FTIR_FAQ

Q13. What is the full English name of ATR? Can you introduce some details about ATR?

A: The full English name of ATR is Attenuated Total Reflectance. This technique is used for the analysis and identification of liquids, pastes, powders, films, and solids. ATR spectroscopy does not require any sample preparation and does not damage the sample. It overcomes the limitations of traditional transmission methods by simplifying the sample preparation and handling process, and greatly expands the application scope of infrared spectroscopy. Currently, this technique is widely used in various fields.

Q14. What crystal options are available for ATR? What are their characteristics?

Common ATR crystal materials include diamond, ZnSe, Ge, Si, KRS-5, and AMTIR.

• Diamond: The hardest material, resistant to acids, alkalis, and chemical corrosion, and is widely used. However, it has strong absorption in the 1800-2300 cm⁻¹ range,so samples that absorb in this area should be avoided.
• ZnSe: The applicable spectral range of ZnSe crystal is 20000-650 cm-1, which meets the test requirements of most samples, but it is not resistant to acid and alkali, has low hardness, and is easily scratched.
• Ge: The measurement spectrum range of Ge crystal is narrow, but its refractive index is high, so it can be used to measure samples with high refractive index;
• KRS-5: KRS-5 has the widest spectrum measurement range, but its hardness is the lowest and it is not corrosion-resistant, so it is rarely used.

Q15. How to clean ATR?

Before sampling infrared spectrum, you need to collect background spectrum first. To ensure that the ATR crystal surface is clean and not contaminated, you need to clean the ATR crystal. Usually use a soft cloth or cotton ball with solvents such as water, ethanol, and acetone to wipe the ATR crystal surface.

Q16. How to prepare samples for ATR?

A: ATR is suitable for testing solid and liquid samples. When measuring solid samples, the solid sample needs to be in close contact with the ATR crystal, so the sample needs to be pressed against the surface of the ATR crystal with the pressure head of the ATR accessory so that the attenuated reflected wave can penetrate into the sample.

When testing liquid samples, for samples that can be coated on the ATR crystal to form a liquid layer, they can be tested directly after coating.

For low-boiling point volatile samples, an ATR accessory with a liquid pool is required.

Q17. What should I pay attention to when using ATR?

Different ATR crystals have different degrees of hardness, acid resistance, alkali resistance, and chemical corrosion resistance. When using them, you should first understand their properties to prevent scratches, corrosion, or even cracks, which may affect the quality of the spectrum or make it impossible to obtain a valid spectrum.

Q18. What are the principles and applications of Specular Reflectance and Reflectance Absorption in reflectance spectroscopy?

Specular Reflectance spectroscopy is used to collect spectral information from smooth, polished solid surfaces, testing ultra-thin films (monolayers) or thin films on metal substrates. Similar to Attenuated Total Reflectance, Specular Reflectance does not require any sample preparation, allowing rapid acquisition of the sample's spectral information.

Q19. What are the types of Specular Reflectance accessories? 

Specular Reflectance accessories are generally divided into fixed angle reflectance accessories and variable angle reflectance accessories. Fixed angle specular reflectance accessories typically come in angles of 10°, 30°, 45°, 70°, 80°, and 85°, where the 80° and 85° accessories are also known as Grazing Incidence Reflection accessories. Variable angle specular reflectance accessories have a continuously adjustable incident angle, generally ranging from 30° to 80°, with some adjustable to a wider range. Users can choose the appropriate specular reflectance accessory based on their specific testing needs. These accessories are mainly used for testing metal surface modifications, resin and polymer films or coatings, paints, semiconductor epitaxial layers, etc. Absolute reflectance accessories can be used to test the absolute reflectance of metals, semiconductors, or windows; even combining an electrochemical cell accessory with a variable angle reflectance accessory to study electrochemical reactions on electrode surfaces.

Q20:How to choose Specular Reflectance Accessories?

The 10° specular reflectance accessory is primarily used for reflectance measurements. It can measure the near-normal reflectance of various surfaces and is recommended for measuring the reflectance of glass. Optosky offers a 10° specular reflectance accessory. It is compatible not only with Optosky's ATP8900 Series and ATP8900Pro Series Fourier Transform Infrared Spectrometers but also with spectrometers from other manufacturers. The 30° and 45° specular reflectance accessories are suitable for measuring the thickness of thick and thin films, typically with an incident depth of more than 1 micron. The optical design of specular reflectance accessories is relatively simple, and they utilize infrared light efficiently, providing high-quality spectral identification of coatings and thick films, and stable data for film thickness measurements. The 80° and 85° grazing angle specular reflectance accessories have a shallow incident depth, generally less than 1 micron, suitable for measuring submicron and nanometer scale thin films, LB films, and monolayers on metal surfaces. As mentioned above, the larger the angle of incidence, the longer the optical path, so the 80° and 85° grazing attachments can provide long-path spectra. Additionally, at an incident angle of 88°, the electric field intensity reaches its maximum value at the metal interface, at which point the sample and the infrared light interact most strongly. However, achieving this angle experimentally is difficult, so 80° and 85° grazing angles are commonly used. Furthermore, the spectral signal from grazing reflection is weak (~10-3 AU), and it is recommended to use a high-sensitivity detector, such as a liquid nitrogen-cooled detector (LN-MCT). Below is an image of the 80° grazing angle specular reflectance accessory.

80° and 85° grazing angle specular reflectance accessories

Q21. What are some considerations when using specular reflectance? 

When measuring specular reflectance spectra, as shown in Figure , it is necessary to perform Kramers-Kronig transformations to convert the reflectance spectra into absorption spectra.

Q22. What is infrared transmission? 

Transmission is the earliest and still a commonly used method for testing in infrared spectroscopy. Most solids, liquids, and gases can be measured using transmission. Common methods include solid pellet pressing, liquid film coating, liquid cells, and gas cells, often relying on specific accessories for testing. Infrared transmission spectroscopy reflects the sample's ability to transmit infrared light at different wavelengths. To obtain an infrared transmission spectrum, it is first necessary to obtain the original infrared light spectrum (background spectrum), then the spectrum of infrared light passing through the sample, and divide the latter by the former to obtain the infrared transmission spectrum of the sample (shown below). The vertical axis of the transmission spectrum, transmittance T, is typically expressed as a percentage (%), representing the ratio of the transmitted light intensity (I) to the incident light intensity (I0).

Q23. What are the common types of transmission accessories? 

Conventional transmission accessories. These are commonly used for testing solid powders. Typically, the sample is ground with potassium bromide powder and then pressed into a transparent solid disk using a pellet press before testing. Testing with transmission accessories requires the use of a pellet press, molds, a mortar, and dry potassium bromide. It also requires using an appropriate concentration of the sample and ensuring that the pellets are transparent. The preparation process is time-consuming, which is why ATR accessories are often used for routine tests now. For samples that require absolute transmission testing (such as silicon wafers), parallel light testing is needed. Optosky's ATP8900 offers a parallel light sample compartment and transmission accessories with various aperture sizes to facilitate user testing.

Gas Transmission Accessories: For gas samples, gas cells are required for testing. Depending on the concentration of the gas, gas cells with different path lengths are used. These can be customized to meet the actual needs of users, including various path lengths, volumes, materials, window types, and temperature-controlled gas cells. Based on actual applications, special gas cells with path lengths up to 24 meters have been designed for users. Additionally, portable gas analyzers and online gas analysis instruments have been developed.

Q24. What are the measurements and considerations for transmission spectroscopy? A: For solid powder samples, it is important to ensure that the potassium bromide is dried before use, that the sample and potassium bromide are ground evenly, and that the pellet is uniformly transparent to obtain a good spectrum. When measuring absolute transmission spectra, parallel light should be used, and it is important to ensure that the sample is perpendicular to the light path.

For liquid samples, it is necessary to select a liquid cell with an appropriate path length. After using a liquid cell, it must be thoroughly cleaned before the next measurement, especially when performing quantitative analysis, to avoid errors caused by sample residues.

For gas samples, a gas cell with an appropriate path length should be selected, and the gas cell's seal must be checked to prevent gas leakage. For the measurement of special gases like hydrogen fluoride, a gas cell made of special materials must be used to prevent corrosion by hydrogen fluoride.

In practice, fluctuations in water and carbon dioxide often appear in the spectrum, typically caused by environmental variations in water and carbon dioxide. Normally, nitrogen purging is used to reduce the interference from water and carbon dioxide, but it does not completely solve the problem. For higher-quality spectral testing, we have developed the vacuum Fourier Transform Spectrometer ATP8900Ad (shown below), which effectively addresses this issue. We tested the spectra under atmospheric pressure (blue) and vacuum conditions (red), and found that the absorption by water and carbon dioxide disappeared, easily eliminating their interference during spectral testing. Especially in the far-infrared range, the absorption peaks of water are more pronounced, and the vacuum infrared spectrometer can obtain high-quality spectra.

Q25. Applications of Transmission Spectroscopy:

1. Transmittance Testing. This includes determining the transmittance of materials like automotive glass, eyeglasses, sunglasses, sunscreen protective films, mobile phone and television screens, plastic packaging, and other related materials.
2. Oil Analysis. Monitoring of water, anti-wear components, oxidation values, nitration values, sulfonation values, and smoke point in gasoline, diesel, and lubricating oils to assess oil quality.
3. Gas Analysis. Monitoring of gases such as carbon monoxide, nitrogen monoxide, nitrogen dioxide, and sulfur dioxide in incinerators, steel plants, and the atmospheric environment.

Q26. Application: Obtaining the spectrum of a solution in a potassium bromide plate.

Q27. Can a 13mm pellet fit into the ATP8900plus? 

Simply open the front cover of the ATP8900plus, place the pressed pellet inside, and proceed with the measurement; this is the simplest method for infrared measurement. Alternatively, an ATR accessory can be used for the measurement.

Q28. Can the ATP8900PLUS measure carbon monoxide and total hydrocarbons without considering methane in the sample, such as in hydrogen fuel? 

Q29. How does the ATP8900PLUS handle noise caused by humidity in DRIFT? A: Use nitrogen purging to reduce the influence of water vapor.

Q30. For the ATP8900PLUS, is it feasible to directly fit a transmission module for liquid measurement? 

Yes.

Q31. Kidney Stone Testing Solution: A: There is a free infrared spectral library for kidney stones. Use the diamond ATR directly for the spectrum ranging from 600-4000 cm-1.

Q32. Can the ATP8900PLUS perform measurements at 20 spectra per second? Can it achieve a spectral resolution of 0.25? Can the signal-to-noise ratio be improved from 40,000:1 to 50,000:1 or higher? What type of ATR crystal material is used? 

The ATP8900Pro can meet this resolution; the signal-to-noise ratio is better than 40,000:1. ATR crystal materials available include diamond, ZnSe, or Ge.

Q33. Is the FTIR spectrometer suitable for testing polymers and plastics? 

ATP8900PLUS with diamond ATR.

Q34. Can the FTIR spectrometer be used to detect powders, pastes, and films? The ATP890PLUS can do this, with a resolution of 1 wavenumber. Additionally, configure with a press, potassium bromide, mortar, etc., and liquid cell windows.

Q35. Is there a significant difference in how the ATP8900PLUS and ATP8900 are used, or are they similar? A: There is no significant difference. Similar to using ATR for liquid measurement, just adding a rotating operation.

Q36. Does the ATP8900 meet EP PH2.2.24 requirements? 

Yes.

Q37. Which module is recommended for testing black rubber? 

A:ATR GE.

Because of refractive index reasons, the refractive index of the crystal must be greater than the sample.

Customer Case 1: Industrial Gas Detection in the Semiconductor Industry:

• Hydrogen Chloride (HCl), concentration from 1 ppm to 2000 ppm,
• Methane (CH4), concentration 5000 ppm, can reach 6000 ppm when wet.
• Gas Temperature: 180°C.

Solution: ATP8900 Plus + 5m heated gas cell + DTGS moisture-proof window. The interface uses a network interface with TCP/IP protocol. DTGS is a pyroelectric detector, and we have added a moisture-proof seal to the detector. DTGS has a linear response, while MCT has a non-linear response. This system is specifically designed for online gas analysis and can continuously monitor real-time gas concentrations. The resolution is better than 1 cm-1, within the range of 5000-500.

Customer Case 2: Application Direction: Testing Petroleum Products, including gasoline, motor oil, and heavy oil. Requires a constant temperature bath for quantitative testing. Also needs to analyze gasoline vapors, requiring a gas cell (non-heated). Solution: ATP8900 with a heated diamond module + transmission module + sealed liquid cell with ZnSe windows + 5cm heated gas cell.

Customer Case 3:

• Measurement Range: Not less than 7800 - 350 cm-1;
• Resolution: Not less than 0.25; 0.5; 1; 2; 4; 8; MIR and FIR 2 at 16 cm-1; 4; 8; Near Infrared 16 cm-1;
• Signal to Noise Ratio: Not less than (4 cm-1, 1 min, 2200 cm-1, peak-to-peak)/ > 30000:1;
• Automatic Console Recognition;
• Software and Spectral Database Availability;
• TGS and MCT Detectors with Automatic Switching;
• Crystals for Attenuated Total Reflectance: Diamond, Ge, or ZnSe.

Solution:Use ATP8900Pro, high resolution 0.25cm-1, dual detector automatic switching, with ATR accessory (crystal type to be chosen). If a microscope is needed, inquire about the user's requirements for a microscope.

Customer Case 4: 

Development and Manufacturing of Ionizing Radiation Detectors based on natural and synthetic diamond as commercial products. Measurement of diamond plates, thickness from 0.20 to 0.50 mm, area from 4.0 to 25.0 square millimeters (based on natural material plates), and area from 4.0 to 400.0 square millimeters (based on synthetic material plates). Raman and FTIR spectroscopy are necessary for input control of obtained diamond plates and monitoring after technical operations (impurity ion injection, high-temperature annealing, etching, and additional polishing of the plate surface). Control of the plates should be conducted in the laboratory under air atmosphere and room temperature. The system should be capable of diagnosing system components, processing and storing data, and recording measurement results. To control the quality of diamond plates, measure the light absorption coefficient (cm-1) as a function of wavelength (wavenumber) within the infrared range. To study diamond, the spectral range should be 800 – 4000 cm-1. Intrinsic absorption of the diamond lattice in the infrared range: 5000 - 1600 cm-1, absorption in diamond due to nitrogen defects (nitrogen being the major impurity in diamond): 1250 - 800 cm-1.

Solution: Use ATP8900 main unit + focuser + miniature sample holder.