In a step toward making diamond a viable material for semiconductors and quantum applications, researchers at Macquarie University developed an etching technique for modifying the surface chemistry of diamond. The highly precise technique can be used to remove as little as 1% of a single atomic layer from the material. Precision etching of the diamond surface is achieved by dosing the surface with pulsed deep ultraviolet (DUV) light at fluences below the ablation threshold. Properties like high thermal conductivity and resistance to electrical breakdown make diamond a valuable material for high-power, high-frequency electronic devices. Moreover, diamond surfaces help stabilize quantum states. The ability to engineer diamond surfaces with atomic-scale precision could improve applications in electronics, quantum devices, and in advanced manufacturing, where even minor adjustments to the configuration of surface atoms can significantly enhance device performance. Schematic diagram showing the large area processing achieved by rastering the focused UV beam. Courtesy of Applied Surface Science (2024). DOI: 10.1016/j.apsusc.2024.161816. The researchers demonstrated that precisely delivered pulses of DUV light can trigger a localized chemical reaction on a diamond surface. The reaction, driven by a two-photon process, removed carbon atoms selectively from the top atomic layer. Using x-ray surface analysis, Hall measurements, and resistance measurements, the researchers tracked the evolution of the surface chemistry and electrical properties of the diamond. Alterations in the surface populations after laser treatment were measured with x-ray photoelectron spectroscopy. The researchers found that laser treatments in the form of sub-monolayer etch doses lowered the valence band by up to 0.2 electron volts (eV). They also observed that diamond surface conductivity increased up to 7 times after laser treatment — an enhancement that was independently confirmed by the team’s collaborators at MIT Lincoln Laboratory. Similar enhancements in conductivity were obtained for doses that removed up to 1600 monolayers. “We were amazed that such a minor adjustment to the surface could yield such a substantial boost in conductivity,” professor Richard Mildren, who led the research, said. The changes in surface chemistry and electrical properties were substantial even when only a small percentage of the top lattice layer was removed. The surface properties of the material evolved rapidly, even for UV doses that removed less than 5% of the top carbon monolayer and fluences less than 1 joule per square centimeter (1 J/cm2). The laser etching method for diamond surfaces provides atomic-level control over the surfaces in a standard air environment. “This level of precision is typically only possible with large, complex vacuum equipment,” researcher Mojtaba Moshkani said. “The ability to achieve it with a simple laser process is truly remarkable." The etching technique is fast as well as precise. In experiments, the laser removed 1% of a monolayer in just 0.2 milliseconds. The combination of speed and precision make the laser etching technique for diamond surfaces promising for large-scale industrial applications, such as wafer processing. “We’ve shown that the process is both rapid and scalable," Moshkani said. “It’s a compelling option for industries requiring advanced material processing.” The new UV etch technique could provide a practical method for treating or enhancing diamond surfaces to benefit quantum and fluorescent diamond applications, as well as diamond electronics. It could potentially be used to improve the performance of diamond devices like field-effect transistors. The team believes that the ability to engineer diamond surfaces with atomic precision could become an essential tool for science and industry. “This is just the beginning,” Mildren said. “We are excited to explore how this technique can be optimized further to unlock the full potential of diamonds in electronics, quantum technologies, and beyond.” The research was published in Applied Surface Science (www.doi.org/10.1016/j.apsusc.2024.161816).
