In situ Nanomechanical Characterization of 1-D Semiconductors

Abstract

The rapid development of one-dimensional (1-D) semiconductor materials has significantly broadened the scientific interests and emerging technological applications. In addition to traditional 1-D semiconductors such as silicon nanowire, all-inorganic perovskites, such as CsPbX₃ (X=Cl, Br, I), have recently received considerable attention due to their significantly enhanced environmental stability and retained excellent optoelectronic properties. Elastic and plastic properties of these 1-D perovskite nanostructures are crucial for their practical applications in developing high-performance flexible or deformable devices. However, mechanical study of these perovskites at micro- and nano-scale remain needed and believed to be important to understand deformation of ionic semiconductors.

Here, mechanical properties of 1-D CsPbX₃ structures (i.e. nanowires and sub-micron pillars) were characterized through in situ nanomechanical methods. The high elasticity of vapor-liquid-solid (VLS) grown single-crystalline CsPbBr₃ nanowires (NWs) were firstly demonstrated by in situ buckling experiments inside a scanning electron microscope (SEM). Tensile elastic strain of ~4% to ~5.1% can be achieved. When configured into photodetector on a flexible substrate, the CsPbBr₃ NW-based device exhibited excellent mechanical reliability after cyclic bending under maximum local tensile strain of ~3-4%, without showing any detectable performance deterioration. The defect-free single-crystalline structure and nanomechanical size effect are responsible for the significantly enhanced elasticity of single crystal NWs. This experimental result provides insights for perovskite NWs’ promising applications in flexible electronics and energy systems.

Furthermore, we discovered unprecedented ultra-high room-temperature compressive plasticity in single-crystalline CsPbX₃ sub-micron pillars, with the maximum achievable strain of ~75%; the pillars of high aspect-ratio can be strikingly deformed into various geometries such as L-shape or cubic shape. This ultra-plasticity is originated from the operation of multiple slips on equivalent {110}<1¯10> slip systems by the aid of consecutive reorientation of pillars, which could effectively eliminate shear localization and premature fracture. The extremely low generalized stacking fault energy (GSFE) of {110}<1¯10> slip system ensures abundant dislocation/slip activities. This work provides insights in understanding covalent crystal plasticity and technological guidance for the design and fabrication of CsPbX₃ devices and sheds light on its potential applications for next-generation deformable electronics.

Lastly, as one of the most important building blocks of modern electronics, 1-D silicon nanostructures, silicon nanowires (NWs) remain to be important for existing Si-based electronics and optoelectronics. The in-depth understanding of the deformation of Si NWs can also serve as a comparison because of its covalent solid nature. The mechanical properties of Si NWs have been widely studied, a noticeable discrepancy exists in the elastic strain of tensile tests that conducted inside different microscopes. Thus, it’s worthy to discuss and explore the effect of electron beam irradiation on mechanical property of Si NW. Here, the electron beam irradiation induced defects are investigated under different electron dose rates. Then, to systematically investigated the correlation between mechanical performance and radiation-induced defects, a series of in situ tensile straining experiments of silicon NWs were carried out inside TEM.

To sum up, the mechanical properties of representative ionic and covalent 1-D semiconductors were characterized through our in situ nanomechanical approach. Our experimental results uncovered the high elasticity in CsPbBr₃ NWs, ultra-plasticity in CsPbX₃ sub-micron pillars, and the electron beam-induced tunable elasticity of Si NWs. These findings provide valuable insights into the future design of flexible or deformable devices based on 1D semiconductors.

Date of Award	5 Aug 2021
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yang LU (Supervisor)