Sensitivity enhancement of a humidity sensor based on poly(sodium phosphate) and poly(allylamine hydrochloride)
MIGUEL HERNAEZ; DIEGO LOPEZ-TORRES; CESAR ELOUSA; IGNACIO R. MATIAS; FRANCISCO J. ARREGUI
The particular behavior of poly(sodium phosphate) (PSP) when it is deposited by means of the spraying layer-by-layer (LbL) technique has been used here to enhance the response of optical fiber humidity sensors. The roughness of the PSP films varies depending on the concentration of the polymeric solutions. In this work, it is demonstrated that this special feature of PSP allows the fabrication of optical fiber humidity sensors with different responses. Particularly, multilayer thin-films made of 10 -3 and 10 -4 M PSP and poly(allylamine hydrochloride) (PAH) solutions have been studied and used for the fabrication of optical fiber interferometers sensitive to humidity. To our knowledge this is the first time that the spray-assisted LbL technique has been used for the fabrication of optical fiber sensors.
Link to source: https://ieeexplore.ieee.org/abstract/document/6688549
Fabrication and characterization of the thin films
First of all, two different thin films (TF1 and TF2) were deposited onto glass slides using the spray-assisted LbL deposition technique. This technique involves different steps that were performed by using a spraying robot (Nadetech Inc.)
Deposition of the Nanocoating and LMR Generation
As mentioned in the abstract, the layer-by-layer electrostatic self assembly (LbL—ESA) technique –, was used to deposit the polymeric thin-film onto the tapered fiber (Fig. 1). Prior to start the process, the substrate was fixed to a 3-axis robotic arm designed by Nadetech Innovations S.L. and immersed in piranha solution (70%H2SO4,30%H2O2) during 10 minutes in order to acquire negative charge. Then, it was rinsed with ultrapure water to remove undesired impurities.