Let’s be honest — not too many of us have a need to deposit nanometer-thick films onto substrates in a controlled manner. But if you do find yourself in such a situation, you could do worse than following [Jeroen Vleggaar]’s lead as he builds out a physical vapor deposition apparatus to do just that.
Thankfully, [Jeroen] has particular expertise in this area, and is willing to share it. PVD is used to apply an exceedingly thin layer of metal or organic material to a substrate — think lens coatings or mirror silvering, as well as semiconductor manufacturing. The method involves heating the coating material in a vacuum such that it vaporizes and accumulates on a substrate in a controlled fashion. Sounds simple, but the equipment and know-how needed to actually accomplish it are daunting. [Jeroen]’s shopping list included high-current power supplies to heat the coating material, turbomolecular pumps to evacuate the coating chamber, and instruments to monitor the conditions inside the chamber. Most of the chamber itself was homemade, a gutsy move for a novice TIG welder. Highlights from the build are in the video below, which also shows the PVD setup coating a glass disc with a thin layer of silver.
This build is chock full of nice details; we especially liked the technique of monitoring deposition progress by measuring the frequency change of an oscillator connected to a crystal inside the chamber as it accumulates costing material. We’re not sure where [Jeroen] is going with this, but we suspect it has something to do with some hints he dropped while talking about his experiments with optical logic gates. We’re looking forward to seeing if that’s true.
Could be useful for those that grind their own telescope mirrors, too.
An old friend in another city which whom I’ve lost touch, ground a 14″ mirror out of Pyrex glass, and sent it to some company to have a layer of silver deposited on it. Silver has the best reflectivity but tarnishes, so it has to be (very carefully) cleaned once in a while. Apparently others use aluminium which is not quite as reflective, but doesn’t tarnish.
My mind was blown when he showed me Saturn and it’s beautiful rings, one cool autumn evening in Bloemfontein, in about 2004.
Unless you plan on coating mirrors for a living or a side gig putting a vacuum system together just for coating is just not cost effective. You can get a mirror coated for around $10 per inch i believe.
Silver vs aluminum. Yes silver reflects more than raw aluminum but an enhanced aluminum coating is almost as good. You can also get a SiO overcoat on the silver which will help protect it from oxidation. But generally you will probably not notice a difference between Si and Al.
Yea, “the internet” seems to agree with what I remember from my elderly friend. Silver about 95%, Aluminium about 90%.
Didn’t know about the SiO overcoat for silver – thanks. I usually get a bunch of SiO up my shorts when wiping out while body surfing.
Yeah and enhanced aluminum is around 99% but has a narrower effective bandwidth.
All this has gotten me to go out to the shop and hook up my system, I had never tested it after I installed the new turbo pump. Sitting now at about 6.5×10^-6 torr which is not bad since it has been at air for a couple years now.
There are generally at least two mirrors in a reflecting telescope, so any improvement you make is multiplied; so, 0.9 * 0.9 = 81% efficiency, but 0.99 * 0.99 = .98%. This is a big difference, like getting more inches of light-gathering capability. Inches in a telescope are VERY expensive (something like ‘footitis’* with boats) especially when considered from a system point of view (more costly glass, heavier telescope, heavier/more expensive mount, more space, etc.). Of course, better reflectivity won’t help the resolving power of the mirror system but it might let you see things that you couldn’t see visually or with film/digital exposure of the same seconds/minutes.
*Boating footitis: you have an X foot boat. You want an X+4 foot boat. Then you get that and you want an Y+4 foot boat.
If photography is anticipated, aluminum reflects more UV than silver, making it more responsive overall to light. And SiO is pretty reactive, I hope you haven’t gotten that in your shorts. ;) Silicon monoxide evaporates much more readily than the dioxide, and a short period of exposure to air converts it to SiO2—durable, and the same stuff that’s getting in your shorts at the most opportune time.
FWIW the newer multilayer dielectric coatings are more reflective even than silver, but my understanding is that they’re a bear to remove when it’s time to recoat.
Anyone thinking of getting into evaporative coating should look at “The Amateur Scientist” and/or ATM book 3. John Stong goes into detail as to what’s required, construction of the system, suitability of different metals for coating, etc.
PS: “The Amateur Scientist” collection is available right now from surplusshed.com. I think it’s on sale for ten bucks now. Any hacker should have a copy, if for no other reason to show what actually can be done. “Build an X-ray machine! Smash atoms! Construct a van de Graff generator! Impress your friends! Loads of laughs!!”
“It’s just a tool and not the goal” wow that’s very impressive. Sometimes I spend too much time on the tool and not the goal.
Also, that ”turbo screw up” must have been a pain of a set back, but like you said it could have been much worse. Fascinating YouTube channel.
I dunno – over 30 years making ‘tools’. It has been a good gig. What is more fun, designing yet another mundane product for consumption by the idiot masses, or making tools for the designers? Methinks the latter is more rewarding and has a more demanding and appreciative audience.
No tool is worth building price wise to use it just once, about the only thing worth making for single use are clamping fixtures and jigs – and then only on those occasions where you need a bespoke solution (which often means you didn’t think through your order of operations enough in first place).
Something like a decent vacuum chamber set up has many other uses though, you might have built it because you needed to silver a mirror, but having built/acquired all the bits you are going to play with cloud chambers, coat other objects just because you can, maybe even create your own flex PCB or 3dimensional PCB – by plating a 3d print perhaps…
And there is the learning along the way – which can be enough on its own, price isn’t everything.
And microphone diaphragms!
Casio uses this process for their metal plated resin watches.
One reason that I’ll never buy myself another Casio watch. The last one looked great until it didn’t, about a year later. The strap and the back were metal, but the case was plastic. The PVD coating started to flake off leaving it looking awful. To add insult to injury, I then discovered after swimming that the 50m waterproof rating was a lie too. I removed the back and whilst giving it what I thought was relatively gentle heat to drive the moisture out, I found that the glass wasn’t silica based either. It bubbled, like many thermoplastics do when the heating isn’t even.
It’s a shame, but Casio don’t seem to give a toss about quality any more. Functionality is great, but if a $150 watch doesn’t last more than a year then it has little value.
As someone who hangs out on silicon servers on Discord, and would like to build a crystal furnace, but is also a toolmaker, I find this very fascinating. I’ve seen Jeroen’s work before, serious props to guys like this.
If you come to complain how cost ineffective this is- you are missing the point of what it allows one to do on their own entirely.
This is the kind of stuff I come to Hackaday for, bravo.
I miss the acceleration of material for better adherence. :D
adherence between which substrates?