Sequential Cation Exchange Generated Superlattice Nanowires Forming Multiple p–n Heterojunctions

Fabrication of superlattice nanowires (NWs) with precisely controlled segments normally requires sequential introduction of reagents to the growing wires at elevated temperatures and low pressure. Here we demonstrate the fabrication of superlattice NWs possessing multiple p–n heterojunctions by converting the initially formed CdS to Cu₂S NWs first and then to segmented Cu₂S–Ag₂S NWs through sequential cation exchange at low temperatures. In the formation of Cu₂S NWs, twin boundaries generated along the NWs act as the preferred sites to initiate the nucleation and growth of Ag₂S segments. Varying the immersion time of Cu₂S NWs in a AgNO₃ solution controls the Ag₂S segment length. Adjacent Cu₂S and Ag₂S segments in a NW were found to display the typical electrical behavior of a p–n junction

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