Organic vapor sensors based on functionalized macroporous Si using single and double-side electrochemical etching

Organic sensors for ethanol vapor detection were developed by means of electrochemical etching of crystalline silicon as initial substrate following two procedures: front side etching (FSE) and front- and backside ("double") surface etching (DSE). The first consists on the attack of the crystalline silicon surface by hydrofluoric acid (HF) in presence of a constant current flow to form a layer of vertically oriented pattern of pores with diameters in the 2-5 μm range and a thickness of about 50 μm. The second procedure is similar to the first one but allowing a similar etching to the opposite side of the silicon wafer. The etching times for both surfaces were adjusted in such a way to produce a free standing porous layer of around 300 μm in thickness. The samples produced by FSE and DSE were submitted to a functionalization methodology using 4-aminopyridine to cover the porous surface. The obtained specimens were mounted in a holder with two soldered contacts and placed in a testing chamber where different flows of ethanol vapors were injected. Conductance responses of both kinds of sensors were recorded and compared between them and with respect to nontreated crystalline silicon samples in terms of sensing capability, reproducibility, and response times. The results indicate that both FSE and DSE sensors have improved sensing properties compared to the nontreated surfaces.