image: Figure1: Working principle of Gigantic-Oxidative Atomic-Layer-by-Layer Epitaxy (GOALL-Epitaxy) and the growth of an artificially designed nickelate structure.
Credit: ©Science China Press
Transition metal oxides host a rich variety of strongly correlated electronic phases, including high-temperature superconductivity, ferromagnetism, antiferromagnetism, and charge density waves. These phases are highly sensitive to the lattice structures and electron occupancy, making the precise design and construction of such oxide materials essential for tuning their functions. A long-standing challenge has been to stabilize artificially designed metastable states in these materials. Current advanced thin-film growth techniques for oxides, including oxide molecular beam epitaxy (OMBE) and pulsed laser deposition (PLD), each have unique advantages. OMBE excels in precise elemental stoichiometry control and atomic-layer-by-layer growth of complex oxide structures, but is limited by its requirement for low-pressure environments due to the vapor pressure of it’s the evaporated materials, which restricts its oxidation capabilities. PLD, on the other hand, offers versatility, relative cost-efficiency, higher growth rates, and a higher pressure tolerance, but it faces difficulty with intuitive stoichiometry control and the growth of complex large-unit-cell metastable structures.
Recently, Laboratory of Superconductivity Mechanism from the Department of Physics, Southern University of Science and Technology (SUSTech), and the Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (QSC-GBA), developed a method called Gigantic-Oxidative Atomic-Layer-by-Layer Epitaxy (GOALL-Epitaxy)， enhancing oxidative power while ensuring atomic-level precision in the growth of complex, artificially designed oxide structures. GOALL-Epitaxy combines the strengths of both PLD and OMBE while effectively mitigates their limitations, increasing oxidative power by three to four orders of magnitude—ideal for complex materials that require extremely strong oxidative environments. The team demonstrated growth of various complex nickelates and cuprates, notably an artificially designed nickelate structure with alternating single and double NiO₂ layers, which serves as a parent structure for high-temperature superconductivity. This accomplishment not only highlights GOALL-Epitaxy’s potential in materials discovery but also expands the parameter space for exploring new high-temperature superconductors and other strongly correlated electronic systems. The research has been published in the 4th issue of National Science Review, in 2025 titled “Gigantic-oxidative atomic-layer-by-layer epitaxy for artificially designed complex oxides,” with Dr. Guangdi Zhou from SUSTech and Dr. Haoliang Huang from QSC-GBA as co-first authors.
The essence of GOALL-Epitaxy lies in the atomic-layer-by-layer deposition in a strongly oxidative environment, similar to "building legos," where different oxide layers are meticulously stacked on an atomically smooth substrate to achieve the designed structure. The strong oxidative power is achieved through liquefaction-purified ozone as the oxidation source, which is injected directly onto the substrate surface in high concentration and high flow rate via a specially designed nozzle. This configuration ensures that ozone reaches the substrate rapidly and provides sustained high-intensity oxidation under high temperatures. GOALL-Epitaxy further utilizes high-energy laser pulses to ablate single-element oxide targets, enabling substantially higher growth pressures than OMBE while achieving atomic-layer precision comparable to OMBE.
Compared to PLD and OMBE, GOALL-Epitaxy provides greater flexibility in both high and low-temperature conditions. Under high temperatures, its powerful oxidation enhances the thermodynamic stability of materials, allowing for kinetic improvements that enhance crystalline quality. In low-temperature conditions, the additional kinetic energy from laser ablation helps to achieve higher lattice quality, supporting a broader range of material systems and artificial lattice structures. These features not only meet the demands for new material design and exploration but also help scientists overcome the limitations of conventional techniques in the growth of specific materials.