Silicon windows for transmission measurement infrared spectroscopy 

Most chemical compounds exhibit characteristic infrared spectra, depending on their molecular symmetry, atomic weights and bond strength. This is an advantage when IR is used for unknown compounds identification, but could be a disadvantage when seeking window materials, which are desired not to have infrared spectrum. Such materials are rare and have several disadvantages. Traditional window materials used in IR spectroscopy are hygroscopic (KBr, NaCl, CsI), fragile, chemically not resistant, expensive (diamond), or are totally absorbing in a part of infrared region (CaF2, SiO2).

Silicon is one from possible IR spectroscopy materials which is often used for ATR technique, but has not been used for transmittance measurements so frequently yet. NICODOM with its over 15 years long experience in FTIR spectroscopy recommends you silicon as an excellent infrared window material, because it is overcoming the main mentioned disadvantages: it is not hygroscopic and is chemically very resistant, resists thermal and mechanical shocks, scratching and fogging and is inexpensive. However, silicon exhibits relatively high refractive index (3.4).

The infrared spectrum of optical grade silicon (purified by zone melting) being used for NICODOM silicon windows shows that this material is transparent in the standard middle infrared spectral region. The 100% line of a NICODOM silicon window shows, that the silicon bands in the MIR region do not exhibit total absorption and can be easily subtracted.

Questions? FTIR@FTIR.CZ

Picture 1: Infrared spectrum of single NICODOM Si window in transmittance scale 0-80%T , spectral range 4000-400 cm-1, FTIR Nicolet Avatar 360 (air as background, Si window as sample)

Picture 2: 100% line of single NICODOM Si window in transmittance scale 97-103% T, spectral range 4000-400 cm-, FTIR Nicolet Avatar 360 (Si window collected as background and sample)

Available sizes (on stock):

32x2 mm undrilled and drilled (suitable for most liquid transmission cells, some gas cells, long pathlength cells, heated cells etc. ),

25x2 mm (different holders for mull techniques, econo gas cells, long pathlength gas cells etc.)

13x2 mm (some types of transmission cells, IR microscopy accessories)

25x1mm (different holders for mull techniques, econo gas cells, long pathlength gas cells etc.)

37x1mm (special purpose)

Other sizes may be available on special request.

Nicodom silicon windows feature the following advantages:

- Mechanically resistant

- Inert - Water, Acids, Bases, Solvents

- Suitable for water/corrosive samples, student labs

- Suitable for standard and special experiments

Material data

- Si is similar to Ge but it hase better resistance to thermal and mechanical shock. Si is very inert, it is only soluble in hot HF or HF/HNO3 mixture. It reacts with F2.

- Transmission: 8400-660 cm-1, 350-70 cm-1

- Refractive Index: 3.4

- % Transmission (at 2000cm-1): 55% by 2mm thickness

- Solubility in water, solvents, acids and basis: insoluble (except of hot HF or HF/HNO3 mixture)

- Density: 2.33 g/cm3

- Melting point: 1420 C

- Hardness (Knoop): 1150 kg/mm2

- pH range: 1-12

Click here for pricelist and ordering info.