Hi Li,

For many years I hand coated slides to make Formvar grids.  The trick to it is speed.  Make your solution according to your protocol.  Then dip your sample and bring out of solution at different speeds.  The faster you go, sometimes the thinner.  But you also have to regulate the withdrawal because it will affect thickness.  It takes practice.

The easiest way is to prepare a cylindrical container with a hole close to the bottom. Introduce a small tube and seal it. Place plastic tubing with a valve to allow emptying the container. Fill the container with the precursor solution, introduce your sample and open the valve. Increasing solution removal speed will deal with higher thickness. If substrate is porous, after coating, it will absorb the solution and thickness variations due to inhomogeneous coating speed will be reduced.