Researchers from the University of Jyväskylä and Aalto University have developed a new method based on laser modification, which allows metal-organic materials to be grown locally one molecule-thick layer at a time. The method enables the precise construction of films of different shapes and offers new ways to modify the properties of materials for various applications.
Atomic layer deposition (ALD) is a method used especially in the semiconductor industry to produce high-quality thin films with atomic layer accuracy. The method was developed in the 1970s by the Finnish Tuomo Suntola, and it has since become an important technology.
In ALD, thin films are grown one atomic layer at a time through controlled chemical reactions between the reactants, as well as their interactions with the surface. This so-called bottom-up method allows for precise film thickness adjustment.
- The applicability of the method would be improved if the films could only be grown in selected areas. In this case, the shape of the films could also be controlled, not just the thickness. Area-selective ALD is currently a key research topic in the field, explains Professor Mika Pettersson from the University of Jyväskylä.
The materials produced in traditional atomic layer deposition are usually inorganic materials, such as zinc oxide (ZnO) or alumina (Al2O3), which are semiconductor and insulating materials.
- However, it is also possible to use molecular materials, in which case we speak of molecular layer deposition. In this case, organic precursors are combined with inorganic precursors, and there are a huge number of opportunities to tailor the properties of materials, says Pettersson.
Thin films can now be grown on precisely the desired areas
Now, researchers from the University of Jyväskylä and Aalto University have developed a method that can be used to grow organometallic materials in an area-selective manner. The method enables the precise construction of films of different shapes, one molecule-thick layer at a time.
- This creates enormous opportunities to modify the properties of materials according to their application target, says Pettersson
The method was made possible by combining the laser processing method of graphene developed in Jyväskylä with the expertise of Aalto University researchers in molecular layer deposition.
- Graphene is a one atom thick carbon film, which is the thinnest material in the world. In the study, graphene was prepared on the surface of the silicon chip, after which laser modification was used to functionalize specific areas with hydroxyl groups (-OH). After this, a europium organic thin film was grown on the surface of the samples, which was selectively formed only in laser-modified areas, because the surface of pure graphene does not react with the starting materials, explains Pettersson.
A new method opens up unlimited application possibilities
The method now developed creates new opportunities for the fabrication of advanced devices. One example of potential applications is the material used in this study, which emits light due to the element europium it contains.
- In our pioneering research, we used the light-emitting organo-europium material as a model example. However, atomic and molecular layer deposition is suitable for a wide range of different thin-film materials. This opens up almost limitless possibilities for the future applications of our new area-selective method, emphasises Professor Maarit Karppinen from Aalto University.
Research is progressing towards practical applications – companies are welcome to join
The researchers are really excited about the new results. When they originally studied the laser modification method of graphene, they did not expect that it could be used to develop completely new methods for atomic and molecular layer deposition.
- The collaboration started when Professor Maarit Karppinen and I were speaking at the same event. We noticed that by combining our expertise, we could create something new. Now we have established in practice the functionality of the ideas of that time. Next, we will start developing applications and hope that companies will be interested in our work, rejoices Pettersson.
In addition to Pettersson and Karppinen, the authors of the publication were University Researcher Andreas Johansson, Postdoctoral Researcher Aleksei Emelianov, Doctors Kamila Mentel, Amr Ghazy, Yu-Han Wang, and Doctoral Researcher Joona Pekkanen. The study was published in the prestigious journal ACS Nano. The research was supported by the Jane and Aatos Erkko Foundation and the European Research Council's ERC Advanced Grant project UniEnMLD.