Since you are sputtering Au, my guess is that it is more related to the depositions parameters (substrate-target distance, deposition pressure and rate). This will vary from system to system, but you should be able to improve results by changing these parameters. If you want to bridge the pores, I think you need a rather isotropic growth, hence higher Ar pressure and lower rate. In any case, the thickness of the Au should be larger than the pore radius.

Thank you Mihai,

Unfortunately, Cressington 208HR does not have a function to control the sputter time and argon pressure. The pore radius is 1um, so do you think that 40nm thick layer is not sufficient for covering the pores?

1 um pore cannot be bridged by 40nm Au, regardless of the sputter coat system you may use. One way would be to use a membrane over the pores that you dissolve afterwards. Even then, tension in your film may lead to cracks or a broken film on top. Please look carefully or send the literature examples you mentioned. Just by curiosity, what is the Ar flow or chamber pressure and the power you use on your system?

Try to fix your sample with an angle respect to gold atoms flux

I don't think that a tilted geometry would allow to cover 1 micron pores with a 40 nm Au film - because the sputtered material is scatterered due to the relatively high pressure compared to evaporation, you will loose the orientation that you have created by tilting the sample. From my personal experience with sputter deposition, especially wit gold, I can only recomment to increase the film thickness as already pointed out by Mihai!

Good luck, Dirk

Thank you all for interesting comments.

I must admit that covering the pores is not possible by increasing the thickness even to 100 nm, and I don't want to consume much of the Au target. Even if the sputtered Au could enter inside the pores and cover a bit of the pore surface, this can serve my purpose.

The Cressington 208HR has a timer function; 5-300 seconds standard and 5-900 seconds when used with the included MTM20 thickness controller. The argon pressure can be adjusted with the needle valve located at the back of the unit. Ther eis no way you can fill 1um pores with a sputter coating system; much smaller pores seems viable. The only way to cover the pores is to cover these with a thin film such as formvar which can be dissolved in ether or chloroform afterwards. You need to experiment which Au thickness can withstand the solvent treatment.

How are you so sure that the gold is not inside the pores? Is the polycarbonate electrically insulating? In that case it should charge in the SEM if it is not coated.