Chemical sensing deposition techniques

Polymers are among the most widely used materials for chemical sensing since they are able to collect and concentrate molecules on sensor surfaces by reversible sorption they can be deposited on several substrates as thin adherent films with easy processing techniques they are available in many kinds having different chemical and sorption properties, which can be used to enhance the selectivity of the sensors last but not least, they are of low cost. 

Bilayer films of poly(ethyleneimme) (positively charged) and poly(ethylene-co-maleic acid) have been used for chemical sensing [49]. The technique of surface plasmon resonance was used to monitor, in-situ, the deposition of these films. Subsequent exposure to aqueous solutions of metal acetate (metal = copper, nickel) resulted in a shift in position of the SPR curve. Phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition have also been exploited for erasable nanoporous antireflection coatings, opening up applications for biore-sponsive materials and membrane applications [50]. 

Other techniques have been used for the fabrication of thin-film metal-oxide gas sensors. At NIST in the USA, Cavicchi et al. (1995) and Semancik et al. (2001) produced gas sensors by chemical vapor deposition (CVD). By applying a current and thus heating the hotplate, sensing films could be deposited locally (i.e. only on heated active areas) using an adequate organ-ometaUic precursor. SnOj and ZnO films were obtained with tetramethyltin and diethylzinc in an oxygen atmosphere. They were deposited onto different seed layers, which played a significant role in terms of gas selectivity. 

Moseley PT, Norris JOW, Williams DE (1991) Techniques and mechanisms in gas sensing. Adam Hilger, Bristol Nakaso K, Han B, Ahn KH, Choi M, Okuyama K (2003) Synthesis of non-agglomerated nanoparticles by an electrospray assisted chemical vapor deposition (ES-CVD) method. J Aerosol Sci 34 869-881 Narendar Y, Messing GL (1997) Mechanisms of phase separation in gel-based synthesis of multicomponent metal oxides. Catal Today 35 247-268... 

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