The Essential Role of Cu Vapor for the Self-Limit Graphene via the Cu Catalytic CVD Method

Because of the inconsistent observations, the Cu catalytic decomposition of methane for graphene synthesis is reexamined, i.e., via the surface absorption, decomposition to atomic carbon, and segregation. Here, we experimentally show the quantity of ambient Cu vapor is the key factor in graphene synthesis, which influences the dropwise condensations for airborne Cu clusters during growth. The massive carburization in Cu clusters and the calculation of carbon solubility in nanosized clusters are performed, experimented, and further examined from the growth of diamond-like-carbon films and ball-like diamonds via Cu vapor assisted growth on SiO₂. The affinitive interactions between Cu vapor, ambient gases, and solid surface are embodied. By combining the molecular dynamics for the redeposited Cu clusters to surface, the vehicle theory of Cu clusters, which transports the atomic carbon to the surface and completes the graphene growth, is thus proposed as the essential puzzle we considered

Complete Replacement of Metal in Metal Oxide Nanowires via Atomic Diffusion: In/ZnO Case Study

Atomic diffusion is a fundamental process that dictates material science and engineering. Direct visualization of atomic diffusion process in ultrahigh vacuum in situ TEM could comprehend the fundamental information about metal–semiconductor interface dynamics, phase transitions, and different nanostructure growth phenomenon. Here, we demonstrate the in situ TEM observations of the complete replacement of ZnO nanowire by indium with different growth directions. In situ TEM analyses reveal that the diffusion processes strongly depend and are dominated by the interface dynamics between indium and ZnO. The diffusion exhibited a distinct ledge migration by surface diffusion at [001]-ZnO while continuous migration with slight/no ledges by inner diffusion at [100]-ZnO. The process is explained based on thermodynamic evaluation and growth kinetics. The results present the potential possibilities to completely replace metal-oxide semiconductors with metal nanowires without oxidation and form crystalline metal nanowires with precise epitaxial metal–semiconductor atomic interface. Formation of such single crystalline metal nanowire without oxidation by diffusion to the metal oxide is unique and is crucial in nanodevice performances, which is rather challenging from a manufacturing perspective of 1D nanodevices