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1998 Progress Report: An Integrated Near Infrared Spectroscopy Sensor for In-Situ Environmental Monitoring
EPA Grant Number: R826190Title: An Integrated Near Infrared Spectroscopy Sensor for In-Situ Environmental Monitoring
Investigators: Levy, Roland A. , Federici, John F.
Current Investigators: Levy, Roland A.
Institution: New Jersey Institute of Technology
EPA Project Officer: Krishnan, Bala S.
Project Period: February 20, 1998 through February 19, 2001 (Extended to February 19, 2003)
Project Period Covered by this Report: February 20, 1998 through February 19, 1999
Project Amount: $322,230
RFA: Exploratory Research - Environmental Chemistry (1997)
Research Category: Engineering and Environmental Chemistry
Description:
Objective:The monitoring and control of hazardous emissions is of major concern to industrial and governmental organizations concerned with the protection of public health and the environment. Environmental monitoring currently involves collection of air samples, which are subsequently analyzed for a large number of hazardous substances such as volatile organic compounds (VOC's). The high cost and time delay associated with such sampling procedure prohibit optimal usage. In this program, we combine the principles of interferometry with those of near infrared evanescent wave absorption spectroscopy to produce a novel integrated sensor capable of monitoring and determining in-situ the concentration of numerous analyte species simultaneously. The sensor is designed to be compact, portable, rugged, and suitable for real-time monitoring of hazardous emissions. It offers numerous advantages over conventional analytical techniques such as gas chromatography and mass spectrometry including small physical size, geometric flexibility, environmental versatility, real-time and in-situ analysis, instrumental reliability, analyte specificity, insensitivity to electromagnetic interference, and low power requirements. The fabrication of this sensor is based on large scale integrated (LSI) circuit-type processes which allow for a high degree of electronic and photonic integration. In addition to offering the advantage of miniaturization, this technology offers high throughput (hundreds of sensors per silicon wafer) which translates into low cost per device. Progress Summary:
During the first year of this program, the effort has focused on developing the technology required to design the waveguide structures, the processes needed to fabricate these structures, and the methodology necessary to model the device performance. The waveguides were fabricated on both 4" and 5" silicon wafers. A 10-15 mm thick SiO2 film was first synthesized by low pressure chemical vapor deposition (LPCVD) or by high pressure oxidation to act as cladding material for the waveguide and prevent light from coupling with the underlying silicon. A 6.8 mm thick phosphorus-doped (8 wt% P) LPCVD SiO2 film was then synthesized to act as core material for the waveguide. This layer underwent patterning using standard lithographic exposure and plasma etching techniques and subjected to a 1050oC anneal to cause viscous flow and rounding of the edges. This rounding-off procedure was found to be necessary to minimize coupling losses between fiber and waveguide. The refractive index of the doped glass was measured to be 1.4666, thus, producing with the underlying SiO2 (n=1.4580) substrate a single mode waveguide device. Deposition of a 0.5 mm thick LPCVD undoped SiO2 buffer layer over the entire wafer and a subsequent lithographic step resulted in selective removal of that layer over the sampling arm of the interferometer. This configuration allowed for exposure of the sampling arm to various gases in the air environment in order to cause a change in the effective refractive index of that arm. The arm coated with the SiO2 buffer layer saw a constant refractive index of n=1.4580. Three, four, five, and six microns-wide waveguides were designed to form the two interferometer paths using a splitting angle of 2o. The sampling and reference arms had a fixed separation of 50 mm and variable lengths (2, 4, 6, 8, and 10 mm). A comparison between calculated and measured dependence of interferometer output on arm length was used for sensor calibration purposes. Future Activities:
With the existence of such a technology platform, the stage is set to evaluate, during the second year of this program, a prototype sensor in terms of its capabilities for monitoring and quantifying multicomponent mixtures of contaminants in air. Results will be used in an iterative fashion to optimize sensor design and fabrication techniques. During the third year, the work will be directed towards the integration of the discrete components of the monitoring system. Journal Articles:
No journal articles submitted with this report: View all 4 publications for this project
Supplemental Keywords:remote sensing, integrated photonics. , Air, Scientific Discipline, Electron Microscopy, Engineering, Chemistry, & Physics, Chemistry, Environmental Chemistry, real time monitoring, waveguide surfaces, remote sensing, organic analyte species, environmental monitoring, infrared spectroscopy sensor, Mach-Zender interferometer, sensor technology, organic contaminants
Relevant Websites:
Progress and Final Reports:
Original Abstract
1999 Progress Report
2000 Progress Report
Final Report