Conductivity of the coating depends on its thickness (usually should be at least 5-10 nm), and density of the islands. To increase island density, it may be necessary to play with conditions of deposition such as concentrations of sensitizing and activating agents, time of each of that steps, and temperature. It also important to keep integrity of the coating to prevent its microcracking while making contacts for conductivity measurements.

I wonder that the probe destroy the film at the contact points for the measurement. The check is easy. You should coat silver paste on two points (arbitrarily) and place the probes of a multimeter.

One of the reasons silver powders are so good in composite conductive adhesives is that the oxide on silver is conductive, and so low resistivity particle to particle contacts can be formed. Hence I do not think this is an oxide problem. I suspect that Yusuke Okawa is correct, it is easy to damage very thin coatings with probes (particularly if they have sharp points).

I have seen similar results with silver deposited on polycarbonate using a completely different chemical reduction of silver onto the surface. I was never able to figure out why, so I'm interested in hearing what people have to say. I can say that we measured it using a flat tipped two-point ohm/square probe that did not penetrate the surface.

Have you checked your surface under microscope or just against the light? Maybe your surface is cracked. And these islands of coating are not connected.

I have seen similar results with a slightly different coating technique (electroless) as well. I was never completely sure what the problem was, but as suggested before, you should use silver conductive paste to form measurement contacts, so that you don't destroy your film. I assume that the problem was a seamingly continuous film on the macroscale, that is actually comprised of small Ag particles with a very high contact resistance due to cracks and some distance between the Ag particles.

Annealing actually decreases the conductivity even further (I tried that as well to get smoother films) and even at moderate temperatures (100 °C), I saw that the layer thickness decreases dramatically (visible even with the naked eye).

I eventually solved the problem by coating for longer times to form thicker films and by using brightening agents that help smooth the film and increase the particle connectivity.

Good luck.

I have little experience with electroless, so I cannot comment on your process. But I suspect the problem lays not in deposition technique. Ag tends to dewet from oxide surfaces. Even at room temperature given time it will form seperated particles. At elevated temperature the diffusion of silver will accelerate dewetting. The size of Ag perticles range from nano to micro and even larger. There is the whole study of Ag dewetting going on with the aim to control the size of Ag particles. You might contribute to that one.

I guess you should hold your glass substrate for longer time let say 40 mins and then use silver paste to electrode the point of contacts for measurement of resistance. It might be the reason that your coating is not uniform and the circuit is open.

I would also suggest to use SEM to check the coating both on the surface and cross section.

I hope this helps

good luck with it

The answers already given are quite interesting and probably point at the origin of your electrical continuity problem correctly. Furthermore, a combination of these may be the cause of your high resistivity. We have observed discontinuities due to the presence of islands which are not fully connected, observed in electron microscopy. The optical microscope does not have sufficient resolution to distinguish such microstructure. We have also observed micro cracks, which are not easy to distinguish. Some times they may be easily observed by optical microscopy in transmission mode, provided the Ag layer is sufficiently thin. In essence, there are several factors that you should explore, in agreement with the previous suggestions given here by other colleagues.

I don't work in that group anymore and I don't have access on my lab journal anymore, so I cannot tell you everything I tried as brightening agent. The thing is that each system, each solution and metal salt need and work with different agents. Nobody can accurately predict which agents work for which solution, so there is a lot of empirical study ahead. What works in quite some systems is As2O3, also Na2SO4 and other sulfur containing salts. There is good literature on brightening agents and you should check out some books on electroless plating and electroplating. They all have chapters on brightening agents.

Good luck

You might not be scintering even at 200C. Try treating the coating with sodium chloride solution or HCl gas (30 seconds)

1), the coating might be very thin and it can be easily damaged by four point probe. and i do not think any oxide film resistance (it is, but it will be negligible).

2), what 'german la fuente' said is might be correct, you should check this with SEM for the continuous or discontinuous. Optical is not sufficient...

Good you solve your problem with others input.

Conductivity of the coating depends on its thickness (usually should be at least 5-10 nm), and density of the islands. To increase island density, it may be necessary to play with conditions of deposition such as concentrations of sensitizing and activating agents, time of each of that steps, and temperature. It also important to keep integrity of the coating to prevent its microcracking while making contacts for conductivity measurements.

I worked with electroless nickel, silver, and copper to find a process to deposit circuits onto printed circuit board dielectrics and onto polymer thick film silver, nickel, or carbon conductors. On glass, you need to be sure that it is cleaned thoroughly. To increase the density of the Sn/Pd catalyst particles on the surface, try treating the glass with a Piranha solution or even better if you have it, plasma cleaner, just before putting into the Sn bath.

Without knowing more about your application, you may not be able to achieve the quality of coating that you need by an electroless deposition. The island growth that results from the catalyst particles produces bridging of metal between the islands. This bridging can be rather fragile and lead to subsequent erratic conductivity behavior over time, especially if handled frequently.

You should also do an adhesive tape test for adhesion of the film to the glass. Do it both with and without a crosshatch pattern and see just how much of the silver is pulled off each way.

The 4-point probe method is not so good for these kinds of deposits because of the difficulty in getting good contact between the electrodes and the film. You'll have better, more reproducible results if you paint a tiny spot of a conductive silver paste at the locations where the electrodes will be placed.

If you really need a high-quality, conductive, thin layer of silver, vapor deposition is the best way. If you can use some other metal than silver, buy some commercial window glass with reflective coating on it. (Be sure that it is a conductive coating! Some of them are not.) These glasses tend to use sputtered gold, nickel, or alloys. It can be a quick way for you to get a high-quality coating with high transmission (typically available is 70%-90% transmission glass). I used this type of glass to obtain a high-quality transparent conductor for making polymer dispersed liquid crystal smart windows. I had a project with a commercial window manufacturer, so it was convenient to buy cheaply large broken pieces that I could readily cut to smaller sizes in the lab.