Coalescence-Induced Growth Doping in a II-VI Magic Size Cluster

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Chemistry

Background:

• Semiconductor magic size clusters (MSCs) offer tunable dimensionality for novel nanostructures.
• Incorporating dopant ions into II-VI MSCs typically leads to surface doping.
• Understanding dopant speciation is crucial for controlling material properties.

Purpose of the Study:

• To investigate the speciation and location of cobalt ions (Co2+) in zinc sulfide (ZnS) MSCs.
• To explore the effect of growth temperature on dopant incorporation in ZnS MSCs.
• To elucidate the mechanism of dopant internalization in Co2+-doped ZnS MSCs.

Main Methods:

• Utilized three distinct cation exchange reactions for Co2+ incorporation into ZnS MSCs at moderate temperatures.
• Employed electronic absorption spectroscopy and ligand field theory to analyze Co2+ speciation.
• Investigated the structural changes and dopant location upon high-temperature growth of doped MSCs.

Main Results:

• At moderate temperatures, Co2+ was found to be surface-substituted, present as a solution precursor, or formed Co-rich impurities.
• High-temperature growth induced the conversion of surface Co2+ to internal sites within the ZnS MSCs.
• The observed internalization is consistent with tetrahedral Co2+ coordinated to sulfur, similar to internally doped quantum dots.

Conclusions:

• The study confirms that Co2+ initially occupies surface sites or forms impurities in ZnS MSCs.
• High-temperature growth promotes Co2+ internalization through a coalescence mechanism, distinct from typical MSC growth.
• This coalescence growth offers a new pathway for creating internally doped semiconductor nanostructures.