Mechanistic Studies on Sintering of Silver Nanoparticles

Abstract

Metal nanoparticles are known to form highly conductive films upon heating below 200 °C. We study the mechanism and morphological changes that occur as 3 nm, thiolate encapsulated, silver nanoparticles are annealed to form conductive films. We use X-ray diffraction (XRD), grazing incidence X-ray scattering (GIXS), and transmission electron microscopy (TEM) to monitor structural changes in the film. We show that the surfactant is present during the entire sintering process, that its presence greatly influences the grain size and crystallite orientation of the resulting film, and that the film becomes fully conductive in the presence of the surfactant. We show that particles that aggregate more rapidly form films that consist of smaller crystallites and are less textured. We further show that digestive ripening can lead to the degeneration of films back into particles, particularly when annealing in air versus an inert environment. Coalescence contributes to crystallite growth when particles are small but can confound both crystallite size and orientation development in the later stages of growth. The interaction of the surfactant with the particle is weakened by moisture, lowering the temperature at which the surfactant disassociates from the particle and sintering begins. Moisture also increases the rate of both aggregation and digestion, drastically changing the morphology of the films at any given temperature.

Printable Materials for the Realization of High Performance RF Components: Challenges and Opportunities

“…This has been more thoroughly discussed in the Ag system by Seifert et al at 200°C and above for >30-minute intervals [31]. Numerous publications [31,55,[69][70][71] have shown that increased annealing temperature or time leads to increased densification of the metal film, which is consistent with well-known ripening phenomena in crystal grain growth.…”

Inkjet‐Printed Flexible Gold Electrode Arrays for Bioelectronic Interfaces

“…[ 33,34 ] Specifi cally in the earlier stages of the process, pre-sintering (or curing) events related to the surfactant molecules take place, which include melting of the organic layer and the formation of a superlattice in which the particles can make direct contact and a percolation path for electrons is formed. [ 33,35 ] .…”

“…[ 34 ] And with the longer sintering time, nanoparticles can approach and merge, forming a percolation path and causing line resistance to decrease several orders of magnitude. [ 34 ] Such particle rearrangement, which eventually culminates in the formation of the already mentioned superlattice, [ 35 ] usually happens in a matrix of molten surfactant and is a diffusioncontrolled process. Thus, the dependence of sintering speed on trace linewidth observed here is due to the diffusion-based mechanism of sintering.…”

Molecular dynamics simulation of electrical resistivity in sintering process of nanoparticle silver inks

“…Several types of mass transport mechanisms may occur during the sintering process, including viscous flow, plastic flow, evaporation-condensation, and material diffusion [5] [21]. All of these different mechanisms may 6 contribute to the neck growth at the initial stage of sintering [6]. Because mass transport mechanisms compete with each other, it is reasonable to simplify the model to be driven by single transport mechanism [19].…”

“…The electrical resistivity of silver nanoparticles thermally cured at low temperatures has been studied from experimental measurements [6,7]. The results show that the sintering time for nano-inks may have a considerably effect on electrical conductivity.…”