Fourier Transform Infrared Spectroscopy (FT-IR)

Figure 1. FT-IR equipment.

Features

Infrared spectroscopy is a method for obtaining information on the molecular structure by measuring infrared absorption due to transitions between vibrational energy levels of molecules. It has the following features:

• Non-destructive

• Vacuum chamber eliminates background absorption from atmospheric components such as CO and HO

• Minute measurement areas of a few tens of micrometres.

• Combining attenuated total internal reflection (ATR), transmission, and/or reflection measurements allows irregularly shaped samples in both liquid and solid states, as well as thicker films (1-2 \(\mu\text{m}\)).

Analysis Examples

• Contaminant identification

• Properties of organic membranes and thin films

• Bound states in SiO films (0.1-1 \(\mu\text{m}\))

• Curing state of resin

• Imidization rate of polyimide

• Plastic degradation

• Adhesive material components

Principle

Infrared spectroscopy utilizes light in the wavelength range of 0.8 to 1000 \(\mu\)m. The mid-infrared region (2.5-25 \(\mu\)m) is referred to as the vibrational spectrum because it results from changes in the dipole moment caused by molecular vibrations. When a molecule is subject to infrared irradiation, each atom and functional group absorb energy according to their respective optical resonance frequency, which is determined by ground and the excited state. This absorption appears as a dip in the infrared spectrum. Atoms have inherent vibrations depending on their molecular context, so the spectra yield information about the molecular structure.

Figure 2. Principle of infrared spectroscopy. The incident light is spectrally normalized to the light source so that the reference spectrum will be flat as shown to the left.

Principle of FT-IR

Instead of scanning the wavelength of the irradiating monochromatic light, FT-IR irradiates the sample with broadband light which enters an interferometer, the length of which is scanned quickly. Fourier transformation of the detector signal converts the position of the interferometer to the corresponding resonant wavelength to obtain an absorption spectrum corresponding to the molecular structure. This method is used to obtain information about the atomic groups in the material. High sensitivity measurement is possible in a short time because the incident light in the whole wavenumber range by continuous light can be measured simultaneously.

Data examples

Figure 3. Example of an FT-IR transmission spectrum. The horizontal axis is displayed in wavenumbers (reciprocal of wavelengths).
Figure 4. Example of measured and library spectra. The measured substance was identified as Nylon®

It is also possible to identify a substance by comparing the obtained absorption spectrum with a library of known spectra.

Data delivery formats

• Spectrum: PDF file

• Spectral data in Microsoft^® Excel^® file (.xlsx) on request

Measurement specifications

Property	Value	Unit	Notes
Maximum sample dimensions	\(200 \times 200 \times 15\)	\[\text{m}\text{m}^{\text{3}}\]	Microscopic measurement
Minimum sample dimensions	\(20 \times 20 \times 20\)	\[\mu\text{m}^{3}\]	Sampling tool needed
Measurement area	\[10 \times 10\]	\[\mu\text{m}^{3}\]	Microscopic measurement

Items for enquiries

• Purpose and scope of the analysis

• Sample information:

  1. Quantity, availability of pre-analysis samples

  2. Structure, shape, dimensions, measurement area and depth, layered structure, material, expected contaminants.

  3. Care instructions

• Delivery date:

  1. Desired delivery dates of preliminary and final results

  2. Handling instructions

• Other relevant information

Caution

• Samples with large infrared absorption may be difficult to measure.