Quote Originally Posted by Photo Engineer View Post

I would like to remind you that the dry layer should be about 10 - 100 microns depending on emulsion which means that the emulsion itself must be put down at about 5 - 7 mils thickness. Can you do that? Resists are put down much thinner.

I guess coating speed for gelatin AgX emulsions needs to be pretty low.

In the context of holography spin coating has been widely used - both for preparing photoresist layers for embossing and the making of holographic optical elements (HOE) mainly. Richard Rallison, one of the pioneers of DCG, put a couple of papers online that explicitly dealt with spin coating. After this passing they are no longer available.

In his paper, Control of DCG and non silver holographic materials (SPIE 1600, 1992), he wrote:

A variable speed turntable capable of 50 to 100 RPM will coat films of gelatin or PVK from 4 to 50 microns on 8 x 10 inch glass or plastic substrates. Plates as small as 3 inch diameter or as large as 16 x16 inches have also been successfully coated with this range and technique. The turntable should be equipped with a surface or arms that will mate to a removable tray that is one or two inches larger than the substrates being coated. We have used ordinary variable speed phonograph players with pie tins turned upside down and glued to the turntables and we have used Dayton variable speed gear motors with heavy duty arms attaches. Both devices worked very well.

Trays have been made up of stainless steel, plexiglass, polyethylene dishpans or modified from aluminum cake and pizza pans. The best trays have straight sides measuring 2 1/2 to 4 inches high and are fitted with 3 rubber posts inside and outside. The posts inside hold the substrate an inch or so off the bottom of the tray and the outside posts serve to level the tray during pouring of solutions and to center the tray during spinning. The spinning tray and substrate may generate useful turbulence that aids in drying and distributing the solution. Excess solution is caught in the tray and emptied between substrates then is easily soaked clean in hot water after a days activities.

An important component that augments drying and uniformity is the blower-heater. It hangs off center and above the whirling tray. Turbulence and heat combine to make uniform coatings in about five minutes. We recommend the use of a variable temperature 600 watt blower such as might be found in the ceilings of some bathrooms. A little experimenting with angle and position will quickly determine the best place to hang this unit in your clean hood or bench area. Coat and examine uniformity by looking for local fringe patterns under a fluorescent lamp or better yet a fluorescent long wave black light.