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Y. Kobayashi and H. Kobayashi
4. For blue-PL arising from excitation with energies higher than 3.76 eV, PL peaks
with energies higher than the (0,0) band are present, and they are attributed to
transition from vibrational excited-states.
5. The excitation spectra show that blue-PL results from the two different
mechanisms: (i) excitation of adsorbed DMA and (ii) band-to-band transition
of Si nanopowder, followed by transfer of photo-generated electrons and holes
to DMA. For mechanism (ii), a photo-generated electron and a hole transfer to
DMA separately, resulting in two (0,0) bands.
6. Only when a photo-generated hole transfers to DMA first, followed by electron
transfer, transition from vibrational excited-states occurs.
7. Si nanopowder easily reacts with strong alkaline (pH>13) solutions, and almost
stoichiometric amount of hydrogen (i.e., ∼1700 mL/g) is generated in a few
minutes.
8. Si nanopowder reacts with water in a neutral pH region between 7 and 9
to generate hydrogen. In this case, the hydrogen generation rate markedly
increases with pH of the solution, while pH doesn’t change by the reaction.
In the first reaction stage, Si nanopowder reacts with OH - ions, generating
hydrogen, silicon oxide, and electrons in the conduction band of silicon oxide,
while in the second reaction stage, electrons are accepted by water molecules
to form hydrogen and OH - ions.
9. In the very early hydrogen generation reaction stage (less than 2.2 mL/g
hydrogen generation), the surface reaction is the rate-determining step, and
then, migration of OH - ions through a silicon oxide layer becomes the ratedetermining step.
10. The hydrogen generation reaction stops when a ∼5 nm silicon oxide layer is
formed on Si nanopowder.
11. The hydrogen generation rate strongly depends on the crystallite size of Si
nanopowder, but it doesn’t depend on the size of its agglomerate.
9.4 Outlook
Si is a nontoxic material, and its medical application is expected. We have proposed
two kinds of medical application of Si nanopowder, i.e., (i) photoluminescence
material and (ii) internal hydrogen generation material. For application (i), Si
nanopowder can be applied to life cell imaging, e.g., to detect cancer cells. Si
nanopowder, especially, blue-PL Si nanopowder, can give much stronger PL than
conventional dyes and is more stable, especially, high photostability, both of which
make the application easier and more effective.
For various diseases, oxidation stress is one of the largest factors to cause
diseases. Hydrogen generation in the body can decrease oxidative stress, and
therefore, it can prevent various oxidative stress-induced diseases. Moreover, for
apparently healthy persons, i.e., persons who don’t suffer from diseases but on
whom addition of a tiny factor causes diseases, a decrease of oxidative stress can
Y. Kobayashi and H. Kobayashi
4. For blue-PL arising from excitation with energies higher than 3.76 eV, PL peaks
with energies higher than the (0,0) band are present, and they are attributed to
transition from vibrational excited-states.
5. The excitation spectra show that blue-PL results from the two different
mechanisms: (i) excitation of adsorbed DMA and (ii) band-to-band transition
of Si nanopowder, followed by transfer of photo-generated electrons and holes
to DMA. For mechanism (ii), a photo-generated electron and a hole transfer to
DMA separately, resulting in two (0,0) bands.
6. Only when a photo-generated hole transfers to DMA first, followed by electron
transfer, transition from vibrational excited-states occurs.
7. Si nanopowder easily reacts with strong alkaline (pH>13) solutions, and almost
stoichiometric amount of hydrogen (i.e., ∼1700 mL/g) is generated in a few
minutes.
8. Si nanopowder reacts with water in a neutral pH region between 7 and 9
to generate hydrogen. In this case, the hydrogen generation rate markedly
increases with pH of the solution, while pH doesn’t change by the reaction.
In the first reaction stage, Si nanopowder reacts with OH - ions, generating
hydrogen, silicon oxide, and electrons in the conduction band of silicon oxide,
while in the second reaction stage, electrons are accepted by water molecules
to form hydrogen and OH - ions.
9. In the very early hydrogen generation reaction stage (less than 2.2 mL/g
hydrogen generation), the surface reaction is the rate-determining step, and
then, migration of OH - ions through a silicon oxide layer becomes the ratedetermining step.
10. The hydrogen generation reaction stops when a ∼5 nm silicon oxide layer is
formed on Si nanopowder.
11. The hydrogen generation rate strongly depends on the crystallite size of Si
nanopowder, but it doesn’t depend on the size of its agglomerate.
9.4 Outlook
Si is a nontoxic material, and its medical application is expected. We have proposed
two kinds of medical application of Si nanopowder, i.e., (i) photoluminescence
material and (ii) internal hydrogen generation material. For application (i), Si
nanopowder can be applied to life cell imaging, e.g., to detect cancer cells. Si
nanopowder, especially, blue-PL Si nanopowder, can give much stronger PL than
conventional dyes and is more stable, especially, high photostability, both of which
make the application easier and more effective.
For various diseases, oxidation stress is one of the largest factors to cause
diseases. Hydrogen generation in the body can decrease oxidative stress, and
therefore, it can prevent various oxidative stress-induced diseases. Moreover, for
apparently healthy persons, i.e., persons who don’t suffer from diseases but on
whom addition of a tiny factor causes diseases, a decrease of oxidative stress can