Surface defect sensors

Chemical sensors for gas molecules may, in principle, monitor physisorp-tion, chemisorption, surface defects, grain boundaries or bulk defect reactions [40]. Several chemical sensors are available mass-sensitive sensors, conducting polymers and semiconductors. Mass-sensitive sensors include quartz resonators, piezoelectric sensors or surface acoustic wave sensors [41-43]. The basis is a quartz resonator coated with a sensing membrane which works as a chemical sensor. 

The technology is available now for flexible and modular automatic inspection systems which make it possible to inspect rotational symmetric mass-produced articles with high throughput for surface defects and dimensions. The handling system of the Easier 03 is able to quickly and reliably separate and convey round parts of different sizes precisely to the sensor units. The optical inspection of engineered seals includes the inspection of geometrical properties and surface defects. 

Abstract An Eddy current method applying a High Temperature Superconductor ( HTS ) DC SQUID sensor operating at Uquid nitrogen temperature (77K) is presented. The method is developed for the detection of surface or surface near defects. We compare the performance of the SQUID system with the performance gained from a commercial Eddy current system, while using identical probes. The experimental data are obtained on defects in gas turbine blades. The advantage of planar conformable probes for the use with the SQUID is discussed. 

Thus, sensor effect deals with the change of various electrophysical characteristics of semiconductor adsorbent when detected particles occur on its surface irrespective of the mechanism of their creation. This happens because the surface chemical compounds obtained as a result of chemisorption are substantially stable and capable on numerous occasions of exchanging charge with the volume bands of adsorbent or directly interact with electrically active defects of a semiconductor, which leads to direct change in concentration of free carriers and, in several cases, the charge state of the surface. 

The experimental studies of the surface properties of monocrystals of oxides of various metals recently conducted at well-controlled conditions [32, 210] enable one to proceed with detailed analysis of separate effects of various factors on characteristics of semiconductor gas sensors. In this direction numerous interesting results have been obtained regarding the fact of various electrophysical characteristics of monocrystalline adsorbents on the value of adsorption-related response. Among these characteristics there are crystallographic orientation of facets [211], availability of structural defects, the disorder in stoichiometry [32], application of metal additives, etc. These results are very useful while manufacturing sensors for specific gases with required characteristics. 

This conclusion is proved by the element analysis of sensors which have registered more than 30 portions of silver emitted from the surface of substrate after completion of deposition of silver on its surface. The experiments on local analysis of tiie sensor indicated that such sensor has areas containing up to 0.3 wt.% of silver in 1 pm. The total amount of silver atoms incident on sensor was 7-10. This means that silver atoms get deposited on the surface of the sensor inhomogeneously, being localized close to defect allocation area which made it possible to detect... 

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