Fourier Transform Infra Red Spectroscopy

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Fourier Transform Infra Red Spectroscopy
Technology Details
Other Names FTIR,  %other names and abbreviations, separated by commas%
Technology %Parent technology%
Equipment List of FTIR equipment
Materials %Optional materials processed%

Fourier Transform Infra Red Spectroscopy (FTIR) Infrared radiation (10,000 - 100 cm-1) is absorbed by organic molecules and transformed in vibrational energy. Even though this absorption is quantized the absorptions show up as bands because of the combination of vibration and rotation modes. Each compound presents a unique spectrum, the infrared absorption spectrum is a fingerprint of the compound. Making this technique widely popular for the identification of organic compounds. Although the infrared is characteristic of the entire molecule, it does happen that certain groups give vibrational bands at same frequencies regardless of the structure of the rest of the molecule. The spectroscopist takes advantage of this fact to identified unkown species by comparing the spectra to that of a known sample.


If this is a "main category" for equipment (i.e. you categorized that equipment page to be this technology), you should list the equipment here with a brief description of that tool's capabilities. Seriously, though, just check out the RIE page.

Equipment 1

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electromagnetic spectrum

The infrared region is the region of the electromagnetic spectrum between 14,000 - 200 cm-1 (0.7-50 ɥm). The MID-IR where the molecular vibrations are excited, is the region between 4000 and 700 cm-1 (2.5-15 ɥm). The near-IR region is between 14,000-4000 cm-1 (0.7-2.5 ɥm) and the far -IR region 700-200 cm-1 (14-50 ɥm)

The selection rules for this spectroscopy dictate that only vibrational modes that produce a change in the dipole of the molecule are visible in the infrared[1]. Thus most of the polar compounds can be identified with this technique. Basically, to measure the absorption spectrum of a substance, it is exposed to the radiation and compare the response to that of the radiation with no sample. This technique measures absorption, in transmission (radiation goes trough the sample), or in reflection (radiation reflects of a reflective surface that contains the sample). The sample can be solid, liquid or gas, in each case the sample container is different. The technique requires that the sample absorption signal is referenced to the signal without the sample, the result is a relative signal given in % of the original signal. This is timely process hence FT-IR was develop to overcome this problem. Most interferometers employ a beamsplitter which takes the incoming infrared beam and divides it into two optical beams. One beam reflects off of a flat mirror which is fixed in place. The other beam reflects off of a flat mirror which is on a mechanism which allows this mirror to move a very short distance (typically a few millimeters) away from the beamsplitter. The two beams reflect off of their respective mirrors and are recombined when they meet back at the beamsplitter. Because the path that one beam travels is a fixed length and the other is constantly changing as its mirror moves, the signal which exits the interferometer is the result of these two beams “interfering” with each other. The resulting signal is called an interferogram which has the unique property that every data point (a function of the moving mirror position) which makes up the signal has information about every infrared frequency which comes from the source. This means that as the interferogram is measured, all frequencies are being measured simultaneously. Thus, the use of the interferometer results in extremely fast measurements. The signal is then Fourier Transformed from time space to frequency space.


Beam splitter





Presenting spectra as transmittance tends to emphasize the smaller peaks, so you can sometimes visually assess your sample better. Absorbance spectra are used for any quantitative analysis, spectral subtractions or other manipulations as the spectra are linear with concentration – transmittance spectra are not. Older literature tended to use transmittance most often, while detailed peak analysis always moved to absorbance, again because of the linearity feature.


FTIR microscopy

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  • Identification of organic materials such as photoresist, oil, greases and polar solvents
  • Identify contaminants
  • Analysis of thin films and coatings
  • Semiconductor materials such as Si, Si oxide, different glasses.
  • III - V compounds,
  • Identify H-content in materials.


Optional description of materials that can be processed by technology. I think the best example of where this comes in handy would be with LPCVD describing the difference between HTO and LTO.

See also

Other related wiki pages


Further reading

  • LNF Tech Talk for Metrology
  • Other stuff, e.g. technology workshop slides
  • External links (can be in another section below, if appropriate)