Current-voltage characteristics of thin-film gas sensor structures based on tin dioxide

The experimental current-voltage (I–U) curves of thin-film structures based on tin dioxide (SnO₂) exhibit nonlinearity in the range of strong applied electric fields. The results of I-U measurements are interpreted within the framework of a model that assumes the drift of adsorbed ions over the film surface. The observed phenomenon can be used both for detecting the impurities in air and for recognizing the types of adsorbed species.     

Laser-deposited tin dioxide and tin acetylacetonate layers for gas sensors

Thin active layers were deposited by the pulsed laser deposition (PLD) method from tin dioxide and tin acetylacetonate targets. The deposition was carried out employing an excimer KrF laser. The structure and parameters of the deposited layers were studied in connection with gas sensor applications. The influence of Ni dopant and Pd catalyst was investigated, employing PLD technology in order to introduce dopants as a multilayered structure. The properties of these layers were studied by Fourier transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies and by measurement of their d.c. resistance. Under reducing gases the resistance of Ni-doped tin dioxide with a Pd catalyst layer decreases by 3 orders and the resistance of tin acetylacetonate with a Pd catalyst by 2 orders (synthetic air versus 1000 ppm H₂. Due to this, such layers are suitable as the active layers of gas sensors.     

Characterization of tin dioxide film for chemical vapors sensor

Recently, oxide semiconductor material used as transducer has been the central topic of many studies for gas sensor. In this paper we investigated the characteristic of a thick film of tin dioxide (SnO₂) film for chemical vapor sensor. It has been prepared by screen-printing technology and deposited on alumina substrate provided with two gold electrodes. The morphology, the molecular composition and the electrical properties of this material have been characterized respectively by Atomic Force Spectroscopy (AFM), Fourier Transformed Infrared Spectroscopy (FTIR) and Impedance Spectroscopy (IS). The electrical properties showed a resistive behaviour of this material less than 300 °C which is the operating temperature of the sensor. The developed sensor can identify the nature of the detected gas, oxidizing or reducing.     

Textured tin dioxide films for gas recognition microsystems

We have studied the microstructure, electrical properties, and gas sensor characteristics of thin tin dioxide (SnO₂) films obtained by RF magnetron sputtering of an oxide target. The synthesized films are composed of crystalline rods with a diameter of 10–60 nm and a length of up to 1000 nm oriented perpendicularly to the substrate plane. This morphology facilitates the access of gas molecules to the side surfaces of crystallites. Use of such SnO₂ films in a multisensor microsystem expanded the spectrum of recognized gases.     

Nanoparticles of antimony doped tin dioxide as a liquid petroleum gas sensor: effect of size on sensitivity

The gas sensitivity exhibited by nanoparticles of 1 wt% Pd catalysed antimony doped tin dioxide (ATO) prepared by a citrate-nitrate process is reported here. The reduction of particle size to <3 nm, a dimension smaller than double the thickness of the charge depletion layer, has resulted in an exceptionally high butane sensitivity and selectivity. The sensitivity and selectivity of ATO particles of different sizes unequivocally proved that reducing the size of particles to below twice the Debye length dimension produces materials with exceptionally high sensitivity and selectivity for sensor applications. The sensitivity of the samples towards 1000 ppm butane varied in the order 98%>55%>47%, for CNP>SP>CP samples having crystallite sizes of the order of 2.4 nm to 18 nm to 25 nm, respectively. The ATO nanoparticles exhibited not only a remarkable increase in gas sensitivity of around 98% towards 1000 ppm butane at 350?°C, but also a preferential selectivity to butane compared to other gases such as CO, CO2, SO2, CH4 and H2. In addition to the exceptionally high sensitivity and selectivity, the developed sensors also exhibited an improved response time and long term stability, which are of paramount importance for practical device development.     

Effects of electron beam irradiation on tin dioxide gas sensors

In this paper, the effects of electron beam irradiation on the gas sensing performance of tin dioxide thin films toward H₂ are studied. The tin dioxide thin films were prepared by ultrasonic spray pyrolysis. The results show that the sensitivity increased after electron beam irradiation. The electron beam irradiation effects on tin dioxide thin films were simulated and the mechanism was discussed.     

Effect of laser treatment on the gas sensitivity of tin dioxide films

It is shown that the sensitivity of antimony-doped polycrystalline SnO₂ films can be increased by treatment with laser pulses. Pis’ma Zh. Tekh. Fiz. 24, 57–60 (April 12, 1998)     

Nanocrystalline tin dioxide: Basics in relation with gas sensing phenomena part II. Active centers and sensor behavior

The experimental data and theoretical concepts on the nature and physicochemical properties of the active centers at the surface of tin dioxide are reported, which are involved in detection of toxic and explosive ambient impurities. The active centers formed at the nanocrystal SnO₂ surface are classified on the basis of their chemical properties, and their role in the interaction of semiconductor nanocrystal oxides with the gases exhibiting the redox properties is confirmed. The chemical modification of the SnO₂ surface aimed at elaborating a controlled amount of specific active centers is shown to be the most efficient method for increasing the selectivity of sensors. Selecting the optimum catalytic modifiers (nanoparticles or clusters of noble metals and their oxides) allows the sensor sensitivity and selectivity of the target gas detection to be increased.     

High gas sensitivity of tin oxide ultrathin films deposited on glasses and alumina substrates

Tin oxide ultrathin films were deposited on optically flat Pyrex glass, optically flat quartz glass and sintered alumina substrates by the ion-beam sputtering method. Films with thickness varying from about 1 to 500 nm were annealed in air at 500 °C for 50 h. The gas sensing properties of these films were investigated at 300 °C against synthetic air containing 0.5% hydrogen. A small substrate dependence of sensor behaviour was observed; however, an overwhelmingly important thickness dependence occurred in all substrates tried. Sensitivities higher than ∼10⁴ or 10⁵ were obtained in films in a narrow thickness range of about 3 to 20 nm, and films thicker or thinner than this were relatively insensitive.     

Effects of annealing on the grain boundary potential barrier of ZnO varistor

Effects of post heat treatment on the potential barrier at the grain boundaries of ZnO varistors will be discussed from the viewpoints of the surface state density and the donor concentration. Leakage current of varistors at a low electric field increases by annealing at 750° C in air or nitrogen due to the lowered barrier height corresponding to the decrease of surface state density, which may be explained with the phase transformation of the bismuth-rich intergranular layer. It is also observed that theV-I non-linearity of the annealed ceramics is generally recovered as the annealing (in air) time is extended. This can be explained by the heightened barrier potential attributed to the decrease of donor concentration in ZnO grains, which was confirmed by aid ofC-V measurements. The decrease of donor concentration by the annealing in air can be considered to be responsible for the thermal oxidation of interstitial zinc ions or oxygen vacancies.     

Computing the mobility of grain boundaries

As current experimental and simulation methods cannot determine the mobility of flat boundaries across the large misorientation phase space, we have developed a computational method for imposing an artificial driving force on boundaries. In a molecular dynamics simulation, this allows us to go beyond the inherent timescale restrictions of the technique and induce non-negligible motion in flat boundaries of arbitrary misorientation. For different series of symmetric boundaries, we find both expected and unexpected results. In general, mobility increases as the grain boundary plane deviates from (111), but high-coincidence and low-angle boundaries represent special cases. These results agree with and enrich experimental observations.     

Enhancing the CO2 sensor response of nickel oxide-doped tin dioxide thin films synthesized by SILAR method

Journal of Materials Science: Materials in Electronics - The present article investigates the chemiresistive gas sensing characteristics of undoped and nickel oxide-doped tin oxide gas sensors at...     

Effect of platinum distribution on the hydrogen gas sensor properties in tin oxide thin films

Tin oxide and platinum layers were deposited on oxidized silicon wafers by ion-beam sputtering. The hydrogen gas sensing properties of undoped films and platinum-doped films were examined at 300°C for films annealed at 500°C. It was observed that the surface platinum when annealed together with the tin oxide film increased the sensitivity and reduced the response time compared with those of undoped films. Longer annealing tended to shift the optimum sensor thickness to a thicker side; the optimum thickness changed from 17 to 37 nm as the annealing time increased from 2 to 50 h. The interdiffusivity between the platinum and the tin atoms in the bulk was negligibly small at 300°C.     

Modeling of quantum effects for ultrathin oxide MOS structures with an effective potential

In this paper, the effectiveness of the effective potential (EP) method for modeling quantum effects in ultrathin oxide MOS structures is investigated. The inversion-layer charge density and MOS capacitance in one-dimensional MOS structures are simulated with various substrate doping profiles and gate bias voltages. The effective mass is used as an adjusting parameter to compare results of the EP model with that of the Schrodinger-Poisson solution. The variation of this optimum parameter for various doping profiles at different gate voltages is investigated. The overestimated average inverse charge depth by the EP method is quantified and its reason explained. The EP model is a good practical simulation tool for modeling quantum effects but more work needs to be done to improve its accuracy near the interface.     

Further refinements in the energy of grain boundaries

Earlier surface dislocation analysis of a grain boundary recognized the tendency of the grain-boundary surfaces to coalesce in order to reduce surface energy. The coalescence process is described by a distribution of surface dislocations on the grain-boundary surfaces. In the present paper, previous analysis is further refined. In particular, the sum of the Burgers vectors of the surface array of grain-boundary dislocations is not equal to the Burgers vector of the grain-boundary lattice dislocation. Instead, the Burgers vector of the surface array is determined as a function of the coalescence of the grain-boundary surfaces. The conservation of Burgers vectors of dislocations is used to predict the presence of a screening array of dislocations. The screening array of dislocations is determined by minimization of the total energy of the configuration. The distortion around the boundary is relaxed by the screening array. In general, the distribution of the screening array is two dimensional. This result has been proved by the presence of a minimum energy configuration for two sets of screening arrays of dislocations situated at different distances from the boundary.     

Field ion microscope studies of the propagation of substrate grain boundaries into an overgrowth

The roles of substrate grain boundaries and substrate surface topography in the nucleation and growth characteristics of thin and thick overgrowths were evaluated through field ion and transmission electron microscopy techniques. The results of these studies, utilizing both electrodeposited and vapor-deposited overgrowths, indicate that the substrate surface topography is generally continued in the overgrowths at thin coverages. Nucleation and growth characteristics are seen to be influenced more by surface asperities than by the existence of grain boundaries on substrate surfaces. Grain boundaries (or the interaction of grain boundaries with the substrate surface) are not observed to be sites for preferential nucleation and growth of thin films although they can act as a source for recrystallization and grain growth in thicker overgrowths (greater than 20μm).     

Development of a gas sensor utilizing chemiluminescence on nanosized titanium dioxide.

A gas-sensing mode based on chemiluminescence generated on the surface of nanosized materials is proposed in the present work. Seven nanosized materials were tested, and chemiluminescence was detected from six of them during the catalytic oxidation of organic vapors in air. The luminescence characteristics of ethanol and acetone vapors passing through the surface of TiO2 chosen were studied with a chemiluminescence-based detection system. The linear range of chemiluminescence intensity versus concentration of organic compounds is 40-400 microg/mL for ethanol and 20-200 microg/mL for acetone dissolved in water, respectively. X-ray powder diffraction and Raman spectrometry were used to investigate the changes in catalytic activity of TiO2 after a 60-h reaction at 380 degrees C. The results showed that the carbon deposited on the surface of TiO2, decreasing the catalytic activity, but can be removed in air by controlling the temperature at 500 degrees C for 3 h. Regenerability and no consumption of sensor substrate signify the long lifetime of the gas sensor.