Need weakly conductive and smooth coating on ceramics

We are looking for a very even weakly conductive coating for alumina or fused silica rods. Ceramic rods are 3.0mm - 5.0 mm in diameter. A target resistance of a 20-cm long rod is in a range of 50-500 MOhm. Rods will be placed in vacuum (10(-8) Torr) and occasionally heated to 200C.

1. Is any way to find a procedure how to produce an even (2-3 % deviation in local resistance/mm value) weakly conductive coating (about 2-10 Mohm /cm) on such a long ceramic rod.

2. Since Tin Oxide is the most widely used smooth coating, is there any way to reduce the layer's conductivity (i.e. increase the resistance/mm) from typical numbers (typical maximum is 10 kOhm/square) to 1 MOhm /square.

3. Is there any use of solutions with polyaniline nanoparticles for making a smooth high resistive coating.

My company is a major tin oxide manufacturer with a wide range of grades available. We have a nanoparticulate transparent electrically conductive material which could be readily coated onto a variety of substrates including alumina, which after a heat treatment process at circa 400 °C would provide a smooth, durable and heat resistant electrically conductive coating.