Ammonia sensing characteristics of nanoparticles as well as nanorods of ZnO,
In2O3
and SnO2
have been investigated over a wide range of concentrations (1–800 ppm) and temperatures
(100–300 °C). The best values of sensitivity are found with ZnO nanoparticles and
SnO2
nanostructures. Considering all the characteristics, the
SnO2
nanostructures appear to be good candidates for sensing ammonia, with sensitivities of 222 and 19 at
300 °C and
100 °C respectively
for 800 ppm of NH3. The recovery and response times are respectively in the ranges 12–68 s and 22–120 s. The
effect of humidity on the performance of the sensors is not marked up to 60% at
300 °C. With the oxide sensors reported here no interference for
NH3 is found
from H2, CO,
nitrogen oxides, H2S
and SO2.
Spintronics and valleytronics are emerging quantum electronic technologies that rely on using electron spin and multiple extrema of the band structure (valleys), respectively, as additional degrees of freedom. There are also collective properties of electrons in semiconductor nanostructures that potentially could be exploited in multifunctional quantum devices. Specifically, plasmonic semiconductor nanocrystals offer an opportunity for interface-free coupling between a plasmon and an exciton. However, plasmon-exciton coupling in single-phase semiconductor nanocrystals remains challenging because confined plasmon oscillations are generally not resonant with excitonic transitions. Here, we demonstrate a robust electron polarization in degenerately doped InO nanocrystals, enabled by non-resonant coupling of cyclotron magnetoplasmonic modes with the exciton at the Fermi level. Using magnetic circular dichroism spectroscopy, we show that intrinsic plasmon-exciton coupling allows for the indirect excitation of the magnetoplasmonic modes, and subsequent Zeeman splitting of the excitonic states. Splitting of the band states and selective carrier polarization can be manipulated further by spin-orbit coupling. Our results effectively open up the field of plasmontronics, which involves the phenomena that arise from intrinsic plasmon-exciton and plasmon-spin interactions. Furthermore, the dynamic control of carrier polarization is readily achieved at room temperature, which allows us to harness the magnetoplasmonic mode as a new degree of freedom in practical photonic, optoelectronic and quantum-information processing devices.
Controlling
plasmonic properties of aliovalently doped semiconductor
nanocrystals in mid-infrared (MIR) spectral region is of a particular
current interest, because of their potential application in heat-responsive
devices and near-field enhanced spectroscopies. However, a lack of
detailed understanding of the correlations among the electronic structure
of the host lattice, dopant ions, and surface properties hampers the
development of MIR-tunable plasmonic nanocrystals (NCs). In this article,
we report the colloidal synthesis and spectroscopic properties of
two new plasmonic NC systems based on In2O3,
antimony- and titanium-doped In2O3 NCs, and
comparative investigation of their electronic structure using the
combination of the Drude–Lorenz model and density functional
theory. The localized surface plasmon resonances (LSPRs) lie at lower
energies and have smaller bandwidths for Ti-doped than for Sb-doped
In2O3 NCs with similar doping levels, indicating
lower free electron density. Surprisingly, the Fermi level is found
to be higher in Ti-doped In2O3 than in Sb-doped
In2O3, suggesting the formation of electron
trap states on nanocrystal surfaces, which reduce carrier density
without significantly impacting their mobility. Controlling the competition
between doping concentration and electron trapping allowed us to generate
LSPR in Ti-doped In2O3 nanocrystals deep in
the MIR region, and tune the absorption spectra from 650 cm–1 to 8000 cm–1. We also demonstrated the possibility
to enhance the intensity of LSPR in these new plasmonic NCs by adjusting
the synthesis and post-synthesis treatment conditions. The results
of this work allow for an expansion of the tuning range of LSPR of
colloidal metal oxide NCs by controlling the electronic structure
of aliovalent dopant and charge carrier trapping.
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