Chapter 358: The end of science is theology?

On Friday, Xu Qiu took Mo Wenlin to conduct the exciton binding energy test of IDIC samples again. The test method is the same as yesterday's ITIC sample, the low-temperature fluorescence luminescence experiment.
The second test was also successful once, but the time consumed did not decrease too much. Starting from around nine in the morning and working until six in the afternoon, I finally got the results.
The results show that the exciton binding energy of IDIC is 112 millielectron volts, which is numerically equivalent to ITIC's 117 millielectron volts.
Based on the results of these two times, plus the distribution map of the HOMO/LUMO energy level on the molecule obtained from the previous DFT simulation, Xu Qiu probably has a conjecture:
"The low exciton binding energy of ADA non-fullerene acceptor materials may be due to the molecular structure of A-D-A.
In the excitons generated in the molecule, the positive charge will be concentrated on the D unit, and the negative charge will be concentrated on the A unit, resulting in the initial splitting of the positive and negative charges inside the molecule, reducing it to completely split into free The energy required for the charge, the apparent phenomenon, that is, the exciton binding energy is low. "
If this guess is to be verified, it will be more difficult.
It is almost impossible to directly prove that it can only be confirmed by a large number of data on the exciton binding energy of different ADA non-fullerene acceptor materials.
Among them, once there is a counterexample, this conjecture will be overturned, or the expression needs to be modified or patched.
This is also normal.
After all, the essence of science is to constantly build, overthrow, and perfect theories.
Just like the establishment of Newton's three laws at the beginning, they are valid in the macro and low-speed world.
But it doesn't hold in the microscopic and high-speed world, so quantum mechanics and the theory of relativity will be supplemented separately later, and these theories also jointly build the cornerstone of the modern physics department.
Of course, these are the current theories, and they may continue to be overthrown and improved in the future.
After all, human beings are mortal wombs with naked eyes. Without X-ray eyes, they can't move near the speed of light, so it is difficult to say exactly what things at the microscopic and high-speed levels look like.
Even if the instrument is tested, is the data displayed by the instrument necessarily true?
Furthermore, what we directly observe must be true?
You can't think about this kind of thing deeply, because thinking about it at the end will inevitably fall into an endless loop of doubt.
Indeed, many things cannot be proven or falsified.
This may be the reason why most foreign scientists have converted to religion, and some people have proposed that "the end of science is theology".
The more you explore, and the closer you are to the boundary of cognition, the more you may feel that you need an absolute "creator" to support the existence of all this.
On Sunday, Xu Qiu began to test another exciton diffusion distance.
There are many methods for this test. A few days ago, he searched the literature and found a total of four methods, and finally chose to use a highly oriented pyrolytic graphite (HOPG) substrate to test the fluorescent signal.
The reason is also very simple. Wei Xingsi did this experiment before when he was in a beautiful country. Xu Qiu directly copied Mr. Wei’s skills. The proficiency is quite satisfactory. The fourth level is 0%. The possible reason is that Mr. Wei did it at the time. Not many times, or because of not conducting experiments on the front line for a long time, proficiency does not increase but decreases.
But in any case, even if you only have second-level and third-level proficiency, it is much stronger than other methods. After all, Xu Qiu has a system, and the system image is always more vivid than the text description in the reference.
After consuming several points, Xu Qiu checked the experimental operation of the fifth-order 100% "HOPG method to test the exciton diffusion distance".
The operation method does not seem to be difficult, just spin-coating the sample on HOPG, then test the fluorescence signal of samples of different thickness, and finally perform fitting.
The experimental principle is also relatively simple. Once the excitons generated by the optoelectronic materials are exposed to light, they will be quenched with a probability of over 99%, and the energy contained in them will be released in the form of heat. The ions have recombined before they diffuse to the HOPG surface, and a fluorescent signal will be emitted.
In other words, if the exciton diffusion distance of the material is relatively long, such as more than 100 nanometers, the fluorescence signal of the sample film about 10 nanometers will be almost 0, because the excitons can diffuse 100 nanometers on average, while the film only has At 10 nanometers, during this process, the probability of excitons moving to the position of the boundary HOPG is very high, and the excitons are all "eaten" by the HOPG, so it is naturally unable to generate a fluorescent signal.
On the contrary, if the exciton diffusion distance is relatively close, such as 10 nanometers, then the film of about 10 nanometers can naturally generate fluorescence signals. At this time, the fluorescence quenching efficiency is about 50%, that is, the luminous intensity is half of the normal intensity. .
In the afternoon, the HOPG that Xu Qiu bought in advance has been delivered by express to the concierge on the second floor of Caiyi.
HOPG refers to pyrolytic graphite, which is a new type of graphite with properties close to single crystal graphite after high temperature treatment.
As the name suggests, this kind of graphite is highly oriented, and a very smooth, high-conductivity surface can be obtained through experimental operations. The surface can be inspected in a scanning tunneling microscope or used as a substrate for other materials under study.
According to the different mosaic angles (mosaic diffusion angles) of HOPG, it can be divided into three levels: A, B, and C.
Grade A has the smallest inlay angle, usually around 0.5 degrees, with the best quality and closest to the properties of single crystals, and of course the most expensive.
The C-level inlay angle is the largest, usually above 1.5 degrees, the quality is the worst, but the price is the cheapest.
The inlay angle of grade B is between A and C, usually around 0.8 degrees.
Xu Qiu shopped around on the Internet and finally found a domestic HOPG manufacturer.
The smallest size they sell is 10101 mm in length, width and height, which is an area of ​​one square centimeter and a height of one millimeter.
With such specifications, it costs 2,000 yuan for A-level and 700 yuan for C-level.
If the specifications are larger, such as 20201mm in length, width and height, the price is 8000 yuan for the A grade, and 4000 yuan for the C grade. If it is 20202 mm in length, width and height, the price will be Tens of thousands.
Of course, regardless of its small size, you can use it dozens or hundreds of times after you buy a small piece of HOPG. Otherwise, if this thing is a one-off, no one can use it.
After all, Xu Qiu needs to prepare more than a dozen samples to test the exciton diffusion distance of a system.
Feeling about the price of the scientific research circle, Xu Qiu finally chose the smallest specification C-level HOPG, and first tried the water with a 700 yuan bargain.
In theory, what he is doing now is an ordinary fluorescence test, which mainly uses the quenching effect of graphite on excitons. The requirements for the substrate should not be as high as that of a scanning tunneling microscope.
Xu Qiu took the courier from the concierge, looked at the courier box, and said casually, "This courier box is so casual, it's just an ordinary small paper box."
After that, he put on disposable PE gloves and began to unpack the express. There was a centrifuge tube inside, and HOPG was wrapped in paper and placed inside.
Unpacking the wrapping paper, the HOPG you got is similar to the description previously seen on the Internet, with a 10101 mm specification, one side is dark gray, the other side is bright gray.
The dark gray side is the reverse side, and the bright gray side is the front side.
HOPG looks like a chip or SD memory card in early mobile phones.
However, Xu Qiu knew that this stuff was high-purity carbon.
Graphite is simply carbon.
With HOPG, the next step is sample preparation.
However, before spin-coating the samples, the "thick" HOPG surface needs to be peeled off to obtain a fresh, smooth surface substrate.
There are some non-mainstream methods, such as direct peeling with tweezers, this is more difficult, and it is easy to damage the HOPG surface.
The more mainstream method is to use tape to stick directly on the HOPG, and then tear it apart.
Although this method is relatively safe, Xu Qiu did not rashly try it in reality, but first went to the simulation laboratory and tried it with 3M tape.
At the beginning, there will be uneven surfaces, or barbs.
After repeated attempts, Xu Qiu finally mastered the technique.
That is to press the tape as tightly and evenly as possible, so that the probability of getting a smooth surface is higher, because if some part is not stuck, it will stay on the surface of the original HOPG body and form barbs.
After peeling, there will be a layer of broken graphite flakes on the tape, and a fresh, smooth surface will be formed on the HOPG matrix.
This method of sticking with tape sounds more "earth", not so tall and not very scientific, but it is precisely the first method of preparing graphene discovered at the beginning.
In 2004, two professors, physicists Andre Gaim and Konstantin Novoselov of the University of Manchester in Great Britain, taped the graphite to the graphite and then tore it off and found that a thin layer was stuck on the tape. Graphite flakes.
This book is nothing new, but they had a whim and took the second piece of tape to stick the remaining graphite flakes on the first piece of tape. At this time, the two pieces of tape were glued together, and then the two pieces of tape were torn apart. It turns out that the remaining graphite flakes on the tape have become thinner~EbookFREE.me~ At this time, many people will feel bored, is it just tearing the tape, and the two professors found that the graphite flakes have become thinner, and they held the third one. Use tape to stick the graphite on the second piece of tape, and then use the fourth tape to stick three pieces of tape...
In this way, sticking and tearing the tape again and again, and finally they got tiny graphite flakes that couldn't be thinner, it was only a layer of atom thick.
This is a single layer of graphite, also known as graphene.
After the birth of single-layer graphene, many scientists are actively exploring the ability to produce larger-scale and higher-quality graphene.
In addition to tape sticking, there are many other graphene preparation methods, such as micro-mechanical peeling method, chemical peeling method, chemical vapor deposition method and so on.
Moreover, the amazing material properties of graphene have also caused extensive research by a large number of scientists in the past decade.
In the end, those two professors also won the 2010 Nobel Prize in Physics.
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