In Simple Terms
Silicon carbide is useful in powerful electronics, but its hard, resistant surface is difficult to smooth. Researchers designed a copper-containing material that helped a polishing liquid remove it much faster while leaving the surface very smooth. The results are promising, but more testing is needed before the method can be used in factories or applied to other materials.
A Useful Material That Resists Shaping
Crystalline 4H silicon carbide is used in power electronics and devices that operate at high frequencies. Its high thermal conductivity helps it handle heat, while its wide band gap and chemical stability make it suitable for applications that must withstand demanding conditions. But the same qualities that make it useful also complicate manufacturing: its surface is reluctant to react, so conventional chemical treatments cannot remove material quickly.
Chemical mechanical polishing, or CMP, relies on two processes working together: chemical reactions alter the outer layer, and abrasive particles mechanically remove it. Conventional polishing rates for 4H-SiC are often below 10 nanometers per minute. That means longer processing times and higher costs, as well as a risk of scratches or damage beneath the surface that could affect the quality of the finished device.
One possible chemical approach is to use Fenton reactions, which produce highly reactive hydroxyl radicals. These radicals can oxidize the resistant silicon carbide surface, converting some of it into an oxide layer that is easier to remove. Conventional iron-based catalysts, however, work best in strongly acidic conditions. Silicon polishing processes, by contrast, tend to use alkaline solutions, where hydrated silicon oxide dissolves quickly. Researchers are therefore looking for operating conditions that balance oxidation, oxide removal, and equipment compatibility without requiring excessive amounts of chemicals to adjust pH.
In a study published in Nature Communications in 2026, a team including Cao, Zhang, and colleagues tested a modified copper catalyst. Their findings suggest that controlling the atoms around copper can speed up the reactions involved in polishing without sacrificing surface smoothness.
Designing Copper’s Surroundings, Not Just Adding Copper
The team developed a material called Cu/ZIF-8, a metal-organic framework modified by incorporating copper into its structure. A metal-organic framework, or MOF, is a porous material made from metal-based units connected by organic molecules. The researchers were not simply adding copper to the polishing liquid. Instead, they altered the local arrangement of atoms around the copper so it could interact more effectively with hydrogen peroxide, a component involved in producing oxidizing radicals.
The researchers prepared the material through ion exchange and partial hydrolysis. Some copper atoms took the place of zinc in the structure, and oxygen-containing groups formed next to the copper, while the overall ZIF-8 framework remained intact. This created an asymmetric local environment with both nitrogen and oxygen bonds. Structural measurements indicated that 3.9 atoms were locally bonded to each copper site—close to four—but the bonds were not arranged symmetrically around it.
These atomic details affect how copper’s electronic orbitals interact with neighboring atoms. According to the study’s interpretation, the arrangement helps copper switch more rapidly between the Cu(II) and Cu(I) oxidation states, a cycle that is important for sustaining catalytic activity. The modified material’s specific surface area fell from 1715 to 1485 square meters per gram. Despite the decrease, it retained a large surface area that allowed it to react with hydrogen peroxide.
How the Team Tested the Idea
The researchers did not rely on a single test to confirm that they had made the material or to explain how it worked. They used X-ray diffraction, infrared techniques, electron microscopy, and elemental mapping to examine its structure, shape, and copper distribution. X-ray measurements also helped identify copper’s oxidation states and its local bonds with nitrogen and oxygen. The team used inductively coupled plasma optical emission spectroscopy to measure the amount of copper in the material and how much might leach into the liquid.
To track free radicals, the team used electron paramagnetic resonance, or EPR. They also performed theoretical calculations using density functional theory, comparing models of zinc-containing ZIF-8, a model in which copper replaced zinc, and another model with a copper site surrounded by three nitrogen atoms and one oxygen atom. This comparison made it possible to estimate the effect of copper itself, and then the additional effect of its asymmetric bonding environment. The computational model, however, represents a typical local site, while the actual material contains a range of different copper environments.
The researchers then added Cu/ZIF-8 to a polishing mixture containing hydrogen peroxide, abrasive silica particles, and a dispersing agent. They examined oxidation using electrochemical methods and surface analysis, then measured roughness with atomic force microscopy and white-light interferometry. These tests were needed to answer two separate questions: Did the catalyst actually speed up the chemical reaction? And did the higher removal rate leave the surface scratched or rough?
The Numbers Show a Jump in Activity and Speed
EPR tests showed that Cu/ZIF-8 produced far more hydroxyl radicals than the reference materials tested by the team. The measured concentration was 17.9 times that produced with iron oxide, Fe3O4; 27.1 times that produced with unmodified ZIF-8; and 131.1 times that produced by hydrogen peroxide alone. These comparisons suggest that combining copper with the modified atomic environment was associated with a substantial increase in radical production, rather than the increase being due simply to the presence of an oxidizing agent in the liquid.
The calculations offered a possible explanation for this behavior. The calculated energy gap fell from 3.67 electron volts in the ZIF-8 model to 2.53 electron volts in the Cu/ZIF-8 model. The calculated hydrogen peroxide adsorption energy also shifted from a positive value of 0.42 electron volts to a negative value of 0.66 electron volts, suggesting that hydrogen peroxide binds more favorably at the catalytic site. The energy required to break the oxygen-oxygen bond fell to 0.47 electron volts, consistent with easier activation of the peroxide and breaking of its bond.
The calculations fit an interpretation in which charge transfer from the bonds to copper helps restore active Cu(I) sites after a reaction. But this remains an explanation supported by modeling and measurements, not a direct view of every step taking place in the liquid. Surface analysis after polishing found more oxygen and a shift in silicon- and carbon-containing bonds toward oxidized forms. Electrochemical impedance measurements also showed evidence of a thicker oxide layer, which the abrasive particles can then remove.
In the main test, the material removal rate for 4H-SiC reached 62.4 nanometers per minute with the catalyst, compared with 4.2 nanometers per minute for the mixture without it. That is not a modest improvement but a major jump under the neutral-pH conditions used in the experiment. Still, this figure alone does not mean the process is ready for commercial production. It comes from a specific laboratory test and needs to be replicated and scaled under real manufacturing conditions.
Faster Polishing, a Smooth Surface—and Some Caveats
In the surface assessment, atomic force microscopy measured an Ra roughness of 0.36 nanometers over an area of 10 × 10 square micrometers. White-light interferometry gave an Sa value of 0.554 nanometers over a larger area of 165 × 137 micrometers. Microscopy images showed that scratches had almost disappeared. The different measurement areas help explain why it is important to report the method and scan size when comparing roughness: each instrument examines a different area and scale of the surface topography.
Raman analysis showed that polishing removed disorder that had been present beneath the surface beforehand. That matters because buried damage may not be visible in an image of the surface alone. On the other hand, mechanical shearing during the process left a small number of periodic stacking-fault defects. The results therefore do not describe a perfectly unchanged surface, free of every alteration. Rather, they show a balance: faster removal and high smoothness, alongside a limited structural effect that deserves further study.
The team ran control experiments to test whether Cu/ZIF-8 particles themselves might have acted as extra abrasives. The results did not support that explanation. Instead, they pointed to the catalyst stimulating the production of chemical radicals at copper sites. The researchers also measured dissolved copper remaining in the neutral-pH waste liquid, finding 0.045 milligrams per liter. That is a limited amount in the reported test, but it is not enough on its own to establish the long-term environmental impact or predict how copper would behave in a large industrial facility.
What the Study Has Not Established
The researchers also tested the catalyst on the titanium alloy Ti-6Al-4V and reported a higher removal rate and lower roughness under mildly acidic conditions at pH 5.5. This was a separate test, distinct from the main result for silicon carbide. It should not be taken as proof that the approach will work equally well on every semiconductor or metal. Other materials that need direct testing include gallium nitride and diamond, both of which are difficult to process at the surface.
Practical questions also remain unanswered because the experiments were short. The study used only one copper loading, so it is not yet known how changing the copper content or the distribution of active sites would affect performance and stability. The catalytic sites could become inactive if the structure degrades or reaction products build up. The results also do not settle the process’s economics, its compatibility with existing manufacturing lines, or whether the removal rate and surface smoothness would remain consistent during extended operation and across large production areas.
According to a note accompanying the study, the work was presented in an accepted version that had not yet undergone final editing, so its findings should be treated as promising research evidence rather than a definitive judgment. The study was published in Nature Communications and attributed to Cao, Zhang, and colleagues; details of the research institution were not provided in the available material. This note does not invalidate the reported numbers, but it puts them in context: the results still need independent evaluation, replication, and scaling.
The Bottom Line
The Cu/ZIF-8 experiment shows that changing the atoms around a copper site could be an effective way to accelerate oxidation reactions in a neutral polishing liquid. In tests on 4H-SiC, the removal rate rose from 4.2 to 62.4 nanometers per minute, while reported roughness remained below one nanometer, scratches were nearly absent, and dissolved copper measured 0.045 milligrams per liter. But industrial performance, long-term catalyst activity, and whether the approach can be applied more broadly remain open questions. The next step is not simply to celebrate the striking result, but to test it over longer periods, with different copper loadings, and on materials and production areas representative of real manufacturing.