Seesaw in the world of 2D materials
By using only one precursor and the same metal substrate, it is possible to synthesize two very different 2D materials – hexagonal boron nitride (hBN) or borophene – by fine-tuning the synthesis parameters. The background “seesaw” mechanism that makes this possible was explained in a new paper by colleague Petrović and collaborators from the University of Duisburg-Essen.
Interplay of Kinetic Limitations and Disintegration: Selective Growth of Hexagonal Boron Nitride and Borophene Monolayers on Metal Substrates
Karim M. Omambac, Marko A. Kriegel, Marin Petrović, Birk Finke, Christian Brand, Frank J. Meyer zu Heringdorf, and Michael Horn-von Hoegen
ACS Nano 17, 17946 (2023). DOI: 10.1021/acsnano.3c04038
A detailed understanding of material synthesis is key to increasing the efficiency of the synthesis process itself (e.g. by reducing its costs or shortening the duration), but also to raising the quality of the material being synthesized. This is also true for 2D materials, whose synthesis often requires sophisticated laboratory equipment and potentially hazardous chemicals, and as such still leaves a lot of room for optimization.
In an article published in the journal ACS Nano, our scientist Marin Petrović and colleagues from the University of Duisburg-Essen reveal new details of the synthesis of two very different 2D materials – hexagonal boron nitride (hBN) and borophene. It has been shown that they can be selectively realized in one and the same experimental setup with a fine adjustment of the synthesis parameters. Changing the substrate temperature (iridium single-crystal) and/or precursor pressure (borazine, B3H6N3) affects several processes that are relevant for the epitaxial growth of the material: diffusion of atoms on the surface, nucleation of the material, decomposition of the precursor and dissolution of atoms in the substrate. The interplay of all these processes can be seen as a “seesaw” mechanism that determines which material will ultimately be formed and what will be its structural quality. Figure 1 shows the electron diffraction data (SPA-LEED) recorded for a number of different synthesis temperatures, from which the evolution from hBN to borophene can be read, as well as the achievement of the optimal quality of hBN for the synthesis at 950 °C.
In an analogous way, by gradually changing the pressure of borazine during the synthesis, the change in growth preference of hBN or borophene on the iridium surface can be monitored. Ultimately, by systematically sweeping through the parametric (T,p) space and analytically modeling the growth process using Venables’ nucleation theory, a phase diagram for the growth of hBN or borophene on the iridium surface was obtained, see Figure 2.