exceed their yield strength, triggering irreversible plastic deformation. Even extremely small plastic strains can induce the initiation and propagation of fatigue cracks, ultimately leading to catastrophic functional failure of the device. Therefore, achieving early identification and accurate assessment of plastic deformation at the micro/nano scale is of vital importance for predicting material failure and ensuring the operational safety of systems. Although electrical impedance changes, as a non-destructive and sensitive parameter, have been widely used for structural damage monitoring at the macroscale, their application in the field of micro/nanodevices remains difficult.

The core challenge currently facing this field is the lack of sufficiently sensitive real-time quantitative monitoring methods to establish a direct link between incipient plastic events and electrical responses. In traditional bulk materials, plastic deformation typically involves the collective motion of a vast number of defects, making the resistance change caused by a single discrete plastic event extremely weak, completely淹没 in the huge background resistance and measurement noise, making early critical damage processes difficult to capture. In addition, although researchers generally recognize that defects such as twins lead to increased resistance, there is still a lack of systematic and in-depth research and quantitative characterization regarding the essential differences in electron transport properties between different types of twin boundaries in nanowires, such as coherent twin boundaries and incoherent twin boundaries, as well as the specific effects of discrete twin dynamics on electrical properties.

In response to the above issues, a team including Wuhan University conducted systematic research using ZEPTOOLS' in-situ TEM measurement system. By synchronizing in-situ transmission electron microscopy with real-time resistance monitoring, the team established, for the first time, a quantitative link between atomic-scale deformation dynamics and electrical responses, successfully achieving precise identification and quantitative diagnosis of different defect evolutions and discrete twin dynamics.

Title: Real‐Time Electrical Monitoring of Plastic Deformation in Tungsten Nanowires
Journal: Advanced Functional Materials
URL: https://doi.org/10.1002/adfm.76097

To elucidate the early damage mechanisms in nanodevices, the research team first focused on the quantitative impact of full dislocation slip on the electrical response of body-centered cubic tungsten nanowires. During uniaxial compression, when the stress reaches a critical value, full dislocations nucleate from the nanowire surface and glide along specific slip systems to the opposite side, leaving single-atom-layer steps on the surface. This change in microscopic geometry is macroscopically manifested directly as a step-like sudden drop in resistance, with a single dislocation slip event measured experimentally causing a resistance decrease of approximately 1.6%. Theoretical resistance changes calculated using an ideal volume-conserving geometric model showed high consistency with the experimental observations, strongly demonstrating that the microscopic geometric variable cross-section effect caused by a single full dislocation slip is the dominant mechanism driving the stepwise resistance decrease in the initial stage of nanowires.

After clarifying the slip mechanism, the research team turned their attention to the deformation twinning nucleation process, which is more damaging to electrical performance. Compared to the modest resistance decrease caused by dislocation slip, the nucleation and instantaneous propagation of twins, due to the introduction of new internal defect interfaces, cause a dramatic step-like surge in nanowire resistance, with a relative increase as high as 36.7% measured experimentally. Using first-principles transport calculations, the researchers found that the electron transmission coefficient in the twinning nucleation region decreased significantly near the Fermi level. This finding indicates that the resistance surge caused by twinning nucleation does not originate from changes in external geometry, but rather from the strong scattering of conduction electrons by the newly formed twin boundaries, thus quantitatively revealing, in essence, the destructive damage mechanism of twin defects on the electrical transport performance of nanodevices.

Since atomic-scale plastic deformation events occur extremely rapidly and are highly concealed, capturing these transient processes places stringent demands on the stability and resolution of characterization instruments. In this study, the researchers welded body-centered cubic tungsten nanotips and fabricated them into dog-bone-shaped nanowires, which were then loaded onto ZEPTOOLS' in-situ TEM sample holder for high-precision micromechanical compression experiments. Through precise control by this instrument, the nanowires underwent plastic deformation at a stable strain rate, while the system's extremely low background measurement noise was far smaller than the discrete electrical signals generated by plastic deformation, ensuring perfect synchronization between high-resolution transmission electron microscopy images and real-time recorded resistance data on the time axis. The application of ZEPTOOLS' in-situ measurement platform completely eliminated interference from instrument noise and contact instability, providing the most critical, high-fidelity data support for subsequent analysis of complex twin boundary dynamic evolution.

Based on the above highly reliable in-situ experimental platform, the research team further explored the more complex mechanisms of twin boundary dynamic migration and structural transformation. During the twin growth stage, conventional layer-by-layer stacking fault expansion produces continuous changes in the nanowire aspect ratio, corresponding to smooth, continuous resistance change curves. However, discrete twin growth mediated by screw dislocation cross-slip and dissociation triggers unique stepwise resistance drops through abrupt changes in the morphology of incoherent twin boundaries. By combining microscopic images and theoretical calculations, the research team quantitatively determined that the inclined incoherent twin boundary, due to its higher density of states near the Fermi level, has a specific resistivity of only 5.22 × 10^-12 Ω cm², significantly lower than that of the coherent twin boundary. The discovery of this electrical characteristic not only successfully distinguished continuous twin thickening from discrete evolution dynamics through clear electrical signals, but also established a new methodology for online diagnosis of complex twin dynamics in low-dimensional metals simply through macroscopic electrical measurements.

ZEPTOOLS, as a Chinese high-end precision instrument company, is a leading supplier of in-situ electron microscopy characterization solutions. Its PicoFemto series of in-situ transmission electron microscopy characterization solutions have successively provided technical support for significant research results from both domestic and international users. The following image shows the ZEPTOOLS in-situ TEM sample holder product used in this research:

JEOL-Compatible In-Situ Probe Holder