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Synthesis of nanocrystals by discharges in liquid nitrogen from Si-Sn sintered electrode.

Kabbara H, Noël C, Ghanbaja J, Hussein K, Mariotti D, Švrček V, Belmonte T - Sci Rep (2015)

Bottom Line: The presence of both vapours does not lead to the synthesis of alloyed nanocrystals but to the synthesis of separate nanocrystals of silicon and tin with average sizes of 10 nm.The synthesis of an am-Si0.95Sn0.05 phase around large silicon crystals (~500 nm) decorated by β-Sn spheroids is achieved if the current flowing through electrodes is high enough.When the sintered electrode is hit by powerful discharges, some grains are heated and tin diffuses in the large silicon crystals.

View Article: PubMed Central - PubMed

Affiliation: Université de Lorraine, Institut Jean Lamour, UMR CNRS 7198, NANCY, F-54042, France.

ABSTRACT
The synthesis feasibility of silicon-tin nanocrystals by discharges in liquid nitrogen is studied using a Si-10 at % Sn sintered electrode. Time-resolved optical emission spectroscopy shows that silicon and tin melt almost simultaneously. The presence of both vapours does not lead to the synthesis of alloyed nanocrystals but to the synthesis of separate nanocrystals of silicon and tin with average sizes of 10 nm. These nanocrystals are transformed into amorphous silicon oxide (am-SiO2) and β-SnO2 by air oxidation, after evaporation of the liquid nitrogen. The synthesis of an am-Si0.95Sn0.05 phase around large silicon crystals (~500 nm) decorated by β-Sn spheroids is achieved if the current flowing through electrodes is high enough. When the sintered electrode is hit by powerful discharges, some grains are heated and tin diffuses in the large silicon crystals. Next, these grains are shelled and fall into the dielectric liquid.

No MeSH data available.


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(a) TEM image of a Si grain decorated by Sn spheroids scratched from the sintered material. (b) TEM image of a Si grain decorated by Sn spheroids obtained after treatment. The Si0.95Sn0.05 layer is delimited by squares. (c) Micro-EDS spectrum corresponding to the silicon crystal in image (a). (d) Micro-EDS spectrum corresponding to the Si0.95Sn0.05 layer in image (b).
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f3: (a) TEM image of a Si grain decorated by Sn spheroids scratched from the sintered material. (b) TEM image of a Si grain decorated by Sn spheroids obtained after treatment. The Si0.95Sn0.05 layer is delimited by squares. (c) Micro-EDS spectrum corresponding to the silicon crystal in image (a). (d) Micro-EDS spectrum corresponding to the Si0.95Sn0.05 layer in image (b).

Mentions: When the ballast resistance is only 1 kΩ, the current is 10 A and spark discharges are much stronger. The erosion mechanism of the sintered target is then completely different. Very large grains of silicon decorated by tin nanoparticles with diameters ranging from 50 to 70 nm are heated by the discharge and shelled. The mean size of the loose grains collected in these conditions corresponds to that of silicon grains of the target. In Fig. 3a,b, two grains are shown, one collected directly by scratching the target before treatment, and one collected by sedimentation after treatment. The grain in Fig. 3a shows only two phases: a large silicon crystalline grain decorated by tin nanoparticles. Micro-EDS analysis (Fig. 3c) shows that silicon does not contain any tin before treatment. The grain in Fig. 3b, obtained by sedimentation after treatment, shows three phases: a large silicon crystalline grain decorated by tin nanoparticles and an amorphous phase. The amorphous irregular layer contains up to 5 wt.% (~1.2 at %) tin after treatment (micro-EDS analysis in Fig. 3d). The amorphous nature is probably due to the very high tin content, which is about 8 times the solubility of tin in solid silicon at 1100–1200 °C3. The amorphous phase was likely formed by melting the outermost part of the silicon crystal followed by rapid quenching as seen in Fig. 3b (areas delimited by squares); this could not be observed in Fig. 3a. During the initial heating and melting, Sn from surrounding nanoparticles has alloyed with the outermost part of the large silicon grains yielding the amorphous alloyed Si-Sn layer. We infer that heating of the silicon grains by the spark discharge promotes the diffusion of tin into silicon, leading to the synthesis of a Si1–xSnx amorphous phase. While micro-EDS confirms the presence of Sn in the amorphous phase, no fingerprint of any Si1–xSnx phase is observed in EEL spectra which show only c-Si and Sn (Fig. 4). This is certainly due to the low amounts of Si1–xSnx. It is interesting to note that irradiation of the amorphous Si-Sn layer by the TEM electron beam, induces tin segregation on the surface of the amorphous Si-Sn phase (see Supplemental Material 5), which further confirm the presence of alloyed tin. The TEM beam-induced segregation forms nano-sized (2–5 nm diameter) “exsolved” tin spheroids. The amorphous phase is expected to be far from thermodynamic equilibrium and the electron irradiation easily leads to the formation of two stable phases (silicon and tin), which could also be a reason for the absence of the Si-Sn EELS fingerprint.


Synthesis of nanocrystals by discharges in liquid nitrogen from Si-Sn sintered electrode.

Kabbara H, Noël C, Ghanbaja J, Hussein K, Mariotti D, Švrček V, Belmonte T - Sci Rep (2015)

(a) TEM image of a Si grain decorated by Sn spheroids scratched from the sintered material. (b) TEM image of a Si grain decorated by Sn spheroids obtained after treatment. The Si0.95Sn0.05 layer is delimited by squares. (c) Micro-EDS spectrum corresponding to the silicon crystal in image (a). (d) Micro-EDS spectrum corresponding to the Si0.95Sn0.05 layer in image (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4664926&req=5

f3: (a) TEM image of a Si grain decorated by Sn spheroids scratched from the sintered material. (b) TEM image of a Si grain decorated by Sn spheroids obtained after treatment. The Si0.95Sn0.05 layer is delimited by squares. (c) Micro-EDS spectrum corresponding to the silicon crystal in image (a). (d) Micro-EDS spectrum corresponding to the Si0.95Sn0.05 layer in image (b).
Mentions: When the ballast resistance is only 1 kΩ, the current is 10 A and spark discharges are much stronger. The erosion mechanism of the sintered target is then completely different. Very large grains of silicon decorated by tin nanoparticles with diameters ranging from 50 to 70 nm are heated by the discharge and shelled. The mean size of the loose grains collected in these conditions corresponds to that of silicon grains of the target. In Fig. 3a,b, two grains are shown, one collected directly by scratching the target before treatment, and one collected by sedimentation after treatment. The grain in Fig. 3a shows only two phases: a large silicon crystalline grain decorated by tin nanoparticles. Micro-EDS analysis (Fig. 3c) shows that silicon does not contain any tin before treatment. The grain in Fig. 3b, obtained by sedimentation after treatment, shows three phases: a large silicon crystalline grain decorated by tin nanoparticles and an amorphous phase. The amorphous irregular layer contains up to 5 wt.% (~1.2 at %) tin after treatment (micro-EDS analysis in Fig. 3d). The amorphous nature is probably due to the very high tin content, which is about 8 times the solubility of tin in solid silicon at 1100–1200 °C3. The amorphous phase was likely formed by melting the outermost part of the silicon crystal followed by rapid quenching as seen in Fig. 3b (areas delimited by squares); this could not be observed in Fig. 3a. During the initial heating and melting, Sn from surrounding nanoparticles has alloyed with the outermost part of the large silicon grains yielding the amorphous alloyed Si-Sn layer. We infer that heating of the silicon grains by the spark discharge promotes the diffusion of tin into silicon, leading to the synthesis of a Si1–xSnx amorphous phase. While micro-EDS confirms the presence of Sn in the amorphous phase, no fingerprint of any Si1–xSnx phase is observed in EEL spectra which show only c-Si and Sn (Fig. 4). This is certainly due to the low amounts of Si1–xSnx. It is interesting to note that irradiation of the amorphous Si-Sn layer by the TEM electron beam, induces tin segregation on the surface of the amorphous Si-Sn phase (see Supplemental Material 5), which further confirm the presence of alloyed tin. The TEM beam-induced segregation forms nano-sized (2–5 nm diameter) “exsolved” tin spheroids. The amorphous phase is expected to be far from thermodynamic equilibrium and the electron irradiation easily leads to the formation of two stable phases (silicon and tin), which could also be a reason for the absence of the Si-Sn EELS fingerprint.

Bottom Line: The presence of both vapours does not lead to the synthesis of alloyed nanocrystals but to the synthesis of separate nanocrystals of silicon and tin with average sizes of 10 nm.The synthesis of an am-Si0.95Sn0.05 phase around large silicon crystals (~500 nm) decorated by β-Sn spheroids is achieved if the current flowing through electrodes is high enough.When the sintered electrode is hit by powerful discharges, some grains are heated and tin diffuses in the large silicon crystals.

View Article: PubMed Central - PubMed

Affiliation: Université de Lorraine, Institut Jean Lamour, UMR CNRS 7198, NANCY, F-54042, France.

ABSTRACT
The synthesis feasibility of silicon-tin nanocrystals by discharges in liquid nitrogen is studied using a Si-10 at % Sn sintered electrode. Time-resolved optical emission spectroscopy shows that silicon and tin melt almost simultaneously. The presence of both vapours does not lead to the synthesis of alloyed nanocrystals but to the synthesis of separate nanocrystals of silicon and tin with average sizes of 10 nm. These nanocrystals are transformed into amorphous silicon oxide (am-SiO2) and β-SnO2 by air oxidation, after evaporation of the liquid nitrogen. The synthesis of an am-Si0.95Sn0.05 phase around large silicon crystals (~500 nm) decorated by β-Sn spheroids is achieved if the current flowing through electrodes is high enough. When the sintered electrode is hit by powerful discharges, some grains are heated and tin diffuses in the large silicon crystals. Next, these grains are shelled and fall into the dielectric liquid.

No MeSH data available.


Related in: MedlinePlus