Martin Vrnata

Thin film gas chemical sensors based on resistive or optical detection (Invited Paper)

Thin films gas sensors based on resistive or optical m-line detection are studied. The focus is on butane detection. Potentially suitable materials for detection are summarized and discussed. Experimental results reached with inorganic and organic layer fabricated by pulsed laser deposition are presented.

Polypyrrole active layers of gas sensors prepared by MAPLE technology

Thin layers of polypyrrole (PPY) were deposited by MAPLE (Matrix Assisted Pulse Laser Evaporation) technology. The deposition was carried out by KrF excimer laser from water and dimethylsulfoxide matrixes. Ablation thresholds (Fth) were determined to be Fth ~ 0.3 J.cm−2for dimethylsulfoxide matrix and Fth ~ 0.45 J.cm−2for water matrix. The roughness of deposited layers was measured by AFM and their chemical composition was characterized by FTIR spectroscopy. Finally, resistance of sensors with PPY active layer was measured in dependence on working temperature and relative humidity of surrounding atmosphere.

Noise in quartz crystal microbalance

There are several mechanisms that are related to fluctuation phenomena in QCM. The aim of our research is oriented to study the sensitivity and influence of different kind of noises on sensor resolution. Our experiments are provided on sensor with sorption layer of polypyrrole which is suitable for detection of water vapor. Based on these experiments, we suppose that 1/f noise caused by quartz internal friction and adoption-desorption (generation-recombination) noise from analyzed gas create the main components of measured noise spectral density. The value of the adoption-desorption noise depends on the physical and chemical parameters of analyzed gas and it is proportional to gas density. Adsorption-desorption kinetics is described by Kolmogorov equation and compared with Wolkenstein and Langmuir equations.

Modification of detection process on ZnO sensors by ultraviolet radiation

The contribution deals with influence of radiation in the near UV region (λ = 396 nm) on detection properties of conductive type gas sensors. The ZnO active layers of the sensors were deposited on Alumina substrates by Pulsed Laser Deposition method. Resulting thickness of active layers was ∼ 450 nm. The dc-sensitivity was evaluated from resistance change under exposition of hydrogen and acetone and toluene vapours in synthetic air. The sensitivity to acetone was doubled using the UV radiation at 250°C.

Comparison of tin oxide chemical sensors prepared by PLD and laser-assisted CVD methods

Tin oxide active layers were deposited by Pulsed Laser Deposition (PLD) and Laser assisted Chemical Vapor Deposition (LCVD) methods. The films were grown on the same substrate chips for the thin layer conductive sensor. Their chemical and morphological properties were studied in connection with gas sensor applications. The influence of the Pd catalyst was tested. The chemical composition was investigated by XPS analysis. A sensitivity to 1000 ppm of hydrogen of about 1090 for PLD and 5 for LCVD was achieved.

Laser-deposited active layers of chemical sensors

Thin active layers of chemical sensor were deposited form tin dioxide targets by the pulsed laser deposition (PLD) method. The deposition was made by employing excimer KrF laser. The bearing part of the senor is an alumina chip provided by Pt-electrodes in the interdigital configuration. They serve for reading of the sensor response - DC resistance of active layer. Under reducing gases the resistance of the active layer decreases. For the stabilization of sensor properties it is necessary to use dopants. In this case the PLD technology enables an original solution-introduction of dopants as a multilayered structure. In order to improve the sensor parameters, catalytic Pt or Pd is vaporized to the surface of active layer in the form of non-aggregated particles.

Laser-annealed deep ohmic contacts

The contribution deals with the results of our work on ohmic contact formation, the process optimization. The contacts should be optimized with respect to chemical composition of metallization, energy density of laser radiation, and repetition rate of laser pulses. These contacts also enable us to interconnect the surface of the samples with a very thin layer under the surface ((delta) -doped layer).