As a scientific researcher who has been engaged in the field of co-frequency spectrum, I certainly hope that co-frequency spectrum can win awards. (Whether it is a physics award or a chemistry award)
Why is the ice surface so slippery? At the earliest, scientists thought that the melting point of ice would decrease under higher pressure, causing the ice on part of the surface to melt into water, so the ice surface would be so slippery. However, after quantitative calculations, it was found that the reduction was far from enough to melt the ice, so this pressure was wrong.
Now scientists know the real reason, that is, there is a layer of water film on the surface of the ice. To prove the existence of this water film, the use of frequency spectrum technology is used.
The world's frontier 125 scientific questions have this problem: How to measure interface phenomena at the micro level?
In my opinion, the frequency spectrum technology is likely to be the answer to this question.
and frequency spectrum (sum frequency generation, abbreviation SFG) is a second-order nonlinear optical process. It was first discovered by Chinese professor Shen Yuanrang at the University of California, Berkeley in 1987.
Professor Shen Yuanrang
During the SFG process, matter interacts with light twice and releases an SFG signal. When two pulsed lasers are irradiated to the same sample at the same time, a light signal with a frequency equal to the sum of the two incident lights will be generated, which is the sum frequency spectrum signal. The frequency of the SFG signal is equal to the sum of the frequencies of the two incident lights, so it is called the sum frequency spectrum (Sum Frequency Generation, SFG). When the frequencies of two incident lights are the same, it is a special case, called frequency doubling (Second Harmonic Generation, SHG) - the frequency doubling is easier to build, and is widely loved in the field of biological imaging because of its simpler principle and easier to build.
Esig=χijk(2)E1E2 , where E represents the electromagnetic field. For a sample with central symmetry, when the two incident photoelectromagnetic field symbols change, the signal electromagnetic field symbols should also change.
Therefore, only samples with asymmetric centers will give the sum spectrum signal . Such samples with an asymmetric center include surface/interface, as well as biological samples with an asymmetric center and self-assembled structures, etc. When one of the two beams of light is infrared light , this process is called and frequency vibration spectrum , which can give the chemical bond vibration spectrum in an asymmetric center environment.
For example, for the water film on the surface of the ice, if the general infrared spectrum or Raman spectrum is used for measurement, the signal of the water film will be completely covered by the ice signal - after all, this water film is too thin. However, in the sum frequency spectrum, since the ice is a group of Ih points and has central symmetry, the SFG signal of bulk ice is zero. Then a strong interface signal can be observed at this time.
By measuring the SFG signal of ice at -28℃, the SFG signal of ice at -3℃ and the supercooled water signal of -3℃, scientists found that the SFG signal of ice at -3℃ is very close to the supercooled water signal of -3℃, so there is a water film on the surface of ice at -3℃. Later, through peak fitting, it was further calculated that there were about 4 layers of water molecules on the ice surface at -3°C.
-3℃ ice SFG signal is very similar to SFG of -3℃ supercooled water, but is far from the SFG signal of -28℃ ice
, and I have some achievements in the complex spectrum microscopy. My mentor Wei Xiong and I built the world's first Transient Vibrational Sum Frequency Generation Microscope and the world's first Fully Collinear Heterodyne Vibrational Sum Frequency Generation Microscope, and the articles were published on PNAS and ACS Photonics respectively.
Currently, the homofrequency spectroscopy technology has been widely used in the characterization of various soft matter and molecules self-assembly fields, achieving one result after another.
Although I think the mutual frequency spectrum technology is not mature enough at present, and the chance of winning the Nobel Prize is not particularly high, I believe it will surely flourish in the future.
