The Gap Between Top Students

The next morning, dawn had barely broken.

Knock, knock, knock!

Li Dong was awakened by a burst of knocking. Still groggy, he got out of bed and opened the door.

Then he saw a large face with dark circles under its eyes leaning toward him.

"Li Dong, how did you sleep last night?"

Zheng Hua asked, forcing himself to sound alert.

This was actually his first time attending the second round of a physics competition as well. There was nothing he could do about it—No. 7 High School's students had never given him such an opportunity before.

So he was even more nervous than Li Dong.

"Well... you need to relax. I know this is your first time competing offline, so don't get nervous. With your ability, as long as you perform normally, making it into the finals definitely won't be a problem."

Li Dong rubbed his sleepy eyes. Seeing Zheng Hua looking as though he were facing a formidable enemy, he found it rather amusing.

Nervous?

What a joke.

Right now, all he could think about was the twenty-thousand-yuan scholarship. He had even planned out how to spend it in his dreams.

First, he would buy his mother a new phone. He had heard Huawei's phones were pretty good, though HarmonyOS apparently still had not properly adapted to the Qidian App.

Then he would buy himself a computer, making it easier to read some cutting-edge foreign papers. As for the rest... he would decide later.

Thinking about how he was about to collect the money, Li Dong was not only not nervous—he was even a little excited.

"Don't worry, Teacher Zheng. I'm not nervous."

After washing up, Li Dong followed Zheng Hua downstairs for breakfast.

In the elevator, Zheng Hua was still going on and on.

"Once you enter the exam room, check the paper first. If you run into something you can't do, don't stubbornly get stuck on it. Do the easy ones first..."

Li Dong could only nod along, letting it go in one ear and out the other.

By the time they reached the restaurant, quite a few students and teachers were already having breakfast.

Li Dong spotted the people from Jiangcheng No. 6 High School at a glance. One bespectacled boy glanced at him, then ignored him and continued eating the breakfast on his tray.

Zheng Hua naturally saw them too, but this time he did not go over to exchange pleasantries. He merely nodded at them in greeting.

Then he led Li Dong to a seat in the corner.

Just then, a commotion suddenly broke out near the restaurant entrance.

A middle-aged female teacher entered, leading a grand procession of more than twenty students.

All of them wore matching blue-and-white school uniforms. Though they held trays in their hands, each one looked calm and composed. Some were even carrying English vocabulary books and memorizing words.

Li Dong clicked his tongue. Memorizing English vocabulary during a physics competition? That level of showing off belonged at Jiang Yizhou's table.

Teachers and students from the other schools in the restaurant could not help stopping what they were doing.

"Chengdu No. 7 High School?"

Someone spoke in a low voice.

Li Dong took a bite of his bun, curious.

"Teacher Zheng, is that Chengdu No. 7 High School?"

Zheng Hua nodded and lowered his voice.

"There are only a little over a hundred people in the entire province who made it into the second round this time, and they alone account for more than twenty of them."

Zheng Hua sighed, his voice carrying both envy and helplessness.

"And you should know that these twenty-plus aren't even their very best students."

"No. 7 High School's real elite students are aiming for gold medals in the International Orsay. Their dream is genuinely to become scientists. They don't even think much of commercial cup competitions like this."

After hearing that, Li Dong nodded, becoming wary.

They were here to steal my twenty thousand yuan!!

After breakfast, the second round of the Huaxuan Cup arrived as scheduled.

The examination rooms this time were three multifunctional conference rooms in the hotel. Nearly two hundred contestants lined up according to their admission ticket numbers. After strict identity verification and security checks, they entered one after another.

Li Dong sat toward the back of the middle section.

The Huaxuan Cup exam paper was mainly divided into multiple-choice questions, fill-in-the-blanks, calculations, and a final high-value "experimental design question."

Li Dong briefly skimmed through the entire paper.

"This is the difficulty level of the Huaxuan Cup?"

Overall, it was fairly average.

And as expected, the questions leaned more toward practical applications, with plenty of traps.

For example, the third multiple-choice question:

[A certain new-energy vehicle uses an electromagnetic eddy-current braking system. When its disc-shaped metal brake rotor spins rapidly in a magnetic field, determine the relationship between braking torque M and angular velocity ω.]

At first glance, this question seemed to require integration, but it actually was not necessary at all. As long as one grasped the two key points—"induced electromotive force E ∝ v ∝ ω" and "Ampere force F ∝ I ∝ E"—one could easily derive that braking torque M ∝ F ∝ ω.

So the answer was B, a linear relationship.

There was also a calculation problem about liquid cooling in a data center.

[Given the specific heat capacity and flow rate of a coolant, determine the thermal resistance network model when the chip surface temperature reaches steady state.]

The question looked flashy, but its essence was simply the first law of Thermodynamics combined with the thermal-electric analogy of Ohm's law.

Temperature difference corresponded to voltage, heat flow corresponded to electric current, and thermal resistance corresponded to electrical resistance.

Li Dong drew the equivalent circuit diagram and quickly calculated the junction temperature.

The more he wrote, the smoother it became...

Until he flipped to the experimental question on the final page.

Li Dong had only given it a rough glance earlier and had not thought much of it. But now, after reading it carefully...

"This question..."

"Did they sanitize and release one of the core problems of lithography machines?"

The question was long and took up an entire page.

This question had three parts. Students with somewhat better grades could probably solve the first two, and they did not even need to be top students.

But the third question—if one called it difficult, it did indeed have Orsay-level difficulty, though not the very highest level.

However, the key was not merely solving it, but how to solve it in the best possible way.

Li Dong subconsciously looked around.

There were still forty minutes left until the end of the exam. Most contestants were still scratching their heads over the earlier calculation problems.

The contestant beside him looked especially young, at most a first-year high school student. He was currently biting his pen and staring blankly at the final question, with large sections of his paper still empty.

"Are kids these days really this competitive? He's already entering competitions like this in his first year?"

Li Dong grumbled inwardly, then withdrew his gaze and looked back at the paper.

Li Dong immediately started writing the first two questions.

[1. Determine the minimum resolvable linewidth δ of this lithography system?]

Solution: From the Rayleigh Criterion formula δ = 0.61λ/NA, substitute λ = 436 nm and NA = 0.35.

δ ≈ 0.76 μm.

[2. Describe two conventional industrial technical solutions and briefly explain their physical principles.]

This explanatory question actually tested the breadth of a student's knowledge. If someone only buried himself in textbooks all day, he might not necessarily know the answer.

But Li Dong had learned about related knowledge when studying university physics.

He had even specifically looked up news articles online.

One solution was to shorten the wavelength, such as using DUV deep ultraviolet light.

The principle was simple: δ was proportional to λ.

The other was to increase the numerical aperture, such as by using Immersion Lithography.

The principle was to use media such as water to increase the refractive index n, thereby increasing NA.

After finishing the first two questions, Li Dong paused at the third.

[3. Based on the core knowledge of high school wave Optics—interference and diffraction—design an innovative solution that can break through the Rayleigh resolution limit above without replacing the light source with one of a shorter wavelength and without using a projection objective.]

Li Dong stroked his chin.

How could one form an image without lenses? How could one improve precision without a shorter wavelength?

Several university-physics and even cutting-edge Optics solutions instantly flashed through Li Dong's mind: near-field optical scanning? Surface plasmons?

"No, those are too far beyond the syllabus. They'd be too troublesome to explain, and the question specifically requires high school wave Optics."

Very quickly, he thought of a solution.

Multiple overlay exposure could be used to precisely shift the mask for repeated superimposed exposures, producing finer lines. Or high-contrast photoresist could be used to improve the sharpness of pattern edges, indirectly increasing actual resolution.

Either approach would work. Just as Li Dong was about to write his answer onto the paper, Basic Physics Perception affected him, making him think of a problem.

"Wouldn't that be too divorced from reality?"

Huaxuan Technology was a company. It needed to make a profit. He could not approach the problem with laboratory logic; he had to consider it through the logic of industrial implementation and profitability.

So Li Dong stopped writing and began to think.

"To achieve the optimal solution under manufacturing constraints—low cost, high stability, and mass producibility..."

Time slowly passed. The first-year student beside him had already finished the experimental question, and he was thinking to himself.

"Sure enough, this difficulty isn't even as high as the questions our school sets itself. Only this experimental question required a bit of thought."

His name was Jiang Sheng, a student from Chengdu No. 7 High School. He had joined this cup competition to see just how vast the outside world really was.

"I'm not coming next year. It's boring."

Then, from the corner of his eye, he noticed Li Dong and the experimental question that Li Dong had yet to start writing.

"Ah, no wonder the teachers say there's still a gap between top students."

After that, he stopped paying attention to Li Dong and began checking his paper.

At this moment, Li Dong finally found an entry point.

He quickly wrote on the paper:

[Solution Name: Dual-Beam Laser Interference Maskless Lithography]

The core principle of this solution was based on wave interference. It did not use traditional lens imaging, but instead used two beams of light to interfere on the wafer surface and form fringes.

Having established the core concept, Li Dong quickly wrote out the derivation.

Suppose two coherent beams with wavelength λ symmetrically illuminated the wafer at an incident angle θ.

According to the condition for interference maxima, bright fringes occurred when the optical path difference Δx = kλ.

From the spatial geometric relationship, the period, or spacing, d of the interference fringes satisfied:

d = λ/(2sinθ)

Therefore, the minimum linewidth, or half-period, was:

δ_min = d/2 = λ/(4sinθ)

[Breakthrough Verification:]

As θ approached 90°, sinθ approached 1.

At that point, the theoretical limit could reach λ/4.

Compared with the traditional Rayleigh limit of 0.61λ/NA, where NA < 1 in air, this solution clearly broke through the conventional limit!

After finishing the derivation, Li Dong simply added the implementation steps: beam splitter splitting -> mirror alignment -> interference exposure.

Li Dong put down his pen and checked the time.

Fifteen minutes remained...