| 1. |
- Baranzahi, Amir, et al.
(författare)
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Chemical sensors with catalytic metal gates - Switching behavior and kinetic phase transitions
- 1998
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 145:10, s. 3401-3406
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Tidskriftsartikel (refereegranskat)abstract
- Rapid transitions in the response of platinum-based chemical sensors occurring at given hydrogen-oxygen concentration ratios are explained by kinetic phase transitions or switching phenomena on the catalytic metal surface. Below the transition point the response of platinum-insulator silicon carbide devices is small and above the transition it is large. It is found that the critical ratio depends on the operation temperature and the properties of the device. Three different cases are identified, namely, injection-, diffusion-, and reaction-rate-determined transitions. At sufficiently large temperatures the transition is injection limited and occurs at the stoichiometric ratio of hydrogen and oxygen in the gas mixture. The implications of the experimental observations on the applications of chemical sensors with catalytic sensing layers are discussed.
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| 2. |
- Baranzahi, Amir, et al.
(författare)
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Gas sensitive field effect devices for high temperature
- 1995
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 26:1-3, s. 165-169
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Tidskriftsartikel (refereegranskat)abstract
- Field effect sensors based on metal-oxide-silicon carbide (MOSiC) devices are used as high temperature gas sensors. They are sensitive to, for example, saturated hydrocarbons and hydrogen and can be operated up to at least 800 degrees C, which make them suitable for several types of combustion control. A metal gate with two layer platinum and a buffer layer of tantalum silicide in between gave a large increase in the long term stability of the sensors. At temperatures below 600 degrees C, the response to ethane in oxygen was shown to have a threshold at a ratio of about 0.38 for the ethane-to-oxygen concentrations. Below this ratio, the surface can be considered as mainly oxygen covered and the response is small. Above this ratio the metal surface is probably mainly hydrogen covered and the response is considerably larger.
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| 3. |
- Baranzahi, Amir, et al.
(författare)
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Kinectic phase transitions and chemical sensors with catalytic metal gates
- 1997
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Ingår i: Chemical & Biological Sensors & Analytical Electrochemical Methods, 1997. - : Electrochemical Society. - 9781566771474 - 1566771471 ; , s. 1-15
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Rapid transitions in the response of platinum based chemical sensors occurring at given hydrogen-oxygen concentration ratios are explained by kinetic phase transitions or switching phenomena on the catalytic metal surface. Below the transition point the response of platinum-insulator silicon carbide devices is small and above the transition large and almost saturated. It is found that the critical ratio depends on the operation temperature and the properties of the device. Three different cases are identified, namely injection-, diffusion- and reaction rate determined transitions. At sufficiently large temperatures the transition is injection limited and occurs at the stoichiometric ratio of hydrogen and oxygen in the gas mixture. The implications of the experimental observations on the applications of chemical sensors with catalytic sensing layers are discussed.
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| 4. |
- Baranzahi, Amir, et al.
(författare)
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Response of metal-oxide-silicon carbide sensors to simulated and real exhaust gases
- 1997
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Ingår i: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 43:1-3, s. 52-59
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Tidskriftsartikel (refereegranskat)abstract
- Field effect devices based on catalytic metal-oxide-silicon carbide (MOSiC) structures can be used as high temperature gas sensors. The devices are sensitive to hydrocarbons and hydrogen and can be operated up to at least 900 degrees C, which make them suitable for several combustion applications, Simulated and real exhaust gases from a car engine have been studied at sensor temperatures from 200 to 650 degrees C, and it was round that the sensor signal is high for excess hydrocarbon and low for excess oxygen. The response time is less than 100 ms and only a small degradation of the devices was observed after several days of operation. The devices also react to changes of the gas composition In the fuel-rich and fuel-lean region. The devices show an interesting temperature dependence in the fuel rich region.
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| 5. |
- Baranzahi, Amir, et al.
(författare)
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Reversible hydrogen annealing of metal‐oxide‐silicon carbide devices at high temperatures
- 1995
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 67:21, s. 3203-3205
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Tidskriftsartikel (refereegranskat)abstract
- We report on a reversible hydrogen annealing effect observed in platinum-silicon dioxide-silicon carbide structures at temperatures above about 650 degrees C. It appears as a decrease of the inversion capacitance in the presence of hydrogen. This phenomenon is shown to depend on hydrogen atoms, created on the catalytic metal, that pass through the oxide and interact with charge generation sites at the oxide-silicon carbide interface. The consequence of the observation for chemical sensors based on silicon carbide is discussed. The results are phenomenological, since no details of the annealing chemistry could be developed from the present experiments. We find, however, that the annealing process and its reversal have activation energies of about 0.9 eV and 2.9 eV/site,respectively.
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| 6. |
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| 7. |
- Kanciurzewska, Anna, et al.
(författare)
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Study on Poly(3,4-ethylene dioxythiophene)-Poly(styrenesulfonate) as a plastic counter electrode in dye sensitized solar cells
- 2007
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Ingår i: Journal of Optoelectronics and Advanced Materials. - 1454-4164 .- 1841-7132. ; 9:4, s. 1052-1059
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Tidskriftsartikel (refereegranskat)abstract
- Dye sensitized solar cells with PEDOT-PSS coated directly on flexible polyester substrate as counter electrode have been fabricated. The behavior of such plastic counter electrode in the presence of I/I-3 redox electrolyte has been investigated with X-ray photoelectron spectroscopy. We have found that some of iodine species are "trapped" within the PEDOT-PSS layer. The presence of I-3, I-2 and PEDOT charge transfer complexes with iodine species may block the surface of the electrode. Furthermore, the PEDOT may be further oxidized (p-doped) during cell operation, which in turn may cause overoxidation and loss of conductivity in the PEDOT-PSS film. Additionally, the interactions between PEDOT and iodine species may be enlarged because of the partial loss of PSS protective counter ion. That has resulted in decrease of PEDOT-PSS catalytic activity for reduction of I-3 to I in the redox electrolyte and has caused worse cell performance than in case of DSSC with Pt counter electrode.
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| 8. |
- Karlsteen, M., et al.
(författare)
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Electrical properties of inhomogeneous SiC MIS structures
- 1995
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Ingår i: Journal of Electronic Materials. - : Springer. - 0361-5235 .- 1543-186X. ; 24:7, s. 853-861
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Tidskriftsartikel (refereegranskat)abstract
- Current-voltage characteristics of metal contacts on 6H-SiC with a thin (5-20 Angstrom) oxide layer have been measured in the temperature range 300 to 1000K. The contacts were investigated in both H-2 and O-2-atmospheres. As the SiC surface was nonideal due to pin holes and other defects generated during the growth process, it was necessary to treat the Schottky contacts as inhomogeneous contacts. The inhomogeneity explains the nonideal current-voltage behavior of the contacts such as ideality factors much larger than unity and voltage dependent ideality factors. It was found that some metals gave Schottky contacts in the entire temperature range, while other metals were ohmic at higher temperatures. Several different contact metals were investigated: Al, Ti, TaSix, and Pd were found to be ohmic at high temperatures, while Pt, Pt+Cr, Ni, Cr and another TaSix contact were found to behave like Schottky contacts in the entire temperature range. This is a preliminary investigation of the electrical characteristics of different metals that could be useful for high temperature gas sensor purposes.
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| 9. |
- Lloyd Spetz, Anita, et al.
(författare)
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High temperature sensors based on metal-insulator-silicon carbide devices
- 1997
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Ingår i: Physica status solidi. A, Applied research. - : John Wiley & Sons. - 0031-8965 .- 1521-396X. ; 162:1, s. 493-511
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Tidskriftsartikel (refereegranskat)abstract
- High temperature gas sensors based on catalytic metal-insulator-silicon carbide (MISiC) devices are developed both as capacitors and Schottky diodes. A maximum operation temperature of 1000 degrees C is obtained for capacitors based on 4H-SiC, and all sensors work routinely for several weeks at 600 degrees C. Reducing gases like hydrocarbons and hydrogen lower the flat band voltage of the capacitor and the barrier height of the diode. The time constants for the gas response are in the order of milliseconds and because of this good performance the sensors are tested for combustion engine control. For temperatures around 600 degrees C total combustion occurs on the sensor surface and the signal is high for fuel in excess and low for air in excess. At temperatures around 400 degrees C the response is more linear. The high temperature operation causes interdiffusion of the metal and insulator layers in these devices; and this interdiffusion has been studied. At sufficiently high temperatures the inversion capacitance shows different levels for hydrogen free and hydrogen containing ambients, which is suggested to be due to a reversible hydrogen annealing effect at the insulator-silicon carbide interface.
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| 10. |
- Lloyd Spetz, Anita, et al.
(författare)
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X-ray photoemission and Auger electron spectroscopy analysis of fast responding activated metal oxide silicon carbide gas sensors
- 1997
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 299:1-2, s. 183-189
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Tidskriftsartikel (refereegranskat)abstract
- Platinum-silicon dioxide-silicon carbide, MOSiC, sensors are possible to operate at high temperatures and show a gas sensitivity pattern which is of interest for many applications including exhaust gases from car engines. The introduction of a buffer layer of tantalum silicide between the metal and the silicon dioxide resulted, after an annealing step, in a very good adhesion of the gate contact and fast responding sensors with improved signal stability. Depth profiling using X-ray photoemission and Auger electron spectroscopy showed that the annealing step converts the tantalum silicide to a mixed phase predominantly containing tantalum pentoxide. Tantalum silicide as well as platinum silicide are also present in the metal-oxide interface region.
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