Yenny Rocio Hernandez Pico

TITLE:

Defect-Driven Functionalities in 2D Material Networks: Tuning Ferromagnetism, Photoconductivity, and Piezoresistivity via Nanosheet Dimensions.

ABSTRACT:

Two-dimensional (2D) materials offer a versatile platform for next-generation electronic, optoelectronic, and sensing devices. In this talk, we present a comprehensive study on the emergent properties of networks formed by liquid-phase exfoliated nanosheets of Bi₂Te₃, MoS₂, and WS.
Recently we reported room-temperature ferromagnetism in Bi₂Te₃ nanosheets produced via solvothermal intercalation, attributed to native point defects such as Te antisites and vacancies. Density functional theory (DFT) simulations reveal that configurations combining Bi–Te antisites and Te vacancies exhibit synergistic magnetic behavior, with magnetization values consistent with experimental hysteresis measurements. In parallel, we have investigated the photoconductive response of MoS₂ and WS₂ networks printed on flexible substrates. Using size-selected dispersions obtained via liquid cascade centrifugation, we demonstrate that both conductivity and responsivity scale inversely with nanosheet lateral size. MoS₂ networks exhibit higher responsivity and sensitivity, attributed to enhanced light absorption and surface hydroxylation. Notably, response time increases with lateral size, marking the first report of this trend in TMD networks. Finally, we have explored the piezoresistive behavior of these networks under tensile and compressive strain using a three-beam bending setup. WS₂ devices show a transition from positive to negative gauge factor (GF) with increasing lateral size, while MoS₂ networks exhibit a reverse transition under compression. These effects are modeled by considering both intrinsic nanosheet GF and strain-induced changes in junction resistance. Conductivity measurements support a percolative transport model, with junction resistance playing a dominant role in strain
sensitivity.
Our findings highlight the critical role of nanosheet dimensions and defect engineering in tailoring the multifunctional properties of 2D material networks, paving the way for scalable applications in spintronics, flexible photodetectors, and strain sensors.

BIO:

Yenny Hernandez is a distinguished physicist and Associate Professor at the Universidad de los Andes in Bogota, Colombia. She currently serves as the Vice Dean of Research for the Faculty of Sciences, a role she has held since 2021. Dr. Hernández earned her undergraduate degree in Physics from the Universidad Nacional de Colombia and her Ph.D. from Trinity College Dublin. She completed postdoctoral research at both Trinity College and the Max Planck Institute for Polymer Research in Germany. A pioneer in the study of carbon-based and two-dimensional materials, Dr. Hernández leads the Nanomaterials Laboratory at Uniandes, focusing on sustainable energy applications. Her research has been widely published in high-impact journals and includes over 46 scientific articles and a recent international patent on graphene-based energy harvesting. She is also co-author of a textbook on waves and fluids and coordinates the university’s Nanoscience and Nanotechnology program. Beyond her academic contributions, she is president of the Humboldt Club Colombia and has been instrumental in promoting international research collaboration, including initiatives with the Lindau Nobel Laureate Meetings. Her leadership continues to shape interdisciplinary research and support the next generation of scientists.