CAREER: Ultrafast Carrier Dynamics in 2D Group-IV Monochalcogenides

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Non-technical Description: Discovery of graphene, recognized by the 2010 Nobel Prize in Physics, ushered an era of research and development of single layer, often called two-dimensional (2D) materials, with potential applications in high-speed optoelectronics, solar energy conversion, and chemical sensors. This project focuses on a new class of 2D materials that includes GeS, SnS, SnSe and GeSe. These materials are environmentally stable, composed of earth abundant elements, and predicted to exhibit unique characteristics such as a high electric conductivity and a spontaneous electric polarization, or ferroelectricity. Ferroelectricity makes them particularly attractive for applications in next generation solar cells as intrinsic electric field facilitates conversion of absorbed light into electric current. This project investigates processes that occur in these materials when they absorb light. Understanding these processes is necessary to lay the foundation to new photovoltaic and optoelectronic devices. The research activities in this project are integrated with educational and outreach activities aimed at inspiring women and students from disadvantaged backgrounds to pursue careers in science and technology and providing them with mentorship and research opportunities. To achieve this goal, the Principal Investigator's team works with Worcester Girls, Inc., a program for high school girls, and hosts annual research forums that bring together undergraduate students from Worcester Polytechnic Institute, Mount Wachusett Community College and other community colleges in Central Massachusetts. Technical Description: This project focuses on dynamics of photoexcited charge carriers in an emergent class of the two-dimensional (2D) van der Waals nanomaterials, group-IV monochalcogenides. These materials have been predicted to possess extraordinary properties such as robust room temperature ferroelectricity and strongly anisotropic electronic and optical properties that can be controlled by external fields. The Principal Investigator's team studies the carrier dynamics over sub-picosecond to nanosecond time scales and aims to uncover the relationship between structure and optoelectronic properties in 2D group-IV monochalcogenide nanostructures. A key objective of this project is development of novel approaches to fast, all-optical control over optical properties and ferroelectric polarization in these materials by means of optical and intense THz pulses. To achieve these objectives, the research team applies all-optical ultrafast techniques including terahertz emission spectroscopy and time-resolved terahertz spectroscopy, time-resolved microscopic photoluminescence and nonlinear excitation with intense terahertz to investigate 2D group-IV nanostructures.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.