Tin Dioxide Thin Films Research Articles

Enhancing the gas selectivity of single-crystal SnO2:Pt thin-film chemiresistor microarray by SiO2 membrane coating

We consider application of SiO2 coating as a coverage membrane to differentiate local gas-sensing properties of tin dioxide thin film employed in gas-analytical single-crystal multisensor microarrays. The approach is tested utilizing homogeneous and non-homogeneous coatings. It is found out that the SiO2 coating of homogeneous thickness, of 7nm, just reduces gas response and gas recognition ability of the microarrays which might be explained by appearance of additional defects in the SnO2 film under Ar+ bombardment assisting the SiO2 deposition. The deposition of SiO2 coating of non-homogeneous thickness, of 2–24nm, results in substantial enhancing of gas selectivity of the developed microarrays

Morphological and Structural Study of Nanostructured Tin Dioxide (SnO<sub>2</sub>) Thin Films by Spray Pyrolysis

Nanostructured SnO2 thin films were deposited on glass substrate using chemical spray pyrolysis technique. Three influent synthesis parameters, namely (i) the precursor concentration (0.2M and 0.5M), (ii) the substrate temperature (250°C and 350°C) and (iii) doping with zinc (Zn) were investigated in term of their effects on the morphology and structure of SnO2 thin films. These films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometry (EDX) techniques. The grain size of the films was observed to increase as the concentration of the precursors is increased. Substrate temperature is proved to be crucial in determining the crystallinity of the films as the films are reported to grow at temperature above 270°C. Besides, the addition of dopant was found to reduce the grain size of the film.

Structural properties and refractive index dispersion of cobalt doped SnO2 thin films

Tin dioxide and cobalt doped tin dioxide thin films were prepared using chemical spray pyrolysis. X-ray diffraction study showed that the deposited films exhibited tetragonal structure with (110) plane as the preferred orientation. The AFM study showed that the rms roughness of undoped films reduced from 20.7 to 15.2 nm due to cobalt doping. The refractive index dispersion curves of undoped and cobalt doped SnO2 thin films obeyed the single oscillator model. The dispersion parameter Ed was found to increase as the doping content was increased, while oscillator energy Eo was found to decrease.

Realizing a SnO2-based ultraviolet light-emitting diode via breaking the dipole-forbidden rule

Although many oxide semiconductors possess wide bandgaps in the ultraviolet (UV) regime, currently the majority of them cannot efficiently emit UV light because the band-edge optical transition is forbidden in a perfect lattice as a result of the symmetry of the band-edge states. This quantum mechanical rule severely constrains the optical applications of wide-bandgap oxides, which is also the reason why so few oxides enjoy the success of ZnO. Here, using SnO2 as an example, we demonstrate both theoretically and experimentally that UV photoluminescence and electroluminescence can be recovered and enhanced in wide-bandgap oxide thin films with ‘forbidden’ energy gaps by engineering their nanocrystalline structures. In our experiments, the tailored low-temperature annealing process results in a hybrid structure containing SnO2 nanocrystals in an amorphous matrix, and UV emission is observed in such hybrid SnO2 thin films, indicating that the quantum mechanical dipole-forbidden rule has been effectively overcome. Using this approach, we demonstrate the first prototypical electrically pumped UV-light-emitting diode based on nanostructured SnO2 thin films. Oxide semiconductors typically possess wide energy gaps between the conduction and valence bands in their electronic structure. This predisposes them to be efficient ultraviolet light emitters, and thus promising components in lighting, display and photonic devices. Yet, in most cases, the optical transition between electronic states that is responsible for this emission is a forbidden one in quantum mechanics. A research team led by Tom Wu and Su-Huai Wei has now circumvented this issue with tin dioxide by altering the material's nanoscale structure, in particular its effective surface. Calculations were carried out that subsequently guided the preparation of hybrid nanocrystalline-amorphous thin films through an annealing step. The tin dioxide thin films were then used to construct an efficient UV light-emitting diode. These findings suggest that engineering the nanostructure of other oxides might also render them optically active. It is commonly believed that bulk SnO2 is not a suitable ultraviolet (UV) light emitter due to the dipole-forbidden nature of its band-edge states, which has hindered its potential use in optical applications. Here, we demonstrate both theoretically and experimentally an effective method to break the dipole-forbidden rule in SnO2 via nano-engineering its crystalline structure. Furthermore, we designed and fabricated a prototypical UV-light-emitting diode (LED) based on SnO2 thin films. Our methodology is transferable to other semiconductors with ‘forbidden’ energy gaps, offering a promising route toward adding new members to the family of light-emitting materials.

Gas-sensitive properties of thin tin dioxide films under the influence of hydrogen sulfide

In order to develop sensors for selective detection of hydrogen sulfide in the air, the characteristics of thin SnO2 films with various additives (Au, Pt) in the volume and deposited catalysts (Pt / Pd, Au) are studied. The films were obtained by magnetron sputtering. The sensor response to H2S (the ratio of the sensor conductivity G1 in the presence of hydrogen sulfide in the gas to the conductivity G0 in the clean air) is studied as a function of the operating temperature and gas concentration in the range 0.1–70 ppm. It is shown that the sensors with the addition of gold in the volume can be used to detect maximum permissible concentrations (7 ppm) of hydrogen sulfide in the working area after stabilization of the characteristics during long-term tests.

Interface formation of nanostructured heterojunction SnO2:Eu/GaAs and electronic transport properties

Thin films of tin dioxide (SnO2) are deposited by the sol–gel-dip-coating technique, along with GaAs layers, deposited by the resistive evaporation technique. The as-built heterojunction has potential application in optoelectronic devices, combining the emission from the rare-earth doped transparent oxide (Eu3+-doped SnO2 presents very efficient red emission) with a high mobility semiconductor. The advantage of this structure is the possibility of separation of the rare-earth emission centers from the electron scattering, leading to a strongly indicated combination for electroluminescence. Electrical characterization of the heterojunction SnO2:Eu/GaAs shows a significant conductivity increase when compared to the conductivity of the individual films, and the monochromatic light irradiation (266nm) at low temperature of the heterojunction GaAs/SnO2:Eu leads to intense conductivity increase. Scanning electron microscopy (SEM) of the heterojunction cross section shows high adherence and good morphological quality of the interfaces substrate/SnO2 and SnO2/GaAs, even though the atomic force microscopy (AFM) image of the GaAs surface shows disordered particles, which increases with sample thickness. On the other hand, the good morphology of the SnO2:Eu surface, shown by AFM, assures the good electrical performance of the heterojunction. The observed improvement on the electrical transport properties is probably related to the formation of short conduction channels at the semiconductors interface, which may exhibit two-dimensional electron gas (2DEG) behavior.

Electrical Properties of Fluorine Doped Tin Dioxide Film Grown by Spray Method

Low resistivity, fluorine-doped tin dioxide thin films were deposited on glass substrates by spray pyrolysis. These films were prepared with different F-doping concentrations from 0 to 33 mol%. The structure of these films was investigated by X-ray diffraction and the surface morphology by Scanning Electron Microscopy. Sample compositions were evaluated using X-ray Photoemission Spectroscopy. According to these results, the films were all polycrystalline with tetragonal crystal structures. Hall measurements were used to probe the dependence of the resistivity on temperature for un-doped SnO2 and F-doped SnO2. The resistivity of un-doped SnO2 slightly increased with increasing temperature. Conversely, the resistivity of F-doped SnO2 slightly decreased with increasing temperature.

Electron transport in semiconducting SnO2: Intentional bulk donors and acceptors, the interface, and the surface

Abstract

Effect of Pt, Pd, Au additives on the surface and in the bulk of tin dioxide thin films on the electrical and gas-sensitive properties

The microstructure and properties of thin (∼100 nm) SnO2 films with noble metals Pt, Pd, Au additives, grown by dc magnetron deposition are studied. It is shown that the introduction of additives into the bulk and the deposition of dispersed catalysts on the semiconductor surface make it possible to control the sensor parameters in pure air and upon exposure to reduction (CO, H2, CH4) and oxidation (NO2) gases. Possible mechanisms for the effect of Pt, Pd, Au on the bulk and surface properties of tin dioxide are discussed. The technological conditions for film growth, which provide the selective detection of low concentrations (10–100 ppm) of CO and H2, below-explosive concentrations (0.5–2.5 vol %) of methane, and trace concentrations (0.05–5 ppm) of NO2 are determined.

Wet chemical preparation of YVO4:Eu thin films as red-emitting phosphor layers for fully transparent flat dielectric discharge lamp

Highly transparent YVO4:Eu thin films were deposited via dip coating of liquid nanoparticle dispersions on glass substrates. Annealing of the nanoparticle layers resulted in restructuring of the material into oriented crystalline films. The crystallinity was confirmed using powder X-ray diffraction. Film thickness was adjusted to 467nm by multiple deposition. The resulting coatings show >99% absorbance for wavelength below 300nm and >90% transmission in the visible spectral range. Under UV-light excitation a bright red photoluminescence with a quantum efficiency of 20% is observed. A planar, transparent dielectric barrier discharge lamp was constructed using YVO4:Eu coated glasses and transparent electrodes made from antimony-doped tin dioxide thin films.

The Influence of Platinum Dopant on the Characteristics of SnO<sub>2</sub>Thin Film for Gas Sensor Application

Doping of platinum on tin dioxide (SnO 2 ) thin film for gas sensor application has been carried out using ion implantation techniques. The SnO 2 thin film has been deposited using dc sputtering method at the conditions; operating pressure 5x10 -2 torr, anode-cathode voltage 2.0 kV, substrate temperature 200 0 C and deposition time one hour. While the Pt ion implantation process were carried out at energy 60 keV and ion doses were varied. From scanning electron microscope (SEM) observation, it was found that SnO 2 :Pt thin film which was deposited by those parameters has a fine morphology with the grain size of thin film was in order of 0.7 – 1.0 μm and thickness 4.16 μm. From crystal structure analysis using XRD it was observed that the crystal planes of SnO 2 :Pt were (110), (101), (200), (211), (300), and (112) . From energy dispersive X-rays analysis (EDX) coupled with SEM, it was found that the chemical composition of SnO 2 :Pt thin film were 66.12%-at O, 1.23 %-at Si, 0.12 %-at Pt and 32.53 %-at Sn. It was also found that the influence of platinum dopant on SnO 2 thin film can reduce significantly the resistance of thin film and from response time and sensitivities measurement showed that for every dose variation for different tested gas has a different respons time and sensitivities (no a specific pattern)

Annealing driven performance and optical effects in nanocrystalline SnO 2 thin films induced by pulsed delivery

Tin dioxide thin films were prepared successfully by pulsed laser deposition techniques on glass substrates. The thin films were then annealed for 30 min from 50 °C to 550 °C at 50 °C intervals. The influence of the annealing temperature on the microstructure and optical properties of SnO 2 thin films was investigated using X-ray diffraction, optical transmittance and reflectance measurements. Various optical parameters, such as optical band gas energy, refractive index and optical conductivity were calculated from the optical transmittance and reflectance data recorded in the wavelength range 300–2500 nm. We found that the SnO 2 thin film annealed at temperatures up to 400 °C is a good window material for solar cell application. Our experimental results indicated that SnO 2 thin films with the high optical quality could be synthesized by pulsed laser deposition techniques.

Yb 3+ effect on the spectroscopic properties of Er–Yb codoped SnO 2 thin films

We have investigated the optical properties of sol–gel thin films of tin dioxide (SnO 2) codoped with Er 3+–Yb 3+ as a function of Yb 3+ concentration. The Judd–Ofelt model has been applied to absorption intensities of Er 3+ (4f 11) transitions to establish the so-called Judd–Ofelt intensity parameters: Ω 2, Ω 4, Ω 6. Various spectroscopic parameters were obtained to evaluate their dependence and the potential of the samples as a laser material in the eye-safe laser wavelength (1.53 μm) as a function of Yb 3+ concentration. An amelioration of the quality factor Ω 4/ Ω 6 was found with Yb content. Both the IR photoluminescence (PL) intensity and the up-conversion emission, from Er 3+ ion in SnO 2, were found to increase with Yb concentration. We show that the Yb 3+ ion acts as sensitizer for Er 3+ ion and contributes largely to the improvement of the spectroscopic properties of SnO 2:Er. The mechanism of up-conversion emission is discussed and a model is proposed. The results showed that sol–gel SnO 2 is promising gain media for developing the solid-state 1.5 μm optical amplifiers and tunable up-conversion lasers.

Influence of pH of colloidal suspension on the electrical conductivity of SnO2 thin films deposited via Sol-Gel-Dip-Coating

Tin dioxide (SnO2) thin films are deposited by the dip-coating technique from colloidal suspensions prepared with distinct pH through the sol-gel method. The decrease of the pH contributes to the destruction of an electrical layer adjacent to particles in solution, leading to a high degree of aggregation among these particles due to the generation of cross-linked bonds (Sn-O-Sn) between them. The aggregation affects the electrical properties of films, because the pH variation produces particle with distinct sizes in the film. Undoped samples prepared from pH 6 leads to the highest conductivity among the investigated undoped samples, in agreement with X-ray diffractograms, which indicate higher crystallinity for lower pH. Arrhenius plot evaluated from temperature dependent conductivity data leads to activation energies of the deepest level between 67 to 140 meV, for the films prepared from suspensions with pH 6 to 11. The most probable explanation for this variation in the conductivity and activation energy is related to distinct potential barriers between grains, due to distinct packing caused by cross-linked bonds formed during suspension phase. Characterization of samples lightly doped with Er3+ confirms that acid pH leads to higher conductivity, but the highest conduction takes place at even lower pH when compared to undoped thin films.

IR reflectance characterization of glass–ceramic films obtained by high pressure impregnation of SnO 2 nanopowders on float glass

Glass–ceramic thin films of tin dioxide on float glass surfaces were obtained using a method based on high pressures and temperatures below the glass transition temperature. SnO 2 thin films were confirmed using XRD, SEM and XRF techniques. These thin films were identified using IR reflectance due to a shift induced by Sn ion content of about ∼100 cm −1 in the main maximum peak position which is typical of stretching vibration intensities of a ν Si −O–Si bridging bonds, or a ν Si – O − nonbridging bonds.

Flame aerosol reactor synthesis of nanostructured SnO 2 thin films: High gas-sensing properties by control of morphology

Tin dioxide (SnO 2) thin films were deposited on commercial alumina chips using a flame aerosol reactor (FLAR) system. The morphology of the thin films was controlled by changing various parameters, such as precursor concentration, burner–substrate distance, and deposition time. Three typical morphologies of the thin films were achieved, i.e., columnar, column–granular, and granular structures. The as-prepared thin films with columnar structures demonstrated improved sensing performance to ethanol vapor, due to their preferred orientation, single crystal phase, and unique morphology.

Analysis of thickness dependence on the electrical properties of tin dioxide films in the presence of LPG gas

Chloride-based inorganic salt was used to prepare multiple layered tin dioxide thin films by sol–gel method. The deposited films were subjected to SEM, XRD and optical studies. Carrier concentrations of the multiple layered films were studied. A comparative analysis of both undoped and Pd-doped SnO 2 multilayered films has been done in the presence of LPG gas to investigate the possibility of their usage as LPG gas sensors.

Insight on Fractal Assessment Strategies for Tin Dioxide Thin Films

Tin oxide is a unique material of widespread technological applications, particularly in the field of environmental functional materials. New strategies of fractal assessment for tin dioxide thin films formed at different substrate temperatures are of fundamental importance in the development of microdevices, such as gas sensors for the detection of environmental pollutants. Here, tin dioxide thin films with interesting fractal features were successfully prepared by pulsed laser deposition techniques under different substrate temperatures. Fractal method has been first applied to the evaluation of this material. The measurements of carbon monoxide gas sensitivity confirmed that the gas sensing behavior is sensitively dependent on fractal dimensions, fractal densities, and average sizes of the fractal clusters. The random tunneling junction network mechanism was proposed to provide a rational explanation for this gas sensing behavior. The formation process of tin dioxide nanocrystals and fractal clusters could be reasonably described by a novel model.

Study of properties of electrical conductivity of Tin dioxide thin films treated with Xenon impulse radiation used as Gas sensors

During of Experimental result of this work , we found that the change of electrical conductivity proprieties of tin dioxide with the change of gas concentration at temperatures 260oC and 360oC after treatment by photons rays have similar character after treatment isothermally. We found that intensive short duration impulse annealing during the fractions of a second leads to crystallization of the films and to the high values of its gas sensitivity.

Study of properties of electrical conductivity of Tin dioxide thin films treated with Xenon impulse radiation used as Gas sensors

During of Experimental result of this work , we found that the change of electrical conductivity proprieties of tin dioxide with the change of gas concentration at temperatures 260oC and 360oC after treatment by photons rays have similar character after treatment isothermally. We found that intensive short duration impulse annealing during the fractions of a second leads to crystallization of the films and to the high values of its gas sensitivity.