Ordered CaSi₂ Microwall Arrays on Si Substrates Induced by the Kirkendall Effect

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Controlling the growth of ordered microstructures is crucial for advanced material applications.
• Reactive deposition epitaxy (RDE) is a technique used for material synthesis.
• The Kirkendall effect, related to diffusion in materials, can influence microstructure formation.

Purpose of the Study:

• To develop a method for synthesizing one-directionally ordered calcium silicide (CaSi2) microwall arrays.
• To investigate the role of the Kirkendall effect in controlling the vertical growth of CaSi2 on silicon.
• To identify key parameters for achieving controlled CaSi2 microstructure.

Main Methods:

• Utilizing the Kirkendall effect within reactive deposition epitaxy (RDE).
• Employing a significantly larger calcium vapor supply than conventional RDE.
• Implementing a two-step heating process.
• Selecting specific crystal orientations of the silicon (Si) substrate surface.

Main Results:

• Achieved one-directionally ordered CaSi2 microwall arrays vertically grown on a Si substrate.
• Identified that increased Ca vapor supply, a two-step heating process, and Si surface crystal axis selection are critical for controlling CaSi2 microstructure.
• Observed the formation of CaSi phase followed by CaSi2 phase at the CaSi/Si interface.
• Demonstrated that the Kirkendall effect enhances vertical interdiffusion of Ca and Si.
• Found that CaSi2 preferentially grows along the Si(111‾ ) plane, enabling nearly vertical growth.

Conclusions:

• The Kirkendall effect, under asymmetric growth conditions, is an effective strategy for obtaining ordered microstructures.
• Optimized synthetic conditions allow for precise control over CaSi2 microwall array morphology.
• This approach offers a pathway for fabricating vertically aligned nanostructures for potential electronic and photonic applications.