Growth mechanism of silicon nanowires from nickel-coated silicon wafer

Abstract

Crystalline silicon (Si) nanowires are important building blocks in devices of photonics, quantum-dots, optoelectronics, and energy. Thermal annealing of metalcovered Si wafers gives rise to clean Si nanowires without metallic catalyst at the tip. The process does not need flammable or toxic gases. However, the growth mechanism is yet elucidated. This project grows Si nanowires by adopting the thermal annealing method: nickel (Ni) is sputtered on Si wafers as catalyst and thereafter a layer of carbon is sputtered to protect Si nanowires from oxidation during thermal annealing. Careful studies via transmission electron microscopy and selected area electron diffraction patterns elucidate the growth process and the relationship between the seeding Ni particle and the grown Si nanowire. The seeding Ni particles are embedded in the Ni-Si-O nanoclusters that are connected with the grown Si nanowires at the end of the nanowire growth. The growth orientation of Ni-seeded Si nanowires is not dictated by surface energy of the various nanocrystal planes, but follows specific structure sensitive principle with the seeding Ni nanoparticles to minimize the mismatch in lattice spacing and dihedral angle at the wire/particle interface. It is inferred that the growth orientation of Si nanowires is determined by the ordered planes of the Ni catalyst particle at the wire/particle interface. The various morphologies of the nanowires are controlled by the diameter and vibration of the Ni-Si-O droplet, the distribution of the Ni-Si, Ni-Si-O y (y≈1) and Ni-Si-O x (x≈2) phases, and the supersaturated content in the Ni-Si-O droplet. III ACKNOWLEDGEMENT I wish to deliver my most sincere and deepest gratitude to my supervisor Prof. Sam Zhang Shanyong for his effective academic advisory, continuous guidance and endless patience. Without his encouragement and care, I can't finish this tough work. I owe sincere thanks to Ms. Guo Jun and Mr. Kong Junhua from School of Material Science Engineering for their characterization assistance and constructive suggestions. Sincere thanks to all the researchers in Prof. Sam Zhang's group for their helpful discussions, suggestions and timely assistance.