We have detected the surface-enhanced Raman scattering (SERS) signals of toluene and 1,2-dichlorobenzene (ODCB) vapors at parts per million concentrations using 1-propanethiol-linked Ag nanoparticles and a fiber optics–coupled Raman spectrograph. Calibration curves were constructed for each detector by plotting Raman band intensity ratios of toluene and ODCB with respect to that of 1-propanethiol as a function of vapor concentration. The detectors showed effective vapor sensing ranges of 0.6 to 600 and 10 to 600 ppm for toluene and ODCB, respectively, following vapor adsorption to the SERS hot spots. We provide evidence for the facility of the SERS detection system for instantaneously discriminating and quantifying respective vapors from a composite vapor.
Recent progress in modified Surface Enhanced Raman Scattering (SERS) using Ag nanoparticles makes them promising optical technique for direct gas sensing of interest. However, SERS has been shown to provide sub ppb level detection of the compounds in the vapor phase. The major problem with the sensitivity scaling-up was in the development of fabrication technology for stability and reproducibility of SERS substrates. We report an optimization of 1-propanethiol coated multiple Ag nanoparticle layers on SiO2 substrate as well as new records of real-time, simultaneous vapor phase detection of toluene and 1-2 dichlorobenzene by the radiation of fiber optic coupled 785 nm diode laser and spectrograph. Multiple depositions of Ag NPs were loaded on SiO2 and soaked in 1-propanethiol solution for 24 hours to modify the surface into hydrophobic due to the characteristics of vapor phase of our interests. Raman bands at 1003 cm-1 and 1130 cm-1 for toluene and 12DCB, respectively were compared to 1089 cm-1 and each gas concentration in 1000 mL flask were calculated as a function of each vapor phase ratio. The saturation of toluene and 12DCB were limited only by 800 ppm and the detectable range was 0.6-800 ppm.
The carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam. The modulation efficiency of terahertz transmission due to transverse-magnetic (TM)-polarized excitation is distinctly higher than that due to transverse-electric (TE)-polarized excitation. Underlying this difference is the enhancement of carrier injection when the TM-polarized light is more transmitted through the surface of organic thin films than the TE-polarization light.
We present that the carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film depends
on the incidence angle of photoexciting beam. At higher incidence angles of photoexciting beam, the modulation
efficiency of terahertz transmission due to TM-polarized excitation is distinctly higher than one due to TE-polarized
excitation. We find that this phenomenon is due to the enhancement of carrier injection which is expected when the
incident light is more transmitted through the organic thin film.