Gold Nitride


Gold nitride

Binary nitrides exhibit a remarkable variety of desirable characteristics such as high melting points, high hardness and a robust chemical stability which makes them useful coating materials. Gold is particularly favoured in the electro-plating of electrical components due to its high conductivity and robustness in the ambient atmosphere which is often improved by combining the parent material with iron, nickel or cobalt.

Gold films incorporating gold nitride are 50 % harder than those without thus gold nitride should provide a better material for contact coatings in electronic circuits. For almost twenty years researchers had tried to synthesize gold nitride but with no success until a method, discovered at Newcastle, created gold nitride by implanting low-energy nitrogen ions into a single Au(110) crystal surface with plasma and reactive ion sputtering.

Atomic force microscope image of a gold nitride surface.
1 x 1 µm AFM image of gold nitride after plasma etching, the arrows show large clusters covered by smaller structures.

N1s photoemission spectra (below) of Au(110) irradiated with 500 eV nitrogen ions at 5770 and 21 700 μC/cm2 doses show two peaks at 396.6±0.2 eV (A) and 402.7±0.2 eV (B).

Peak A, at 396.6 ± 0.2 eV lies close to the binding energies for chemisorbed nitrogen on Cu(110) of 396.5–396.8 eV (depending on coverage) while peak B corresponds to nitrogen deeper in the crystal. Peak A corresponds to a surface AuxN phase and is the first direct observation of a gold nitride.

This technique, which attracted significant national and international media attention, offers the possibility of producing gold nitride at commercial scales to be used in place of more expensive gold coatings with significant environmental benefits.

Gold nitride XPS N1s core levels spectra obtained for nitrogen ion doses of 5770 and 21 700 μC/cm2 at 300 K.
Photoemission spectra obtained for nitrogen ion doses of 5770 and 21 700 μC/cm2 at 300 K - peak (A) shows the first direct evidence of gold nitride


Patterned gold nitride film
Electron beam patterns on a gold film containing gold nitride. Oxygen photoemission spectra as irradiation progresses shown inset

Ongoing research is directed towards the further study and characterization of this new material and already significant results have been published.

Recent work has shown how nitrogen species in gold nitride films decompose under x-ray irradiation. This could allow patterns to be written directly into gold nitride surfaces through electron beam or photon based lithographic techniques and would open up its potential uses in industrial applications.




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Scientists create gold substitute - BBC News October 2003

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