1. Introduction
Recently, the luminescent porous silicon (PS) has
been regarded as attractive material for various
sensor applications [1-4]. Chemical sensors based on
PS photoluminescence (PL) can bring advantages due to
a strong sensing of PL efficiency to adsorbates. In
fact, the adsorption of some molecules results in the
reduction or even disappearance of the strong visible
PL that recovers entirely after the removing of solvents
[5, 6], because no net chemical reaction occurs during
the adsorption/desorption of molecules. The mechanisms
of PL quenching by adsorbates are summarised in [1,
7 - 9] and include the following models: (i) the increase
of the non-radiative recombination rate in the nanoparticles
due to the alteration of the dielectric medium outside
the Si nanocrystallites; (ii) the enhancement of the
non-radiative vibronic coupling to the surface vibrational
modes; (iii) the change of the nanoparticle surface
electronic structure; (iv) the capture increase on the
non-radiative traps at the forming of the strain-induced
defects when molecules are adsorbed, etc. The correlation
between PL quenching and solvent dipole moment, established
by authors of [6], means that the solvent induces the
capture of electrons or holes by the surface traps.
The molecules with the large dipole moment as methanol
or ethanol quench the PL stronger in comparison with
the weak quenching by benzene or toluene having a small
dipole moment. The reversible quenching phenomenon has
been interpreted as the stabilisation of the surface
traps by the alignment of molecular dipoles on the PS
surface. Usually, the PL quenching is accompanied
by the asymmetrical shape of the PL spectrum. The blue
shifting or the decrease of the emission in the long
wavelength region was observed after the treatment in
the boiling CCl4 [10], organoamine molecules
[11], C2H5OH [12], and methanol
[13]. However, there are the experimental evidences
of anomalous behaviour of PL quantum efficiency at the
adsorption of some molecules [14, 15]. Taking into consideration
that the PL of PS is correlated closely with the nanostructure
of porous materials and their surface reactivity, the
nature of the observed asymmetrical shape of the PL
is correlated with the inhomogeneity of the luminescent
layer. Thus, the study of the alteration of PL properties
in various environments can be a useful tool for the
analysis of the PS inhomogeneity. To get an understanding
of the effects of the structural- chemical inhomogeneity
on PL, that can take place in the electrochemically
etched PS, the spectra and kinetics of PS emission in
the ambient atmosphere and saturated acetone vapours
were investigated in present work.
abstract
1. Introduction
2. Experimental
3. PL of multilayer PS film:
simulation
4. PL of the inhomogeneous PS
film: Influence of The acetone adsorption
5. Conclusions
Captures for the figures
References
V.A.Skryshevsky
Radiophysics Department, Kiev Shevchenko
University,
64 Vladimirskaya, 01033, Kiev, Ukraine, fax.+380-44-2656744,
e-mail: skrysh@uninet.kiev.ua
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