Ž . Sensors and Actuators B 65 2000 270–272 www.elsevier.nlrlocatersensorb Semiconductor sensors for fluorine detection — optimization for low and high concentrations L. Bartholomaus a, ) , A.A. Vasiliev b , W. Moritz a ¨ a Humboldt-UniÕersity Berlin, Inst. of Phys. Chemistry, Bunsenstr. 1, 10117 Berlin, Germany b RRC ‘‘KurchatoÕ Institute’’, 123182 Moscow, Russian Federation Accepted 4 August 1999 Abstract For the detection of fluorine, two different preparation methods for semiconductor gas sensors were developed, the first for Ž . Ž . concentrations between 10 and 1000 ppm type I and another for concentrations between 0.01 and 10 ppm type II . The sensitivity of ŽŽ .. type I sensors is about 116 mVrlg p F . It is possible to detect gas concentrations down to 0.1 ppm using this sensor. The main 2 disadvantage is that the sensor response kinetics depends strongly on concentration. The sensors response is fast for measurement of high Ž . concentrations between 10 and 1000 ppm but the response time is not acceptable for the detection of small concentrations. Type II ŽŽ .. sensors show a sensitivity of 28 mVrlg p F for gas concentrations between 0.006 and 10 ppm. This sensor is very fast in the detection 2 of small concentrations of gas. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Fluorine; LaF ; ISFET 3 1. Introduction The determination of fluorine is very important for environmental monitoring. The highest tolerable level is, for example, 0.1 ppm in Germany. For the detection of fluorine, electrochemical cells are wx produced by several companies 1 . They all have a liquid electrolyte as the main disadvantage. Recently we sug- gested to detect fluorine using a MIS structure with the w x ionic conductor LaF as the sensitive layer 2,3 . A prob- 3 lem of this structure was the bad reproducibility of the Ž ŽŽ ... sensitivity 60–200 mVrlg p F . 2 This was solved with a special pretreatment of the sensor in 1000 ppm of fluorine. After this pretreatment, a wx stable sensitivity was found between 0.1 and 1000 ppm 4 . The remaining disadvantage of this sensor was the dependence of the response kinetics of the system on the gas concentration. The sensor response kinetics was get- ting rather slow with smaller concentrations of fluorine. Therefore, our main aim was to investigate this response ) Corresponding author. Tel.: q 49-30-2093-5550; fax: q 49-30-2093- 5553; e-mail: lars@elsa.chemie.hu-berlin.de Fig. 1. Scheme of a sensor based on n-SirSiO rSi N rLaF rplatinum. 2 3 4 3 0925-4005r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0925-4005 99 00337-8