Transcript 幻灯片 1 - University of Guelph

Motivation
• There has been increasing interest in the fabrication and
characterization of 1D magnetic nanostructures because of
their potential applications in high-density magnetic memory,
giant magnetoresistance (GMR) sensors, and
magnetoelectronic devices.
• Because the magnetic properties of magnetic nanowires are
highly dependent on their size, shape, and crystallinity,
controlled fabrication of these magnetic nanomaterials with
uniform size and shape remains an important issue.
• Magnetic barcode nanowires consisting of alternating
structures of ferromagnetic and nonmagnetic materials, such
as NiFe/Cu, Ni/Cu, and Co/Cu have been examined.
Experimental
• Fabrication of porous alumina templates
• Fabrication of Co/Pt magnetic barcode nanowires by
electro-deposition
• Structural characterization of Co and Pt nanowires
What is porous anodic alumina?
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Anodic Oxidation
(DC)
Electropolished Al Foil
Al2O3 on Al substrate
Porous Anodic Alumina (PAA) - Al2O3
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• Powerful template for the fabrication of
nano-devices in fields of electronics,
optoelectronics, magnetics, energy
storage, photocatalysis, photonics,
biosensors, ultra-filtration, and CVD
micro-reactor
• Densely packed arrays of columnar
hexagonal cells with straight
nanochannels
• Controllable sizes of nanopores: ranging
from 5-300 nm in diameter, 0.1-300 um
in thickness
• Pore density as high as 108-1011
pores/cm2
• Aspect ratio (depth divided by width) as
high as 1000~3000
• Morphology of synthesized materials:
nanodot, nanowire/pillar/disk/rod, metal
nanohole arrays, and nanotube.
Electrodeposition
• A thin Au layer was sputtered on
one side of the porous alumina
templates
• The pure Co, Pt, and Co/Pt
magnetic barcode nanowires were
grown, respectively, in a single
electrolyte with a pH of 3.0
containing 0.3 M CoSO4, 0.03 M
K2PtCl6, and 0.485 M H3BO3 by
using a pulsed-electrodeposition
technique. (alternative constant
potentials of -1000mV to deposit
cobalt segments and -350mV to
deposit platinum segments were
applied.)
Modulated magnetism in the Co/Pt barcode nanowires corresponding to the
aspect ratio change indicates that the magnetic properties of barcode
nanowires can be tuned easily by controlling the relative thickness of the
cobalt segments in the Co/Pt magnetic barcode nanowires.
Alternatively, we have observed that reactive ion etching (RIE) is a highly effective method for
removing the electrode layer under mild conditions. RIE etching was performed at a fixed RF
power (200W) and constant vacuum condition (60 mTorr) while flowing argon gas (7 sccm).
The porous alumina templates were then dissolved Large amounts of individual free-standing
magnetic barcode nanowires of exceptionally high quality (Figure 4a-h) are obtained
successfully in a variety of different barcode structures after removing the porous alumina
templates.
Conclusion
• They have demonstrated a massive fabrication of a variety of
barcode Co/Pt nanowires by using a simple and highly
effective deposition and releasing process.
• Modulation of magnetism is possible by controlling the aspect
ratio and magnetic segment thickness of the barcodes, and
further enhancement of ferromagnetism of such 1D barcodes
is straightforward via a thermally induced phase transition
process.
• In particular, these free-standing Co/Pt magnetic barcode
nanowires and Co/Pt alloy nanowires have potential
applications as key building blocks for 1D-based
magnetoelectronic devices.