Gold nano-particle formation from crystalline AuCN: Comparison of thermal, plasma- and ion-beam activated decomposition

In this work, in addition to the conventional thermal process, two non -conventional ways, the plasma and ion beam activations are described for preparing gold nanoparticles from microcrystalline AuCN precursor. The phase formation at plasma and ion beam treatments was compared with that at thermal treatments and the products and transformations were characterized by thermogravimetry-mass-spectrometry (TG -MS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). TG -MS measurements in Ar atmosphere revealed that AuCN decomposition starts at 400 degrees C and completes at approximate to 700 degrees C with evolution of gaseous (CN)(2). XPS and TEM show that in heat treatment at 450 degrees C for 1 h in Ar, loss of nitrogen and carbon occurs and small, 5-30 nm gold particles forms. Heating at 450 degrees C for 10 h in sealed ampoule, much larger, 60-200 nm size and well faceted Au particles develop together with a fibrous (CN)(n) polymer phase, and the Au crystallites are covered by a 3-5 nm thick polymer shell. Low pressure Ar plasma treatment at 300 eV energy results in 4-20 nm size Au particles and removes most of the nitrogen and part of carbon. During Ar+ ion bombardment with 2500 eV energy, 5-30 nm size Au crystallites form already in 10 min, with preferential loss of nitrogen and with increased amount of carbon residue. The results suggest that plasma and ion beam activation, acting similarly to thermal treatment, may be used to prepare Au nanoparticles from AuCN on selected surface areas either by depositing AuCN precursors on selected regions or by focusing the applied ionized radiation. Thus they may offer alternative ways for preparing tailor-made catalysts, electronic devices and sensors for different applications.