Stringlight Research Institute, basement level one, Carbon‑Based Materials Research Center.
The air here was profoundly different from the floors above, filled with server‑fan hums and keyboard clacks. A near‑sacred silence enveloped the entire space; only occasional, almost imperceptible motor‑driven sounds from ultra‑high‑precision equipment, or the faintest hiss of liquid nitrogen cycling through pipes, reminded people that time had not frozen here. Air passed through multiple filtration layers, so clean it carried hardly a speck of dust; constant low temperature made each breath crisp and cool. This was Xiuxiu's newly opened battlefield—a microscopic world deeper and more fundamental than mastering extreme ultraviolet light.
Xiuxiu stood before an observation window of a core laboratory, wearing a specially‑made anti‑static clean‑room suit, lending her vivid features an unusual solemnity. Through thick borosilicate glass, she gazed at the complex equipment running inside—a deeply modified ultra‑high‑speed centrifuge. Unlike lithography machines, massive and filled with mechanical beauty, it more resembled a slumbering metal giant clam; within it, at over one hundred thousand revolutions per second, a silent yet crucial screening was underway.
Yet the real‑time data jumping on the display beside the device poured cold water repeatedly on any hope just ignited. The curve representing semiconductor carbon‑nanotube purity, after a brief, encouraging climb, stubbornly lingered again around 98.7 percent, like an exhausted climber helplessly facing that last one‑percent‑plus yet chasm‑like vertical cliff.
99.9999 percent. Six nines. This seemingly simple number stood like a wall of sighs before the dream of carbon‑based chips, cold and cruel.
Carbon‑based chips—this was the next milestone Xiuxiu had charted for Stringlight Research Institute, indeed for humanity's entire semiconductor industry, after successfully summiting High NA EUV lithography technology. Some internally even called it the "ultimate answer in the post‑Moore era." Its core concept was using carbon nanotubes—hollow tubular structures formed by rolling a single layer of carbon atoms, only one to two nanometers in diameter—to replace traditional silicon material as transistors' core channels. Theoretically, carbon nanotubes possess carrier mobility far surpassing silicon, meaning electrons shuttle faster within them, with lower energy consumption; plus their excellent thermal conductivity could solve chips' increasingly severe heat issues. A processor based on carbon‑nanotube arrays could achieve performance‑per‑watt ratios tens or even hundreds of times that of current top silicon‑based chips, enough to support truly strong artificial intelligence's computing demands, or extend mobile device battery life to weeks.
But theory's beauty is always shattered by reality's roughness. And reality's first, deadliest obstacle comes from carbon nanotubes' own love‑hate "chirality."
"Chirality"—a term borrowed from life sciences describing an object's inability to perfectly superimpose with its mirror image—is cleverly borrowed to define carbon nanotubes' structure. Imagine rolling a sheet of graphene—a perfect hexagonal grid—into a seamless cylinder at different angles and directions. This rolling manner—specifically, the rolling vector (m, n)—determines the nanotube's "chirality." Precisely this seemingly tiny rolling‑style difference endows carbon nanotubes with entirely different electrical properties.
When the rolling vector satisfies m - n = 3k (where k is an integer), the resulting carbon nanotube exhibits metallic character, like an ultra‑fine metal wire. When m - n ≠ 3k, it behaves as a semiconductor—exactly what transistor fabrication requires. The problem is: whether through arc‑discharge, laser ablation, or currently mainstream chemical vapor deposition, mass‑produced carbon nanotubes resemble a kaleidoscope containing countless "chirality" varieties, shaken randomly by God. Metallic and semiconducting nanotubes mix together, entangling each other, nearly inseparable.
Worse, these different‑chirality carbon nanotubes have minimal differences in physical and chemical properties, especially density and size. Attempting to separate them efficiently, at high purity, is as difficult as precisely picking all exactly‑ten‑centimeter‑long spaghetti strands from a pot of thoroughly cooked, identical‑composition pasta while ignoring those 9.9‑centimeter or 10.1‑centimeter ones.
Xiuxiu's team currently was assaulting the method known as the "gold standard" for purification—density‑gradient ultracentrifugation. Its principle, macroscopically understood, resembles making cocktails where different‑density liquors naturally form layers. They first prepared a special medium in centrifugation tubes—a gradient solution where density varies continuously from tube bottom to top, typically made of heavy liquids like iodixanol. Then, they carefully loaded crude carbon‑nanotube mixtures, appropriately surface‑modified chemically to enhance dispersibility, atop the gradient liquid.
When the ultra‑high‑speed centrifuge starts, generating hundreds of thousands times gravity's centrifugal force, all matter within the tube "sediments" toward the tube bottom according to its own "sedimentation coefficient"—a physical parameter closely related to particle size, shape, and density—and stops at the gradient‑liquid layer matching its own density, eventually forming one or more bands, thick or thin, in different colors.
Ideally, semiconducting carbon nanotubes would, due to subtle structural differences, possess slightly different sedimentation rates and equilibrium densities than metallic ones, thus resting at different heights in the gradient liquid. Through fine‑tuning gradient‑medium formulation, centrifugation speed and time, theory said separation could be achieved.
"Theoretically…" Xiuxiu silently repeated the words, a bitter trace curling her lips. The curve on screen refusing to rise further was direct visualization of the vast chasm between theory and reality. They had optimized nearly every optimizable parameter: gradient‑liquid density range, centrifugal force magnitude and duration, carbon‑nanotube dispersion concentration and surfactant type, even temperature‑control precision during centrifugation… Young Ph.D.s in the team almost treated the centrifuge as a lover, day‑and‑night guarding, recording every minute change, trying every conceivable improvement.
The result: they could raise semiconductor carbon‑nanotube purity from initial below 70 percent, all the way to near 99 percent. This itself was breakthrough‑level progress publishable in top journals. But 99 percent meant nothing for chip manufacturing.
Chips are Moscow of the digital world, the ultimate embodiment of order and precision. Hundreds of billions of transistors must faithfully execute "on" and "off" commands according to preset logic, allowing zero error. Even if just one percent, even one‑tenth percent metallic carbon nanotubes mix within semiconducting arrays, it's like burying countless tiny, unpredictable conductive channels in insulating dams. They would leak electricity when they shouldn't, destroying transistors' on‑off ratios, introducing noise, causing logic errors, ultimately collapsing entire chip functionality. Six‑nine purity was the bottom line ensuring that, when fabricating chips containing hundreds of billions or even trillions of carbon nanotubes, statistically determined fatal defects caused by metallic tubes remain at an acceptable level.
"Teacher Xiuxiu," a slightly hoarse voice sounded behind her. It was core team member Dr. Chen, a materials expert, dark circles under eyes, face etched with fatigue and frustration. "Results from the thirty‑seventh parameter combination batch are out… still no success. Highest purity stabilizes fluctuating between 98.6 and 98.9 percent. We tried your last suggestion—introducing specific‑frequency ultrasonic pre‑treatment before centrifugation, hoping to disperse some bundles—but effect was minimal, may have introduced new structural defects."
Xiuxiu turned, looking at Dr. Chen and several other researchers behind him, also showing weariness. They were backbone members following her since the lithography machine project, experiencing DUV light‑source power‑instability anxiety, EUV mirror thermal‑distortion despair, and ultimate success's tear‑fulfilling ecstasy. They were accustomed to assaulting massive, complex yet clearly‑targeted engineering fortresses. But this carbon‑nanotube purification problem before them resembled intangible fog; you know the way out lies ahead yet cannot find the beam piercing it. This sense of defeat felt more enervating than facing any specific lithography‑machine technical bottleneck.
"I've seen the data." Xiuxiu's voice was calm, showing little emotion. "Thank you for your hard work."
She walked to the nearby electronic whiteboard, densely covered with formulas, parameters, and mind‑maps. She picked up the touch‑pen but didn't write immediately; just lightly tapped its tip on the node representing "chirality separation" at whiteboard center.
"Have we… taken the wrong path?" a young researcher muttered softly, voice small yet clear in the lab's silence.
That sentence pierced the suffocating air like a needle. Yes, does density‑gradient centrifugation itself have insurmountable theoretical limits? Like using ever‑finer sieves cannot separate grains of identical size. Should we completely abandon this path, turn to other possible technical directions? Like utilizing certain biomolecules' selective binding with specific‑chirality nanotubes? Or, develop a brand‑new separation technology based on electric‑field or magnetic‑field effects? Or even, could we control growth at source, directly produce single‑chirality carbon nanotubes? Although that sounded more like fantasy.
Various thoughts swirled in team members' hearts; doubt's emotion began spreading subtly. Sustained high‑intensity investment, endless repetitive trial‑and‑error, were gradually eroding their edge and confidence.
Xiuxiu's gaze slowly swept each young or no‑longer‑young face, seeing confusion, fatigue, and that barely perceptible wavering in their eyes. She remained silent a moment, then, surprising everyone, smiled faintly. The smile was light, like a breeze dispersing some gloom.
"Remember when we started immersion lithography?" Her voice wasn't loud but held peculiar penetrating power. "Everyone said adding a drop of water between lens and silicon wafer was fantasy. Water's fluctuations, bubbles, contamination, refractive‑index variation with temperature… any one problem seemed enough to sentence this technical route to death. What did we have then? Besides fragmentary concepts brought back from ASML, almost nothing."
She paused, eyes seemingly traversing time‑space back to those days in a simple lab, debugging water‑droplet control systems repeatedly before the initial second‑hand DUV lithography‑machine prototype.
"Back then, we also faced a process starting from zero, even from 'negative.' No ready‑to‑use technology, no reliable supply chain, even few people believed we could succeed. But we came through." Her tone remained steady, but the power it contained made everyone straighten their backs. "What did we rely on? Not because we knew all answers from start, but because we believed problems must have answers, and were willing to try the dumbest method—testing one parameter at a time, eliminating one possibility at a time."
She turned her gaze back to that silent centrifuge, the discouraging curve on screen.
"Now, the carbon‑nanotube purification we face, in some sense, is more fundamental and difficult than lithography machines. Because it touches material's origin, deeper underlying physical and chemical laws. We might not be able to predict results through precise modeling and simulation like designing lithography‑machine optical systems. We face a high‑throughput, statistical separation process filled with complex fluid dynamics, surface chemistry, and colloidal science we haven't fully understood."
"But," she emphasized, eyes sharpening, "this doesn't mean we have no path forward. It only means we need to return to our original heart, back to that 'starting from negative' state. Forget we once mastered extreme ultraviolet light, forget we once stood atop world lithography technology. Here, at carbon‑based chips' starting point, we and any laboratory worldwide just entering this field are all explorers, all students."
She took the pen, drew a forceful dot below the horizontal line representing purity target on whiteboard.
"We are here now," she pointed at that dot, "far from the goal. Density‑gradient centrifugation may not be the final answer, or not the complete answer. But it's the most powerful tool we currently hold. Until we find better tools, what we should do is not doubt and abandon, but use it to its extreme."
She began rapidly writing on whiteboard, listing several new thinking directions:
"First, have we overly focused on macroscopic separation conditions while ignoring carbon nanotubes' microscopic state within dispersions? For example, do different‑chirality nanotubes have subtler differences in surface charge distribution, binding energy with surfactant molecules? Can we introduce more advanced characterization methods—like in‑situ spectroscopy or cryo‑electron microscopy—to observe nanotube behavior during centrifugation in real time?"
"Second, is the centrifugal field itself 'smart' enough? Our current centrifugation process is static, uniform. Could we design dynamic, gradient‑varying centrifugal fields? Or, couple other physical fields during centrifugation—like a specific‑frequency alternating electric field—leveraging minute differences in dielectric constants of different‑chirality nanotubes to amplify differences in their sedimentation behavior?"
"Third, regarding the medium. Iodixanol is mainstream currently, but is it the optimal choice? Could we screen or design a brand‑new gradient medium with higher 'recognition' for carbon‑nanotube chirality? An 'intelligent' medium capable of actively engaging in weak yet specific interactions with particular‑chirality nanotubes?"
Each direction she wrote pointed toward a path requiring massive time and effort to verify, each filled with uncertainty. But her eyes showed no hesitation, only a pure curiosity and resolve belonging to scientific explorers.
"Dr. Chen," she turned to the materials expert, "you lead, organize personnel, focus on assaulting the first direction. Contact the institute's characterization‑analysis center; we need the most cutting‑edge equipment support."
"Xiao Li," she addressed the young researcher who raised doubt earlier, "you're adept at simulation. The second direction—about composite physical fields concept—you're responsible for preliminary research and feasibility analysis. Submit reports directly for any computational resources needed."
"Professor Wang over there," she looked at another senior researcher, "he has deep expertise in polymer and colloidal chemistry. Please ask him to assist us, develop screening and design work for new gradient media targeting the third direction."
She issued instructions clearly and methodically; the team's somewhat scattered attention re‑coagulated. Goals were decomposed; tasks clarified. Though the road ahead remained fog‑shrouded, at least they knew where to step next, how to swing their picks against this hard‑rock reality.
"Comrades," Xiuxiu finally said, voice not loud but firm, "the carbon‑based chip path is our own choice—Stringlight's core strategy for the next decade, even two decades. It's difficult, possibly harder than any challenge we've faced before. But precisely because it's hard, it's worth conquering. If we only did easy things, Stringlight wouldn't have today. Don't fear returning to 'starting from negative.' Exploring the unknown is our mission."
She gestured, "Alright, everyone get moving. Send me the detailed analysis report of the thirty‑seventh batch data. Also, notify the project group: tomorrow morning eight o'clock, meet here. I want to hear your preliminary thoughts on these three new directions."
Researchers responded affirmatively, faces showing renewed fighting spirit replacing fatigue. They dispersed quickly, returning to stations or computers; the lab again filled with dense keyboard tapping and low discussion voices.
Xiuxiu didn't leave immediately. She walked again to the observation window, quietly gazing at that centrifuge. The curve on screen remained stubborn, but what she saw in her eyes was no longer merely current failure. She saw the relit light in team members' eyes, the new ideas awaiting verification on the whiteboard, that winding yet inevitably future‑leading path.
She recalled Mozi occasionally half‑jokingly saying her technological Long March was a "heroic epic." Previously she always felt this description too grand, even somewhat pretentious. She was just an engineer, a problem‑solver. But now, standing at the frontier of this more primitive, deeper microscopic‑material territory, she suddenly understood somewhat.
Epics aren't always iron‑horsed, swallowing mountains and rivers. More often, they are the day‑after‑day, tedious yet tenacious assaults on seemingly insignificant yet impregnable technical barriers in unknown laboratories. They are the courage to calmly analyze data, adjust parameters after countless failures, then tell oneself and the team "start from negative."
Carbon‑nanotube purification was merely the first formidable pass on the Long March road. Beyond lie harder trials: nanotube‑array alignment, electrode contacts, device integration… countless barriers.
But she knew she wasn't fighting alone. Behind her was this team she personally nurtured—hard‑battle‑capable. Behind her was Stringlight Research Institute's globally‑top‑tier R&D platform and resources. Beside her were partners like Yue'er, of extraordinary wisdom, perhaps providing unexpected inspiration at most basic physical‑chemical principles. Supporting her was Mozi's controlled capital power—enough to sustain long‑term, high‑intensity investment—and his precise judgment of future trends.
The "iron triangle" they constituted was the most solid rear‑guard in this unknown territory.
Xiuxiu inhaled deeply the clean, cool air, turned, and walked away from the observation window with firm steps. She needed immediately return to her office, carefully review those piled‑high data and analysis reports. Night remained long, and conquering this new material continent's journey had just begun. That 0.0001 percent purity gap, like the universe's birth‑singularity, contained infinite possibilities, awaiting ignition by her will and wisdom, and the entire team's unceasing efforts, eventually erupting with brilliant light illuminating the new era. This light would originate not merely from mastered physical light, but from created and tamed matter itself. This was a path richer in imagination, more challenging than chasing Moore's Law—and she was already on it.