Emerson A. Floriano

Bio: Emerson A. Floriano is an academic researcher from Sao Paulo State University. The author has contributed to research in topics: Thin film & Heterojunction. The author has an hindex of 6, co-authored 10 publications receiving 103 citations. Previous affiliations of Emerson A. Floriano include University of São Paulo.

Preparation of TiO2/SnO2 thin films by sol-gel method and periodic B3LYP simulations.

Abstract: Titanium dioxide (TiO2) thin films are grown by the sol–gel dip-coating technique, in conjunction with SnO2 in the form of a heterostructure. It was found that the crystalline structure of the most internal layer (TiO2) depends on the thermal annealing temperature and the substrate type. Films deposited on glass substrate submitted to thermal annealing until 550 °C present anatase structure, whereas films deposited on quartz substrate transform to rutile structure at much higher temperatures, close to 1000 °C, unlike powder samples where the phase transition takes place at about 780 °C. When structured as rutile, the oxide semiconductors TiO2/SnO2 have very close lattice parameters, making the heterostructure assembling easier. The SnO2 and TiO2 have their electronic properties evaluated by first-principles calculations by means of DFT/B3LYP. Taking into account the calculated band structure diagram of these materials, the TiO2/SnO2 heterostructure is qualitatively investigated and proposed to increase th...

Evaluation of bulk and surfaces absorption edge energy of sol-gel-dip-coating SnO2 thin films

Abstract: The absorption edge and the bandgap transition of sol-gel-dip-coating SnO2 thin films, deposited on quartz substrates, are evaluated from optical absorption data and temperature dependent photoconductivity spectra. Structural properties of these films help the interpretation of bandgap transition nature, since the obtained nanosized dimensions of crystallites are determinant on dominant growth direction and, thus, absorption energy. Electronic properties of the bulk and (110) and (101) surfaces are also presented, calculated by means of density functional theory applied to periodic calculations at B3LYP hybrid functional level. Experimentally obtained absorption edge is compared to the calculated energy band diagrams of bulk and (110) and (101) surfaces. The overall calculated electronic properties in conjunction with structural and electro-optical experimental data suggest that the nature of the bandgap transition is related to a combined effect of bulk and (101) surface, which presents direct bandgap transition.

Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

Abstract: Aiming for the investigation of insulating properties of aluminum oxide (Al2O3) layers, as well as the combination of this oxide with tin dioxide (SnO2) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of SnO2 thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al2O3 are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that tetragonal Al2O3 is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide and the transport properties of SnO2 as well. Results indicate a fair insulation when four layers or Al2O3 are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO2 alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication that this combination may be useful for transparent devices.

Optical and Transport Properties of Rare-earth Trivalent Ions Located at Different Sites in Sol-gel SnO2

Abstract: Photoluminescence and photo-excited conductivity data as well as structural analysis are presented for sol-gel SnO2 thin films doped with rare earth ions Eu3+ and Er3+, deposited by sol-gel-dip-coating technique. Photoluminescence spectra are obtained under excitation with various types of monochromatic light sources, such as Kr+, Ar+ and Nd:YAG lasers, besides a Xe lamp plus a selective monochromator with UV grating. The luminescence fine structure is rather different depending on the location of the rare-earth doping, at lattice symmetric sites or segregated at the asymmetric grain boundary layer sites. The decay of photo-excited conductivity also shows different trapping rate depending on the rare-earth concentration. For Er-doped films, above the saturation limit, the evaluated capture energy is higher than for films with concentration below the limit, in good agreement with the different behaviour obtained from luminescence data. For Eu-doped films, the difference in the capture energy is not so evident in these materials with nanoscocopic crystallites, even though the luminescence spectra are rather distinct. It seems that grain boundary scattering plays a major role in Eu-doped SnO2 films. Structural evaluation helps to interpret the electro-optical data.

Role of the heterojunctions in In2O3-composite SnO2 nanorod sensors and their remarkable gas-sensing performance for NOx at room temperature

Abstract: Establishing heterostructures, as a good strategy to improve gas sensing performance, has been studied extensively. In this research, In2O3-composite SnO2 nanorod (ICTOs) heterostructures have been prepared via electrospinning, followed by calcination. It is found that In2O3 can improve the carrier density and oxygen deficiency of SnO2. In particular, the 3ICTO (Sn : In atom ratio of 25 : 0.3) nanorods with special particle distributions show an excellent sensing response towards different concentrations of NOx at room temperature. The highest sensing response is up to 8.98 for 100 ppm NOx with a fast response time of 4.67 s, which is over 11 times higher than that of pristine SnO2 nanorods at room temperature and the lowest detection limit is down to 0.1 ppm. More significantly, it presents good stability after 30 days for NOx of low concentration (0.1 ppm and 0.5 ppm). In addition, the rational band structure model combined with the surface depletion model which describe the NOx gas sensing mechanism of 3ICTO are presented. The 3ICTO nanorods may be promising in the application of gas sensors.

Improvement of sensing properties for SnO2 gas sensor by tuning of exposed crystal face

Abstract: In this study, a SnO2 nanosheet was successfully synthesized under moderate conditions without using any additive. The crystal growth direction and the mainly exposed crystal face of the SnO2 nanosheet were investigated. The relationship between the exposed crystal face and the gas sensing properties was also investigated. It was confirmed that the SnO2 nanosheet has a plain size of ˜100 nm and a mainly exposed (101) plane. The SnO2 nanosheet exhibited selectively higher sensor signal response for H2 than CH4 gas, while the SnO2 nanoparticle with a mainly exposed the most stable (110) plane, which was prepared for comparison purposes, exhibited a selectively lower sensor signal response for H2 than CH4 gas. The 90% response and recovery times for the SnO2 nanosheet were faster than those for the SnO2 nanoparticle for both H2 and CH4 gases. Different chemical states were observed on the SnO2 surfaces. Therefore, it was considered that the reaction with the target gas on the SnO2 nanoparticle was dominantly induced by oxygen adsorbed on the SnO2 surface. However, the reaction was dominantly induced by oxygen bound to Sn on the SnO2 nanosheet, due to the ease of conversion of the Sn valency state according to adsorption and desorption of oxygen on the (101) surface as compared to the (110) surface.

Metaloxide Nanomaterials and Nanocomposites of Ecological Purpose

Abstract: The features of the properties and creation of nanocomposite metal oxide materials, especially TiO2, ZnO, SnO2, ZrO2, and Fe3O4, and their applications for ecology are considered in the article. It is shown that nanomaterials based on them are very promising for use in the ecological direction, especially as sorbents, photocatalysts, and sensitive layers of gas sensors. The crystallochemical characteristics, surface structure, and surface phenomena that occur when they enter the water and air environment are given for these metal oxides, and it is shown that they play a significant role in obtaining the sorption and catalytic characteristics of these nanomaterials. Particular attention is paid to the dispersion and morphology of metal oxide particles by which their physical and chemical properties can be controlled. Synthesis methods of metal oxide nanomaterials and ways for creating of nanocomposites based on them are characterized, and it is noted that there are many methods for obtaining individual nanoparticles of metal oxides with certain properties. The main task is the correct selection and testing of parameters. The prospects for the production of metal oxide nanocomposites and their application for environmental applications are noted, which will lead to a fundamentally new class of materials and new environmental technologies with their participation.