Technical University of Moldova

About: Technical University of Moldova is a education organization based out in Chisinau, Moldova. It is known for research contribution in the topics: Thin film & Raman spectroscopy. The organization has 520 authors who have published 899 publications receiving 17930 citations. The organization is also known as: Universitatea Tehnică a Moldovei.

Metal oxides for solid-state gas sensors: What determines our choice?

Abstract: The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Gas response control through structural and chemical modification of metal oxide films: state of the art and approaches

Abstract: In this review the structural and physical–chemical properties of nanoscaled metal oxide films (SnO2 and In2O3), aimed for solid state chemical sensors were analyzed. It has been shown that structural factor even for nanoscaled materials is complicated conception. One has to consider not only size, but also such a parameters as crystallite shape; nanoscopic structure; crystallographic orientation of nanocrystallites planes, forming gas sensing surface; film agglomeration; phase composition; surface architecture. The methods suitable for control of these structural and physical–chemical parameters have been discussed. Results, mainly obtained during study of both SnO2 and In2O3 thin films deposited by spray pyrolysis have been used for showing an opportunity of structural engineering of metal oxides for optimization of gas sensing characteristics.

The role of morphology and crystallographic structure of metal oxides in response of conductometric-type gas sensors

Abstract: This review paper discusses the influence of morphology and crystallographic structure on gas-sensing characteristics of metal oxide conductometric-type sensors. The effects of parameters such as film thickness, grain size, agglomeration, porosity, faceting, grain network, surface geometry, and film texture on the main analytical characteristics (absolute magnitude and selectivity of sensor response (S), response time (τres), recovery time (τrec), and temporal stability) of the gas sensor have been analyzed. A comparison of standard polycrystalline sensors and sensors based on one-dimension structures was conducted. It was concluded that the structural parameters of metal oxides are important factors for controlling response parameters of resistive type gas sensors. For example, it was shown that the decrease of thickness, grain size and degree of texture is the best way to decrease time constants of metal oxide sensors. However, it was concluded that there is not universal decision for simultaneous optimization all gas-sensing characteristics. We have to search for a compromise between various engineering approaches because adjusting one design feature may improve one performance metric but considerably degrade another.

Rapid fabrication technique for interpenetrated ZnO nanotetrapod networks for fast UV sensors.

Abstract: Au contacts. The B-FTS approach exhibits the unique feature of ultra-rapid growth of ZnO nanotetrapods within few milliseconds and simultaneously in situ bridging electrical contacts. These bridging nanotetrapods were directly integrated on a chip and demonstrated signifi cantly improved performances as a UV photodetector. Comparison of the UV photodetectors performances built from interpenetrating ZnO nano-microstructures fabricated by B-FTS and C-FTS techniques are presented. Fastest response/recovery time constant (≈32 ms) under 365 nm UV light irradiation of B-FTS-made photodetectors (on/off ratio ≈4.5 ◊ 10 3 at 2.4 V) is reported. Different type of nanojunctions formed between neighbor nanowires or nanotetrapods (with ‘arm’ thickness <50 nm) could be the reason for such improved characteristics. The role of nanojunctions in fast UV photodetectors from networked ZnO nanowires and nanotetrapods is discussed. On the basis of the rapid B-FTS fabrication process and fast UV photodetection capabilities, such networked ZnO nanotetrapods can be potential candidates for various nanosensor applications.

Sensing characteristics of tin-doped ZnO thin films as NO2 gas sensor

Abstract: NO 2 gas sensor was fabricated by successive ionic layer adsorption and reaction (SILAR) technique and rapid photothermal processing (RPP) of the Sn-doped ZnO film. The experimental results shows that tin doping of zinc oxide thin films improve the sensor element sensitivity to 1.5 ppm NO 2 in air and downshift the operating temperature. The influence of variation of Sn concentration in the chemical bath and the RPP temperature on NO 2 sensitivity of thin film sensor elements was investigated in this work. Higher sensitivity was obtained at 5–10 at.% tin concentration in the solution of ions and RPP temperature of 550–650 °C. Increasing the Sn concentration in doped ZnO samples more than 10 at.% as well as decreasing the oxygen partial pressure leads to the NO 2 gas sensitivity decrease. It looks promising to use the inexpensive tin-doped zinc oxide thin films obtained by SILAR method and RPP in smart gas sensing devices that are able to recognize gas species in low concentrations and are demanded for continuous environmental monitoring.