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Porous silicon nanocrystals in a silica aerogel matrix.

Amonkosolpan J, Wolverson D, Goller B, Polisski S, Kovalev D, Rollings M, Grogan MD, Birks TA - Nanoscale Res Lett (2012)

Bottom Line: Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres.No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised.Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK. d.wolverson@bath.ac.uk.

ABSTRACT
Silicon nanoparticles of three types (oxide-terminated silicon nanospheres, micron-sized hydrogen-terminated porous silicon grains and micron-size oxide-terminated porous silicon grains) were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation.

No MeSH data available.


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Fourier transform infrared transmission spectra in the attenuated total reflection configuration. Partially oxidised porous silicon (top), free SO nanoparticles (magenta), aerogels containing nanoparticles of SO (green) and LH (blue) types, and pure silica aerogels (bottom). The spectra are all baseline corrected and normalised to 3% transmission at the Si-O-Si absorption band at approximately 1,100 cm−1 so as to show the relative strength of the Si-H modes indicated by the vertical dashed lines. The peaks indicated by arrows in the aerogel spectra are due to CH3 absorptions.
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Figure 4: Fourier transform infrared transmission spectra in the attenuated total reflection configuration. Partially oxidised porous silicon (top), free SO nanoparticles (magenta), aerogels containing nanoparticles of SO (green) and LH (blue) types, and pure silica aerogels (bottom). The spectra are all baseline corrected and normalised to 3% transmission at the Si-O-Si absorption band at approximately 1,100 cm−1 so as to show the relative strength of the Si-H modes indicated by the vertical dashed lines. The peaks indicated by arrows in the aerogel spectra are due to CH3 absorptions.

Mentions: Finally, we have tested the above conclusions using FTIR, since this provides a sensitive identification of Si-O-Si and Si-H vibrational modes via their IR absorption bands at around 1,030 and 1,180 cm−1 (Si-O-Si) and 2,000 to 2,200 cm−1 (Si-H, Si-H2 and Si-H3 stretches) [9,27]. On Figure 4, the vertical dashed lines show the positions of the bands associated with the three Si-H stretching modes. These modes are readily seen in, for example, conventional electrochemically etched PSi (top) even after it is several months old and substantially oxidised (which is indicated, for instance, by the presence of the band at 790 cm−1 marked by the dotted line [9]). The Si-H modes are also weakly present in the IR spectra of the nanoscale silicon particles before and even after aerogel preparation (second from top) despite the fact that they are mostly oxidised. The FTIR spectra of the composite aerogels made using LH particles, however, do not show any sign of these bands, and we obtain spectra that are dominated by the IR absorption of silica aerogel (shown at the bottom of Figure 4 for comparison) even for samples that contain sufficient concentrations of nanoparticles that they are opaque for visible light. The silica aerogel IR spectra show the expected Si-O modes but also two weak modes arising from Si-CH3 groups indicated by the two arrows [28]. The fact that these are only weak is consistent with the aerogel surface being hydrophilic (a large Si-CH3 coverage leads to a hydrophobic surface). Finally, as one would expect, we see no sign of Si-H modes in the aerogels containing large, oxidised particles, and their FTIR spectra (not shown in Figure 4) are very similar to those of our silica aerogels and those reported in the past [28]; we note that the Si-Si modes of the bulk silicon cores will not be detected via IR absorption.


Porous silicon nanocrystals in a silica aerogel matrix.

Amonkosolpan J, Wolverson D, Goller B, Polisski S, Kovalev D, Rollings M, Grogan MD, Birks TA - Nanoscale Res Lett (2012)

Fourier transform infrared transmission spectra in the attenuated total reflection configuration. Partially oxidised porous silicon (top), free SO nanoparticles (magenta), aerogels containing nanoparticles of SO (green) and LH (blue) types, and pure silica aerogels (bottom). The spectra are all baseline corrected and normalised to 3% transmission at the Si-O-Si absorption band at approximately 1,100 cm−1 so as to show the relative strength of the Si-H modes indicated by the vertical dashed lines. The peaks indicated by arrows in the aerogel spectra are due to CH3 absorptions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 4: Fourier transform infrared transmission spectra in the attenuated total reflection configuration. Partially oxidised porous silicon (top), free SO nanoparticles (magenta), aerogels containing nanoparticles of SO (green) and LH (blue) types, and pure silica aerogels (bottom). The spectra are all baseline corrected and normalised to 3% transmission at the Si-O-Si absorption band at approximately 1,100 cm−1 so as to show the relative strength of the Si-H modes indicated by the vertical dashed lines. The peaks indicated by arrows in the aerogel spectra are due to CH3 absorptions.
Mentions: Finally, we have tested the above conclusions using FTIR, since this provides a sensitive identification of Si-O-Si and Si-H vibrational modes via their IR absorption bands at around 1,030 and 1,180 cm−1 (Si-O-Si) and 2,000 to 2,200 cm−1 (Si-H, Si-H2 and Si-H3 stretches) [9,27]. On Figure 4, the vertical dashed lines show the positions of the bands associated with the three Si-H stretching modes. These modes are readily seen in, for example, conventional electrochemically etched PSi (top) even after it is several months old and substantially oxidised (which is indicated, for instance, by the presence of the band at 790 cm−1 marked by the dotted line [9]). The Si-H modes are also weakly present in the IR spectra of the nanoscale silicon particles before and even after aerogel preparation (second from top) despite the fact that they are mostly oxidised. The FTIR spectra of the composite aerogels made using LH particles, however, do not show any sign of these bands, and we obtain spectra that are dominated by the IR absorption of silica aerogel (shown at the bottom of Figure 4 for comparison) even for samples that contain sufficient concentrations of nanoparticles that they are opaque for visible light. The silica aerogel IR spectra show the expected Si-O modes but also two weak modes arising from Si-CH3 groups indicated by the two arrows [28]. The fact that these are only weak is consistent with the aerogel surface being hydrophilic (a large Si-CH3 coverage leads to a hydrophobic surface). Finally, as one would expect, we see no sign of Si-H modes in the aerogels containing large, oxidised particles, and their FTIR spectra (not shown in Figure 4) are very similar to those of our silica aerogels and those reported in the past [28]; we note that the Si-Si modes of the bulk silicon cores will not be detected via IR absorption.

Bottom Line: Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres.No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised.Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK. d.wolverson@bath.ac.uk.

ABSTRACT
Silicon nanoparticles of three types (oxide-terminated silicon nanospheres, micron-sized hydrogen-terminated porous silicon grains and micron-size oxide-terminated porous silicon grains) were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation.

No MeSH data available.


Related in: MedlinePlus