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Efficient fabrication of nanoporous si and Si/Ge enabled by a heat scavenger in magnesiothermic reactions.

Luo W, Wang X, Meyers C, Wannenmacher N, Sirisaksoontorn W, Lerner MM, Ji X - Sci Rep (2013)

Bottom Line: Magnesiothermic reduction can directly convert SiO2 into Si nanostructures.Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature.By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA.

ABSTRACT
Magnesiothermic reduction can directly convert SiO2 into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature. By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively. Fusion of NaCl during the reaction consumes a large amount of heat that otherwise collapses the nano-porosity of products and agglomerates silicon domains into large crystals. Our methodology is potentially competitive for a practical production of nanoporous Si-based materials.

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Related in: MedlinePlus

FESEM images showing morphologies of Si/Ge oxides, Nano-SiGe and Bulk-SiGe.(a) SiGe oxides; (b) Bulk-SiGe; (c) Nano-SiGe; (d) An enlarged FESEM image of Nano-SiGe corresponding to the red-square marked area in (c).
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f3: FESEM images showing morphologies of Si/Ge oxides, Nano-SiGe and Bulk-SiGe.(a) SiGe oxides; (b) Bulk-SiGe; (c) Nano-SiGe; (d) An enlarged FESEM image of Nano-SiGe corresponding to the red-square marked area in (c).

Mentions: Besides nanoporous Si, we have further utilized the same synthetic procedure to fabricate a nanoporous Si/Ge composite that may have wide applications in semiconductors32, thermolelectrics3334, as well as electrochemical energy devices353637. A composite of Si/Ge oxides were first prepared by a reported sol-gel method with modification (molar ratio between Si and Ge: 9/1)38. The nanoparticle morphology of the Si/Ge oxide composite is shown in Figure 3a. The particle size is around 30 nm, as shown in a TEM image (Supplementary Fig. S5a). A high angle annular dark field scanning TEM (HAADF-STEM) image and the corresponding Si and Ge EDX mappings reveal that GeO2 particles are encapsulated in the matrix of SiO2 larger particles with a clear contrast (Supplementary Fig. S5b). The brighter parts match the Ge EDX mapping. MRRs were conducted for Si/Ge oxides with and without NaCl additive at 650°C for 2.5 h under Ar. Without NaCl additive, a Si/Ge product collected after a similar procedure for diatom (designated as Bulk-SiGe) comprises large agglomerates with macropores, as a representative SEM image shows (Fig. 3b). On the other hand, with NaCl, the nanoparticle morphology of Si/Ge oxides has been well-maintained after the MRR, as shown by the FESEM images (Fig. 3c and d). It is evident that the Si/Ge composite (referred to as Nano-SiGe) is composed of nanoparticles sized around 10 nm. EDX analysis also verifies that little oxides exist in the final Nano-SiGe products (Supplementary Fig. S6).


Efficient fabrication of nanoporous si and Si/Ge enabled by a heat scavenger in magnesiothermic reactions.

Luo W, Wang X, Meyers C, Wannenmacher N, Sirisaksoontorn W, Lerner MM, Ji X - Sci Rep (2013)

FESEM images showing morphologies of Si/Ge oxides, Nano-SiGe and Bulk-SiGe.(a) SiGe oxides; (b) Bulk-SiGe; (c) Nano-SiGe; (d) An enlarged FESEM image of Nano-SiGe corresponding to the red-square marked area in (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3713525&req=5

f3: FESEM images showing morphologies of Si/Ge oxides, Nano-SiGe and Bulk-SiGe.(a) SiGe oxides; (b) Bulk-SiGe; (c) Nano-SiGe; (d) An enlarged FESEM image of Nano-SiGe corresponding to the red-square marked area in (c).
Mentions: Besides nanoporous Si, we have further utilized the same synthetic procedure to fabricate a nanoporous Si/Ge composite that may have wide applications in semiconductors32, thermolelectrics3334, as well as electrochemical energy devices353637. A composite of Si/Ge oxides were first prepared by a reported sol-gel method with modification (molar ratio between Si and Ge: 9/1)38. The nanoparticle morphology of the Si/Ge oxide composite is shown in Figure 3a. The particle size is around 30 nm, as shown in a TEM image (Supplementary Fig. S5a). A high angle annular dark field scanning TEM (HAADF-STEM) image and the corresponding Si and Ge EDX mappings reveal that GeO2 particles are encapsulated in the matrix of SiO2 larger particles with a clear contrast (Supplementary Fig. S5b). The brighter parts match the Ge EDX mapping. MRRs were conducted for Si/Ge oxides with and without NaCl additive at 650°C for 2.5 h under Ar. Without NaCl additive, a Si/Ge product collected after a similar procedure for diatom (designated as Bulk-SiGe) comprises large agglomerates with macropores, as a representative SEM image shows (Fig. 3b). On the other hand, with NaCl, the nanoparticle morphology of Si/Ge oxides has been well-maintained after the MRR, as shown by the FESEM images (Fig. 3c and d). It is evident that the Si/Ge composite (referred to as Nano-SiGe) is composed of nanoparticles sized around 10 nm. EDX analysis also verifies that little oxides exist in the final Nano-SiGe products (Supplementary Fig. S6).

Bottom Line: Magnesiothermic reduction can directly convert SiO2 into Si nanostructures.Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature.By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA.

ABSTRACT
Magnesiothermic reduction can directly convert SiO2 into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature. By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO2) and SiO2/GeO2 into nanoporous Si and Si/Ge composite, respectively. Fusion of NaCl during the reaction consumes a large amount of heat that otherwise collapses the nano-porosity of products and agglomerates silicon domains into large crystals. Our methodology is potentially competitive for a practical production of nanoporous Si-based materials.

Show MeSH
Related in: MedlinePlus