Mechanical Characterization of Two-Segment Free-Standing ZnO Nanowires Using Lateral Force Microscopy

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Mechanical characterization of quasi one-dimensional nanostructures is vital for nanoelectromechanical systems (NEMS).
• Existing literature shows significant variability in mechanical properties like Young's modulus and fracture strength for nanowires.
• This variability stems from differences in nanowire quality, testing methodologies, and simplified mechanical models.

Purpose of the Study:

• To perform orientation-controlled bending and fracture studies on vertical zinc oxide (ZnO) nanowires.
• To accurately determine the mechanical properties of ZnO nanowires using a calibrated advanced microscopy technique.
• To investigate the factors governing the fracture behavior of ZnO nanowires.

Main Methods:

• Utilized lateral force microscopy (LFM) for mechanical testing of wet chemically grown vertical ZnO nanowires.
• Calibrated the atomic force microscope's lateral force signal using a diamagnetic levitation spring system.
• Applied a two-segment mechanical model to analyze bending curves from 14 individual nanowires.

Main Results:

• Determined an average bending modulus of 108 ± 17 GPa for ZnO nanowires, which is 23% lower than bulk ZnO.
• Observed average fracture strain and stress exceeding 3.1 ± 0.3% and 3.3 ± 0.3 GPa, respectively.
• Identified the nanowire/substrate interface quality as the primary factor governing fracture.

Conclusions:

• The calibrated LFM technique provides a reliable method for accurate mechanical characterization of vertical nanowire arrays.
• ZnO nanowires exhibit distinct mechanical properties compared to bulk material, influenced by their nanostructure.
• Interface engineering is critical for controlling the fracture behavior and enhancing the reliability of ZnO-based NEMS.