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

• Published in: Journal of solid state chemistry 2017-02, Vol.246, p.65-74
• Main Authors: Beck, Mihály T., Bertóti, Imre, Mohai, Miklós, Németh, Péter, Jakab, Emma, Szabó, László, Szépvölgyi, János
• Format: Article
• Language: English
• Subjects: ARGON IONS; AuCN; CARBON; COMPARATIVE EVALUATIONS; CRYSTALLIZATION; CRYSTALS; GOLD; Gold nanoparticles; HEAT TREATMENTS; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ION BEAMS; NANOPARTICLES; NITROGEN; Paracyanogen; PLASMA; Plasma activation; REACTION KINETICS; SURFACE AREA; TEM; THERMAL GRAVIMETRIC ANALYSIS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY PHOTOELECTRON SPECTROSCOPY; XPS
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2016.10.031

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°C and completes at ≈700°C with evolution of gaseous (CN)2. XPS and TEM show that in heat treatment at 450°C for 1h in Ar, loss of nitrogen and carbon occurs and small, 5–30nm gold particles forms. Heating at 450°C for 10h in sealed ampoule, much larger, 60–200nm size and well faceted Au particles develop together with a fibrous (CN)n polymer phase, and the Au crystallites are covered by a 3–5nm thick polymer shell. Low pressure Ar plasma treatment at 300eV energy results in 4–20nm size Au particles and removes most of the nitrogen and part of carbon. During Ar+ ion bombardment with 2500eV energy, 5–30nm size Au crystallites form already in 10min, 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. Proposed scheme of the decomposition mechanism of AuCN samples: heat treatment in Ar flow (a) and in sealed ampoule (b); Ar+ ion treatment at 300eV (c) and at 2500eV (d). Cross section sketches illustrate the Au phase formation and the corresponding TEM micrographs are shown as top views. The dotted lines represent the original boundaries of the AuCN crystals. [Display omitted] •AuCN decomposes between 400 and 700°C with evolution of gaseous (CN)2.•Epitaxial relationship is established between Au and parent AuCN crystals.•Ar plasma treatment results in similar phase transition than the thermal treatment.•Plasma and ion-beam activation offer alternative way for preparing Au nanocrystals.•Reaction mechanisms of Au particle formation at the three treatments are proposed.