Vladimir Myslik

The response of tin acetylacetonate and tin dioxide-based gas sensors to hydrogen and alcohol vapours

The aim of this work is to investigate the properties of gas sensors with active layers prepared by pulsed laser deposition (PLD) technology. The active layers were deposited on planar sensor chips with interdigital platinum electrodes. The deposition was carried out from tin dioxide and tin acetylacetonate (SnAcAc) targets by KrF excimer laser. In some cases Pd catalyst was sputtered on the surface of the active layer. The ‘as-deposited’ sensors were submitted to heat treatment. The chemical composition of heat treated active layers was studied by XPS method. This method revealed the oxidation state of palladium and the distribution between organic and inorganic phase during the deposition of SnAcAc. The DC responses of the sensors to a reducing atmosphere containing 1000 ppm of hydrogen, methanol, ethanol, n-propanol and n-butanol were also measured. The maximum sensitivity S (ratio of sensor resistances SaRair/Rgas) achieved 67 for hydrogen, 21 for methanol, 50 for ethanol, 71 for n-propanol and 44 for n-butanol. The temperature of maximum sensitivity (Tmax )t o distinct gases, the influence of molecular weight of detected gas on Tmax and the influence of molecular weight on the sensor response speed are also discussed. # 2000 Elsevier Science B.V. All rights reserved.

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.

Comparison of laser technology and RTA on Pt/Sn/Pd ohmic contacts to GaAs

In this paper we have studied the performance of Pt/Sn/Pd contact structures on n+)-GaAs plates. An absorbing cap layer is necessary to use in the case of a laser annealing. Pt layer deposited by sputtering with the thickness of 12 nm gives the best parameters. The semiconductors plates were cleaned prior the deposition of metallization by various solutions, the lowest contact resistance was obtained in the case of H2O2:NH4OH:H2O. The laser annealing was compared with RTA method, which was not suitable for this contact structure.

SnO 2 and SnAcAc Thin Film Sensors Created by Laser

Inorganic and organic tin based thin films were created by pulsed laser deposition (PLD) on special alumina chips. Influence of dopants and catalysts was studied. Sensitivity of Sn- based layers to hydrogen, methanol, ethanol, n- propanol and n- buthanol based layers to was measured.

Laser technology in the preparation of Pt/doping element/Pd/n+-GaAs contacts

The performance of W/Pt/doping element/Pd and Pt/doping element/Pd ohmic contacts has been investigated, where Ge, Si, and Sn were employed as doping elements. The contacts were deposited by vacuum sputtering on n+-GaAs substrate plates and GaAs or AlGaAs epitaxial layers, then annealed by a power YAG:Nd laser. The influence of the doping elements on the parameters for ohmic contacts was not significant, with germanium being the best, we obtained a minimum value of rc equals 5 X 10-6 (Omega) cm2. The layers of GaAs and AlGaAs were prepared with (delta) -doping by MOVPE epitaxial growth method. The minimal values of contact resistivities of 1.1 X 10-4 (Omega) cm2 and 7.35 X (Omega) cm2 were achieved.

Deposition of thin polymer films by pulsed excimer laser ablation

Deposition of thin Polytetrafluorethylene (PTFE) film by laser ablation deposition (LAD) technique is briefly described. The method utilization, transport conditions, and optimal setup are presented. The paper also deals with the methods of prepared thin films characterization (scanning electron microscopy, x-ray diffraction, and Fourier transform infrared spectroscopy) and comments on all data achieved from all characterization measurements.

Conductive Gas Sensors Prepared Using PLD

This contribution deals with conductive thin film gas sensors fabricated using laser technology. The principles of the pulsed laser deposition (PLD) technology is explained. Hybrid PLD systems, based on a combination of PLD and magnetron sputtering, PLD and RF discharges, and PLD with two laser targets are also presented. The growing layers can be modified by an ion beam. Organic films can be grown using the cryogenic MAPLE technology. Nanocrystalline and nanocomposite thin films for gas sensors can be deposited. Examples of layer fabrication and testing of layer properties for gas sensors are given.

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.

Thin film tin oxide chemical sensors created by laser CVD and PLD techniques

Tin oxide thin films based chemical sensors have been developed by means of laser induced chemical vapor deposition (L-CVD) and pulsed laser deposition (PLD) methods. The chemical composition of sensors was studied by XPS. By these two methods the tin oxide films were deposited at identical chemical chips and the sensitivity to hydrogen was measured and compared. An improvement of the sensitivity by using noble metal catalysts was observed. In addition, the possibility of detection Co, CH4, SO2, NO2 and N2O gasses on the films deposited by L-CVD technique and to alcohol vapor on the films deposed by PLD was studied.