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For integrated photonics, waveguide structures based on rare-earth-activated glasses are potential candidates for implementing compact integrated light sources and amplifiers. However, rare-earth ions (REs) possess low absorption cross-section, and this limits the light emission and amplification efficiency. As long as the REs are involved, there are other phenomena detrimental to their luminescence quantum yield including ion-ion interactions and non-radiative relaxation processes. To solve such problems, photonic glass-ceramics can be strategic solutions. Transparent glass-ceramics combine interesting properties of both amorphous and crystalline phases and offer specific characteristics of capital importance in photonics. More important, photonic glass-ceramics can tailor and enhance the spectroscopic properties of the rare-earth ions depending on their compositions and nature. In this work, we studied SnO2-nanocrystal-based transparent glass-ceramic planar waveguides activated by rare-earths to give solutions for the problems mentioned above and enhance the rare-earth luminescence efficiency for integrated photonics. SiO2–SnO2:Er3+ planar waveguides containing 30 mol% SnO2 nanocrystals were fabricated by sol-gel method and dip-coating technique. The planar waveguides were assessed by various characterization techniques to ensure the applicability of such glass-ceramics for integrated photonics. The experimental assessment of the SiO2–SnO2:Er3+ planar waveguides focused on the key considered photonic characteristics including the structural, morphological, spectroscopic, and especially optical waveguiding properties. The photoluminescence measurements put in evidence the role of SnO2 nanocrystals as efficient Er3+ luminescence sensitizers. Moreover, the incorporation of Er3+ ions in SnO2 nanocrystals was demonstrated to reduce the effect of non-radiative relaxation processes on the luminescence of the Er3+ ions and thus led to higher luminescence efficiency. Majority of the Er3+ ions (97%) was confirmed to be imbedded in the SnO2 nanocrystals. The SiO2–SnO2:Er3+ glass-ceramic planar waveguides have confined propagation modes, step-index profile with high confinement of 82% at 1542 nm and especially, low losses of 0.6 ± 0.2 dB/cm at 1542 nm.

The gas-sensing properties and mechanism and the role of the shell thickness of structurally well-defined SnO2/NiO heterostructures are studied. One-dimensional (1D) SnO2/NiO core–shell nanowires (...

SnO2 is one of the most employed n-type semiconducting metal oxide (SMOX) in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, we introduce one-dimensional (1D) SnO2-SiO2 core-shell nanowires (CSNWs). SnO2 nanowires (NWs) are synthesized by vapor–liquid–solid deposition and the amorphous SiO2-shell layer with varying thicknesses (1.8-10.5 nm) was grown by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show lower baseline conductance as compared to the Pristine SnO2 NWs, due to an enhancement of the electron depletion layer. The SnO2-SiO2/N CSNWs (N representing the number of SiO 2 ALD cycles) sensors show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response markedly depends on the thickness of the SiO2-shell layer and the working temperature. The SnO2-SiO2/60 CSNWs sensor (ca. 4.8 nm SiO2 shell thickness) was the best performing sensor in terms of selectivity and sensitivity exhibiting a response of 160 (ca. 7-folds higher than the pristine SnO2 NWs) towards 500 ppm of hydrogen at 500 °C with a lower detection limit at ppb-level (0.082 ppm). The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increased in the width of the electron depletion layer due to the strong electronic coupling between the SnO2 core and SiO2-shell layer, respectively. The remarkable sensing performances of the SnO2-SiO2/N CSNWs can be attributed to the homogeneous and conformal SiO2 shell layer by ALD,electronic coupling between the core and the shell, the optimized shell thickness and high surface area provided by the 1D SnO2 NWs network.

Among oxide semiconductors, p-type Mn3O4 systems have been exploited in chemo-resistive sensors for various analytes, but their use in the detection of H2, an important, though flammable, energy vector, has been scarcely investigated. Herein, we report for the first time on the plasma assisted-chemical vapor deposition (PA-CVD) of Mn3O4 nanomaterials, and on their on-top functionalization with Ag and SnO2 by radio frequency (RF)-sputtering, followed by air annealing. The obtained Mn3O4-Ag and Mn3O4-SnO2 nanocomposites were characterized by the occurrence of phase-pure tetragonal &alpha, Mn3O4 (hausmannite) and a controlled Ag and SnO2 dispersion. The system functional properties were tested towards H2 sensing, yielding detection limits of 18 and 11 ppm for Mn3O4-Ag and Mn3O4-SnO2 specimens, three orders of magnitude lower than the H2 explosion threshold. These performances were accompanied by responses up to 25% to 500 ppm H2 at 200 &deg, C, superior to bare Mn3O4, and good selectivity against CH4 and CO2 as potential interferents. A rationale for the observed behavior, based upon the concurrence of built-in Schottky (Mn3O4/Ag) and p-n junctions (Mn3O4/SnO2), and of a direct chemical interplay between the system components, is proposed to discuss the observed activity enhancement, which paves the way to the development of gas monitoring equipments for safety end-uses.

In this work, layered hybrid composites formed by tin oxide (SnO) nanoparticles synthesized by hydrolysis and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) have been analyzed. Prior to the composite study, both SnO and PEDOT:PSS counterparts were characterized by diverse techniques, such as X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), photoluminescence (PL), atomic force microscopy (AFM), optical absorption and Hall effect measurements. Special attention was given to the study of the stability of the polymer under laser illumination, as well as the analysis of the SnO to SnO2 oxidation assisted by laser irradiation, for which different laser sources and neutral filters were employed. Synergetic effects were observed in the hybrid composite, as the addition of SnO nanoparticles improves the stability and electrical conductivity of the polymer, while the polymeric matrix in which the nanoparticles are embedded hinders formation of SnO2. Finally, the Si passivation behavior of the hybrid composites was studied.

SnO prepared by soft chemistry exhibits a black color and semiconducting properties. The X-ray diffraction indicates a tetragonal symmetry (SG: P4/nmm) with nano crystallites of an average size of 85 nm. The forbidden band, determined from the diffuse reflectance is found to be 1.46 eV. The electrical conductivity occurs by polaron hopping and follows an Arrhenius type law with activation energy of 0.21 eV, the change in the slope at 526 K is attributed to the oxidation to SnO 2 . The photo-electrochemical study shows n type conduction with a flat band potential of −0.45 V, close to the photocurrent onset potential (−0.40 V). The electrochemical impedance spectroscopy shows the bulk contribution of SnO (R b = 1.7 kΩ cm 2 ) and decreases down to 1.89 kΩ cm 2 under illumination. The photocatalytic properties have been evaluated for the first time for to the oxygen evolution. The valence band, deriving from Sn 2+ : 5p orbital with a potential (−0.80 V SCE /5.55 eV), is suitably positioned with respect to O 2 /H 2 O level (∼0.6 V SCE ), leading to water oxidation under visible light. The best performance occurs at pH ∼ 7 with an oxygen liberation rate of 23 µmol mL h −1 (mg catalyst) −1 and a quantum efficiency of 1.2%. An improvement of ∼13% is observed on the system SnO/clay.

Outstanding performance of perovskite solar cells (PSCs) is closely linked to the optoelectrical properties of charge transporting layers. Herein, amino trimethylene phosphonic acid (ATMP) and KOH are mixed (ATMP-K) and incorporated in a SnO2 precursor solution to significantly improve the performance of the electron transport layer (ETL) SnO2 in PSCs. Combining density functional theory (DFT) calculations and experiments, it is demonstrated that ATMP-K effectively passivates the oxygen vacancy and reduces the hydroxyl groups on the surface of SnO2, resulting in a larger perovskite grain size and better energy-level alignment with perovskites. ATMP-K boosts the power conversion efficiency (PCE) of the PSCs from 20.99% to 23.52%. When applying in a perovskite/silicon heterojunction tandem solar cell, the device delivers an efficiency up to 24.75% with a high VOC of 1.94 V, compared with 22.67% and 1.85 V of the reference cells. Furthermore, ATMP-K-modified PSCs also show extraordinary ability to absorb Pb2+ ions after their degradation in water, offering a facile strategy for reducing Pb leakage.

Made available in DSpace on 2020-12-10T19:38:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-12 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) MRSEC Program of the National Science Foundation This work reports on the gas sensor response of undecorated 1D stannous oxide nanobelts and those decorated with Pt and Pd nanoparticles. The sensor device responses to H-2, CO and NO2 were measured in dry air baseline atmosphere as functions of the analyte concentration (1-1000 ppm) and temperature (100-350 degrees C). Noble metal decorated SnO devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap. Gas sensing results also showed superior selectivity to H-2 for metal-decorated nanobelts. Based on the findings in this work, we propose an array based on SnO structures capable of detecting and distinguishing reducing and oxidizing gases. Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Araraquara, SP, Brazil MIT, Dept Mat Sci & Engn, Cambridge, MA 02139 USA Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Araraquara, SP, Brazil FAPESP: 2012/51195-3 FAPESP: 2013/08734-3 FAPESP: 2013/18511-1 FAPESP: 2014/50725-4 CNPq: 447760/2014-9 CNPq: 443138/2016-8 MRSEC Program of the National Science Foundation: DMR - 141,980

Numerous studies have addressed the utilization of oxide thin-film transistor (TFT)-based complementary logic circuits that are based on two-dimensional (2D) planar structures. However, there are fundamental limits to the 2D planar structured complementary logic circuits, such as a large dimension and a large parasitic resistance. This work demonstrated a vertically stacked three-dimensional complementary inverter composed of a p-channel tin monoxide (SnO) TFT and an n-channel indium-gallium-zinc oxide (IGZO) TFT. A bottom-gate p-channel SnO TFT was formed on the top-gate n-channel IGZO TFT with a shared common gate electrode. The fabricated vertically stacked complementary inverter exhibited full swing characteristics with a voltage gain of ~33.6, a high noise margin of 3.13 V, and a low noise margin of 3.16 V at a supplied voltage of 10 V. The achieved voltage gain of the fabricated complementary inverter was higher than that of the vertically stacked complementary inverters composed of other oxide TFTs in previous works. In addition, we showed that the vertically stacked complementary inverter exhibited excellent visible-light photoresponse. This indicates that the oxide TFT-based vertically stacked complementary inverter can be used as a sensitive photo-sensor operating in the visible spectral range with the voltage read-out scheme.

Made available in DSpace on 2019-10-04T12:39:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-07-16 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) There is an increasing concern about NOx emission, and many studies have been carried out using metal oxide semiconductors (MOS) aiming its detection. Among the MOS, the SnO micro-disks present a high sensor response and a great selectivity toward NO2. Nevertheless, sensor signal, limit of detection (LOD), and recovery time are related to the experimental setup used to carry on the measurements. Thus, two different heating methods (self-heating and external heating) have been carried out to understand in what manner they change the sensor properties of the SnO micro-disks onto interdigitated electrodes. The external heating method presented higher sensor signal, best LOD, and lower recovery time, mainly due to the lack of a temperature gradient between the SnO disks and the chamber atmosphere. On the other hand, response time was shown to be the same regardless of the method. Briefly, the authors used thermodynamic equations to better understand the temperature effect on the gas-solid interactions occurring between SnO disks and NO2 species. Univ Surrey, Adv Technol Inst, Guildford, Surrey, England Sao Paulo State Univ, Dept Phys Chem, Araraquara, Brazil Sao Paulo State Univ, Dept Phys Chem, Araraquara, Brazil FAPESP: 2013/07296-2 FAPESP: 2015/21033-0 FAPESP: 2017/12870-0 FAPESP: 2017/26219-0 CNPq: 447760/2014-9 CNPq: 303542/2015-2 CNPq: 443138/2016-8

In this work, semiconductor tin oxide (II) (SnO) nanoparticles and plates were synthesized at room conditions via a hydrolysis procedure. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the high crystallinity of the as-synthesized romarchite SnO nanoparticles with dimensions ranging from 5 to 16 nm. The stability of the initial SnO and the controlled oxidation to SnO2 was studied based on either thermal treatments or controlled laser irradiation using a UV and a red laser in a confocal microscope. Thermal treatments induced the oxidation from SnO to SnO2 without formation of intermediate SnOx, as confirmed by thermodiffraction measurements, while by using UV or red laser irradiation the transition from SnO to SnO2 was controlled, assisted by formation of intermediate Sn3O4, as confirmed by Raman spectroscopy. Photoluminescence and Raman spectroscopy as a function of the laser excitation source, the laser power density, and the irradiation duration were analyzed in order to gain insights in the formation of SnO2 from SnO. Finally, a tailored spatial SnO/SnO2 micropatterning was achieved by controlled laser irradiation with potential applicability in optoelectronics and sensing devices.

The electronic and atomic structures of amorphous transparent tin oxides have been investigated by a combination of X-ray spectroscopy and atomistic calculations. Crystalline SnO is a promising p-type transparent oxide semiconductor due to a complex lone-pair hybridization that affords both optical transparency despite a small electronic band gap and spherical s-orbital character at the valence band edge. We find that both of these desirable properties (transparency and s-orbital valence band character) are retained upon amorphization despite the disruption of the layered lone-pair states by structural disorder. We explain the anomalously large band gap widening necessary to maintain transparency in terms of lone-pair stabilization via atomic clustering. Our understanding of this mechanism suggests that continuous hole conduction pathways along extended lone pair clusters should be possible under certain stoichiometries. Moreover, these findings should be applicable to other lone-pair active semiconductors.

In this study, the effects of capping layers with different metals on the electrical performance and stability of p-channel SnO thin-film transistors (TFTs) were examined. Ni- or Pt-capped SnO TFTs exhibit a higher field-effect mobility (μFE), a lower subthreshold swing (SS), a positively shifted threshold voltage (VTH), and an improved negative-gate-bias-stress (NGBS) stability, as compared to pristine TFTs. In contrast, Al-capped SnO TFTs exhibit a lower μFE, higher SS, negatively shifted VTH, and degraded NGBS stability, as compared to pristine TFTs. No significant difference was observed between the electrical performance of the Cr-capped SnO TFT and that of the pristine SnO TFT. The obtained results were primarily explained based on the change in the back-channel potential of the SnO TFT that was caused by the difference in work functions between the SnO and various metals. This study shows that capping layers with different metals can be practically employed to modulate the electrical characteristics of p-channel SnO TFTs.

The surface of SnO2 nanowires was functionalized by chitosan for the development of room-temperature conductometric humidity sensors. SnO2 nanowires were synthesized by the seed-mediated physical-vapor-deposition (PVD) method. Chitosan layers were deposited on top of the SnO2 nanowires by spin coating. Surface morphology, crystal structure, and optical properties of the synthesized hybrid nanostructure were investigated by scanning electron microscope, grazing incidence X-ray diffraction, and UV&ndash, Vis absorption measurements. During electrical conductivity measurements, the hybrid nanostructure showed unusual behavior towards various relative humidity (RH) concentrations (25%, 50%, 75%), under UV-light irradiation, and in dark conditions. The highest sensor responses were recorded towards an RH level of 75%, resulting in 1.1 in the dark and 2.5 in a UV-irradiated chamber. A novel conduction mechanism of hybrid nanowires is discussed in detail by comparing the sensing performances of chitosan film, SnO2 nanowires, and chitosan@SnO2 hybrid nanostructures.

Planar perovskite solar cells and modules were realized by using low temperature solution-process fabrication procedures. The photovoltaic performance was improved by optimizing a SnO2 electron transport layer and its interface with the perovskite layer. We achieved a power conversion efficiency (PCE) of 17.3% on small area cell (0.09 cm2) with negligible hysteresis and a steady-state PCE equal to 17.4%. Furthermore, shelf life tests showed a relative decrease of only 5% in PCE from its initial value after 1000 h of storage in dark conditions in air (RH 20%). Up-scaling of the technology was implemented entirely in air with fabrication of modules with a high aperture ratio of 91%. The modules delivered a maximum PCE of 13.1% obtained on an active area of 13.8 cm2 and of 11.9% on an aperture area of 15.2 cm2 representing state of art performance for fully low temperature solution processed planar perovskite solar modules

Se prepararon sensores basados en SnO dopados con paladio (0, 1, 3, 5 y 7%) mediante el método de impregnación húmeda. Para caracterizarlos, se usaron las técnicas de espectroscopía infrarroja con transformada de Fourier (FTIR), adsorción y desorción de N2 (BET), difracción de rayos X (XRD), microscopía electrónica de barrido (SEM) y espectroscopia de energía dispersiva de rayos X (EDX). Los sensores se evaluaron con etanol para que conformaran, junto a dos sensores comerciales, una nariz electrónica (E-nose) que lograse detectar componentes volátiles del aroma en vinos peruanos. Los resultados fueron interpretados a través del análisis de componentes principales (PCA) con la finalidad de buscar una técnica que complementase la información recolectada por la cromatografía de gases (GC) y la cromatografía líquida (HPLC), y justamente comparando los PCAs obtenidos del GC y el HPLC con los resultantes de la E-nose se encontró que estos últimos clasificaban mejor las muestras. Fue posible diferenciar tanto vinos de la misma uva como de distinta cepa. Además, se logró detectar vinos adulterados, lo cual contribuye a la industria vitivinícola en el control de su producción con la finalidad de mejorar la calidad de esta bebida para el consumidor. SnO-based sensors doped with palladium (0, 1, 3, 5 and 7%) were prepared by the wet impregnation method. To characterize them, the techniques of infrared spectroscopy with Fourier transform (FTIR), adsorption and desorption of N2 (BET), XRD, scanning electron microscopy (SEM), and X-ray dispersive energy (EDX) spectroscopy were used. The sensors were evaluated with ethanol to form, together with two commercial sensors, an electronic nose (E-nose) that could detect volatile aroma components in Peruvian wines. The results were interpreted through principal component analysis (PCA) to find a technique that complemented the information collected by gas chromatography (GC) and liquid chromatography (HPLC), and by comparing the PCAs obtained from GC and HPLC with those resulting from E-nose. It was found that the latter classified the samples better. It was possible to differentiate both wines from the same grape and from a different strain, and to detect adulterated wines, which contributes to the wine industry in controlling its production to improve the quality of this drink for the consumer. Os sensores baseados em SnO dopados com paládio (0, 1, 3, 5 e 7%) foram preparados pelo método de impregnação por via húmida. Para caracterizá-los, as técnicas de espectroscopia infravermelha com transformação de Fourier (FTIR), adsorção e dessorção de N2 (BET), XRD, microscopia eletrônica de varredura SEM) e espectroscopia de energia dispersiva de raios-X (EDX). Os sensores foram avaliados com etanol para formar, junto com dois sensores comerciais, um nariz eletrônico (E-nose) que poderia detectar componentes de aroma volátil em vinhos peruanos. Os resultados foram interpretados através da análise de componentes principais (PCA) para encontrar uma técnica que complementasse a informação coletada por cromatografia gasosa (GC) e cromatografia líquida (HPLC) e comparando os PCA obtidos de GC e HPLC com os resultantes do E-nose, descobriu-se que este classificou melhor as amostras. Foi possível diferenciar os vinhos da mesma uva e de uma variedade diferente. Além disso, foi possível detectar vinhos adulterados, o que contribui para a indústria do vinho no controle de sua produção, a fim de melhorar a qualidade desta bebida para o consumidor.

Glass photonics are widespread, from everyday objects around us to high-tech specialized devices. Among different technologies, sol-gel synthesis allows for nanoscale materials engineering by exploiting its unique structures, such as transparent glass-ceramics, to tailor optical and electromagnetic properties and to boost photon-management yield. Here, we briefly discuss the state of the technology and show that the choice of the sol-gel as a synthesis method brings the advantage of process versatility regarding materials composition and ease of implementation. In this context, we present tin-dioxide-silica (SnO2-SiO2) glass-ceramic waveguides activated by europium ions (Eu3+). The focus is on the photorefractive properties of this system because its photoluminescence properties have already been discussed in the papers presented in the bibliography. The main findings include the high photosensitivity of sol-gel 25SnO(2):75SiO(2) glass-ceramic waveguides; the ultraviolet (UV)-induced refractive index change (Delta n similar to -1.6 x 10(-3)), the easy fabrication process, and the low propagation losses (0.5 +/- 0.2 dB/cm), that make this glass-ceramic an interesting photonic material for smart optical applications.

In this work, we prepared zinc stannate (ZTO) thin films by RF sputtering starting from a sintered ceramic target with Zn:Sn ratio 2:1, by varying the argon/oxygen pressures during the deposition process. Thin films were deposited on alumina substrates at 400 °C, and subsequently annealed at 600 °C in the air. The transparency typical for the as-deposited films was preserved even after their annealing at 600 °C in the air, where the high temperature was crucial for the improvement of the crystalline Zn 2 SnO 4 , ZTO phase, as confirmed by Raman measurements. Additionally, the post-deposition thermal treatment resulted in porous ZTO films suitable for gas sensing application. The structural and surface morphological properties of thin films were investigated by Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX). Finally, the gas sensing properties towards nitrogen dioxide, ethanol and acetone have been tested, showing the high potentiality of this material as the gas sensor for ethanol and acetone at 400 °C, and nitrogen dioxide at 200 °C.

We report LPG sensing of gold (Au)-sensitized SnO2 nanostructured film fabricated by an easy spray pyrolysis deposition method whose surface morphology is confirmed by field-emission scanning electron microscopy and atomic force microscopy images and structure by X-ray diffraction pattern. Energy dispersive X-ray spectrometer analysis has carried out for finding elemental composition. The SnO2 film is uniform and consists of spherical particles of ∼10 nm. The highest gas response observed at 780 ppm LPG concentration for pristine SnO2 is 28%, at operating temperature 623 K, which is greatly improved on Au sensitization up to 57% with 60 s rapid response time at 598 K operating temperarture. The high gas response is due to electronic effect and catalytic spill-over effect of Au sensitization. The improved sensing mechanism has throughly been explored .

Sn-based oxide materials as an anode of lithium ion batteries (LIBs) suffer from the unavoidable mechanical stress originated from huge volume changes during lithiation/delithiation reactions. We synthesized the hierarchical SnO nanobranches (NBs) decorated with Sn nanoparticles on Cu current collector using a vapor transport method. The Sn-decorated SnO NBs as an anode of LIB showed good electrochemical performance with high reversible capacity retention of as high as 502 mAh/g and rate capability of 455 mAh/g at a current density of 2.0 A/g after 50 cycles. Through the morphological and crystal structure analyses after the charge and discharge processes, it was found that the morphology of Sn-decorated SnO NBs was transformed to nanoporous layered-structure, composed of Sn and lithium oxide, during the repeated lithiation/delithiation reactions. The free-volume of Sn-decorated SnO NBs and nanoporous layered-structure effectively accommodate the huge volume changes and enhance the electrochemical cyclability by facilitating the diffusion of Li-ions. Electronic supplementary material The online version of this article (doi:10.1186/s40580-016-0070-1) contains supplementary material, which is available to authorized users.

SnO2 is an n-type semiconductor with rutile crystalline structure and display many interesting optical properties. However, there are limited reports on effect of Mn doped SnO2 on optical properties, prepared by mechanochemical processing. This paper reports the effect of Mn doping on structural and optical properties of SnO2 nanoparticles (Sn1-xMnxO2, x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) prepared by mechanochemical processing in a high energy ball mill and heat-treated at 600 °C. Phase analysis of the dried powders was carried out from the data obtained by X-ray Diffraction (XRD) of the samples. The peak shifting in XRD patterns indicate that Mn ions were successfully doped into the SnO2 crystal lattice with successive increase in dopant levels. Average crystallite size, was calculated based on Scherrer's equation, and was found to vary from 24 to 35 nm. Blue shift in Eg at x>0.02 may be affected by decrease in crystallite size. Red shift in Eg with increasing Mn concentration (x ≤ 0.02) could be attributed to either sp-d exchange interaction and to the increasing crystallite size of the SnO2 nanoparticles. The quantum confinement effect was suggested to be the dominant reason for the changes in Eg. The reduction in emission intensity could be due to non-radiative recombination processes promoted by Mn ions with increasing Mn content.

Made available in DSpace on 2019-10-04T12:31:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-10-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this study, individual nanofabricated SnO micro-disks, previously shown to exhibit exceptional sensitivity to NOx, are investigated to further our understanding of gas sensing mechanisms. The SnO disks presenting different areas and thickness were isolated and electrically connected to metallic electrodes aided by a Dual Beam Microscope (SEM/FIB). While single micro-disk devices were found to exhibit short response and recovery times and low power consumption, large interconnected arrays of micro-disks exhibit much higher sensitivity and selectivity. The source of these differences is discussed based on the gas/solid interaction and transport mechanisms, which showed that thickness plays a major role during the gas sensing of single-devices. The calculated Debye length of the SnO disk in presence of NO2 is reported for the first time. Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Araraquara, SP, Brazil Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Araraquara, SP, Brazil FAPESP: 2013/07296-2 FAPESP: 2015/21033-0 FAPESP: 2017/26219-0 CNPq: 447760/2014-9 CNPq: 303542/2015-2 CNPq: 443138/2016-8

Bottom gated thin-film transistors (TFTs) with various sputtered SnO active layer thicknesses ranging from 10 to 30 nm and different passivation layers have been investigated. The device with 20 nm SnO showed the highest on/off ratio of 1.7 × 104 and the smallest subthreshold swing of 8.43 V dec−1, and the mobility (0.76 cm2 V−1 s−1) was only slightly lower than in TFTs with a thicker SnO layer. However, both the mobility and the on/off ratio of the 15 nm SnO TFT dropped significantly by one order of magnitude. This indicated a strong influence of the top surface on the carrier transport, and we thus applied an organic or an inorganic encapsulation material to passivate the top surface. In the 20 nm TFT, the on/off ratio was doubled after passivation. The performance of the 15 nm TFT was improved even more dramatically with the on/off ratio increased by one order of magnitude and the mobility increased also significantly. Our experiment shows that polymethyl methacrylate passivation is more effective to reduce the shallow trap states, and Al2O3 is more effective in reducing the deep traps in the SnO channel.

Work on the design of new TiO2 based photocatalysts is described. The key concept is the formation of composite structures through the modification of anatase and rutile TiO2 with molecular-sized nanoclusters of metal oxides. Density functional theory (DFT) level simulations are compared with experimental work synthesizing and characterizing surface modified TiO2 . DFT calculations are used to show that nanoclusters of metal oxides such as TiO2 , SnO/SnO2 , PbO/PbO2 , ZnO and CuO are stable when adsorbed at rutile and anatase surfaces, and can lead to a significant red shift in the absorption edge which will induce visible light absorption; this is the first requirement for a useful photocatalyst. The origin of the red shift and the fate of excited electrons and holes are determined. For p-block metal oxides the oxidation state of Sn and Pb can be used to modify the magnitude of the red shift and its mechanism. Comparisons of recent experimental studies of surface modified TiO2 that validate our DFT simulations are described. These nanocluster-modified TiO2 structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with a correct choice of nanocluster modified can be applied to other reactions.

SnO 2 powders pure and added with W 6+ at two different loadings (1 and 5 W mol%), were prepared via a sol–gel route. Thick films prepared from the powders were used as CO and NO 2 gas sensors. The morphology of the powders was analyzed by TEM, HRTEM and that of films by SEM. The goal of obtaining powders and films made by nanosized particles, even after thermal treatments at 850°C was attained. The effect of W on the response of powders and films towards CO and NO 2 was studied by FT-IR and conductance measurements, respectively. W markedly lowered the response of SnO 2 towards CO and markedly enhanced its ability to sense NO 2 . Surface species formed by CO and NO 2 interaction were investigated.

PbO is a layer compound which exists in two polymorphic forms, a red tetragonal (\ensuremath{\alpha}) and a yellow orthorhombic (\ensuremath{\beta}) modification. Ab initio band-structure calculations are presented for both phases. The calculated energy gaps are in agreement with optical data. The band-structure calculations are used to discuss the chemical bonding in the \ensuremath{\alpha} and \ensuremath{\beta} phases. It is found that the Pb 6s states are strongly hybridized with O 2p orbitals. Thus the so-called Pb (6s${)}^{2}$ lone pair in PbO takes part in the chemical bonding, and cannot be considered as an inert pair. Photoelectron spectra of the valence band and of some core levels are presented for \ensuremath{\alpha}- and \ensuremath{\beta}-PbO. The observed valence band is in good agreement with the calculated band structure.

Hard X-ray photoelectron spectra have been recorded for Sn, SnO2, SnO and SnS. The binding energies of the core levels of elemental Sn from 2s up to, and including, 4d have been determined with least squares fitting and calibrated against an Au 4f standard. For the oxides and the sulphide data on Sn 3p, 3d core levels’ binding energies and relative intensities are presented together with the binding energies of O 1s, S 1s and 2p. This study thus serves as a picture of tin's core level spectra compared to those of some of its oxides and a sulphide taken at photon energies beyond Al Kα and Mg Kα.