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Formation of silicon nanowire packed films from metallurgical-grade silicon powder using a two-step metal-assisted chemical etching method.

Ouertani R, Hamdi A, Amri C, Khalifa M, Ezzaouia H - Nanoscale Res Lett (2014)

Bottom Line: Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets.The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time.Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l'Énergie, Technopôle de Borj-Cédria, BP 95, 2050 Hammam-Lif, Tunisie.

ABSTRACT
In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.

No MeSH data available.


X-ray diffraction diagram of the untreated raw Si powder and Si powder after 60-min MACE.
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Figure 8: X-ray diffraction diagram of the untreated raw Si powder and Si powder after 60-min MACE.

Mentions: Three samples were left for etching times of 30, 60, and 90 min. SEM micrographs of these samples are displayed in Figure 6. They reveal that all facets of the SiμGs are covered with a densely packed film of self-organized nanowires. Some SiNWs were perpendicular to the facets but others slanted to the SiμG surfaces.According to these micrographs, after 30 min, nanosized Si pinecones began to appear. Some of them reach 0.2-μm height. As the etching time increases to 60 min, more nanowires were formed having 2.5-μm height. The average diameter of the wires is approximately 100 nm. After 90 min, Si pinecones disappeared whereas the SiNWs appeared taller, having 10-μm height. However many SiNWs were broken; some others congregated together (Figure 6c). The increasing etching rate observed in the last sample corresponding to 90-min etching time might be attributed first to the high density of defects in the starting SiμGs and then to the complete dissolution of the small-sized grains as a consequence of the decrease in the total surface area of the powder. Figure 7 depicts the etching time effect on the grain size distribution of the powder.Indeed, each etched SiμG is composed of a solid core covered by a densely packed film of SiNWs. A short etching duration ensures only the formation of a shallow thin film of SiNWs with thicknesses not exceeding 10 μm. Nevertheless, too long etching leads to a complete dissolution of the small SiμG. Since the initial Si powder consists of SiμG with a wide range of sizes (from 1 to 120 μm), only a part of them could be more or less partially nanostructured. It is obviously expected that the etching process would dissolve completely all silicon grains having a size dimension smaller than twice of the SiNW height. On the other hand, grains having a random shape with disparate sizes in two or three dimensions, simply, become smaller. SiμGs whose size exceeds 20 μm keep their size practically stable. This effect is confirmed by the GSD patterns displayed in Figure 7. Grain size frequencies shift towards medium-sized grains. Accordingly, the metal-assisted chemical etching narrows the GSD of the starting powder.On the basis of the XRD patterns in Figure 8, one may state that the lattice structure of the nanowires is nearly identical to that of bulk silicon.


Formation of silicon nanowire packed films from metallurgical-grade silicon powder using a two-step metal-assisted chemical etching method.

Ouertani R, Hamdi A, Amri C, Khalifa M, Ezzaouia H - Nanoscale Res Lett (2014)

X-ray diffraction diagram of the untreated raw Si powder and Si powder after 60-min MACE.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4209156&req=5

Figure 8: X-ray diffraction diagram of the untreated raw Si powder and Si powder after 60-min MACE.
Mentions: Three samples were left for etching times of 30, 60, and 90 min. SEM micrographs of these samples are displayed in Figure 6. They reveal that all facets of the SiμGs are covered with a densely packed film of self-organized nanowires. Some SiNWs were perpendicular to the facets but others slanted to the SiμG surfaces.According to these micrographs, after 30 min, nanosized Si pinecones began to appear. Some of them reach 0.2-μm height. As the etching time increases to 60 min, more nanowires were formed having 2.5-μm height. The average diameter of the wires is approximately 100 nm. After 90 min, Si pinecones disappeared whereas the SiNWs appeared taller, having 10-μm height. However many SiNWs were broken; some others congregated together (Figure 6c). The increasing etching rate observed in the last sample corresponding to 90-min etching time might be attributed first to the high density of defects in the starting SiμGs and then to the complete dissolution of the small-sized grains as a consequence of the decrease in the total surface area of the powder. Figure 7 depicts the etching time effect on the grain size distribution of the powder.Indeed, each etched SiμG is composed of a solid core covered by a densely packed film of SiNWs. A short etching duration ensures only the formation of a shallow thin film of SiNWs with thicknesses not exceeding 10 μm. Nevertheless, too long etching leads to a complete dissolution of the small SiμG. Since the initial Si powder consists of SiμG with a wide range of sizes (from 1 to 120 μm), only a part of them could be more or less partially nanostructured. It is obviously expected that the etching process would dissolve completely all silicon grains having a size dimension smaller than twice of the SiNW height. On the other hand, grains having a random shape with disparate sizes in two or three dimensions, simply, become smaller. SiμGs whose size exceeds 20 μm keep their size practically stable. This effect is confirmed by the GSD patterns displayed in Figure 7. Grain size frequencies shift towards medium-sized grains. Accordingly, the metal-assisted chemical etching narrows the GSD of the starting powder.On the basis of the XRD patterns in Figure 8, one may state that the lattice structure of the nanowires is nearly identical to that of bulk silicon.

Bottom Line: Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets.The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time.Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l'Énergie, Technopôle de Borj-Cédria, BP 95, 2050 Hammam-Lif, Tunisie.

ABSTRACT
In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.

No MeSH data available.