Abstract
In the present study, we report a controlled growth of tin oxide and tin oxide: carbon nanoparticles by an integrated method comprising of the gas phase agglomeration, electrical mobility based size selection, and in–flight sintering steps. The effect of in-flight sintering temperature and variation in growth environment (N2, H2 and O2) during nanoparticle formation, morphology and composition has been investigated by carrying out High Resolution Transmission Electron microscopy and X-Ray diffraction studies. The results highlight the novelty of the present technique to grow alloy and core-shell nanoparticles in which the stoichiometery (x) of SnOx and the mode of incorporation of carbon into the tin oxide lattice (alloy or core-shell structure), along with well-defined size can be controlled independently. Detailed Photoluminescence (PL) studies of well sintered monocrystalline SnO, SnOx and SnO2 nanoparticles along with SnOx:C and SnO2:C alloy and C@SnO core-shell nanoparticle has been carried out. The shift in the position and nature of PL peaks due to band edge, Sn interstitials and oxygen vacancy defect level energy states has been understood as a function of stoichiometery and nanoparticle structure (alloy and core-shell). These results suggest the possibility of tailoring the position of these levels by controlling the size, composition and alloying which is potentially important for gas sensing, photoconductivity and photo-electrochemical applications.
Highlights
Tin is known to primarily exist in two oxide states, stannic (SnO2) and stannous (SnO), with some reports on the existence of other phases such as Sn3O4 and Sn2O3
The results of the present study clearly show the versatility of the present nanoparticle growth technique to synthesise controlled stoichiometery of tin oxide nanoparticles along with their nanoparticle size
XRD results clearly confirm the formation of nanoparticles having different phases: SnO, SnO2 and sub-stoichiometeric SnOx grown by using different ambient during growth and sintering
Summary
Tin is known to primarily exist in two oxide states, stannic (SnO2) and stannous (SnO), with some reports on the existence of other phases such as Sn3O4 and Sn2O3. Photoluminescence (PL) is an important tool to obtain information about the nature and concentration of defects and impurities in the nanocrystals.[12,13] Bulk SnO2 is known to behave as a direct band gap semiconductor with selection rules due to their special wave function symmetry making transitions forbidden, nanostructure materials are known to break this selection rule.[14] Non-radiative nature of indirect bandgap is well known for bulk SnO and SnO2, strong luminescence is observed in their nano-counterparts.[4] Optical properties of nanostructures due to confinement exhibit interesting results as the particle size becomes comparable to the Bohr radius of the exciton and because of the enhanced surface to volume ratio. The luminescence is generally believed to come from defects such as oxygen vacancies and tin interstitial or dangling bonds.[1] It is important to study the effect of carbon alloying and core-shell formation on the PL processes. Detailed XRD and PL spectroscopy studies of these nanostructures has been carried out to understand the effect of carbon incorporation on the structural and stoichiometeric defects
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