2 research outputs found
Giant O<sub>2</sub>‑Induced Photoluminescence Modulation in Hierarchical Titanium Dioxide Nanostructures
We
demonstrate exceptionally large modulation of PL intensity in
hierarchical titanium dioxide (TiO<sub>2</sub>) nanostructures exposed
to molecular oxygen (O<sub>2</sub>). Optical responsivities up to
about 1100% at 20% O<sub>2</sub> concentrations are observed in hyperbranched
anatase-phase hierarchical structures, outperforming those obtainable
by commercial TiO<sub>2</sub> nanopowders (up to a factor of ∼7
for response to synthetic air) and significantly improving the ones
typically reported in PL-based opto-chemical gas sensing using MOXs.
The improved PL response is discussed in terms of the specific morphology
of hierarchical structures, characterized by simultaneous presence
of small nanoparticles, large surface areas, and large voids. These
characteristics guarantee an optimal interplay between photogenerated
charges, PL-active centers, and adsorbed gas molecules. The results
highlight the potentialities offered by hierarchical structures based
on TiO<sub>2</sub> or other MOXs and open interesting scenarios toward
the development of all-optical and/or hybrid (opto/electrical) chemical
sensors with improved sensitivity
Direct Evidence of Polar Ordering and Investigation on Cytophilic Properties of Pyroelectrified Polymer Films by Optical Second Harmonic Generation Analysis
Pyroelectrification
(PE) has been proposed as a low-cost electrode-free
tool for orienting and aligning dipole molecules in polymer layers,
by means of the electric field produced by a pyroelectric crystal
under appropriate thermal stimulations. Probing and assessing the
coherent polarization arrangement is of fundamental importance for
the process control and optimization but is also a challenging task.
In fact, the probing operation must be noninvasive and avoid any disarrangement
the dipoles and thus without interfering with the resulting surface
charges. Here we show that the PE-induced polar ordering can be probed <i>in situ</i> by an electrode-free analysis based on the measurement
of the intensity of the second-harmonic optical wave generated by
the polymer film. In fact, the results show a substantial enhancement
of the second-order susceptibility of the polymer layer, caused by
the PE-induced dipoles alignment. Moreover, thanks to this approach,
it is demonstrated the ability of PE process to polarize polymer layers
even in the “noncontact configuration”, i.e., when a
dielectric spacer (glass substrate) is placed between the pyroelectric
crystal and the polymer film