Limits...
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.


Raman spectra of a representative selection of composite samples. Raman spectra of silica aerogel (black, top) and aerogels containing (top to bottom) LH, LO and SO particles (blue, red and green, respectively). The vertical dashed lines indicate the Raman shifts of (left) the bulk silicon and (right) the silica D2 defect modes. For one of the aerogels containing LO particles, a representative fit to the data (discussed in the text) and its three components are shown (black and grey solid lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3475076&req=5

Figure 2: Raman spectra of a representative selection of composite samples. Raman spectra of silica aerogel (black, top) and aerogels containing (top to bottom) LH, LO and SO particles (blue, red and green, respectively). The vertical dashed lines indicate the Raman shifts of (left) the bulk silicon and (right) the silica D2 defect modes. For one of the aerogels containing LO particles, a representative fit to the data (discussed in the text) and its three components are shown (black and grey solid lines).

Mentions: In Figure 2, we show the Raman spectra of a representative selection of composite samples. At the top, we show the Raman spectrum of a pure silica aerogel; the bands at 485 and 620 cm−1 are, respectively, the D1 and D2 defect bands of the silica matrix (their microscopic origin has been widely debated: see [1,26] and references therein). The first-order Raman scattering of the Γ-point mode of bulk silicon gives a line at 521 cm−1, and as Figure 2 shows, the LH aerogel composites show a line close to this position (with a Lorentzian lineshape, centre at 522 cm−1, FWHM 12 to 14 cm−1). This implies that the Raman scattering is now dominated by the remaining solid silicon core of the PSi particles and, therefore, that there is very little of the porous shell remaining (however, the PL spectra of Figure 1 do demonstrate that there are some NPs still present in the LH aerogel).


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)

Raman spectra of a representative selection of composite samples. Raman spectra of silica aerogel (black, top) and aerogels containing (top to bottom) LH, LO and SO particles (blue, red and green, respectively). The vertical dashed lines indicate the Raman shifts of (left) the bulk silicon and (right) the silica D2 defect modes. For one of the aerogels containing LO particles, a representative fit to the data (discussed in the text) and its three components are shown (black and grey solid lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Raman spectra of a representative selection of composite samples. Raman spectra of silica aerogel (black, top) and aerogels containing (top to bottom) LH, LO and SO particles (blue, red and green, respectively). The vertical dashed lines indicate the Raman shifts of (left) the bulk silicon and (right) the silica D2 defect modes. For one of the aerogels containing LO particles, a representative fit to the data (discussed in the text) and its three components are shown (black and grey solid lines).
Mentions: In Figure 2, we show the Raman spectra of a representative selection of composite samples. At the top, we show the Raman spectrum of a pure silica aerogel; the bands at 485 and 620 cm−1 are, respectively, the D1 and D2 defect bands of the silica matrix (their microscopic origin has been widely debated: see [1,26] and references therein). The first-order Raman scattering of the Γ-point mode of bulk silicon gives a line at 521 cm−1, and as Figure 2 shows, the LH aerogel composites show a line close to this position (with a Lorentzian lineshape, centre at 522 cm−1, FWHM 12 to 14 cm−1). This implies that the Raman scattering is now dominated by the remaining solid silicon core of the PSi particles and, therefore, that there is very little of the porous shell remaining (however, the PL spectra of Figure 1 do demonstrate that there are some NPs still present in the LH aerogel).

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.