Plasma Deposited Porphyrin/Phthalocyanine Films as Promising Optical Gas Sensing Materials
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1010-V07-02
Plasma Deposited Porphyrin/Phthalocyanine Films as Promising Optical Gas Sensing Materials Gianluigi Maggioni1, Michele Tonezzer2,3, Sara Carturan1, Alberto Quaranta2,3, Katerina Severova2,4, and Gianantonio Della Mea2,3 1 University of Padua c/o, LNL-INFN, Viale dell'Universit‡, 2, Legnaro (PD), I-35020, Italy 2 LNL-INFN, Legnaro (PD), I-35020, Italy 3 DIMTI, University of Trento, Trento, I-38050, Italy 4 Institute of Physical and Applied Chemistry, Brno University of Technology, Brno, 61200, Czech Republic
ABSTRACT Free based 5,10,15,20 meso-tetraphenyl porphyrin (H2TPP) and copper phthalocyanine (CuPc) films have been produced by means of a recently developed plasma based technique named glow discharge induced sublimation (GDS). The two macrocycles have been also deposited, for the sake of comparison, by means of commonly used deposition techniques, i.e. H2TPP by spin coating (SPIN) and CuPc by vacuum evaporation (VE). The physical properties of the films have been characterized by means of Fourier transform infrared analysis (FT-IR), scanning electron microscopy (SEM) and nitrogen physisorption measurements. FT-IR spectra point out the high purity of the GDS samples while SEM images and physisorption measurements highlight the much higher surface roughness and porosity of GDS samples with respect to the VE and SPIN ones. Optical sensing measurements, performed in differently concentrated ethyl alcohol atmospheres, highlight that GDS samples yield much higher response intensities than SPIN and VE films, short response times and complete recovery.
INTRODUCTION Porphyrins and phthalocyanines are macrocyclic compounds which have been arousing increasing attention in the last decade due to their peculiar electrical and optical properties. Particularly interesting are the optical properties of these macrocycles, such as the intense absorption of visible light and the chemical stability upon illumination. These properties have been used for developing optical chemical sensors, since the interaction between the analyte and the macrocycle gives rise to measurable changes of the light absorption of the macrocycle. In order to be exploited as sensing materials, porphyrins and phthalocyanines must be usually deposited as solid films onto a suitable substrate. A large number of chemical techniques (spin coating, LangmuirñBlodgett, etc.) has been used and studied for this purpose [1,2]. Fewer efforts, on the contrary, have been made to produce thin films by means of vacuum deposition techniques in spite of the fact that these techniques assure several advantages with respect to the standard chemical methods such as great reproducibility, uniformity and stricter control of the film thickness. Moreover, the vacuum deposition techniques produce thin films without using any extraneous compound such as organic solvents, thus allowing to obtain very pure samples.
Sample purity is expected to play an important role in the chemical sensing field, because the presence of retained solvent in the film can partially hind
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