1. Synthesis of Metal-Semiconductor
Hybrid Nanostructures
Juan Angel Castro, Department of Biological Sciences, Dmitriy Khon, Department of Chemistry, St. Mary’s University, San Antonio, TX 78228
MATERIALS AND METHODS
INTRODUCTION
ACKNOWLEDGMENTS
The final process consisted of different precursors such as Zinc
Acetate, Cadmium Oxide and Lead Oxide to synthesize Au/ZnS,
Au/CdS, and Au/PbS, respectively. The cation exchange reaction
utilizes tributylphosphine, which acts as phase-transfer agent by
transporting metal ions to the surface of the core nanoparticles. The
synthesis of the metal-semiconductor nanostructures took place with
the injection of the precursor solution and tributylphosphine at 60°C. In
accordance to the THSAB, the precursor molecules used in the
synthesis of metal-semiconductor nanostructures are hard acids. In turn,
the tributylphosphine (soft base) transports the precursor ions (hard
acids), to the core of the nanoparticle. These ions will exchange with
silver allowing the silver (soft acid) to interact with tributylphosphine
(soft base). Therefore, the sulfur shell (hard acid) will interact with the
precursor ions which are hard bases. The absorbance spectra for the
Metal-Semiconductor Nanostructures can be seen in Figure 3.
The synthesis of Metal-Semiconductor Hybrid Nanostructures is
summarized in Figure 1. Synthesis of Gold (Au) nanostructures was
attained by dissolving Gold III Chloride in Acetone --in a multi-neck
round bottom flask with septa. Once connected under argon flow,
oleylamine was added and allowed to react for 30 minutes at 100°C.
After the synthesis of Au cores a Silver (Ag) shell was used to coat
them. Au/Ag core synthesis consisted of consecutive additions of the
AgNO3/H2O precursor at 120°C. Rapid addition of AgNO3/H2O caused
isolated Ag nanoparticles to form. Synthesizing the Ag shell offers
thermodynamic control, growth control and a useful characteristic by
the Theory of Hard-Soft Acids and Bases (THSAB) which categorizes
the Ag as a soft acid. The next step was to modify the silver-compound
shell with an amorphous structure of the Au/Ag. To modify the shell,
sulfur was dissolved and diluted with oleylamine which was carefully
injected in a drop-wise manner. This reaction occurred at 25°C and was
terminated once a desired absorbance graph was attained for the
Au/Ag2S nanoparticles. According to the THSAB, sulfur is considered
to be a soft base. The absorbance spectra for Au, Au/Ag and Au/Ag2S
can be seen in Figure 2.
As a result from the multistep and cation exchange reactions, successful
Metal-Semiconductor Hybrid Nanostructures where synthesized.
Transmission Electron Microscopy (TEM) was used to confirm the
core/shell morphology of the final product.. Figure 4 shows the images
obtained for each intermediate nanostructure in the synthesis of Metal-
Semiconductor Hybrid Nanostructures. Unfortunately, the TEM image
of the Au/PbS was not obtained.
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of Hybrid Core-Shell Nanostructures with Large
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Schneider, Grégory, Gero Decher, Nicolas Nerambourg, Raïssa Praho,
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Nanoparticles Ensheathed with Layer-by-Layer Assembled
Polyelectrolytes."Nano Letters 6.3 (2006): 530-36. Print.
Pearson, Ralph G. "Hard and Soft Acids and Bases, HSAB, Part 1:
Fundamental Principles."Journal of Chemical Education 45.9
(1968): 581. Print.
Metal-Semiconductor Hybrid Nanoparticles offer quantum dots that
consist of a heterostructure with a metal core and a monocrystalline
semiconductor shell. The application of these nanostructures can be
utilized for the production of Light Emitting Diodes (LED’s), Lasers,
Solar Cells and Biosensing. For this experiment, the metal core
consisted of a gold precursor while the monocrystalline shell consisted
of CdS, PbS, or ZnS. The synthesis of these Metal-Semiconductor
Nanoparticles were attained via a series of reactions involving a cation
exchange. Following The Theory of Hard-Soft Acids and Bases, which
utilized Tributylphosphine, the cation exchange reaction was able to
proceed. Tributylphosphine acts as a phase-transfer agent which
transports metal ions to the surface of the nanoparticle core by binding
to the free cations in solution. The final nanostructures synthesized
during this process were Au/CdS, Au/PbS and Au/ZnS. Transmission
Electron Microscopy (TEM) was utilized to confirm the core/shell
morphology of the final product.
Figure 2: The absorbance for Au. Au/Ag and Au/Ag2S. Each intermediate
absorbs at different wavelengths allowing the differentiation between these
nanostructures.
Au Au/Ag Au/Ag2S
Au/CdS Au/ZnS
No TEM available for
Au/PbS
Figure 1: Synthesis process and intermediate nanoparticles for the production
of Metal-Semiconductor Hybrid Nanostructures.
Figure 3: The absorbance spectra for the Metal Semiconductor Nanostructures
Au/CdS, Au/PbS and Au/ZnS.
Figure 4: The Transmission Electron Microscopy (TEM) images for the intermediate
nanostructures obtained throughout the synthesis of Metal-Semiconductor Hybrid
Nanostructures.
T=60 °C
Metal-
Semiconductor
Gold III Chloride
Acetone
Oleylamine
Gold
Cores
T=100 °C T=120 °C T=25 °C
Au/Ag
core-shell
Au/Ag2S
CONCLUSION
REFERENCES
This research was supported in part by Saint Mary’s University
Research Grant. I would like to thank Dr. Dmitriy Khon and Dr.
Richard Cardenas for providing me with the opportunity to participate
in this project. I also would like to thank Dr. Mikhail Zamkov and his
group for welcoming me into their laboratory at Bowling Green State
University and allowing me to take part in this research project.