Quantum Dots 101: How to Make a Lightbulb That is a Million Times Smaller Than an Ant

Quantum Dots are marvelous little crystalline structures that work as electrical semiconductors and emit light.  But that's not all they do.  Dr. Jennifer Hollingsworth of the Center for Integrated Nanotechnologies at the Los Alamos National Laboratory, talked about the many potential applications of these tiny wonders.  Veteran broadcast journalists Judy Muller and George Lewis moderated the talk with Dr. Hollingsworth. 

Transcript

Science Straight Up

Season 4, Episode 4

Jennifer Hollingsworth, Los Alamos National Lab

Judy Muller and George Lewis, moderators

GEORGE: From Telluride Science, it’s Science Straight Up.  And this time….

JENNIFER: It has been said that the 21st century will depend as much on photonics – that’s the science of light -- as the 20th century depended on electronics. So welcome to the world of light.

GEORGE:  And Jennifer Hollingsworth of the Center for Integrated Nanotechnologies at the Los Alamos National Laboratory generates light from little specks she calls quantum dots, or QD’s. I’m George Lewis.

JUDY: And I’m Judy Muller.  Dr. Hollingsworth is one of the scientists who gathered in Telluride, Colorado for a series of workshops put on by Telluride Science.  As a way of giving back to the community, these scientists deliver Town Talks, sharing their insights and discoveries.

GEORGE: When Dr. Hollingsworth spoke at the conference center in Mountain Village, she displayed a photo of herself, smiling triumphantly, behind a row of flasks with liquid glowing in a rainbow of different colors.

JUDY:  Those flasks were filled with quantum dots, which have begun to light up our lives …part of the revolution in nano-technology.

JENNIFER: Beautiful things to be made from the Nano regime, also very, very useful things, the 21st century has seen a myriad of nanomaterials actually being implemented in real technologies. //From the anti-bacterial band aids that use silver nanoparticles to super hydrophobic fabrics, very water repellent, dirt repellent, to very light and strong materials that can be used to create tennis rackets for example, in particular Carbon Nanotube based structures.

GEORGE:  Before we go farther, here’s a hitch-hikers guide to the nano-verse. A meter is a little longer than three feet, right?  A nanometer is one billionth of that. By comparison, a human hair is 80,000 to 100,000 nanometers wide.  Even those of us with thinning hair have tens of thousands of nanometers.

JUDY: Or another way of putting it, a nanometer is a million times smaller than an ant. What Dr. Hollingsworth and her colleagues are brewing in their lab are quantum dots, in the range of 2 to 10 nanometers.  They are crystalline structures that act as semiconductors and they can be made to light up.

JENNIFER: It has been said that the 21st century will depend as much on photonics – that’s the science of light -- as the 20th century depended on electronics. So welcome to the world of light.

GEORGE:  The color of light that the quantum dots emit depends on the size of the dots.  They actually can be grown to glow blue or green or red or whatever.

JENNIFER: And we can tune it very precisely now from the ultraviolet and blue all the way well into the infrared. // And so quantum dots work with light, they change it, and they make it. // we take photons and convert from one color to another for display technologies, lighting technology, solar conversion.

JUDY: The research gave birth to a company called ubi-QD…a little play on words there…the QD standing for quantum dots. The company makes a quantum dot plastic film that can be stretched over greenhouses.

JENNIFER: And the quantum dots absorb solar energy, and they convert it into other colors of light. It's not just a filter, they're actually absorbing the light and emitting photons in a different color. And they specifically choose the quantum dots to emit light in colors that the plants can use better to grow. And so it's a very interesting and relevant I'd say, technology. 

GEORGE:  They’re pretty versatile. They can use light to produce a different kind of light. They can use electricity to produce light like an LED.  They can use light to produce electricity.  They can be used in camera sensors or video displays.  And because they’re really, really tiny, they can be used in medicine, injected into the body to target, say, cancer cells.

JENNIFER: The quantum dots emit light and we can use that light to image cancer cells, we can tag the cancer cells now and see them because of the light being emitted by the quantum dot.

JUDY:  Not only see the cancer cells but kill them.  All you need is a bit of laser light.

JENNIFER: One example that looks like a PacMan, it has our giant quantum dot in, the center, and then it's enveloped in glass, and then in a thin layer of gold.// 

But the reason we add the gold shell on the outside, is because if you hit the gold shell with another laser, typically infrared, the gold will heat up. And then you can actually thermally ablate basically kill destroy the cancer cell. And the other bit that I thought was cute about that structure was, as I mentioned, the the giant quantum dot, the intensity of its the light that it emits is linearly dependent on the temperature. And so as the gold is heating up the local nano scale environment, the quantum dots feeling that right, and so it's losing some intensity, but a linear linear way that we know so we can tell you what the temperature is. As you know, when you're ablating the cell when the cell is being killed, we know the local temperature because the quantum.is Now your thermometer, so it's like a nanoscale thermometer.

JUDY FROM TALK:  Thank you.

GEORGE FROM TALK: Yeah, thank you very much.

JUDY FROM TALK:  I actually got that.

GEORGE FROM TALK: You said that this was going to become the age of photonics that the 21st century that the 20th century was the age of electronics. //Do I trade my MacBook Pro in for a computer that runs on light instead of electricity?

JENNIFER: Yeah, and it may actually be a combination, like hybrid technologies, right? Light may not do everything. The reason people like photons, safer communication, even potentially, is building blocks for future quantum computers, is that the photon travels at the speed of light, and it doesn't interact a whole lot with the environment. So if you could embed the photon with information, you can actually move that information around very efficiently. And so it's another tool we have now to build these communication or computing technologies.

JUDY:  They ran into a few hitches on their way to the age of photonics.  Over time, exposure to light, oxygen and water can cause quantum dots to flicker and burn out.  But then, they discovered how to grow a protective shell over the dots.

JENNIFER: We just happened to be growing one composition shell on top of the core, out a very thick layer of thick layers of the shell, that Wow, these guys are actually showing suppressed blinking. Let's push on that, you know, and see what happens. So as my graduate advisor likes to say, even a blind pig will sometimes find a truffle. And so, you know, we hate to //admit it, but  a lot of discoveries are serendipity. But once you make that discovery, and then you go back and try to figure out why it works, then that becomes the basis of a new design criteria. You know, so it's, it's a little bit of that 

JUDY: You had to be very excited when you saw that. 

JENNIFER: Oh, it was, I can still visualize that day. And I'm looking at my postdocs notebook, and we're staring at this data set. And we're like, Oh, my God, // It was working.

But now we've we know what makes it work. And so we've applied that knowledge to other compositions. And so now we have non blinking behavior that spans the ultraviolet blue all the way into the infrared. And so, yeah, so that's the next step. 

GEORGE: So what's the warranty on my quantum dot light bulb gonna be?  

JUDY: Or the television right? 

JENNIFER: Yeah, I mean, well, and so so you can, you can also, you can build a better light bulb, you can build a better quantum dot. You can also just encase these things in, you know, like a matrix right glass or polymer that protects them from the nasties, you know, from oxygen from water.

JUDY: The nasties?

JENNIFER: Nasty things that make them die.

GEORGE: Or, the things that make us live oxygen, water.

JENNIFER: Yeah, and so you can attempt to fix the climate itself, which is what we do in my lab, because we're chemists. But you know, companies will probably do a lot more with matrix development. Right. So put them into a glass or something that's, that's going to just protect them from the environment.

GEORGE: Here’s a fun fact.  You can use quantum dots in printer ink.  Even do 3-D printing.

JENNIFER: Actually, we have a 3d printer in my lab. And the cutest thing we've ever printed is a little size model of the Statue of Liberty, that incorporated our quantum dots. The in this case, they happen to be quantum dots that emit in the infrared. So when you make them glow, you can't see them by eye, but when you detect them with an infrared detector, lo and behold, the Statue of Liberty is glowing. Yeah. So um, they're very convenient, chemically. Because you can do a lot with them. Yeah, either at the individual particle level, or on the ensemble level. So they're fun. That answer your question. Okay.

GEORGE I lift my quantum dot beside the golden door. 

JUDY: It is a national lab and I’m just curious…I have to ask, are there defense applications for quantum dots? And can you talk about it? Don't worry, it'll never leave this room. (laughter)

JENNIFER: Yeah,I can talk about some of the stuff.

Right, so just like a tennis racket benefits from lighter, stronger materials, right? You can imagine that you can build a lighter, stronger gun, the armor that. So there's armor made by made of carbon nanotube films that actually outperform Kevlar in terms of flexibility, and the ability to withstand an impact.

There's a little bit fancier stuff that's more relevant to quantum dots would be sensor technologies. So you can detect chem, bio radiation threats, you could develop catalysts that can actually break down the warfare agents. Right. So that's another type of nano material.

Something I've worked on, or I should say that basic science version of it. We call it tag track locate. So you can use things that emit light, you know, saying in a visible spectral range to tag objects of interest, shall we say? And, yeah, so there's lots of different applications, and many that many of them are parallel to what's happening in the commercial realm.

GEORGE:  Can you talk in layman's language about how you grow these, these dots? What's the manufacturing process like? 

JENNIFER: Yeah, so in the laboratory, we use a vessel glass, and it's called a flask is your glass vessels that alright, think of your pot in the kitchen. And, and we don't, we add a solvent. So you might add water to heat up some pasta or whatever, right? So so we had a solvent, that's typically in our case, like a non aqueous solvent. So okay, a high boiling liquid in and we heat that up. And then we inject very quickly, typically, so called chemical precursors. So these are like the ingredients in a recipe. And then those precursors, these are molecules that will break down at the high temperatures, that which we've brought the solvent and react together mix together to form the quantum dot, right, so so we have a molecule that brings in the cadmium, for example, and a molecule that brings in the Selenium. And so that together, they form cadmium selenide quantum dot. Now, the reason they stay the size of a nanoparticle and don't just keep growing, is we have another ingredient in the pot, which are called ligands. And these are molecules that actually can bind to or interact with the surface of the nanoparticle as it's growing, and kind of help stabilize it in that in that size. So they don't just keep growing. 

GEORGE: Ever try to make a soufflé?  You have to get the ingredients and the temperature and the timing just right.  And by carefully watching the clock, Dr. Hollingsworth and her colleagues can grow tiny quantum dots that glow blue or bigger ones that glow red.

JENNIFER: And so some of these reactions can happen very, very quickly, like in seconds. And so you have to we say, quench the reaction, quickly, if you want to keep the size, very, very tiny, right? So you allow them to react in in seconds, and you add, say, cold solvent to freeze and cool down the reaction very, very quickly, so that the particle stopped growing. And then you let it go 10 More seconds, and you get the next size. 10 more seconds, give the next size, it really depends. There are different types of reactions. Now, it as you might imagine, there's a lot of potential for human error and variability. // Actually, an interesting avenue for change really and then in the nanomaterials community is to push towards automation, and try to remove the human hand as much as possible from the synthesis. And so in our lab, we've developed an automated reactor system that relies on sort of fluidics, to do all the addition of the precursor and the extraction of, of ALEC watts. And so for the control, the temperature in the stirring, and so forth, others use robots, robotics. 

GEORGE: How difficult is it to scale this up to make industrial quantities of this stuff? 

JENNIFER: It's actually it's been done, it's being done. I mean, so I have a, I had a former postdoc, for example, who actually worked for one of the nano or quantum dot companies. And he said, it was interesting, depending on the scale, that they were producing the nanoparticles that in some cases, they're just using giant flasks so just make your flask big. But on the other extreme end, they were they had what look like, you know, when you brew beer, or I mean, right, so the big vats the big metal that's, so they're going quantum dots and these massive vats. Right, so. So that's one way. 

JUDY: Business Wire magazine called 2023, the year of the quantum dot. And because they're very interested in televisions and computers, and what are some of the real practical things that we could see? Well, maybe not in our lifetime--  sad, but I mean, soon. that would affect our lives in terms of what quantum dot nanotechnology could do for us? 

JENNIFER: Well, I mean, they already are in television, televisions, forms of displays, right? //So say, for example, on display technology or television set, because you can make quantum dots that emit colors that are very pure. Okay. Right. And so you can get better color density and quality, 

better saturation..

JUDY: We can watch more television?

JENNIFER: I mean, you can argue whether that's very important, is that right? It's the grand scheme of things. Yeah. It's a commercial product that certainly, that some people enjoy. Right? So Oh, yeah. So it's relevant. Medical applications, secure communication, and better computers, faster computing, I would argue, would be relevant for this coming century. Quantum Computing, 

JUDY: We will entertain questions from the audience.  And has anybody got any questions?

AUDIENCE MEMBER: I would like know, just explain the basics of how you know how you measure the size of these quantum dots. 

JENNIFER: We image them, or we, we take pictures of them using what's called electron microscopy. So it's very much like an optical camera, except for instead of photons that allow you to see things, we use electrons. And the reason you can use electrons is because they, they, they're, their wavelength is ultra, ultra small, you know, so it's smaller than the objects we're trying to image.// We're all we're trying to see is the size. And so So yeah, it's like take

A picture, but with electrons instead of light.// And once you know the correlations between the color of light that they emit, and their size, then basically I don't even have to get the TM or the electron microscope. I just get the spectrum. I know where it's emitting, I know what the size is.

AUDIENCE MEMBER: If you look at the trajectory in history of semiconductor electronics, from the discrete transistor to the seven nanometer technologies that are available today//there exists or are available//Technologies, which allow us to discreetly isolate and integrate optical technologies on a chip, which would include electrical and optical communication channels. Is that the next step in the development of quantum bit applications?

JENNIFER: So it's the future is going to really be based on quantum science. It's going to be based on things that are very, very small. So sub seven nanometers it’s going to be based on properties that go beyond seven nanometers not just simply electronics.

GEORGE: Back in the 1960s, Gordon Moore at Intel Corp correctly prophesied that you could double the number of transistors on an integrated circuit every couple of years. My first transistor radio, when I was a teenager, I had seven transistors, my smartwatch has billions of them, right. So when you're down at the nano level, aren't you getting toward the end of the road in terms of being able to build semiconductors in a tiny space? 

JENNIFER: If that's all you're looking at is the traditional semiconductor based technologies. 

GEORGE: Right. But if you're looking beyond that…

JENNIFER:  So you have to get, you know, do the realm of quantum mechanics takes over? So people are looking at single atom level,

GEORGE: Which is pretty wild stuff, right?

JENNIFER:  Yeah. But other other types of physics takes over. And so it? So how do you break Moore's law? And it's not simply going to be going down in size, it's going to be looking at other phenomena that allow you to do things differently, right? You already alluded to the fact that in traditional computing it’s a zero-one bit. A q-bit is just like, unbelievably more powerful. Right? You typically visualize it as a as a sphere, right? And so all of the information is every little point on that sphere. And, you know, and so the superposition of all of those states. So it's just so much beyond what we can do with the conventional Moore's Law approach. 

GEORGE: You ain't seen nothing yet.

JENNIFER: You ain’t seen nothing yet. Yeah, I mean, that again, that's from the chemists perspective.

JUDY: Do we have any more questions? 

AUDIENCE MEMBER:  How would you deliver these particles for cancer therapy? Can you take a pill?  Can you take it as a pill?

JUDY: That's a great question.

JENNIFER: Yeah, that's a good question. All right. So the idea too, would not be that you initially flush your whole system with them, although you could. But you'd probably try to target, you know, the tumor. The for example. So whether there would be injection in the area of the tumor, right or not, I mean, I'm not a medical person, either. But yeah, so I think I think it'd be more targeted, rather than, you know, full body, because basically, they have to be in the vicinity of the cancer, to be able to find it and bind to the cell.

And then there's tricks you can play too, by the way, I think, you know, in terms of circulating the nanoparticles have to be of a certain size. So sometimes we might want to make them a little bit bigger than we actually synthesize them. For remember, right, you know, I think something more in the range of 80 nanometers or 100 nanometers, is more ideal than these very tiny particles in terms of penetrating into a tumor and getting through and circulating in the body, but yeah, sorry. Yeah. The other thing is too if you're relying on light to make them work, you know, so for example, the thing we made, you have to hit the gold with an infrared light source and unfortunately, infrared penetrates the skin pretty well. So if if your nanoparticles are, you know, inside under under the skin, we should be able to get an infrared light source through, but you may have to actually put a fiber optic into the body close. to where the tumor is to activate the nanoparticle, it really depends on what you're trying to do. Others are using nanoparticles to deliver chemical cancer cures so that's another option.

GEORGE:  That’s all the time we have, or as they say at Los Alamos lab, dots dot.  Let's give a big hand to Jennifer Hollingsworth of the Los Alamos Labs for enlightening us.

(applause)

JUDY: enlightening us with a light bulb enlightening us. Yes, it is a million times smaller than an ant. So how many ants does it take to change a lightbulb?

Jennifer….thank you for that presentation and thank you all for coming. (applause crossfade to theme)

JUDY:  That’s it for this edition of Science Straight Up. And George, do you think they’ll come up with a quantum dot that will attack your punster cells?

GEORGE: That would be a difficult pun-dertaking, Judy.  We’d like to thank the Telluride Mountain Village Homeowners’ association for providing our venue at the conference center, where our session was recorded live.  Dean Rolley of Dragonfire productions is our excellent audio engineer, assisted by Vicki Phelps, who keeps him on the level.

JUDY: Alpine Bank is a keynote sponsor of Telluride Science.  Mark Kozak is Executive Director, Cindy Fusting is executive manager. Annie Carlson runs donor relations and Sara Friedberg is lodging and operations manager. For more information, to hear all our podcasts, and if you want to donate to the cause, go to telluride science-dot-o.r.g.

I’m Judy Muller.

GEORGE: And I’m George Lewis, inviting you to join us next time on SCIENCE STRAIGHT UP.