A team of researchers from universities around the world, led by Professor Yu Zou from the University of Toronto Engineering, has discovered a new method for controlling dislocation motion in crystalline materials using electric fields. The research, published in the journal Nature Materials, has implications for the manufacturing and properties of materials like semiconductors that are brittle and difficult to work with.
Dislocation is a linear crystallographic defect within a crystal structure that contains an abrupt change in the arrangement of atoms. This defect can affect the strength, ductility, toughness, thermal and electrical conductivities of crystalline materials like steel and silicon. In crystalline solids, good ductility and formability are generally achieved by dislocation movement. As such, metals that have highly mobile dislocations can be deformed into final products through compression, tension, rolling, and forging. However, ionic and covalent crystals generally suffer from poor dislocation mobility, making them too brittle to process using mechanical methods.
The research team used an in-situ transmission electron microscopy to observe dislocation motion in zinc sulfide, which was driven solely by an applied electric field in the absence of mechanical loading. Dislocations that carried negative or positive charges were both triggered by the electric field. The researchers observed dislocations moving back and forth while changing the direction of the electric field. They also found that the mobilities of dislocations in an electric field depend on their dislocation types.
Ph.D. candidate Mingqiang Li, the first author of the new paper, said that “this research opens the possibility of regulating dislocation-related properties, such as mechanical, electrical, thermal, and phase-transition properties, through using an electric field, rather than conventional methods.” Li added that “since most semiconductors are brittle due to their poor dislocation mobility, the electric-field-controlled dislocation motion in this new study may be used to enhance their mechanical reliability and formability.”
The study provides direct evidence of dislocation dynamics controlled by a non-mechanical stimulus, which has been an open question since the 1960s. The researchers also ruled out other effects on the dislocation motion, including Joule heating, electron wind force, and electron beam irradiation.
The research has important implications for improving the properties and manufacturing processes of typically brittle ionic and covalent crystals, including semiconductors – a crystalline material that is a central component of electronic chips used for computers and other modern devices. The electric-field-controlled dislocation motion may be used to enhance the mechanical reliability and formability of semiconductors. Additionally, the work offers an alternative method to reduce defect density in semiconductors, insulators, and aged devices that doesn’t require traditional tedious thermal annealing, which uses temperature over time to reduce defects of a material.
Zou said that “as we work towards the application of this technology, our aim is to collaborate with the materials and manufacturing industries, particularly semiconductor companies, to develop a new manufacturing process to reduce defect density and improve the properties and performance of semiconductors.” While this initial study has focused on zinc sulfide, the team is planning to explore a wide range of materials, from covalent crystals to ionic crystals.
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