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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.


Photoluminescence spectra of large and small Si NPs before and after incorporation into aerogels. Photoluminescence spectra of free-standing PSi NPs of type LH (red dash-dot, second to top) and SO silicon nanospheres (blue dash-dot, third from top) and the silica aerogel without any particles (green dashed, bottom). The black, solid lines show PL spectra of aerogel-NP composites for a series of concentrations of LH particles increasing upwards (the initial concentrations in the gel preparation increase by factors of approximately 2 from 0.005 to 0.167 mg/ml). The arrow (bottom right) indicates the excitation energy of 3.81 eV (325 nm). All spectra are normalised to unit peak height. Top spectrum: un-normalised PL spectra of free-standing PSi NPs of type LH in vacuum (solid line) and in the presence of oxygen (dashed line); the arrow shows how the intensity drops on introduction of oxygen. No such change is observed for the same particles once incorporated in aerogel.
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Figure 1: Photoluminescence spectra of large and small Si NPs before and after incorporation into aerogels. Photoluminescence spectra of free-standing PSi NPs of type LH (red dash-dot, second to top) and SO silicon nanospheres (blue dash-dot, third from top) and the silica aerogel without any particles (green dashed, bottom). The black, solid lines show PL spectra of aerogel-NP composites for a series of concentrations of LH particles increasing upwards (the initial concentrations in the gel preparation increase by factors of approximately 2 from 0.005 to 0.167 mg/ml). The arrow (bottom right) indicates the excitation energy of 3.81 eV (325 nm). All spectra are normalised to unit peak height. Top spectrum: un-normalised PL spectra of free-standing PSi NPs of type LH in vacuum (solid line) and in the presence of oxygen (dashed line); the arrow shows how the intensity drops on introduction of oxygen. No such change is observed for the same particles once incorporated in aerogel.

Mentions: In Figure 1, we show the photoluminescence spectra of the large and small Si NPs in powder form before incorporation into the aerogels (the spectra are normalised to the PL peak height to highlight changes only in the shape of the bands). The PL spectrum of the large porous grains is dominated by silicon nanoparticles within the porous shell of each grain, so that the PL spectra of both PSi NPs and Si NSs are similar, though the PL band of the Si NSs is centred at a slightly higher energy and has a slightly lower width, suggesting a narrower size distribution for the Si NSs. When incorporated into aerogel, we see that the PL spectra of the composites are essentially those of the Si NPs still until the lowest concentrations are reached (going from top to bottom of Figure 1, which shows data for aerogels containing LH-type particles). For the lowest concentrations, the Si NP PL becomes weak in comparison to the broader, higher-energy emission from the silica aerogel itself, which is shown in the bottom PL spectrum and is typical of luminescent silica aerogels [21]. Essentially the same sequence of PL spectra is obtained also for the Si NPs of type LO in aerogel. This demonstrates that, in a first approximation, we can consider the PL of the composites as a superposition of the spectra of the Si NPs and the silica matrix; there is no evidence from this data for any interaction between the two.


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)

Photoluminescence spectra of large and small Si NPs before and after incorporation into aerogels. Photoluminescence spectra of free-standing PSi NPs of type LH (red dash-dot, second to top) and SO silicon nanospheres (blue dash-dot, third from top) and the silica aerogel without any particles (green dashed, bottom). The black, solid lines show PL spectra of aerogel-NP composites for a series of concentrations of LH particles increasing upwards (the initial concentrations in the gel preparation increase by factors of approximately 2 from 0.005 to 0.167 mg/ml). The arrow (bottom right) indicates the excitation energy of 3.81 eV (325 nm). All spectra are normalised to unit peak height. Top spectrum: un-normalised PL spectra of free-standing PSi NPs of type LH in vacuum (solid line) and in the presence of oxygen (dashed line); the arrow shows how the intensity drops on introduction of oxygen. No such change is observed for the same particles once incorporated in aerogel.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475076&req=5

Figure 1: Photoluminescence spectra of large and small Si NPs before and after incorporation into aerogels. Photoluminescence spectra of free-standing PSi NPs of type LH (red dash-dot, second to top) and SO silicon nanospheres (blue dash-dot, third from top) and the silica aerogel without any particles (green dashed, bottom). The black, solid lines show PL spectra of aerogel-NP composites for a series of concentrations of LH particles increasing upwards (the initial concentrations in the gel preparation increase by factors of approximately 2 from 0.005 to 0.167 mg/ml). The arrow (bottom right) indicates the excitation energy of 3.81 eV (325 nm). All spectra are normalised to unit peak height. Top spectrum: un-normalised PL spectra of free-standing PSi NPs of type LH in vacuum (solid line) and in the presence of oxygen (dashed line); the arrow shows how the intensity drops on introduction of oxygen. No such change is observed for the same particles once incorporated in aerogel.
Mentions: In Figure 1, we show the photoluminescence spectra of the large and small Si NPs in powder form before incorporation into the aerogels (the spectra are normalised to the PL peak height to highlight changes only in the shape of the bands). The PL spectrum of the large porous grains is dominated by silicon nanoparticles within the porous shell of each grain, so that the PL spectra of both PSi NPs and Si NSs are similar, though the PL band of the Si NSs is centred at a slightly higher energy and has a slightly lower width, suggesting a narrower size distribution for the Si NSs. When incorporated into aerogel, we see that the PL spectra of the composites are essentially those of the Si NPs still until the lowest concentrations are reached (going from top to bottom of Figure 1, which shows data for aerogels containing LH-type particles). For the lowest concentrations, the Si NP PL becomes weak in comparison to the broader, higher-energy emission from the silica aerogel itself, which is shown in the bottom PL spectrum and is typical of luminescent silica aerogels [21]. Essentially the same sequence of PL spectra is obtained also for the Si NPs of type LO in aerogel. This demonstrates that, in a first approximation, we can consider the PL of the composites as a superposition of the spectra of the Si NPs and the silica matrix; there is no evidence from this data for any interaction between the two.

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.