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Chip-scale Mid-Infrared chemical sensors using air-clad pedestal silicon waveguides.
MedLine Citation:
PMID:  23620303     Owner:  NLM     Status:  Publisher    
Towards a future lab-on-a-chip spectrometer, we demonstrate a compact chip-scale air-clad silicon pedestal waveguide as a Mid-Infrared (Mid-IR) sensor capable of in situ monitoring of organic solvents. The sensor is a planar crystalline silicon waveguide, which is highly transparent, between λ = 1.3 and 6.5 μm, so that its operational spectral range covers most characteristic chemical absorption bands due to bonds such as C-H, N-H, O-H, C-C, N-O, C[double bond, length as m-dash]O, and C[triple bond, length as m-dash]N, as opposed to conventional UV, Vis, Near-IR sensors, which use weaker overtones of these fundamental bands. To extend light transmission beyond λ = 3.7 μm, a spectral region where a typical silicon dioxide under-clad is absorbing, we fabricate a unique air-clad silicon pedestal waveguide. The sensing mechanism of our Mid-IR waveguide sensor is based on evanescent wave absorption by functional groups of the surrounding chemical molecules, which selectively absorb specific wavelengths in the mid-IR, depending on the nature of their chemical bonds. From a measurement of the waveguide mode intensities, we demonstrate in situ identification of chemical compositions and concentrations of organic solvents. For instance, we show that when testing at λ = 3.55 μm, the Mid-IR sensor can distinguish hexane from the rest of the tested analytes (methanol, toluene, carbon tetrachloride, ethanol and acetone), since hexane has a strong absorption from the aliphatic C-H stretch at λ = 3.55 μm. Analogously, applying the same technique at λ = 3.3 μm, the Mid-IR sensor is able to determine the concentration of toluene dissolved in carbon tetrachloride, because toluene has a strong absorption at λ = 3.3 μm from the aromatic C-H stretch. With our demonstration of an air-clad silicon pedestal waveguide sensor, we move closer towards the ultimate goal of an ultra-compact portable spectrometer-on-a-chip.
Pao Tai Lin; Vivek Singh; Juejun Hu; Kathleen Richardson; J David Musgraves; Igor Luzinov; Joel Hensley; Lionel C Kimerling; Anu Agarwal
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-4-25
Journal Detail:
Title:  Lab on a chip     Volume:  -     ISSN:  1473-0189     ISO Abbreviation:  Lab Chip     Publication Date:  2013 Apr 
Date Detail:
Created Date:  2013-4-26     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101128948     Medline TA:  Lab Chip     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Materials Processing Center, Massachusetts Institute of technology, Cambridge, MA 02139, USA.
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