Crafting new functionalities in two-dimensional materials. In our group, we combine advanced nanofabrication techniques from top-down (e.g. etching and lithography) to bottom-up (e.g. chemical vapor deposition) methods in order to develop novel strategies to fabricate a variety of morphologies in low-dimensional 2D materials and explore the resulting induced local electronic properties. Here we display key highlights from our group about nanofabrication results. For the complete list of publications from our lab, please check here.

Scanning electron microscopy image of Mo/MoS2 core-shell nanopillar arrays

We experimentally demonstrate a strategy based on the combination of top-down and bottom-up methods for the position-controlled fabrication of Mo/MoS2 core-shell one-dimensional nanopillar arrays at the wafer scale. This morphology offers a much higher degree of nonlinear optical signal localization properties, improving that of the regular flake configuration by more than a factor 10.

Here we present a systematic study of the growth of v-MoS2 nanosheets based on the sulfurization of a pre-deposited Mo–metal seed layer. We demonstrate that the sulfurization process at high temperatures is driven by the diffusion of sulfur from the vapor–solid interface to the Mo seed layer. Furthermore, we verify an enhanced nonlinear response in the resulting v-MoS2 nanostructures as compared to their horizontal counterparts. Our results represent a stepping stone towards the fabrication of low-dimensional TMD-based nanostructures for versatile nonlinear nanophotonic devices.

Vertically-oriented MoS2 nanosheets for nonlinear optical devices“, M. Bolhuis, J. Hernanzed-Rueda, S. E. van Heijst, M. Tinoco Rivas, L. Kuipers, and S. Conesa-Boj, Nanoscale, 12, 10491 (2020)

SEM images of regular arrays of Mo nanopillars exhibiting (a) square, (b) circular, (c) triangular, and (d) hexagonal cross-sections respectively.

In this work, mixed 2H/3R free-standing WS2 nanostructures displaying a flower-like configuration are fingerprinted by means of state-of-the-art transmission electron microscopy. Their rich variety of shape-morphology configurations is correlated with relevant local electronic properties such as edge, surface, and bulk plasmons. Machine learning is deployed to establish that the 2H/3R polytype displays an indirect bandgap. The findings of this work represent a stepping stone towards an improved understanding of TMD nanomaterials based on mixed crystalline phases.

“Illuminating the Electronic Properties of WS2 Polytypism with Electron Microscopy“, S. E. van Heijst, M. Mukai, E. Okunishi, H. Hashiguchi, L. I. Roest, L. Maduro, J. Rojo, and S. Conesa-Boj, Ann. Phys. (Berlin) 533, 2000499 (2021)