La Quinta Columna on strong light absorption in graphene

March 05, 2022

La Quinta Columna comments on a recent study that talks about the light absorption capacity of graphene, including UV light. 

The Spanish team already knew about this property of this nanomaterial and had even shown videos of people who had their arms illuminated with UV light and, to their surprise, their blood vessels glowed.

This new study also mentions the magnetic property of graphene.

As time progresses, it is becoming clear that everything said about graphene last year was true.

Orwell City brings the words of La Quinta Columna.

Link: Rumble

Ricardo Delgado: The following article talks about graphene and its relationship with light absorption. I don't know if you watched a video, José Luis, in which I presented a blood test of two vaccinated people. With very little time of exposure to UV light, those graphene-like objects appeared next to the red blood cells. And one thing I'm realizing —because I need to keep analyzing— is that when I exposed them to normal light —from a flashlight, for example— there was no activity at all. But when I illuminated them with UV light, there was a phenomenon of movement. It stopped with the pulses. But they were the erythrocytes that were around that material that we all know and that, in addition, we know absorbs UV radiation. 

Dr. Sevillano: That's right. 

Ricardo Delgado: It's very peculiar. Let's take a look at this article. The researchers say... The article is dated February 23, 2022. It's a week old. Researchers discover abnormally strong light absorption in graphene. It absorbs it. That's weird, isn't it? No. Not really. All kinds of energy are absorbed by this material. 

Scientists from University of Regensburg, Massachusetts Institute of Technology (MIT), Moscow Institute of Physics and Technology, and the University of Kansas have discovered abnormally strong light absorption in graphene. The effect arises from the conversion of ordinary electromagnetic waves into super-slow surface waves running through graphene. The observation is of fundamental interest and shows in an impressive way how the interaction of Bernstein modes, collective excitations of electrons driven by their cyclotron motion, and the smearing of electric fields at the smallest scales due to nonlocality can influence the radiation absorption of graphene. Radiation absorption of graphene. This behavior could serve as the basis for extremely sensitive infrared and terahertz detectors much smaller than existing ones... 

Notice that when they talk about detectors in the field of microtechnology, the THz band appears.

...with similar absorption efficiency. Everyday experience teaches us that the efficiency of light energy harvesting is proportional to the absorber area. The solar panel "fields" that dot many deserts are a clear indication of this. Can an object absorb radiation from an area larger than itself? It turns out yes, and graphene makes it possible. It's possible when the frequency of light is in resonance with the movement of electrons in the absorber. In this case, the absorption area of the radiation is on the order of the square of the wavelength of the light, although the absorber itself can be extremely small. 

And pay attention. 

In order to receive electromagnetic waves —from radio frequencies to the ultraviolet range— with the lowest possible losses, resonant absorption phenomena are used. Two classes of resonances are particularly promising for these applications: the first and most fundamental is called the cyclotron resonance and occurs when the frequency of the incoming electromagnetic wave matches the frequency at which the electron spins in a circular path in an applied magnetic field. The second resonance results from the synchronous movement of electrons and the EMF from one sample boundary to the other and is called plasmon resonance. 

Surely, this is where the subject of plasmonic antennas comes from. 

Both resonances have been successfully investigated experimentally in different systems. However, the observed effect of absorption enhancement has been comparatively small in most of the semiconductors studied so far. Until graphene entered into scene. Here they talk about the concept of resonance so that graphene absorbs as much energy as possible. A substance that can also be found layered in conventional pencil leads. 

We're talking about graphene.

 Its high purity not only allows plasma oscillations, rapid oscillations of electron density, to occur in the structure, but also preserves it additionally, as electrons can pass from one boundary of the sample to the other without ever encountering impurities. Exposing graphene to a magnetic field creates the conditions for cyclotron resonance by forcing the electrons into orbits. Radiation provided by a terahertz laser was used to excite graphene leading to a... 

The terahertz band is the band at which graphene is excited. 

...leading to a surprising result: While the photosignal was relatively small at the conventional cyclotron resonance, the researchers observed a huge photoresponse at its double frequency. A detailed comparison of the experiment with theory shows that the strong photosignal is due to the interaction of the double cyclotron and plasmon resonances into so-called Bernstein modes. 

Alright. Well, there it talks with a lot of technicalities. They were defined before, but you have to internalize them. 

The more light graphene absorbs, the more it heats up and the more its resistance changes leading to a larger photosignal. Hence, the change in resistance of graphene under the action of light... 

Note that we're talking about light radiation, such as ultraviolet radiation. a measure of its absorptivity. It's a capacitor, an energetic capacitor, so it's not surprising that it then generates a discharge. The more light graphene absorbs, the more it heats up and the more its resistance changes leading to a larger photosignal. 

Well, it repeats the same thing a lot here. 

In this regime graphene is expected to be a super absorber. That is, it will not only capture light from an area larger than its geometric size, it will be able to capture light from an area larger than the square of the wavelength. The anomalously low plasmon velocity in magnetized graphene creates all the prerequisites for this. Yet some people were saying that graphene didn't generate magnetism... 

Well... The article is interesting. On the one hand, it tells us that graphene is related to light. That it absorbs as much ultraviolet radiation as any other radio frequency. And also, it multiplies the signal and emits a much higher response than the surface it has. Something that doesn't, that doesn't happen with other material.

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