The growth of non-planar epitaxial nanostructures on muscovite mica via van der Waals epitaxy.

• Main Author: Muhammad Iqbal Bakti Utama.
• Other Authors: School of Physical and Mathematical Sciences
• Format: Final Year Project
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials
• Online Access: http://hdl.handle.net/10356/48720
• Institution: Nanyang Technological University

Epitaxial non-planar nanostructures such as semiconductor nanowire array may serve as a valuable platform to study various nanoscale phenomena and to develop novel device concepts with augmented performance and functionalities. However, despite the improved ability of nanostructures to relax strain elastically, a well-crystalized epitaxy of nanostructure is still strongly dependent on the lattice matching of the material with the substrate. The requirement for a suitable substrate restricts the material-substrate variations into homoepitaxy and limited combinations of heteroepitaxy. Hence, the explorations for the development of various nanowire array-based technologies are severely hampered since a myriad of interesting material properties unique to a particular compound cannot be harvested. An epitaxy mechanism called van der Waals epitaxy circumvents such limitation. By utilizing layered substrates, the heterointerface is connected via weak van der Waals interactions instead of covalent chemical bonds, as typically occurred in a conventional heteroepitaxy. Here we show that, by utilizing only (001) muscovite mica substrates in a catalyst-free vapor transport technique, the van der Waals epitaxy enabled the growth of well-crystallized nanowire arrays from various semiconductor compounds irrespective of the lattice mismatch with the substrate. We then establish the characteristics of the van der Waals epitaxy in nanowire array as a case study of non-planar nanostructures. Cross-sectional electron microscopy analysis revealed that the epitaxy is of incommensurate nature, which we believe to be responsible in alleviating the lattice matching requirement. We then extend the applicability of the van der Waals epitaxy by synthesizing non-planar, polytypic tripod nanocrystals epitaxially from II-VI semiconductors for the first time. Our results effectively illustrate the versatility of the van der Waals epitaxy to serve as a universal epitaxy strategy and the possibility for the preparation of other materials and other nanoarchitectures with higher complexity.