High density nonmagnetic cobalt in thin films.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Thin Film Technology

Background:

• Discovery of high-density (HD) nonmagnetic cobalt in nanoscale thin films grown on Si(111).
• This unique cobalt phase exhibits both nonmagnetic and superconducting properties.
• Previous studies noted a natural cobalt oxide layer on the film surface.

Purpose of the Study:

• Investigate factors influencing the growth of HD nonmagnetic (NM) cobalt layers.
• Determine the effect of capping layers, film thickness, and substrate type on NM cobalt formation.
• Understand the role of substrate crystallinity in achieving the desired HD NM cobalt phase.

Main Methods:

• Fabrication of nanoscale cobalt thin films on different substrates (Si(111), silicon oxide, cobalt oxide).
• Application of a thin gold capping layer to some cobalt films.
• Systematic variation of cobalt film thickness.
• Characterization of the resulting cobalt layers to identify the HD NM phase.

Main Results:

• HD NM cobalt layers consistently form when cobalt films are capped with gold and grown on Si(111) substrates, irrespective of film thickness.
• Growth of cobalt films on oxide substrates (silicon oxide, cobalt oxide) does not yield HD NM cobalt layers.
• The crystalline nature of the substrate is identified as the critical factor for HD NM cobalt formation.

Conclusions:

• The formation of high-density nonmagnetic cobalt is critically dependent on the substrate's crystalline structure.
• Gold capping layers and varied film thicknesses support the growth of this phase on suitable crystalline substrates.
• Amorphous oxide substrates inhibit the formation of the superconducting nonmagnetic cobalt phase.