Having personally worked with Guo while he was setting up his lab, I'm really pleased to see him linked on this website. The man is damned smart and it's very true what he said. For those wonder how it all works check out: http://www.optics.rochester.edu/workgroups/guo/team/guo.htm and some of his papers.
Researchers Create Gold Aluminum, Black Platinum, Blue Silver
21–30 of 45 posts
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#22FTA: Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the color won't fade or peel, says Guo Oversold. This is technically true, but any corrosion (or even scratching) will muck up the visible-wavelength-scale features on which this effect depends. I'd have to believe this kind of image would be far more fragile than a simple paint would be...
Perhaps a plastic coating to preserve the microstructures... Still valuable, the colors apparently can be dialed up to order, unlike paint etc which depends upon mixing and batch etc.
A polymer coating would indeed help. In the jargon, we call that stuff "paint". :)
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#23Earlier quoted context omitted.
Perhaps a plastic coating to preserve the microstructures... Still valuable, the colors apparently can be dialed up to order, unlike paint etc which depends upon mixing and batch etc.
A polymer coating would indeed help. In the jargon, we call that stuff "paint". :)
I think the GP meant a varnish, not a paint.
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#24A line from star trek: "Transparent aluminum???"
All metals are transparent if the layer is thin enough.
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#25Earlier quoted context omitted.
[deleted]
"its equivalent to top layer being transparent that lets light through one way but doesn't let it reflect back" That would be a violation of the laws of thermodynamics. It's impossible to make a one way mirror. If you could, you could allow light through from one side, and collect free energy, since one side would be hotter than the other.
Of course you can make imperfect or active one-way mirrors.
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#26FTA: Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the color won't fade or peel, says Guo Oversold. This is technically true, but any corrosion (or even scratching) will muck up the visible-wavelength-scale features on which this effect depends. I'd have to believe this kind of image would be far more fragile than a simple paint would be...
As a material scientist myself, I was curious about their study. So I pulled up their paper in JAP.
My first thought before reading was that the high intensity laser pulses were causing local heating such that any impurities in the solid (ie carbon) diffused onto the surface. Nope, they did an EDS scan and platinum was clearly the dominant element. There were traces of carbon but I think this was due to impurities in the microscope.
So basically what happens (my educated guess) is that the laser pulses break up the surface structure such that different phonon (http://en.wikipedia.org/wiki/Phonon) modes are excited when certain wavelengths of light are shined on the surface. Just so happens that wavelengths in the visible range are absorbed so the sample appears black. To create different colors, I guess they just found the correct amount of power and wavelength laser pulse to create the phonon mode that they need.
I don't believe they oversold their technique. Scratching won't really cause this phenomenon. Corrosion maybe, but I doubt they could achieve the same optical properties. Fragility is a legitimate concern, but I'm guessing that if they are interested in industrial applications they will do mechanical testing of the structures.
EDIT: I'd also like to add that I think it's perfectly OK for a scientist to upsell their work. We live and die by the grant system, and funding agencies are all looking for "broader impacts." I'm rather impressed that their group was able to drum up this much press.
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#27I was wondering... how do you control those lasers? To have a pulse of one femtosecond you would need something running at petahertz... of course I'm missing something...
Femtosecond lasers are actually common nowadays. We use a Ti-sapph at my lab. Unless I'm crazy, Prat's answer is actually unrelated to your question. It's an article about pulse shaping, which is used to, well, change the shape of an ultra-short pulse. Not generate it. What you want to look for is mode-locking. Essentially it's based on interference. You have a lot of standing waves in a laser cavity and lock them so…
Thanks.. that explains the generation of the pulse - the link I posted probably relates to fine tuning the shape to get the desired color.
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#28A line from star trek: "Transparent aluminum???"
All metals are transparent if the layer is thin enough.
Not if you etch a pattern of holes in the layer!
http://www.uni-stuttgart.de/aktuelles/presse/2009/116.en.htm...
Re: Researchers Create Gold Aluminum, Black Platinum, Blue Silver
#29Earlier quoted context omitted.
"its equivalent to top layer being transparent that lets light through one way but doesn't let it reflect back" That would be a violation of the laws of thermodynamics. It's impossible to make a one way mirror. If you could, you could allow light through from one side, and collect free energy, since one side would be hotter than the other.
Of course you can make imperfect or active one-way mirrors.
Not sure what an imperfect one-way mirror is. Do you mean, something that is mostly one way? Because, no, you can't.
And you can't make an active one-way mirror either (at least not without inputting energy) - see http://en.wikipedia.org/wiki/Maxwells_demon