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2 Synthesis of Quantum Dots
2.2 Metal/Metal Oxides Quantum Dots
2.2.1 Microwave Irradiation
Recent advances in technology have now made microwave irradiation a novel
synthetic method for the preparation of nanosized materials since the chemical reaction rate of microwave heating is as much as 1000 times faster than the conventional
heating (Gawande et al. 2014). The use of microwave irradiation has become increasingly popular in inorganic synthesis, especially synthesis of metal oxides. Recently,
nanostructured metal oxides such as Fe 2 O 3 (Qiu et al. 2011), NiO (Song and Lian
2010), ZnO (Yang et al. 2013), CuO (Lu and Wang 2011), and Co 3 O 4 (Yan et al.
2010a) have been successfully prepared by a microwave-assisted process.
Zhou et al. (2014) shown a unique method to synthesis a Co 3 O 4 QDs/graphene
compound by a microwave irradiation process. Graphene oxide (GO) sheets as
precursors were synthesized by chemical exfoliation of flake graphite powder by
an improved Hummers process. Graphene nanosheet was prepared via the thermal
reduction of graphene oxide (GO) sheets in air atmosphere at 200 °C for 30 min
then in Ar atmosphere at 450 °C for 3 h. Co 3 O 4 quantum dots/graphene composite
was synthesized by a facile microwave irradiation process. In a typical synthesis,
69 mg of grapheme nanosheets were dispersed in the varied solvent of 20 mL of
deionized water and 30 mL of ethyl alcohol under sonication for 30 min. Then 1 g
of Co(CH 3 COO) 2 · 4H 2 O was dissolved in the above solution and 5 mL of 25%
NH 3 · H 2 O was put in. The mixture was sonicated for about 10 min to form a homogeneous fuscous slurry. The suspension was finally moved into a microwave oven
(XH MC-1) with reflux equipment and was heated at 81 °C for 5 min by microwave
irradiation with a power of 500 W. The black products were collected by several
rinse-centrifugation cycles with distilled water and absolute ethanol and were dried
overnight in vacuum at 60 °C for further characterization.
2.2.2 Heat Reduction
Germanium QDs (Ge QDs) embedded in an N-doping GN matrix with a sponge-like
architecture (Ge/GN sponge) was synthesized by freeze-drying and then a thermal
reduction procedure (Fig. 2.2a–c). In a typical fabrication procedure, 0.2 g GeO 2
was put into 5 mL distilled water. After adding 1 mL ethylenediamine (EDA), the
suspension came to be clear under the thermal situations. Then, some graphite oxide
(GO) was out into the solution. Dilute the mixture to 20 mL with distilled water
and continue stirring for 20 min. The mixture was then freeze-dried for one day.
To finish, Ge/GN sponge was prepared by calcining the solid precursor in flowing
H 2 /AR (7 vol% H 2 ) atmosphere at 650 °C for 2 h. Pure GN was also synthesized via
the same process but no GeO 2 was added. Ge QDs were well distributed in N-doped
GN interconnects, about 2–5 nm. Based on the whole memory influence and network
2 Synthesis of Quantum Dots
2.2 Metal/Metal Oxides Quantum Dots
2.2.1 Microwave Irradiation
Recent advances in technology have now made microwave irradiation a novel
synthetic method for the preparation of nanosized materials since the chemical reaction rate of microwave heating is as much as 1000 times faster than the conventional
heating (Gawande et al. 2014). The use of microwave irradiation has become increasingly popular in inorganic synthesis, especially synthesis of metal oxides. Recently,
nanostructured metal oxides such as Fe 2 O 3 (Qiu et al. 2011), NiO (Song and Lian
2010), ZnO (Yang et al. 2013), CuO (Lu and Wang 2011), and Co 3 O 4 (Yan et al.
2010a) have been successfully prepared by a microwave-assisted process.
Zhou et al. (2014) shown a unique method to synthesis a Co 3 O 4 QDs/graphene
compound by a microwave irradiation process. Graphene oxide (GO) sheets as
precursors were synthesized by chemical exfoliation of flake graphite powder by
an improved Hummers process. Graphene nanosheet was prepared via the thermal
reduction of graphene oxide (GO) sheets in air atmosphere at 200 °C for 30 min
then in Ar atmosphere at 450 °C for 3 h. Co 3 O 4 quantum dots/graphene composite
was synthesized by a facile microwave irradiation process. In a typical synthesis,
69 mg of grapheme nanosheets were dispersed in the varied solvent of 20 mL of
deionized water and 30 mL of ethyl alcohol under sonication for 30 min. Then 1 g
of Co(CH 3 COO) 2 · 4H 2 O was dissolved in the above solution and 5 mL of 25%
NH 3 · H 2 O was put in. The mixture was sonicated for about 10 min to form a homogeneous fuscous slurry. The suspension was finally moved into a microwave oven
(XH MC-1) with reflux equipment and was heated at 81 °C for 5 min by microwave
irradiation with a power of 500 W. The black products were collected by several
rinse-centrifugation cycles with distilled water and absolute ethanol and were dried
overnight in vacuum at 60 °C for further characterization.
2.2.2 Heat Reduction
Germanium QDs (Ge QDs) embedded in an N-doping GN matrix with a sponge-like
architecture (Ge/GN sponge) was synthesized by freeze-drying and then a thermal
reduction procedure (Fig. 2.2a–c). In a typical fabrication procedure, 0.2 g GeO 2
was put into 5 mL distilled water. After adding 1 mL ethylenediamine (EDA), the
suspension came to be clear under the thermal situations. Then, some graphite oxide
(GO) was out into the solution. Dilute the mixture to 20 mL with distilled water
and continue stirring for 20 min. The mixture was then freeze-dried for one day.
To finish, Ge/GN sponge was prepared by calcining the solid precursor in flowing
H 2 /AR (7 vol% H 2 ) atmosphere at 650 °C for 2 h. Pure GN was also synthesized via
the same process but no GeO 2 was added. Ge QDs were well distributed in N-doped
GN interconnects, about 2–5 nm. Based on the whole memory influence and network