II WORKSHOP ON CHEMICAL SENSORS AND BIOSENSORS 9 APPLICATIONS OF POROUS SILICON AS A GAS SENSOR G. Di Francia 1 , L. Quercia 1 ,G. Iadonisi 2 , V. La Ferrara 2 , L. Lancellotti 2 , D. Ninno 2 ,C. Baratto 3 ,E. Comini 3 , G. Faglia 3 and G. Sberveglieri 3 1 CR-ENEA Loc. Granatello, 80055 Portici(Napoli), Italy 2 INFM, Dip. di Scienze Fisiche, Università di Napoli “Federico II” Mostra d’Oltremare, Pad. 19, 80125 Napoli, Italy 3 INFM Dip. di Chimica e Fisica dei Materiali, Universita' di Brescia Via Valotti 9, 25133 Brescia, Italy ABSTRACT: Porous Silicon has been the most investigated material over the last decade. The main aim of this work is to describe its potential applications as gas sensor discussing reported data and authors’ experimental findings. Fabrication methods and material properties as well as the possible mechanisms of interaction with the environment are also discussed. Keywords: Sensor, Porus Silicon, Nanophase. INTRODUCTION In 1956 [1] it was observed that as a result of anodization in hydrofluoridric acid solutions a brownish film formed on a crystalline silicon wafer. The film was considered an amorphous layer produced by an autodisproportionation reaction. Some years later, Theunissen [2] demonstrated that it was the result of an etching process leaving essentially a crystalline layer: thus, in proper conditions silicon