Hydrophilic Sparse Ionic Monolayer‐Protected Metal Nanoparticles: Highly Concentrated Nano‐Au and Nano‐Ag “Inks” that can be Sintered to Near‐Bulk Conductivity at 150 °C

Abstract

Here, monolayer‐protected gold and silver nanoparticles with extremely high solvent dispersibility (over 200 mg mL−1 in water and glycols) and low coalescence temperature (approximately 150 °C, measured by the percolation transition temperature Tp) are developed, to reach conductivities better than 1 × 105 S cm−1. These materials are suitable for inkjet and other forms of printing on substrates that may be solvent‐ and/or temperature‐sensitive, such as for plastic electronics, and as bus lines for solar and lighting panels. This is achieved using a new concept of the sparse ionic protection monolayer. The metal nanoparticles are initially protected by a two‐component mixed ligand shell comprising an ω‐functionalized ionic ligand and a labile ligand. These are selectively desorbed to give a sparse shell of the ω‐ionic ligands of ca. 25% coverage. Through a systematic study of different monolayer‐protected Au nanoparticles using FTIR spectroscopy, supported by XPS and DSC, it is shown that Tp is not determined by thermodynamic size melting or by surface area effects, as previously thought, but by the temperature when ca. 80% of the dense monolayer is eliminated. Therefore, Tp depends on the thermal stability and packing density of the shell, rather than the size of the metal core, while the solubility characteristics depend strongly on the exposed terminal group.

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

“…For RF, bulk σ is extremely important because of skin-depth effects, which unlike DC components cannot be compensated for by simply printing thicker with lower σ metals. With tailored silver (Ag) chemistries, researchers have been able to obtain near-bulk σ of Ag with DW methods [21,22]. Since Ag is relatively inexpensive and the chemistry is very well understood, Ag-based inks have become ubiquitous in DW processes.…”

“…Similarly, Li et al have recorded thermal conductivity 65% of bulk Ag by utilizing ink with a 2 : 1 ratio of 10 nm Ag NPs to 50 nm Ag NPs to decrease the porosity [73]. Separately, for Au, half of the bulk conductivity has been demonstrated on carefully tailored ligand chemistry and particle sizes at 150°C; however, this was in a thin film ink and not printed [22]. There have been a number of mechanistic explanations proposed for the decrease in DC resistivity observed during sintering.…”

Jettable fluid space and jetting characteristics of a microprint head

“…More recently, it has been actively studied also for the manufacture of functional thin films, including conductive metal tracking (Dearden et al 2005;Xue et al 2006;Sivaramakrishnan et al 2007;Osch et al 2008;Soltman & Subramanian 2008;Meier et al 2009;Perelaer et al 2009;Anto et al 2010), polymer organic L.-Y. Wong and others semiconductor devices (Kobayashi et al 2000;Sirringhaus et al 2000;Duineveld et al 2002;Kawase et al 2003;Arias et al 2004;Bale et al 2006;Berggren, Nilsson & Robinson 2006;Xia & Friend 2006;Li et al 2007;Aernouts et al 2008;Hoth et al 2008;Singh et al 2009), photoresist films (Fakhfouri et al 2009) and bio-films (Newman, Turner & Marrazza 1992;Hughes et al 2001;Roth et al 2004;Nakamura et al 2005).…”

A Simple Process for Synthesis of Ag Nanoparticles and Sintering of Conductive Ink for Use in Printed Electronics

“…The percolation temperature (T p ) is the operationally defined temperature at which the film of metal nanoparticles undergoes an insulator-to-metal transformation. 17 In terms of the percolation temperature, the most important issue in decreasing the sintering temperature is not the size of the nanoparticles but the organic ligand, which melts at a low temperature. 18 Furthermore, using differential scanning calorimetry (DSC), Moon et al 19 and Kim and Moon 20 observed exothermic peaks of metal nanoparticles during the sintering process.…”