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Tailoring Fast Directional Mass Transport of Nano-Confined Ag–Cu Alloys upon Heating: Effect of the AlN Barrier Thickness
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posted on 2019-01-17, 00:00 authored by Vicente Araullo-Peters, Claudia Cancellieri, Mirco Chiodi, Jolanta Janczak-Rusch, Lars P. H. JeurgensThis study addresses
the phase stability and atomic mobility of
Ag–Cu40at.% nano-alloys confined by AlN in a nanomultilayered
configuration during thermal treatment. To this end, nanomultilayers
(NMLs) with a fixed Ag–Cu40at.% nanolayer thickness
of 8 nm and a AlN barrier nanolayer with variable thickness of 4,
8, or 10 nm were deposited by magnetron sputtering on sapphire substrates
and subsequently isothermally annealed for 5 or 20 min in air in the
range of 200–500 °C. The microstructure of the as-deposited
and heat-treated NMLs was analyzed by X-ray diffraction, scanning
electron microscopy, transmission electron microscopy, and energy
dispersive spectroscopy. Annealing of the thicker AlN barrier layers at T > 300 °C leads
to
the formation of an interconnected network of line-shaped Cu(O) protrusions
on the annealed NML surface. The well-defined outflow pattern of Cu(O)
originates from the thermally induced surface cracking of the top
AlN barriers with subsequent fast mass transport of Cu along the Cu/AlN
interfaces toward the surface cracks. The thinnest (i.e., 4 nm thick)
AlN barrier layers exhibit a relatively open grain boundary structure
and act as nanoporous membranes upon heating, resulting in the formation
of a dense and homogenous distribution of Cu(O) and Ag droplets on
the NML surface. These findings demonstrate that the microstructure
(i.e., layer thicknesses, interface coherency, and texture) of hybrid
nanolaminates can be tuned to provide defined pathways for fast, directional
transport of the confined metal to the surface at relatively low temperatures,
which might open new routes for low-temperature bonding of micro-
and nano-scaled systems.
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Keywords
NML surfaceoutflow patternmass transport10 nmannealed NML surfacethicknessnano-scaled systemsinterface coherencyAlN barrier nanolayer8 nmstudy addressesAlN barrier layersAg dropletsTailoring Fast Directional Mass TransportAlN Barrier Thicknessscanning electron microscopygrain boundary structureAlN barrier layers exhibittransmission electron microscopysapphire substratesAlN barriersnanoporous membranesCu20 minphase stabilityheat-treated NMLssurface cracksenergy dispersive spectroscopynanomultilayered configurationX-ray diffraction
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