Archive for June, 2012

What Are Quantum Dots ?

Thursday, June 28th, 2012

quantum dot

If you cut a material into thin 2D planes, it “pinches” the electrons in the material — confines them in one dimension. They can still move in the 2 dimensions of the plane. Slice that plane into 1D “lines” and the electrons moving in the material now are confined in 2 dimensions and have only 1 degree of freedom — down the length of the wire.

Now slice the wire into tiny chunks. These little islands of metal or semiconductor material, each consisting of from a few hundred to a thousand or so atoms, confine the electrons in all 3 dimensions of our 3D space. You would think the electrons would mind this confinement, but they love it: these tiny islands called “quantum dots” can hold a bunch of free electrons as a sponge holds water. It’s a little like electron flypaper: even “free” electrons would rather hang around the cluster of atoms that make up the quantum dot than fly around in empty space.

Quantum dots have unique properties that can be controlled by, among other factors, the simple size of the cluster of atoms making up the dot. Larger quantum dots tend to glow red when stimulated, but if you make smaller dots you can get all the colors of the spectrum; make the dot small enough and you can make it emit ultraviolet. What this means is that you can get an infinite number of colors from the exact same chemical ingredients, just made in different size dots. No more cadmium yellow or titanium white — with cadmium selenide (CdSe)or cadmium sulfide (CdS) you can get all the colors of the rainbow with only two ingredients.

If you make the quantum dot really small, you can even get it to emit white light. You might think that is no big deal, since “white” LEDs are now available. But those LEDs are not really glowing with a continuous spectrum of white light. They are emitting several different colors whose mixture the eye interprets as white. With small enough quantum dots, however, it really is white light.

Quantum dots have the potential to revolutionize several fields of endeavor, including solar cell technology. Traditional solar cells are made from silicon, either monocrystalline, polycrystalline, or amorphous. Researchers have discovered, however, that it is possible to make solar energy conversion devices very simply if quantum dots are used: simply paint some CdSe nanoparticles onto a transparent conductor and you can get electric current from light. The ability to “paint” solar energy collectors on walls or roofs instead of having to install separate solar panels could have tremendous applications in the housing industry as well as many others.

In the field of medicine, quantum dot color tunability is inspiring a whole new generation of diagnostic technology. Quantum dots can be encapsulated with nonreactive nontoxic material and attached to structures designed to bind to the receptors on particular types of cells, such as cancer cells. Injected into the bloodsteam, these targeted dots bind preferentially to the tumor cells, and can then be stimulated to emit signals showing the location and size of the tumor. This will happen even if you didn’t even know there was a tumor. Instead of irradiating the whole body with x-rays or doing a whole body MRI scan — and then combing through the imaging trying to identify cancerous tissue, you cold simply inject some cancer-binding quantum dots, what for them to rummage around in there, and then stimulate them to see if they congregated anywhere.


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Flight Plan

Thursday, June 7th, 2012


Is your life taking off? Do you feel yourself soaring on the wings of the wind? Is life opening up abundance for you?

dead endOr do you feel stalled, stuck in a dead-end job with no hope?

I know what that feels like. I’ve had good and bad jobs. I’ve worked in office cubicles developing Web pages, and I’ve worked the drive-through window at a Wendy’s. I’ve delivered pizza. I’ve even done time as a substitute teacher.

One thing I’ve learned is, you need to have a plan. If you do not plan for the future, you end up getting whatever Fate tosses you.

It’s easy to get stuck in a rut, just existing and surviving from day to day with no progress or improvement. We humans have a tendency to make the best of what we have (which is a good thing if it keeps us sane), which helps make life livable but also closes off our options. We spend so much time wearing down life’s rough corners that we lose the distinction between temporary acceptance of difficulty and resignation to its perpetuity.

For individual humans, this might mean dealing with a grouchy boss or a pair of shoes that don’t fit. For human societies, instead of squeaky shoes we have toxic waste dumps and the misery of the poor.

It is easy for the individual to tell ourselves that we will get better shoes when we can afford it. Similarly, societies tell themselves that things will get better when the economy improves, or that we will all rest easier and be less paranoid once our Most Wanted have been captured. For individuals, this kind of rationalization might lead to foot problems. For societies, it can lead to tyranny: to Wars against drugs, crime, terrorism, etc. that never end, or to restrictions and loss of freedoms that never seem to get restored.

It is no longer enough for us to survive. It is no longer enough to congratulate ourselves on not blowing up the planet so far. It is time for us to file a flight plan as a species. It is time to plan for prosperity.


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