Mid-Infrared Chemical Sensors Utilizing Plasma-Deposited Fluorocarbon Membranes

Abstract

In this study, plasma-polymerized films are evaluated as enrichment membranes deposited at the surface of mid-infrared transparent waveguides for liquid-phase chemical sensing utilizing evanescent field absorption spectroscopy. Fluorocarbon films were deposited onto zinc selenide (ZnSe) waveguides from plasma-polymerized pentafluoroethane (CF(3)CHF(2)) vapor. Excellent optical transmission of ZnSe waveguides after plasma deposition confirms compatibility of the infrared transparent substrate with this low-temperature, solvent-free film deposition process. The liquid-phase enrichment characteristics for plasma membranes were investigated via evanescent field absorption spectroscopy of a model analyte (tetrachloroethylene); the limits of detection were below 300 ppb (v/v) in water. Plasma-polymerized films are known for their excellent mechanical and chemical stability, while offering tunable chemical and physical characteristics during the deposition process. Future application of this coating strategy for depositing robust enrichment membranes with tunable batch production capability imparts an attractive route toward application-oriented development of next-generation mid-infrared chemical sensors applicable in harsh environments.

Mid-infrared materials and devices on a Si platform for optical sensing

“…The incorporation of such films into chemical sensors has been heavily researched since the late 1980s [68, 69]. EPLs have been demonstrated as efficient and highly sensitive coatings for diverse evanescent waveguide-based optical monitoring systems [70–76]. On exposure to specific analytes, the polymeric coatings will change their internal structure reversibly or irreversibly at the nano-level by swelling with an analyte.…”

“…Many different polymer materials have been compared to determine the most effective enrichment layer for specific analytes [70, 77, 78]. The optical properties of polymer film swelling versus film thickness have also been studied [79].…”

The ways to the trace level analysis in infrared spectroscopy

“…Fluorocarbon films deposited onto IREs have been successfully developed for trace organic contaminant determination in water. 46 Tetrachloroethylene was selected as model analyte providing limits of detection below 300 nL L À1 .…”

A pocket-sized 3D-printed attenuated total reflection-infrared filtometer combined with functionalized silica films for nitrate sensing in water

“…8 It was demonstrated that the sensitivity of this technique can be vastly increased using selective enrichment layers coated on ATR crystals that cover the volume probed by the evanescent field. [9][10][11] Until now, they have been primarily employed for enriching apolar substances into hydrophobic coatings. In this context, we have successfully shown that organically functionalized mesoporous silica films can also be employed.…”