We report results on the development of an optical fiber long period grating sensor for organic vapor monitoring. A silk fibroin ovelayer with a thickness of the order of 400 nm is drop casted on the fiber cladding surface to enable sensing of volatile organic compound vapors. For increasing methanol vapor pressure up to 100 mbar the wavelength of the long period grating attenuation band exhibits a negative shift up to a maximum value of 4 nm. The strength of the grating attenuation band is also altered reaching a 0.27 dB strength decrease under the same maximum methanol vapor pressure. Furthermore, the recovery behavior of the sensor is presented and preliminary results of the response of the sensor to isopropanol and ethanol vapors are briefly discussed.
The possibility to control the energetic properties of the molecules before their deposition can be a great advantage in the growth of ordered films of organic materials. To this end we have developed a new deposition method based on supersonic molecular beam. With this method the kinetic energy, the momentum and the internal energy can be controlled varying the properties of the supersonic expansion. Very interesting results are achieved with oligothiophene where the thin flims several hundred on nm thick grown with this method show optical, morphological and structural characteristics similar to the single crystal. Supersonic molecular beam deposition (SuMBE) is therefore proposed as an interesting method to study and to improve the performance of organic based devices.
Recent results obtained in the growth of organic materials by supersonic molecular beams (SuMBE) are presented. Compared to other vacuum deposition methods, it allows an accurate control on the initial state (kinetic energy, momentum, flux, etc.) of the molecules during the deposition process. We show that such feature can be efficiently exploited to prepare films, the structure and morphology of which resemble those single crystals, therefore achieving unprecedented control on their optical and electronic properties even for relatively thick samples (> 500 nm). We also report on the use of SuMBE for processes of co-deposition with the aim of functionalizing or doping organic semiconductors. We achieved co-depositions of a p-type semiconductor, as metal phthalocyanines, with an n- type semiconductor, as fullerenes, without phase segregation between the two compounds and with a high control on the deposition parameters. This aspect is very attractive for the growth of organic p-n junction in view of improving photovoltaic cells and gas sensors.
A novel approach to the deposition of high quality films of oligothiophenes has been developed. It is based on an original seeded supersonic molecular beam combined with an ultra high vacuum deposition chamber. This method gives an unprecedented control on film properties. Several quaterthiophene films under different beam conditions have been prepared and characterized by optical absorption, photoluminescence, tapping mode atomic force microscopy, secondary electron microscopy and x-ray diffraction. Morphology, structure and optical response are controlled by the beams' parameters. Highly ordered films, up to several hundreds of nm thick, show well resolved vibronic structures in low temperatures fluorescence spectra as only the best published data on films a few monolayers thick do.