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Fourier Transform Infrared Spectroscopy (FTIR)

Fourier Transform Infrared Spectroscopy (FT-IR) is an effective analytical technique for quickly identifying the “chemical family” of a substance. Typically, organic and polymeric  compounds (and to a lesser degree, inorganic compounds) produce a “fingerprint” IR spectrum, which can be compared to EAG’s extensive reference database and the unknown component’s chemical family or actual identity may be determined.

FT-IR measures the absorbance of infrared light by a sample and generates a spectrum based on the functional groups in the material. In addition to typical sample preparation methods (such as micro-extraction, dilution, KBr pellet and mulling techniques), EAG also utilizes various Attenuated Total Reflectance (ATR) accessories, which allows insoluble or multi-layer samples to be examined directly.

Ideal Uses
  • Characterization and identification of complex mixtures of materials, including gases, liquids and solids
  • Identification of organic contaminants (e.g. particles, residues) on the macro and micro scales
  • Quantification of O and H in Si and SiOx, and H in SiN wafers (Si-H vs. N-H)
Technical Specifications

Signal Detected: Infrared absorption
Elements Detected: Molecular functional groups (NOT elements)
Detection Limits: 1-10 wt% (quantification of known components);  5-20 % (identification of unknown components)
ATR Depth Resolution: 6-2.5 µm
Transmission FTIR: Infrared light passes through the entire sample
Imaging: Mapping: Available upon request
Lateral Resolution/Probe Size: > 15-50 µm

Strengths
  • Capable of identifying organic functional groups and often specific organic compounds
  • Extensive spectral libraries for compound and mixture identifications
  • Ambient conditions (vacuum is not necessary; applicable for semi-volatile compounds)
  • Minimum (limit of detection) analysis area: ~15 µm.  Rule-of-thumb: if you can see the sample by eye, it most likely can be analyzed.
  • Can be quantitative with appropriate standards and uniform sample thicknesses
  • Complementary to Raman spectroscopy
Limitations
  • Limited surface sensitivity (typical limit of detection is a film thickness of 25 nm)
  • Only specific inorganic species exhibit an FTIR spectrum (for example: yes: silicates, carbonates, nitrates and sulfates; no: titinia, aluminas, oxides, etc)
  • Sample quantitation requires the use of standards
  • Glass absorbs infrared light and is not an appropriate substrate for FTIR analysis.
  • Water also strongly absorbs infrared light and may interfere with the analysis of dissolved, suspended or wet samples
  • Simple cations and anions, e.g., Na+ and Cl–, do not absorb FTIR light and hence cannot be detected by FTIR; identification of mixtures / multiple sample components may require additional laboratory preparations and analyses
  • Metals reflect light and cannot be analyzed by FTIR

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