Chapter 1540 Atomic Array

A few hours later, late that night.

Chang Haonan leaned over a precision in-situ optical measurement device, staring through the observation window at the changes in the light spot projected by the internal laser interferometer.

Li Yabo was operating a computer at the side, and a curve showing the change of the material's refractive index with the laser wavelength was drawn on the screen in real time.

"Teacher, look, sample 12A-03 now shows a very clear negative refractive index window, right in this near-infrared band." Li Yabo pointed to the curve on the screen that suddenly dropped into the negative value area.

Chang Haonan nodded slightly, but the joy in his expression was fleeting: "What about the others?"

“12A-01和12A-04都失败了，没有出现负区。12A-02刚开始有微弱负值，但很快就消失了……”栗亚波快速切换着数据流，“12A-05和12A-03出现的时间差不多，但波动情况很不乐观……”

As reported by Li Yabo, among the six metal-based thin film samples that had just completed strong magnetic field polarization treatment, only four temporarily showed negative refraction.

In three of them, like popped bubbles, the negative refraction signals on the screen fluctuated violently within a few minutes, and finally disappeared completely, with the curve returning to the mediocre positive area.

Only one sample, numbered A3, maintained its negative refractive property, although its intensity was slowly decreasing.

"It's been thirty minutes, and A-3 is still holding on. This is one of our best results in recent times." Li Yabo took off his glasses and rubbed both sides of his nose.

His voice was a little tired, but mostly helpless. "We tried to repeat the magnetization failure samples, and each time the result was... like a lottery."

“The results are not reproducible, are they?”

Chang Haonan knew that the development of negative refractive index materials was not a one-day task, nor was it the focus of his work in the previous stage, but he still read all the routine reports every month carefully.

"Yeah..." Li Yabo opened a folder on the computer, which contained a large number of data files named after sample numbers.

I scrolled the mouse wheel several times but couldn't get to the bottom.

"Since I took over this project, I have conducted more than 900 effective tests, and only two of them lasted for seven days, and of course they eventually failed." He sighed, "The more troublesome problem is that the specific results are different every time. A sample that successfully showed negative refraction properties last time may fail to convert in the next test. Sometimes it is impossible to analyze it."

"Pull out all the transmission electron microscopy (TEM) characterization results for those failed and relatively stable samples." Chang Haonan stood up and stretched his body briefly, "Compare the differences between these two types of samples."

Li Yabo quickly operated the computer and opened several imaging files.

Chang Haonan came closer and wanted to see the differences in the microscopic structure.

But about half of the images were not clear, making it difficult to see anything of value.

“The imaging effect is indeed not ideal.” Li Yabo took the initiative to explain, “In fact, for the most unstable samples, the characteristics are basically gone after the in-situ refractive index measurement, and there is no chance to do TEM at all... All we can do is to persist for a relatively long time.”

High-resolution TEM images flashed quickly on the screen, showing the artificially induced lattice structure with specific periodicity inside the material.

Chang Haonan browsed quickly, brows furrowed.

Although the image resolution is high, those truly free and unlocalized atoms or electrons are invisible in the static TEM image, and their dynamic defects or arrangement flaws cannot be captured.

The "defect" contrast he wanted to observe was almost non-existent in the existing characterization results.

"Teacher, do you have a new idea?"

Li Yabo was keenly aware of Chang Haonan's surging thoughts.

"Hmm..." Chang Haonan nodded, "Just now in the office, I said that the idea of ​​artificially inducing a periodic lattice is similar to building blocks on the beach, which will fall down in a gust of wind."

Li Yabo agreed: "Indeed, including the sample taken from the engine at the beginning, it completely lost its characteristics after about twenty days."

"Then." Chang Haonan's tone became excited, "Why don't we change our thinking? Why not let the materials organize themselves?"

"Organize it yourself?"

Li Yabo repeated doubtfully.

"Yes!" Chang Haonan pulled a piece of paper from the side, "Use the light field itself! Use coherent light of a specific wavelength, a specific mode, and sufficient strength to 'drive' the atoms or electrons in the material! We don't set the lattice positions for them artificially, but let them adjust their states spontaneously and collectively through interaction under the action of the light field, forming a dynamic, stable superlattice that resonates with the light field!"

As he spoke, he drew several schematic diagrams of photon excitation on paper:

"Think of Bose-Einstein condensation! Think of superfluidity! These are all macroscopic quantum phenomena of 'collective action' of particles at low temperatures!"

His thoughts became clearer and his speech became faster:

"Can we induce a similar... optical superfluidity in a specific material system under the command of the light field? Let the atoms no longer fight each other, but respond to light as a whole? The medium formed in this way can theoretically be completely free of manufacturing defects and be original and pure! Its optical properties may far exceed our current imagination!"

This idea was so bold and subversive that Li Yabo was stunned for a moment.

Fortunately, he quickly came to his senses and realized that this idea really broke away from the traditional framework of material design and went straight to the core of atomic manipulation!

However, constructing an atomic array is extremely difficult, and at least currently there is no method with a high success rate.

Therefore, it is unlikely to directly verify the feasibility of Chang Haonan's conjecture.

Only the other way around.

"In other words, we are now trying to prove that the instability of the sample is caused by defects at the atomic level?"

"Yes, that's the key!" Chang Haonan clicked twice at the blurry electron microscope image on the screen. "It would be best if we could directly see that in the more unstable samples, the atoms are more chaotically arranged and have more defects, while the relatively stable ones have fewer defects. However, the current transmission electron microscope results cannot meet this requirement."

TEM is inherently incapable of characterizing free atoms, and the imaging results are also projected onto a two-dimensional plane, making it difficult to meet such stringent and unique requirements.

The two of them fell into a brief silence. The only sound in the laboratory was the low hum of the instruments.

"Perhaps... Atom Probe Tomography (APT)?" Chang Haonan suddenly spoke up, breaking the silence. "It can preserve the composition and position information of individual atoms! Yabo, have you done APT characterization before?"

At least in the recent reports, he did not remember any APT-related results.

"We have only done this on a few early batches of samples... APT is too expensive and time-consuming, and it only gives the three-dimensional position and composition of atoms, without lattice structure information, which is not very helpful for our previous research." Li Yabo scratched his head, "Fortunately, the data is still stored."

"Quick, adjust it!" Chang Haonan ordered immediately, "Compare it with the transmission electron microscopy results of the same sample!"

The data was quickly called up and displayed in two windows side by side: on the left was a three-dimensional point cloud of atomic positions output by APT, with colorful images representing different elements; on the right was a transmission electron microscope image of the same sample area.

The two stared with bated breath, trying to superimpose the two images.

However, disappointment soon struck.

The APT point cloud image has obvious local distortion and stretching in three-dimensional space, which cannot be perfectly matched with the lattice structure shown in the transmission electron microscope image.

"The distortion is too severe," Li Yabo frowned. "It doesn't match at all... Even if we select a few zero points and stretch them, the result will be completely unreliable."

The room fell silent again.

"How about... try to use the algorithm to correct the APT data... and try to fit it?"

Li Yabo looked at Chang Haonan beside him with hope.

In his eyes, his boss's ability in the field of algorithms is unparalleled, and he has turned decay into magic countless times.

However, this time, Chang Haonan shook his head:

"It's difficult... The two devices are different, the sample preparation process is different, the measurement order is also different... The four-dimensional coordinate system is different. Correcting after the fact is like shooting at a bull from a distance. The error will only get bigger..."

Having said this, he suddenly paused.

Soon, a new idea emerged!

"Unless..." Chang Haonan took a deep breath, "Unless the transmission electron microscope and the atom probe can be integrated into one device..."

"what?"

Li Yabo was not an expert in the field of microstructure characterization, and he was completely stunned when he heard this proposal.

"After completing high-resolution structural imaging under the transmission electron microscope, we can directly perform atom probe tomography on the same sample, at the same position, and in the same coordinate system." Chang Haonan gestured on the screen, "In this way, we can use the clear lattice image of TEM as a map to correct the local distortion of APT three-dimensional reconstruction and output a superposition result with perfect spatial matching!"

Li Yabo has become accustomed to the feeling of knowledge flowing through his cerebral cortex. He quickly ignores the details he does not understand and quickly thinks about the feasibility of the technical path:

"But in terms of engineering..." He looked embarrassed. "The existing TEM and APT in our laboratory are all imported... Domestic TEM is just starting out, there are only a few models, and the resolution is not top-notch. As for the three-dimensional atomic probe... there is no commercial model in China. Where can we customize such a super device?"

Three of the four giants in microstructural characterization are from North America and one is from Japan.

Therefore, although the Wassenaar Arrangement was in name only more than a decade ago, China has only been able to obtain products but has found it difficult to access core technologies, and its research started relatively late.

"The equipment is not the problem!" Chang Haonan said firmly, "Although the research on negative refractive materials is top secret, this equipment is actually not that sensitive..."