Infrared microscope measurements

The spatial resolution of the Raman microprobe is about an order of magnitude better than that obtainable using an infrared microscope. Measurement times, typically of a few seconds, are the same as for other Raman spectrographs. To avoid burning samples, low (5—50-mW) power lasers are employed. 

It is relatively easy to produce a highly sensitive MCT detector with a small area detecting element. This is an advantage, as the magnitude of noise from the element is proportional to the square root of the area of the photosensitive region. Hence, a small area element of MCT detector can be effectively used for infrared microscopic measurements typically, this has a shape of a square with sides <1 mm long. 

A small-size target specimen will often need to be removed from a matrix in which it is buried by using a knife, scalpel, or needle in an appropriate and safe manner, depending on the conditions surrounding it. If the target specimen is covered by a layer of some other material this may need to be scraped off Infrared microscopic measurements are utilized in many areas of study. In order to satisfy the various needs, in addition to straightforward transmission measurements, various types of reflection measurements such as specular reflection, attenuated total reflection (ATR), and transmission-reflection measurements (described later) can be performed with an infrared microscope designed for such purposes. 

This time-resolved measurement method can be applicable to relatively slow transient phenomena, as its time-resolved measurements are undertaken while the movable mirror is at rest. The number of applications of step-scan FT-IR spectrometry to time-resolved measurements currently is more than that by any other method, and it has been applied to various studies in many fields such as studies of biomolecules, liquid crystals, polymers, photochemical reactions in zeolites, oxidation-reduction reactions on electrode surfaces, and excited electronic states of inorganic complexes. Further, this method has been applied to time-resolved measurements in combination with attenuated total reflection (ATR) (see Chapter 13), surface-enhanced infrared absorption (see Section 13.2.2) [10, 11], infrared microscopic measurements (see Chapter 16) [12], and infrared spectroscopic imaging (see Chapter 17) [13]. 

After the experiment, the experimental charge is prepared for analysis of the diffusion component or species. The analytical methods include microbeam methods such as electron microprobe, ion microprobe, Rutherford backscatter-ing, and infrared microscope to measure the concentration profile, as well as bulk methods (such as mass spectrometry, infrared spectrometry, or weighing) to determine the total gain or loss of the diffusion component or species. Often, the analysis of the diffusion profile is the most difficult step in obtaining diffusivity. 

Fourier transform infrared microscopes are equipped with a reflection capability that can be used under these circumstances. External reflection spectroscopy (ERS) requires a flat, reflective surface, and the results are sensitive to the polarization of the incident beam as well as the angle of incidence. Additionally, the orientations of the electric dipoles in the films are important to the selection rules and the intensities of the reflected beam. In reflectance measurements, the spectra are a function of the dispersion in the refractive index and the spectra obtained are completely different from that obtained through a transmission measurement that is strongly influenced by the absorption index, k. However, a complex refractive index, n + ik can be determined through a well-known mathematical route, namely, the Kramers-Kronig analysis. 

The optical layout for the measurement of biological samples (cells) is shown in Figure 29.3b. The sample was irradiated with co-linear IR and visible light beams. The transient fluorescence from the sample was collected from the opposite side by an objective lens. In this optical layout, the spatial resolution was determined by the objective numerical aperture (NA) and the visible fluorescence wavelength IR superresolution smaller than the diffraction limit of IR light was achieved. Here, Arabidopsis thaliana roots stained with Rhodamine-6G were used as a sample. We applied this super-resolution infrared microscope to the Arabidopsis thaliana root cells, and also report the results of time-resolved measurements. 

One of the important functions of this infrared microscope is the measurement of the IR spectrum from a spatial region smaller than the diffraction limit. This possibility is already illustrated in Figure 29.4e. The TFD-IR spectrum, that corresponds to the IR absorption spectrum, was measured from a fluorescence region smaller than the IR diffraction limit. Infrared spectroscopy in a sub-micron region will be possible by using a high NA objective lens with the confocal optical system. 

Yano, K., Ohoshima, S., Gotou, Y., Kumaido, K., Moriguchi, T. and Katayama, H. (2000) Direct measurement of human lung cancerous and noncancerous tissues by Fourier transform infrared microscopy Can an infrared microscope be used as a clinical tool Anal. Biochem., 287, 218-225. 

Specialised sampling techniques such as attenuated total reflectance (ATR) and diffuse reflectance (DR) have been found to be exhemely effective and hence have gained considerable popularity. Microsampling, for measuring very small samples, has become a common technique over the last decade as beam condensers and infrared microscopes (plus accessories) have been improved. 

Figure 3. Broadband spectrum of a conventional 2000 Globar IR source (short dashed line), and the spectrum of the NSLS synchrotron source (solid line) limited by an experimental throughput of 4.4><1 O 4 mm2sr. This is the etendue for a 1 pm by 1 pm sample measured with an infrared microscope. The measured, background limited Noise Equivalent Power (NEP) of a Mercury Cadmium Telluride (MCT) (long dashed line) detector is shown. This detector is operated at liquid nitrogen temperatures.

Figure 5.18 Schematic illustration of the sample used for the IR microscopic observation at the interfacial boundary of DHDPE and LLDPE(2). (a) The cover slit for infrared spectral measurement was set at the open box position, (b) The sample was shifted from the contact position to measure the infrared spectra at the position x.

NIR imaging in the 900 to 1700 nm range has been applied to moisture content analysis. Infrared microscopes have also been used to measure the temperature of samples, and scanning versions have been built to enable maps of temperature distribution to be obtained. 

Infrared signal measured through various aperture sizes using a synchrotron source versus a Globar source. Data collected with a confocal IR microscope and a single-point detector. (Reprinted from ref. 72.)... 

Fig. 6.12. Determination of diffusion coefficients of deuterated PE s in a PE matrix by infrared absorption measurements in a microscope. Concentration profiles obtained in the separated state at the begin of a diffusion run and at a later stage of diffusive mixing (the dashed lines were calculated for monodisperse components the deviations are due to polydispersity) (left). Diffusion coefficients at T = 176°C, derived from measurements on a series of d-PE s of different molecular weight (right). The continuous line corresponds to a power law D M. Work of Klein [68]...

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