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EMS 679 is a solution which forms a dense SiO2 layer when applied to a substrate either by spinning, dipping or spraying. The SiO2 layer is dense enough to act as a sodium barrier after appropriate heat treatment for temperatures experienced in the manufacture and use of liquid crystal displays. For most barrier applications EMS 679, undoped, is adequate. If desired, EMS 679 can also be supplied doped with Boron or Phosphorous to enhance the sodium blocking. Films with index of refraction greater than that of SiO2 (1.46) can be obtained by doping the EMS 679 with Titanium. Films of EMS 679 will exhibit microscopic ridges, a requirement for a base for liquid crystal operation.


1. Treatment of substrates prior to coating. The substrates should be free of organic residues. Standard glass cleaning procedures will prove adequate for glass substrates.

2. Deposition of EMS 679

a. Dipping
For large substrates, or for asymmetrical substrates, where spinning is not practical, EMS 679 may be applied by dipping to obtain a stable film which does not crack on densification. It may prove necessary, depending upon the substrate, to dilute the EMS 679. Suitable diluents are methyl alcohol, ethyl alcohol (denatured grade is satisfactory) or isopropyl alcohol. Films with uniform thickness will be obtained if the substrates are protected from stray air currents. If the liquid from which the substrates are being withdrawn is disturbed, non-uniform films may result. The thickness of the solid film will depend upon the solute concentration in the liquid and the angle and speed of withdrawal of the substrate. A common difficulty experienced with dipping is accumulation of a bead of liquid when the end of the substrate is withdrawn from the liquid. The bead may be removed by touching the end of the substrate with absorbant paper. Alternatively, after drying, this edge of the substrate may be cut away.

b. Spinning
Substrates up to 6" x 6" are conveniently coated by spinning. For 6" x 6" substrate about 2 ml of solution is sufficient to completely cover the substrate uniformly. At a spin speed of 3000 rpm, a film thickness of 2000 angstroms will result.

3. Densification

After deposition the film is densified by heating from room temperature to 450oC in air followed by slow cooling to anneal the glass film and prevent distortion of the glass substrate. As a result of the heat soak the film will be reduced in thickness by about 10 to 15%.

4. Specification of EMS 679

a. Density: 0.887 grams/cubic centimeter
b. Viscosity: 1.25 cp at 25oCentigrade
c. Index of refraction: 1.45
d. Contamination limits

Na < 1 ppm Ni < 1 ppm Cu < 1 ppm
Cr < 1 ppm Fe < 1 ppm Mn < 1 ppm
Al < 1 ppm

5. EMS 679 is supplied in polyethylene bottles. The solution is filtered through a 0.2 micron filter directly into the bottle and may be used directly from the bottle. EMS 679 is guaranteed for six months when stored at room temperature. At -20oC the solution will exhibit an indefinitely long shelf life.

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Material Safety Data Sheet