3 Spin-Polarized Plasmonics: Fresh View …
57
more structure is observed for the particle both below and above the Fermi level
(corresponding to 0 eV). This is not surprising, since the particle has additional
states due to the presence of the surface. Notably, the pronounced peaks around the
Fermi level in both spin channels are discrete and broadened in the cluster compared
to bulk.
3.3 Methods
In this work, the oleic acid (OA) coated cobalt nanoparticles were fabricated by
the high temperature reduction of cobalt salt in the presence of trioctylphosphine
(TOP) as a surfactant and lithium triethylborohydride as a reducing reagent [49–
51]. Cobalt nanoparticles were synthesized using a method similar to that of Sun
and Murray [52]. The reduction of cobalt nanoparticles was conducted under inert
atmosphere. At room temperature, 0.13 g (0.019 M) of anhydrous cobalt chloride,
0.3 mL (0.018 M) of oleic acid and 30 mL (1.87 M) of dioctyl ether were mixed
together under purged nitrogen gas in the three-necked flask containing magnetic
stir bar and heated to 100 °C. Then 1.5 mL (0.063 M) of trioctylphosphine, which
was injected via syringe and the temperature raised to 205 °C. At this temperature, a
strong reducing reagent, 1.5 mL (0.236 M) lithium triethylborohydride, was added
in solution and the cobalt nanoparticles begin to grow immediately. The blue colour
of the solution turns to black upon nucleation and growth of cobalt nanoparticles.
The reaction was terminated by cooling the solution to room temperature and 20 mL
(4.8 M) of anhydrous ethanol was added to precipitate the particles. The solution
was aged overnight at room temperature in order to attach cobalt nanoparticles to the
magnetic stir bar in the flask. The cobalt nanoparticles are removed from a magnetic
stir bar and washed several times with ethanol by centrifugation. Finally, oleic acid
coated cobalt nanoparticles were suspended in 8 mL of hexane.
To address the mechanism of new type of plasmons specific for magnetic
nanoparticles our work involves the structural electron microscopy, superconducting
quantum interference device (SQUID) magnetometry, dynamic light scattering
(DLS), and spectroscopy of Co nanoparticles. The structural and magnetic characterizations prove the single-domain and superparamagnetic properties of nanoparticles
required for spin dependent channels of plasmon oscillations. The magnetic field
induced aggregation of nanoparticles in our experiments results in the suppression
of the resonance quality.
3.4 Structural Properties
The scanning electron microscopy (SEM) energy dispersive X-ray (EDX) image of
the cobalt nanoparticles synthesized by the high temperature decomposition of cobalt
salt (Fig. 3.3).
57
more structure is observed for the particle both below and above the Fermi level
(corresponding to 0 eV). This is not surprising, since the particle has additional
states due to the presence of the surface. Notably, the pronounced peaks around the
Fermi level in both spin channels are discrete and broadened in the cluster compared
to bulk.
3.3 Methods
In this work, the oleic acid (OA) coated cobalt nanoparticles were fabricated by
the high temperature reduction of cobalt salt in the presence of trioctylphosphine
(TOP) as a surfactant and lithium triethylborohydride as a reducing reagent [49–
51]. Cobalt nanoparticles were synthesized using a method similar to that of Sun
and Murray [52]. The reduction of cobalt nanoparticles was conducted under inert
atmosphere. At room temperature, 0.13 g (0.019 M) of anhydrous cobalt chloride,
0.3 mL (0.018 M) of oleic acid and 30 mL (1.87 M) of dioctyl ether were mixed
together under purged nitrogen gas in the three-necked flask containing magnetic
stir bar and heated to 100 °C. Then 1.5 mL (0.063 M) of trioctylphosphine, which
was injected via syringe and the temperature raised to 205 °C. At this temperature, a
strong reducing reagent, 1.5 mL (0.236 M) lithium triethylborohydride, was added
in solution and the cobalt nanoparticles begin to grow immediately. The blue colour
of the solution turns to black upon nucleation and growth of cobalt nanoparticles.
The reaction was terminated by cooling the solution to room temperature and 20 mL
(4.8 M) of anhydrous ethanol was added to precipitate the particles. The solution
was aged overnight at room temperature in order to attach cobalt nanoparticles to the
magnetic stir bar in the flask. The cobalt nanoparticles are removed from a magnetic
stir bar and washed several times with ethanol by centrifugation. Finally, oleic acid
coated cobalt nanoparticles were suspended in 8 mL of hexane.
To address the mechanism of new type of plasmons specific for magnetic
nanoparticles our work involves the structural electron microscopy, superconducting
quantum interference device (SQUID) magnetometry, dynamic light scattering
(DLS), and spectroscopy of Co nanoparticles. The structural and magnetic characterizations prove the single-domain and superparamagnetic properties of nanoparticles
required for spin dependent channels of plasmon oscillations. The magnetic field
induced aggregation of nanoparticles in our experiments results in the suppression
of the resonance quality.
3.4 Structural Properties
The scanning electron microscopy (SEM) energy dispersive X-ray (EDX) image of
the cobalt nanoparticles synthesized by the high temperature decomposition of cobalt
salt (Fig. 3.3).