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. 2020 May 29;5(22):13416-13423.
doi: 10.1021/acsomega.0c01678. eCollection 2020 Jun 9.

Reactive Sintering of Cu Nanoparticles at Ambient Conditions for Printed Electronics

Xiaofeng Dai  1 , Teng Zhang  1 , Hongbin Shi  1 , Yabing Zhang  1 , Tao Wang  1
Affiliations

Reactive Sintering of Cu Nanoparticles at Ambient Conditions for Printed Electronics

Xiaofeng Dai et al. ACS Omega. .

Abstract

A new approach is presented to overcome the disadvantages of oxidation and harsh sintering conditions of Cu nanoparticle (Cu NP) conductive inks simultaneously. In this process, oleylamine (OAM) adsorbed on particles was effectively eliminated via the reactive desorption by formic acid in alcohols; meanwhile, Cu ion was generated on the surface. The desorption of OAM resulted in more severe surface oxidation of Cu NPs. The oxide (Cu2O) and Cu2+ distributed on the Cu NP surface could be reduced to Cu(0) by NaBH4 solution and take on the role of soldering flux to weld particles into a blocky structure. With the compact coalescence of particles without oxides, the resistivity of metal patterns could fall below 20 μΩ·cm and exhibit proper adhesion. Thanks to the sintering of Cu NPs at ambient conditions, the conductive patterns could be facilely formed on thermosensitive substrates. As the oxide state of Cu would be reduced during sintering, the partially oxidized Cu nanoparticles could be directly applied to conductive inks.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Reaction of OAM and HCOOH
Figure 1
Figure 1
FT-IR profiles of OAM, 10 vol % HCOOH (EtOH) immersion liquid treated in vacuum, Cuf, and HCOOH.
Figure 2
Figure 2
XRD patterns of the particles: as-synthesized, 10 vol % HCOOH (EtOH) immersion, followed by 3 wt % NaBH4 solution immersion.
Figure 3
Figure 3
TEM images of the particles: (a) as-synthesized, (b) 10 vol % HCOOH (EtOH) immersion, (c) followed by 3 wt % NaBH4 solution immersion.
Figure 4
Figure 4
Schematic illustration of the chemical sintering mechanism.
Figure 5
Figure 5
Final resistivity of the metal layer treated by HCOOH solution and followed by 0.75 wt % NaBH4 immersion for different time periods. (a) 10 vol % HCOOH in ethanol and (b) 10 vol % HCOOH in methanol.
Figure 6
Figure 6
Cu2+ content in HCOOH alcohol immersion liquid.
Figure 7
Figure 7
Final resistivity of the metal layer treated by HCOOH solution, followed by 0.75 wt % NaBH4 solution for different time periods. (a) 5 vol % HCOOH in ethanol, (b) 10 vol % HCOOH in ethanol, (c) 20 vol % HCOOH in ethanol, (d) 5 vol % HCOOH in methanol, and (e) 10 vol % HCOOH in methanol.
Figure 8
Figure 8
(a) Resistivity of the metal layer treated by 10 vol % HCOOH ethanol solution, followed by different NaBH4 concentrations for 3 min. (b, c) Scanning electron microscopy (SEM) images of Cu layer after immersing in 3 wt % NaBH4 for 3 min and (d–f) scanned images of metal films sintered with different concentrations of NaBH4 for 3 min.
Figure 9
Figure 9
(a) Resistivity of the metal layer treated by 10 vol % HCOOH methanol solution, followed by different NaBH4 concentrations for 9 min. (b) Scanned images of metal films sintered with different concentrations of NaBH4 for 9 min.
See this image and copyright information in PMC

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