T. Doll
University of Mainz
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Publication
Featured researches published by T. Doll.
Thin Solid Films | 1997
Alexandra Neubecker; Thomas Pompl; T. Doll; Walter Hansch; Ignaz Eisele
For the deposition of nickel oxide (NiO) a molecular beam deposition process in an ozone atmosphere was developed. Pure gaseous ozone is received from a cooling system, which stores only O3 at −78°C from a O2/O3 gas mixture stream, created with an ozone generator. The ozone is released by heating up the system to room temperature. For the deposition process nickel is evaporated while a constant ozone partial pressure is adjusted in the growth chamber. The reactive species of ozone reacts on the substrate surface with the impinging metal atoms to form the compound. This process was carried out in an ultra high vacuum (UHV) chamber to create pure nickel oxide films at room temperature and to study the fundamental layer properties for sensor applications. These films were characterized with respect to their stoichiometric and optical properties by Auger Electron spectroscopy and ellipsometry. The gas sensitivity of the films (as deposited and annealed) on various gases (H2, NH3, NO2, SO2, CO) was investigated by work function measurements.
Sensors and Actuators B-chemical | 1998
T. Doll; A. Fuchs; I. Eisele; G. Faglia; S. Groppelli; Giorgio Sberveglieri
Abstract Indium oxide thin films were deposited on silicon substrates for work function sensing as well as on alumina (Pt) conductivity sensors. A correlation of work function and conductivity measurements due to ozone in dry and humid air reveal that a chemisorption state dominates both sensor effects at temperatures below 200°C. The influence of humidity is found to be comparatively small for these films. The work function method provides a sensitivity maximum at low concentrations of some ppb of ozone stable down to a substrate temperature of 40°C. For HSGFET work function sensors with an In 2 O 3 –Si 3 N 4 system a response of 120 mV from 100 ppb of ozone in humid air is estimated for heaterless operation at room temperature. However, thermal desorption cycles will be necessary even for a restricted use of such sensors based on sputtered In 2 O 3 films.
Sensors and Actuators B-chemical | 1999
Bernhard Ostrick; Jens Mühlsteff; Max Fleischer; Hans Meixner; T. Doll; Claus Dieter Kohl
Abstract In this work, it was found that exposure of barium carbonate to carbon dioxide (0.003%–5%) as active gas in wet synthetic air as carrier gas leads to an increase in work function between 50 and 150 meV at room temperature. Other carbonates show a similar behaviour and lower sensitivities. Without humidity in the carrier gas, the sensitivity of barium carbonate disappears. Measurements were performed on pressed pellets, thick films (10–100 μm) and thin films (1–2 μm) of the material using a Kelvin probe with gold grid as reference electrode. The effect was found to be independent of preparation. Between 23°C and 100°C, maximum sensitivity is reached at about 50°C. The work function change is attributed to the formation of dimeric HCO3− species which have been identified using diffuse reflectance infrared fourier transform (DRIFT) spectroscopy.
Sensors and Actuators B-chemical | 1994
B. Flietner; T. Doll; Josef Lechner; M. Leu; Ignaz Eisele
Abstract We have developed a novel hybrid technique for manufacturing gas-sensing field-effect structures (GasFETs) with an air gap. To prove the efficiency of the device, gas measurements with the well-known Pt (sensitive layer) and H2 (gas) system have been carried out at room temperature. Samples produced identically show reproducible signals of the same magnitude. Simultaneously, we have recorded the electrical response of a platinum-coated Kelvin probe. Results obtained by the hybrid GasFETs are transferrable to those obtained by the Kelvin probe. With the new technology for device fabrication, our transducer meets the requirements for measuring work-function changes caused by gases on a wide variety of sensitive layers.
Sensors and Actuators B-chemical | 1996
T. Doll; Josef Lechner; Ignaz Eisele; K.D. Schierbaum; W. Göpel
Thin evaporated films of potassium iodide (KI) are highly sensitive to ozone in work function measurements. Among various other materials KI is well suited for limit detection in the ppb range in normal humid air with work function sensors like SGFET. The cross-sensitivities to other oxidants are comparatively small which is due to a redox system of highly oxidated states on the layer surface as is found by XPS analysis.
Sensors and Actuators B-chemical | 1998
A. Fuchs; M Bögner; T. Doll; Ignaz Eisele
Abstract Hybrid suspended gate FET (HSGFET) with a thin potassium iodide (KI) sensitive layer were proven to be well suited as a reproducible ozone sensor operating at room temperature with an excellent resolution in the low ppb region. The impact of humidity limits the applicability of the sensor to moderate ambient conditions.
Sensors and Actuators B-chemical | 2000
R Winter; K. Scharnagl; A. Fuchs; T. Doll; Ignaz Eisele
Abstract Indium oxide and indium aluminium oxide thin films for low-temperature work function sensors were grown on silicon substrates by molecular beam evaporation (MBE). Depending on the substrate temperature and the oxygen partial pressure during film growth, different stoichiometry and morphology were obtained. After depositing, the films were annealed in oxygen. The films were characterized by AES, RBS, XRD and SEM. The stoichiometry of the layers varies between pure In 2 O 3 and a composition of pure indium and In 2 O 3 . All the films are polycrystalline with a grain size up to 300 nm. Thicker films form a porous layer. The indium aluminium oxide films show no crystalline phases. Both as-grown and annealed films were tested for NO 2 , CO, CO 2 , NH 3 , Cl 2 and O 3 at room temperature and 130°C by Kelvin probe measurements in dry and humid air. In 2 O 3 films show a high sensitivity to NO 2 , CO and CO 2 . A higher sensitivity for the porous layers is obtained due to the greater surface.
Sensors and Actuators B-chemical | 1999
K Scharnagl; M Bögner; A. Fuchs; R Winter; T. Doll; Ignaz Eisele
Abstract A thin semiconducting PtO2 film is exposed to several gases at room temperature. This exposure causes a work function change at the surface of the film due to adsorption of the molecules. It is found that there is a strong dependence of the adsorptivity, i.e., the amount of work function change per unit time, on the magnitude of an electrical field that is applied perpendicular to the film surface. This induced adsorptivity change is known as the electroadsorptive effect. In order to modulate the adsorptivity significantly, the electrical field strength must exceed 104 V/cm. This requirement can be achieved by using hybrid suspended gate FET (HSGFET) with an air gap height smaller than 1 μm. Thus metal oxides may be used as sensitive layers even at room temperature.
Sensors and Actuators B-chemical | 1994
M. Leu; T. Doll; B. Flietner; Josef Lechner; Ignaz Eisele
Abstract We have developed a new hybrid technique for gas sensors based on field effect structures (GASFET). A wide range of materials can be used as sensitive layer (e.g., inorganic or organic, metal or oxide) for a selective detection of different gases. GASFET with an air gap using as sensitive layer different materials (Pt, SnO2, Ga2, O3, V2O5) were built. The interactions of these different sensitive layers with various gases were investigated. Gas measurement were carried out at room temperature (25 °C) and at 70 °C. Work function changes of these senstitive layers upon exposure to hydrogen, ammonia, nitrogen dioxide and carbon monoxide as well as all mixtures of two gases were recorded. The carrier gas was synthetic air. Matrices representing the signals as a function of two gas concentrations were obtained. By means of pattern recognition and analytical techniques we are able to identify the gaseous species and to evaluate their concentration if only one gas is present in the gas mixture. When two gases are mixed, they can be identified and their concentrations can be approximated.
Sensors and Actuators B-chemical | 1994
B. Flietner; T. Doll; Josef Lechner; M. Leu; Ignaz Eisele
Abstract We have developed a novel hybrid technique for manufacturing gas-sensing field-effect structures with an air gap. It is possible to find an optimum non-critical range for all technological parameters to ensure reliable evaluation of a work-function response caused by a gas reaction. To prove the efficiency of the device, room-temperature gas measurements with the well-known Pt (sensitive layer) and H 2 (gas) system have been carried out. Samples that are identically produced show reproducible signals of the same magnitude. Simultaneously we have recorded the electrical response of a platinum-coated Kelvin probe. It is shown that the results are transferable to those obtained by the Kelvin probe.