In addition, their electrical properties are extremely sensitive to the effect of electron-accepting and donating gases, so their gas sensing properties have been widely explored since about twenty years [2, 3]. In this regard, ozone (O3) sensors based on thin films of nickel phthalocyanine (NiPc) for pollution control have been proposed [4, 5] , as other phthalocyanine-based sensors for reducing gases as ammonia (NH3) [6].The literature shows that most of gas sensors based on semiconducting molecular materials are based on resistors, which principle of detection are merely based on the changes of resistance depending on the electronic nature of the gas analytes under study. One of the authors of this manuscript have reported some few examples of phthalocyanines as sensitive element in molecular field effect transistors-based gas sensors [3, 7].

Schottky diode sensors based on inorganic materials as Si or III-V compounds as InP have been also proposed [8-10] , as well as inorganic p-n junctions [11]. The chemical sensitivity of such devices, but based on conducting polymers, has been discussed in terms of work function modulation [12].Concerning molecular materials, metal/OS junctions have been extensively studied since early eighties [13]. The realization of organic heterojunctions has been made possible thanks to the confirmation of n-type semiconducting behavior in molecular materials [14]. Originally, these materials were used as n-channels organic field-effect transistors (OFETs) [15, 16] and in organic photovoltaic cells [17, 18].

Very recently, heterojunctions [19, 20] between copper phthalocyanine (CuPc) and perfluoro-copper phthalocyanine (Cu(F16Pc)) have been used to control the electrical characteristics of an OFET [21]. On the other hand, fluorinated phthalocyanines as Zn(F16Pc) had been shown to be sensitive to reducing gases due to the withdrawing effect of fluorine atoms [6, 22]. This causes fluorinated phthalocyanines to be easier reduced than non-substituted phthalocyanines, then more inert to oxidization.In this work, we propose a structure made from both p- and n-type semiconducting materials, namely non-substituted nickel phthalocyanine (NiPc) and nickel hexadecafluorophthalocyanine (Ni(F16Pc)), in a combined organic heterojunction-Schottky diode configuration, (Au|Ni(F16Pc)|NiPc|Al), as a novel device based on organic materials able to be used in gas sensing applications.

For comparison purposes, single layer samples having the same electrode configuration are also Brefeldin_A discussed. The diode-like performance of the device is presented and discussed, besides its sensitivity and reversibility to an electron donor agent as ammonia (NH3). The use of the electrical features of organic junctions based on OSs presented in this paper constitutes a new principle of transduction for gas sensing applications.