Silver nanoprisms grown into structural colors by high power LEDs

How to chemically synthesize silver nanoparticles, then grow them into triangular nanoprisms with light from a variety of LEDs. Each color LED creates a different size nanoprism, which has its own characteristic color.

Chemicals sourced from Amazon/eBay

20ml glass vials with PTFE lined cap (do not use metal-lined): Environmental Express APC1675P Already gone from Amazon

Comparison of CD, DVD, Blu-ray discs with electron microscope:

Great way to find related papers:
Research sources:

[ThisOldTony]

the projects you come up with never cease to amaze me. great work!

[Nighthawkinlight]

Oh no. I have a centrifuge in shipping right now that I bought for dewatering nano particles. I did not realize until seeing that separation chart how much of a challenge is ahead for me and my $100 ebay centrifuge.

Really excellent project/video as always!

[zilog]

Fun fact, this triangular gran of the silver particles is why analog film companies call some of their stock, TRI-grain or Delta. Extar has a tri grain and illford Delta has this shape. it makes for a higher definition exposure.

[tjhowse]

A potentially fun follow-up experiment: Rig up a jig that lets you both illuminate the liquid with a specific wavelength OR sample it with the spectrometer in situ. This way you can turn off the illumination long enough to sample the absorption spectrum at regular intervals. It would be cool to watch the peaks shifting on the absorption spectrum in time-lapse.

[johnqpublic]

I'm definitely saving this for later. In a few minutes the kids go to bed and roughly 45 minutes later I shall kick back in my recliner with this on the TV. Glorious Saturday Night Commence!

[Pay-No-Mind]

Ben, this is super cool, every time I see an upload from you I know I'm going to not only learn something new and cool but then end up down a rabbit hole for the next few weeks, lol so thank you :)

[TheHuesSciTech]

If the reactivity of the particles is "encouraged" by a given wavelength of light, it makes sense to me that they'd therefore react and grow *until* they're no longer (strongly) absorbing that wavelength. If that's the reason, that also explains why irradiating with a lower wavelength of light doesn't shrink the particles. TL;DR: if we assume the reaction occurring here is strictly crystal growth and that reaction is *enhanced* by light absorption, then we expect both effects that you seemed slightly surprised by (absorption wavelength != exposure wavelength; and the inability to reduce the absorption wavelength.)

[chaosfactor]

Ben, one of the ways that nanoparticles are prepared for TEM is to place a droplet onto your substrate, wait for some time for the particles to settle/adhere to the substrate, blot the supernatent out with filter paper, and optionally wash by dropping wash solvent and blotting. There are a lot of surface modification tricks to try to get more particles to stick, such as plasma cleaning, UV-ozone, spin coating charged polymer solutions, etc. It might take a few iterations of sample loading (e.g. apply multiple droplets) to get enough visible sample. Definitely not easy and unfortunately not well described in literature (generally passed down via institutional knowledge in labs studying nanoparticles).

[jeolman]

I love your old JEOL JSM T-200. I worked for JEOL for about 10 years in the early 90's. I had several of that model in my service area, along with the later 300 series models. They are a great little scope when working properly. The 10nm resolution is only with Gold on carbon @ maximum KV very short working distance. The sample must be heated to ~ 100C before being transferred to the vacuum. Also must have very good chamber vacuum. low e-6 torr minimum. It is a pain, and I can remember the struggles when resolution had to be demonstrated.

[craoun]

One sidenote concerning the stability of the NaBH4-solution: You could basify it in advance (to like pH 10-11), which would increase it's lifespan by orders of magnitude. Just seems like a possibility, since the final reaction mixture needs to be basic anyway. So a mixed stock solution of NaOH and NaBH4 could be used instead of two separate ones, since the required amount of NaOH is also known (2mL 50mM NaOH stock solution)

[peterwilson]

When I needed to image citrate-terminated gold nanoparticles in SEM, I used to deposit them onto poly-electrolyte multilayers. Surprisingly simple to set up. Simply prepare your imaging surface (the CD ROM in your case) by alternatively dipping it in solutions of polystyrene sulfonate (PSS; a negatively charged polyelectrolyte) washing with water, then dipping into poly diallyl dimethyl ammonium chloride (PDAC; positively charged), and washing in water again. Repeat the process 3-5 times to ensure a good coating of the poly electrolytes. Make sure you finish the treatment with PDAC so the surface will tend to be positively charged, so that the negatively charged nanoparticles will adhere to the surface. Simply leave this surface in the nanoparticle solution for an hour or two and you should have a even monolayer of individual particles to look at.

[TheExplosiveGuy]

Dang, I never knew how much I wanted a multispectrum monochromatic LED light, that is a super cool idea! I've got 9 different wavelengths of laser pointers which are also very cool for studying light absorbtion in different materials but now that I see this video I need the LED equivalent. It's amazing how much LED technology has evolved in just the last decade, being able to get this many monochromatic LEDs with such a high output power for the relatively low price they cost is incredible.

I also think a flashlight version would be pretty great too, with a wheel inside that rolls through all the different wavelengths so only one is on at a time, that would be neat...

[nitehawk]

10:08 I have been wanting to build one of these to test out astrophotgraphy light pollution filters. Mouser sells some very specific LED wavelengths, such as 656.28 for Hydrogen Alpha.

[thrustin]

Great video! I worked and made AgNP for my SERS research in grad school at UCSB. I made "bare" borate capped nanoparticles with just borohydride, but they were very tricky to get right and unstable once any contamination got into them. You can also use citrate directly as a reducing agent to make "nanoegg" ovaloids by heating a AgNO3 and citrate solution. These will provide stable citrate capped AgNP. Also, majority of absorbed light usually goes into creating plasmons (surface plasmon resonance). The electrons excited by this process can go on to participate in reactions, like reducing Ag ions in solution onto their surface. Might be an explanation on why the AgNP grow irreversibly with intense light.

[Muonium]

I wish I had a friend like Ben IRL to just unashamedly totally nerd out with over spectroscopy, electron microscopes, cryogenics, lasers, x-rays, and superconductors.... 😿

[byronwatkins]

I think photoelectric effect is interacting with plasmon resonances. Short wavelength (high energy) light causes electrons to be ejected from the particle surfaces and then the solvent captures a silver ion to neutralize the particle. This continues until the particle gets small enough that its plasmon resonance frequency equals the light's frequency; at this point, the plasmon resonance shields the particle's surfaces from the light. Once the particle is too small, no longer wavelength light can reach it to cause dissolution. You could check this model by adding some fresh solution to see whether the color could be reddened in that case. Adding fresh silver ions will allow all particles to grow until the photoelectric effect arrests the growth. Plasmon resonances will have normal modes in triangular prisms. Probably, the underlying fcc structure of silver plays a part in the triangular shape.

[petergoestohollywood]

What always fascinates me the most is how people somehow managed to figure out this works in the first place. Thanks for sharing.

[nitehawk]

2:15 I love the branding on that Sodium Citrate. "It's Just"

[Zappero]

I love this channel. Every video is well researched and really well presented. The downside is we get a video every 2 months. 100% quality over quantity.

[PedroDaGr]

The red-shift is due to inherent energy losses in the system (basically non-reactive vibrational modes). If you use flourescent nanoparticle systems as a model, I think it can help make sense of the situation. Basically, not all of the energy you put into the system is available for the output, be it fluorescence or building the particle. This is why the shift is always in the red (aka lower energy) direction comparted to the exciting wavelength.