The mechanism of generating nanoporous Au by de-alloying amorphous alloys

Abstract

De-alloying, i.e. selective dissolution of alloys, is currently studied to produce nanoporous gold items suited for use in catalysis, electrochemical applications, sensors and actuators. Both crystalline and amorphous alloys can be selectively etched. In the former, less noble atoms are removed from surface terraces of grains layer by layer, while noble ones form mounds. These evolve by undercutting and electrolytepercolation to form a ligament network. The mechanism of ligament development by de-alloying amorphous alloys is unknown. Here we show that for de-alloying a Au-based glass, in this case Au 40 Cu 28 Ag 7 Pd 5 Si 20 , percolation of the electrolyte through cracks of the native surface oxide initiates the formation of protuberances which are soon undercut. An interlayer develops, where Au crystals germinate, grow to nanometer size by diffusion and impinge. This is how ligaments start to coarsen. The interlayer is found at all stages between coarsened ligaments and amorphous phase. The ligaments are defective polycrystals, as opposed to single crystals obtained from crystalline alloys.

Excellent long-term reactivity of inhomogeneous nanoscale Fe-based metallic glass in wastewater purification

“…Furthermore, in the enlarged SEM image (Fig. 10f), nanoporous structures with characteristic sizes of 20-50 nm can be observed, which are interpreted as typical selective corrosion morphology [47][48][49]. Volume shrinkage as a result of selective corrosion, i.e., de-alloying, has been commonly detected in nanoporous structures when compared with their bulk precursors [50][51][52][53], and is consistent with the observed results in Fig.…”

Nanoporous gold thin films synthesised via de-alloying of Au-based nanoglass for highly active SERS substrates

“…The images indicate that ligaments with an average size of 24±5nm are formed (Fig 3a), confirming the SEM images, while the lattice fringes are oriented in various directions. This observation confirms that the impingement of nanocrystals which are formed during de-alloying leads to a nanocrystalline network of rough ligaments [22]. XPS measurements were performed to reveal the chemical composition at the top surface of film and to estimate the residual sacrificial elements left after de-alloying 1M HNO 3 at 70 °C with different times.…”

“…This unique structure is attractive to obtain a uniform nanoporosity by the de-alloying method. Actually, previous reports showed that the de-alloying of amorphous ribbons gave porous self-standing materials made of Au ligaments constituted by fine crystals containing residual trapped solute elements, e. g. Ag and Pd [20,22]. Nanoglass, as a new kind of metallic glass proposed by Jing et al [23], consists of nanometer sized glassy grains separated by glassy interfaces [24] of reduced density with respect to the density of the bulk glass [25].…”

A comparison of de-alloying crystalline and amorphous multicomponent Au alloys

“…The combination of morphology and residual elements occurring only in the case of de-alloying a metallic glass might be of relevance for specific applications in catalysis or sensing [6,27].…”