- Postech's Professor Lee Dae-su team develops 'selective atomic gradient' design method

- Adjusting atomic layer arrangement alone achieves electrical directionality in metals

- Leakage current in ultrathin insulators reduced; heat-sensing performance up roughly 100-fold

A schematic diagram illustrating how polarity is achieved through selective atomic gradients. [Provided by Postech]
A schematic diagram illustrating how polarity is achieved through selective atomic gradients. [Provided by Postech]

A new material design method has been developed that surpasses the conventional limits of metals and ultrathin insulating materials — not by changing the types or quantities of atoms used, but simply by altering the order in which they are stacked. The approach introduces a "gradient" into the arrangement of atomic layers without adding any new elements.

The Ministry of Science and ICT announced Friday that a joint research team — comprising Professors Lee Dae-su, Lee Gil-ho and Choi Si-young of Pohang University of Science and Technology (Postech) and Professor Park Se-young of Soongsil University — had successfully imparted new functions to both metals and ultrathin insulating materials by precisely controlling the compositional arrangement of atomic layers.

The findings were published in the international journal Science.

Conventionally, adding new elements or altering elemental ratios has been the primary approach to endowing materials with new properties. The drawback is that this process can alter or eliminate the material's original advantages.

Metals are a prime example. It has been difficult to simultaneously preserve a metal's inherent high electrical conductivity while achieving "polarity" — a state in which atoms are arranged with a bias toward one side. Ultrathin insulating materials used in semiconductors and other applications have also faced limits on how thin they can be made, as leakage current worsens as thickness decreases.

The research team found the solution in the order in which atoms are stacked. They developed a "selective atomic gradient" design method that keeps intact the atoms determining a material's electronic properties while varying, layer by layer in the thickness direction, the ratio of specific atoms of differing sizes.

By introducing layer-by-layer differences in atomic ratios — much like a color gradient that shifts gradually — the atoms became slightly biased in one direction, generating polarity. Reversing the atomic layer arrangement also reversed the direction of polarity. By contrast, uniformly mixing the same types and quantities of atoms produced no such directionality.

The effect was pronounced when applied to metal thin films. The material retained high electrical conductivity while exhibiting varying resistance depending on the direction of current flow. Reversing the atomic layer arrangement also inverted the direction of the resistance difference. This demonstrated the possibility of designing electrical directionality into a material at the fabrication stage.

Performance improvements were also confirmed in an ultrathin insulating material approximately 5.1 nanometers thick. Leakage current — electricity escaping outside the insulator — was significantly reduced, while the material's ability to store electrical energy remained high.

Postech Professors Lee Dae-su, Lee Gil-ho and Choi Si-young, and Soongsil University Professor Park Se-young, who conducted the research. [Provided by the Ministry of Science and ICT]
Postech Professors Lee Dae-su, Lee Gil-ho and Choi Si-young, and Soongsil University Professor Park Se-young, who conducted the research. [Provided by the Ministry of Science and ICT]

Particularly notable was the material's ability to convert temperature changes into electrical signals, which was roughly 100 times higher than that of a representative comparison thin film of similar thickness. Reversing the atomic layer arrangement also reversed the direction of the electrical signal generated by temperature changes.

The technology has potential applications in directional electronic devices that operate differently depending on current direction, spintronics, next-generation transistor ultrathin insulating films with reduced leakage current, infrared and thermal sensors, and energy harvesting devices.

The research team plans to extend the selective atomic gradient design to quantum materials such as magnetic materials and superconductors. The goal is to develop it into a universal material design technology capable of realizing desired functions through atomic arrangement alone, by identifying new quantum and topological properties that emerge when existing physical properties combine with polarity.

"We have demonstrated that by simply changing the order in which atoms are stacked — without adding any new elements — it is possible to preserve a material's original strengths while adding new functions," said Professor Lee Dae-su. "We plan to pursue follow-up research to extend this approach to a variety of materials including magnetic materials and superconductors, and to realize it in actual devices such as ultrathin insulating films and thermal sensors."


nbgkoo@heraldcorp.com