Nanoscale Crystal Growth: The Importance of Interfaces and Phase Boundaries Kristallväxt på Nanometer Skala: Vikten av Ytor och Gränser

Sammanfattning: Surfaces and interfaces have a special significance to nanotechnology because the surface/volume ratio of nanomaterials is larger than for bulk materials. Therefore, interfaces of nanomaterials are usually more important to the properties of nanomaterials than for larger scale materials. Furthermore, crystal growth occurs at the interfaces between the growing crystals and the supply media. An understanding of the interfaces is therefore essential to understanding growth. Nanoscale crystal growth of three, two, and to some extent one-dimensional crystals has been explained in the context of crystalline interfaces. This understanding has helped improve production of nanostructures and devices that are both scientifically and commercially beneficial. This dissertation expands on the importance of interfaces and atomistic processes occurring at these interfaces; explaining the growth and control of different nanocrystals. A brief review of crystal growth terminology and theory is given. A new technology recently developed to produce compound semiconductor quantum dots is described within the context of the interfaces involved. The majority of the dissertation will focus on explaining and understanding growth of one-dimensional nanostructures, called nanowires, grown in a three-phase system. The currently accepted growth mechanism for nanowires of this type is the vapor-liquid-solid (VLS) mechanism. The VLS and similar mechanisms lack details about the atomistic processes involved in wire growth. When these atomistic processes are examined, it is revealed that there are several different names describing what are proposed to be ?different? mechanisms that in reality rely on the same atomistic processes. The key to understanding nanowire growth lies in understanding the atomistic processes occurring at the interfaces. Due to the fundamental similarities in the mechanisms with different names, the name ?Preferential Phase-Boundary Nucleation? (PPBN) is suggested as a replacement for the many different names. Unlike previous names this name is relevant to the processes as well as emphasizing the importance of the phases and the interfaces. A better understanding of interfaces and the processes that occur at them leads to a greater understanding and control of the growth of crystalline nanostructures.