- Plasmons are to plasma as photons are to light. They are quantized oscillations. Let’s begin the explanation with your microwave oven. There are electromagnetic oscillations inside that are cooking your food. Look through the glass and you see through little holes. Since the wavelength of the microwave energy is bigger that the diameter of the holes the microwaves can not pass through and cook your eyeballs. A quarter wavelength of the microwaves is 3 ¼ centimeters. The holes are much smaller.
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- The same principle applies to light waves. Visible light has wavelengths of 400 to 700 nanometers, ranging from blue light to red light. Take a thin sheet of gold and drill holes in it tinier than 400 nanometers. Shine a light on the gold sheet and the light should be blocked. Light should not go through the holes.
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-------------------- But, it does?
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------------------- What is going on?
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- This is how plasmons were first discovered. The holes are much smaller than the wavelength of light so science did not know how it was possible for light to get through the gold foil holes?
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- In 1989 physics discovered the answer. The “plasmons” were quantized plasma oscillations have a much higher frequency. Just as “Photons” are quantized electromagnetic oscillations and “Phonons” are quantized mechanical oscillations, , “Plasmons” are quantized plasma oscillations. The plasmon oscillations have 10 times shorter wavelength then visible light. They can pass right through the holes.
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------------------- But, what is plasma?
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- Plasmas are a state of matter. It is like gas, liquids , and solids. By volume and by mass plasmas are the most common state of matter in the universe. Our Sun and all the stars are made of plasma. So is most of interstellar space. The planet Jupiter accounts or the most “non-plasma” like me and you, in our Solar System and it is only 0.1% of the mass of the Solar System.
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- Plasma was first discovered in 1879 in the Crookes Tube, essentially the Cathode Ray Tube, or CRT, of today. Plasma was then defined as an ionized gas or region that has balanced electric charges of positive ions and free negative electrons. At low temperatures ions and electrons combine to form neutral atoms and the plasma usually becomes a gas.
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- Throughout antiquity glass makers have used plasmonics. You see them in the stained glass in church windows. The glass is coated with a metal such as copper or gold. In most metals the plasma wavelength is in the ultraviolet making them shiny or reflective to visible light. Copper and gold have electron interband transitions that are in the visible light wavelengths allowing time to absorb light rather than reflect it. This gives the glass the distinct colors. The ancients did not know why it worked but never the less they learned to use it to create beautiful art.
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---------------------- How does it work?
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- A plasma oscillation occurs when a metal with free electrons is in an external electric field pointing to the right. Electrons will move to the left exposing positive ions that are on the right. Then the electric field is reversed or goes away and the electrons then move to the right repelled by each other and attracted to the positive ions on the right . The electrons oscillate back and forth at the plasma frequency until the energy is lost in damping oscillations. These oscillations are at much shorter wavelengths than the wavelengths of light.
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- In metals, light of frequency below the plasma frequency is reflected because the metal screens the electric field of the light. Light of frequency above the plasma frequency is transmitted through because the free electrons can not respond fast enough to provide a screen.
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- Plasmons have many uses and we are just beginning to learn them. Besides church windows they are in solar cells , fiber optic cables, computer chips, cancer therapy, disease detection, biosensors for viruses, and more to come.
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- perforated metal foil is being used in biosensors that can trace a virus in blood and saliva samples. the perforations are coated with different proteins that bind to the antibodies. If the antibodies accumulate on top of a group of holes , the plasmons can not pull the light through allowing the virus to be seen. These biosensors could detect dangerous viruses in airport screenings.
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- In solar cells silicon only traps the short blue and green wavelengths, the longer red wavelengths pass through without generating power. A solar cell lined with metallic nanoparticles, plasmons oscillate about on the surface intensifying the light. Nanoparticles along the bottom of the cell allow plasmons to bend the light 90 degrees so the long red wavelengths can be trapped making electric conversion more efficient.
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- Plasmon oscillations have very short wavelengths and can carry very large mounts of data directly from the fiber-optic cables into the computer chip.
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- Plasmonic nanoparticles can be used to cure cancer. Gold particles 100 nanometers in diameter with a silicon core can be injected in to the blood. The particles enter the cancerous tumors that have porous blood vessels. Infrared radiation that is harmless to the patient radiates the plasmons trapping the light energy and heating the tumor to 120 degrees killing the cancer cells. Healthy cells absorb 40 nanometer particles so they are not affected.
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- Plasmonic nanoparticles are used in high resolution spectroscopy.
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- The more we learn abut the applications of plasmons the more innovation will change our lives. Announcement will be made shortly, stay tuned.
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email and with requested reviews at http://jdetrick.blogspot.com/ Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Monday, December 17, 2012
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