FTIR / Fourier-Transform Infrared Spectroscopy

Infrared Spectroscopy is a resonance vibrational spectroscopic technique for the structural characterization of materials. As such, it is recording the energy of vibrating molecular entities in gases, liquids and crystalline or amorphous solids. The energy and width of the vibrational spectral features depend on the local structural arrangement of the vibrating unit and the particular type of vibration. Not all molecular vibrations are observable in the infrared spectra: a particular vibrational mode is infrared-active only if the dipole moment of the vibrating entity is modified during the vibration. Fourier transform infrared spectrometers average spectral scans to collect high quality spectra with high resolution as well as excellent accuracy and precision in energy. They are equipped with continuum radiation sources and appropriate high sensitivity infrared detectors. Depending on energy, they are conventionally distinguished as far- (5-50 meV, 40-400 cm-1), mid-(50-500 meV, 400-4000 cm-1), or near-infrared (~0.5-1.5 eV, 4000-12000 cm-1) spectrometers.

Measurements are typically performed in transmittance or one of several reflectance configurations, depending on the sample. Besides contributing to the fundamental understanding of structure and bonding, the infrared spectra are molecular fingerprints suitable for identification purposes. Spectral intensities scale with the concentration of the vibrating species in the sample and can, therefore, be employed for quantification studies following suitable calibration. Multivariate analysis chemometric algorithms can be applied over large spectral sets for classification, identification and quantification. Infrared is complementary to Raman spectroscopy and the acquisition of both the infrared and Raman spectra of a material is usually desirable.

Tool

(1) FT/IR-6300, mid and far infrared spectrometer by JASCO equipped with gold coated optical mirrors provides higher throughput in the Near-IR region and enables expansion to FT-Raman measurement. The spectrometer is designed for a wide range of critical research and development applications, offers the absolute highest level of performance in the industry with the highest signal-to-noise specifications. The FT/IR-6300 includes the Rapid Scan (20 Hz) feature as standard for tracking high speed chemical reactions and other processes. Step scan and full vacuum capabilities are also available. Working range: 15000-20cm-1, Maximum resolution: 0.07 cm-1, Signal-to-noise ratio: 50,000:1.

(2) FT/IR-6200, mid infrared spectrometer by JASCO provide capabilities from education and routine analysis to high-end research applications, featuring high quality, performance and reliability. It is also designed with flexibility and expandability in mind to meet with a wide range of expanding application requirements. Working range: 7800-350cm-1, Maximum resolution: 0.25 cm-1, Signal-to-noise ratio: 45,000:1.

(3) IRT-5000 FTIR Microscope by JASCO used with FT/IR-4000 spectrometer, combining both micro and macro FTIR measurement, offering the most advanced microscopy and imaging systems. The system are typically used in the mid-IR for materials identification and forensic analysis. The IRT-5000 FTIR Microscope includes an automatic carousel with a choice of cassegrains and refractive elements for observation and measurement whereas a mid-band MCT detector is included. IQ Mapping function can be used for Transmission/Reflectance or ATR measurements allows multi-point, line, area and ATR mapping experiments without moving the sample stage, in addition to single-point measurements. IQ Mapping can be used to measure and image an area up to 400 x 400 µm using a 16× Cassegrain objective. Working range: 7800-600cm-1, Maximum resolution: 0.25 cm-1, Signal-to-noise ratio: 8,000:1, Spatial resolution of ~10 μm.

Additional Tools

(a) 10 degree specular reflection accessory (10spec of PIKE technologies), for determination of sample reflectivity at a near-normal angle.
(b) 30 degree specular reflection accessory (30spec of PIKE technologies) for routine fixed angle specular reflection accessories for measurements of films and coatings.
(c) 80 angle specular reflection accessory (80spec of PIKE technologies) for measurement of thin films and monolayers.
(d)- Diffuse reflectance (DRIFT), EasiDiff of PIKE technologies, allows the analysis of powdered and solid samples, eliminates the need for tedious and time-consuming preparation of KBr pellets.
(e) Diffuse reflectance (DRIFT), Spectra-Tech Collector II of Thermo Scientific with high temperature/vacuum chamber (0-900oC) allows the study of samples in heated gaseous environments.
(f) Attenuated Total Reflection (ATR): MIRacle (PIKE technologies), single reflection ATR. Crystal: ZnSe.
(g) Equipment for sample preparation (cutting and polishing of hard solids, the preparation of KBr dispersions etc).

Applications

Fourier transform infrared spectroscopy and micro spectroscopy , can provide fundamental information on the molecular structure of organic and inorganic components, and is one of the most versatile analytical techniques for the non-destructive, chemical characterization for the structure analysis of solid, liquid or gas samples. Methods: Infrared transmittance and reflectance spectroscopy and microscopy. Information: Fundamental understanding of light-matter interactions in the infrared region. Understanding structure-property correlations in materials. Examples include: the structural investigation ceramic and polymeric materials, organic and inorganic compounds, carbon-based materials, microplastics Identification by IR mapping measurement, chemical identification of particles and smallest contaminations, the examination of the homogeneity of coatings, glazes and analysis of the distribution of a multitude of different components in a complex mixture. Characterization of biomaterial surfaces at the micro scale and analysis of corrosion products formed on various metal surfaces and artifacts. Drug identification, fiber analysis and paint and varnish analysis.

Sample Specifications

Sample preparation for infrared spectroscopy depends on the measurement technique. IR microscope can be utilised for sample observation prior to measurement whereas powder, liquid and solid samples can be measured with the combination of one or more techniques. (a) Transmittance in the mid-infrared is performed on thin films (thickness depending on film and substrate optical properties) or powder dispersions in KBr martix. (b)  Specular reflectance (incl. 10, 30, 80 angle) requires optically flat samples, typically 20 × 20 × 5 (height) mm3 is size. (c) ATR requires no preparation for powders or liquids. (d) Diffuse Reflectance (DRIFTS) requires no preparation for powders.
(d) The infrared microscope accommodates solid samples with ca. 50 × 50 × 10 mm3 maximum dimensions and a reasonably good reflecting surface (with low roughness for the case of the ATR objective).

Additional Information

Dr. Michael Karakassides, mkarakas@uoi.gr
Dr. Alkiviadis Paipetis, paipetis@uoi.gr

Tool

(1) Equinox 55S and Tensor II mid-infrared FTIR spectrometers by Bruker, equipped with a Hyperion microscope, a diffuse reflectance, a 85o grazing angle and several ATR accessories (single and multiple reflection elements, heatable etc.). Working range 400-6000 cm‑1. Used for the structural characterization of a variety of materials in a non-invasive manner.

(2) Hyperion 2000 mid-infrared microscope by Bruker, coupled to one of the above spectrometers, equipped with a single element MCT detector, an automated xy stage, mirror lenses for transmittance and specular reflectance measurements, a Ge-ATR lens, and software for infrared mapping with a spatial resolution of ~10 μm. Working range 600-5000 cm‑1.

(3) Vector 22N near-infrared FTIR spectrometer by Bruker, equipped with a diffuse reflectance optical fiber bundle for powder samples, various path-length transmission fibers for liquids and an integrated sphere unit with a rotating cup sample holder. Working range 4000-12000 cm‑1. Ideal for the non-invasive measurement of the vibrations involving hydrogen, the monitoring of chemisorbed H2O or organics on inorganic anhydrous templates without interference from the latter, the real-time monitoring of chemical reactions etc. Very suitable for industrial high through-put applications, especially if coupled with chemometric algorithms. Very suitable for spot measurements on large samples.

(4) Vertex 80v vacuum far- and mid-infrared FTIR spectrometer by Bruker, equipped with a 11o specular reflectance accessory. Capable for infrared transmittance and reflectance measurements in the region 30-7500 cm-1. Ideal for the continuous stitch-less acquisition of the absorption coefficient, refractive index and dielectric permittivity spectra from monolithic polished samples.

Additional Tools

(a) An environmental cell enabling the purge-drying of samples, their exposure to variable and controlled relative humidity, the in-situ H/D exchange etc. The cell is fitted to the single reflection ATR cells, or to the NIR powder probe, or to both, for simultaneous ATR-NIR measurements of materials and processes. A humidity generator coupled with the environmental cell.
(b) Various variable temperature accessories including a Linkam FTIR 600 cell operating from liq. N2 to 300oC in transmittance or reflectance.
(c) A suite of chemometric software routines of the OPUS software for classification, identification, quantification applications and data mining.
(d) Equipment for sample preparation (cutting and polishing of hard solids, the preparation of KBr dispersions, etc).

Applications

Infrared transmittance and reflectance spectroscopy and microscopy. Fundamental understanding of light-matter interactions in the infrared regime. Development of structure-property relationships. High-throughput acquisition, data manipulation and multiple regression analysis.
Examples include: the structural investigation of amorphous and ionic solids, the characterization of surface coatings and cross sections, the study of chemisorption and other self-assembly phenomena on solids, the study of phase transitions (crystallization, polymorphism etc.), the study of chemical heterogeneity at variable scales from microns to meters, quality control and real-time diagnostics in industrial environments.

Sample Specifications

Sample preparation for infrared spectroscopy depends on the particular technique and measurement configuration used. Whenever possible, measurement is non-invasive and requires no sample preparation.
In very general terms: (a) Transmittance in the mid-infrared is performed on thin films (thickness depending on film and substrate optical properties) or dispersions in KBr or CsI (with known ion-exchange and/or hydrolysis problems depending on sample). (b) Specular reflectance (incl. grazing angle) requires optically flat samples, typically 20 × 20 × 5 (height) mm3 is size. (c) ATR requires no preparation for liquids. A special press is used to bring powder samples (1-5 mg) in good contact with the single reflection elements. (d) The infrared microscope accommodates solid samples with ca. 50 × 50 × 10 mm3 maximum dimensions and a reasonably good reflecting surface (with low roughness for the case of the ATR objective). (e) NIR can handle almost any type of solid or liquid sample, powders, pastes, etc..

Additional Information

(midIR, NIR) Dr. Georgios D. Chryssikos, gdchryss@eie.gr
(vacIR) Dr. Dimitrios Palles, dpalles@eie.gr

Tool

EQUINOX 55 spectrometer

Additional Tools

(a) Attenuated Total Reflection (ATR): MIRacle (PIKE technologies) or a single refection Golden Gate™ Heated Diamond ATR Top Plate GS10542 (up to 200°C) and Micro Reaction Flow Cell Anvil. Sampling accessory to allow for many different sampling options in the quantitative and qualitative analysis of solids, liquids, pastes and microsamples by FTIR spectroscopy.
(b) Diffuse reflectance (DRIFT) “The selector” of Graseby Specac. Allows the analysis of powdered and solid samples.
(c) Grazing angle unit (Bruker). Provides in-situ FTIR monolayer investigation of films at an air/liquid interface and variable grazing incidence angle measurements of thin film coatings on solid reflective surfaces.

Applications

Polymeric materials (bio-polymers, bio-degradable polymers etc.), composites, carbon based nanostructures (e.g. graphene oxide, modified CNTs etc.), nanomaterials. Segmental orientation studies in macromolecular systems may also be applied using appropriate polarizer. In-situ measurements in order to monitor structural alterations as function of temperature may be also applied using specific ATR accessory.

Sample Specifications

Sample preparation is required for transmission experiments using KBr pellets (pulverised samples mixed with KBr powder). In the same type of experiments, film thickness is critical for the identification of specific vibrational bands (depends on composition). DRIFT experiments are applied on powdered samples, while specular reflectance measurements require flat/reflective surfaces. For the ATR measurements no specific sample preparation is required, however, the sample is pressed upon the diamond surface in order to achieve good interface contact. Nitrogen purging in the sample compartment is possible for measurements under inert atmosphere.

Additional Information

Dr. George Voyiatzis, gvog@iceht.forth.gr

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