Figure 1. O-PTIR equipment.
Features
Infrared (IR) spectroscopy is a method for obtaining information on
the molecular structure by measuring absorption due to transitions
between vibrational energy levels of molecules.
O-PTIR has the following advantages:
High spatial resolution (<1 \(\mu
m\)) for both imaging and spectral measurements
Non-destructive measurement
Fourier transform IR (FT-IR) spectroscopy libraries can be
applied
Application Examples
Material identification and quantization in a variety of
inhomogeneous materials:
Polymer blend block copolymers
Polymeric nanocomposite materials
Defect and contamination analysis
Principle
Light absorption is detected via thermal expansion of the sample. The
light source is a pulsed, wavelength-tuneable IR LASER.
First, the top of the sample is irradiated as shown in (1) of Figure 2. The absorption in the sample then
causes an instantaneous thermal expansion, which then is detected (2) by
a continuous-wave (CW), visible LASER probe (532 nm) that shares the
optical axis with the IR LASER. By changing the wavenumber of the IR
light and continuously irradiating the sample, it is possible to obtain
an absorption spectrum by monitoring the reflection and scattering of
the probe light (3). Since absorption is detected directly, O-PTIR
yields the same result as FT-IR spectroscopy.
Figure 2. Principle of
O-PTIR
Figure 3. Schematic O-PTIR spectrum.
Data example
Figure 4 shows an example of a
measurement of a thin-film polystyrene (PS)/polycaprolactone (PCL)
sample.
The spatial distribution of the two components is visualized by probe
LASER reflectance and infrared absorption images. The infrared
absorption image shows the probe intensity (proportional to absorption)
at each wavenumber, and the compositional distribution is indicated by
the ratio of the probe intensities of each wavenumber. It is also
possible to analyse the IR spectra at specified regions of interest
(ROI), as shown in Figure 5.
Figure 4. Raw image
(left) and PCL and PCL (centre) and PS (right) distribution determined
by O-PTIR signal ratios at IR light wavenumbers 1192 and 1492 \(\text{c}\text{m}^{\text{-1}}\).
Figure 5. O-PTIR
spectra of PCL and PS at the ROIs indicated by the spots in the image
insert.
Plotted spectra and images: PDF file
Spectral data in comma-separated text file (.csv) on request
Measurement specifications
Maximum sample dimensions
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\[\text{m}\text{m}^{\text{2}}\]
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Sample surface must be parallel to the horizontal plane
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\[\mu\text{m}^{\text{2}}\]
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Minimum resolvable feature
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\[\text{c}\text{m}^{- 1}\]
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Maximum surface roughness
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High-resolution measurement may require sample
horizontalization.
Flaking reduces surface roughness but may be difficult for irregularly
shaped samples
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Items for enquiries
Purpose and scope of the analysis
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Quantity, availability of pre-analysis samples
Structure, shape, dimensions (area, thickness) in the ROI, layer
structure, material, expected composition
Desired delivery dates of preliminary and final results
Information on sample processing that may have introduced
contaminants
Caution
This method is subcontracted
Samples with a large infrared absorption may be difficult analyse
Films thinner than 200 nm may be difficult analyse