(2mq) 2D Materials for Applications in Optoelectronics, Energy Harvesting and Beyond

2D materials, Epitaxial thin films, Optoelectronics, Defect Engineering

An increased thrust for smarter and energy efficient devices has led to the search for newer materials with enhanced functionalities. Graphene has taken center stage in the lively area of electronics. Monolayers of 2D transition metal dichalcogenides due to their tunable properties, have shown immense promise in applications such as optoelectronics, flexible electronics and spintronics. However, despite the enormous potential shown by atomically thin sheets of these layered 2D materials, they are far from commercialization. A major roadblock has been the lack of scalable techniques for synthesis and manipulation of these materials. In this presentation, the focus will be on some unique and upcoming approaches to grow and defect engineer wafer scale epitaxial 2D materials which can drastically improve their functionalities. We discuss some unique quick throughput characterization techniques developed by us for estimating defect densities in these materials. Other approaches to potentially tune the properties of these materials like phase engineering and strain engineering are discussed. We envision the ability to scalable fabrication and modulation these materials in a controllable fashion can open-up additional knobs to tune their properties, thus making them more marketable for various applications. Further, future directions, funding possibilities and possible collaboration opportunities going forward for applications of these defect engineered/phase modified 2D materials in various upcoming applications like membrane separation, as single photon emission (SPE) sources, remote epitaxy and energy harvesting will be highlighted and discussed. A summary of my current research interests and experiences which will broadly drive my future research are highlighted in Figure 1.

Going forward, some of the areas that I am interested to explore applications of 2D materials are in quantum information storage and manipulation, energy harvesting and sustainable separation processes. Some of my research ideas going forward are summarized as follows:

1. Understanding valley selective charge transfer/energy transfer pathways in 2D material heterostructures: Quantum applications Introduction/Relevance: Energy transfer and charge transfer often are the predominant mechanisms dictating carrier relaxation pathways in photoexcited heterostructure systems. These processes in donor–acceptor systems are the basis of many fundamental studies as well as numerous technological applications ranging from quantum optoelectronics to energy harvesting. Why 2D materials: Mastering the understanding of these carrier relaxation pathways relies heavily on precise control of the donor-acceptor proximity. Given their atomic thinness and seamless integration capabilities, two-dimensional materials are ideal for fundamental understanding of these charge and energy transfer processes. Additionally, in monolayer TMDCs, breaking of the inversion symmetry allows access to valley degree of freedom meaning σ+ polarized light can selectively excite the K valley and σ− polarized light to excite the K′ valley. The Gap: While charge transfer and energy transfer have been studied for various 2D TMDC heterostructures, the role of selective excitation of a particular valley/pseudospin in these charge/energy transfer processes has not been systematically explored.

Goal: With extensive experience in large area growth, transfer and optical measurements with 2D materials, we want to explore the role of selective excitation of a particular valley in the energy and charge transfer processes in 2D TMDC systems. The efficient control and manipulation of valley selective energy and charge transfer processes can pave way for applications in quantum information processing and storage, optoelectronics and spintronics.

2. Phase modulated/ Defect engineered large area 2D films for electrocatalysis/photocatalysis: Energy harvesting Introduction/Relevance: Converting carbon dioxide into useful C-based products, revolutionizing industrial ammonia generation and clean hydrogen are some of the grand scientific challenges with the potential to solve critical global energy and greenhouse gas threats. We wish to explore the use of these semiconducting 2D material thin films as catalysts for these applications. The gap: However, a major challenge in this regard is the fact that the basal plane of pristine TMDC coatings of materials like MoS2 and WS2 are inactive to catalysis. However, various engineering techniques have been used to modulate the activity of their surface and make them more active. For example, defect free basal plane 2H MoS2 and WS2 do not provide ideal binding to the HER intermediates thus limiting their use as coating materials for HER applications. However, phase transformation to 1T increases the activity of the basal planes making them active to catalysis.

Goal: We wish to explore these engineered large area 2D thin films for various electrocatalysis/photocatalysis applications. We will be interested in looking into large area 2H to 1T transformed MoS2 films for applications in hydrogen evolution, CO2 reduction and ammonia production. We also wish to investigate defect engineered large area films of 2D materials for these applications. With an eye towards next-generation technologies with lower energetic costs and greenhouse gas emissions, we aim to explore these tailored 2D materials for some of these catalytic applications.

3. Tuning 2D materials for applications in membranes/separation processes: Sustainability Introduction/Relevance: Membrane based processes have found applications in waste-water treatment and recycling, CO2 capture and separation of dyes from effluent streams to name a few. However, a major roadblock in the commercialization of membrane-based technologies has been the tradeoff between permeability and selectivity. The gap: While high permeability and selectivity are desired for most commercial separation processes, conventional materials haven’t been able to simultaneously provide high flux and selectivity. Why 2D materials: Monolayer TMDCs/2D materials offer a potential solution to this problem by maximizing the flux due to their thinness while retaining selectivity by engineering pores on these materials.

Goal: With extensive experience in large area growth, transfer and manipulation, we want to explore the applications of these ultrathin 2D materials for sieving applications for separation processes in collaboration with other groups that have experience in separation processes.

Teaching Interests:

Transport Phenomena, Chemical Reactor Design, Fluid Mechanics, Heat Transfer

Right from my childhood, educators and teachers have had a crucial role in shaping my career. Be it my parents who made me understand the importance of ethics or the sports teacher who inspired me to be disciplined or peers who made me more social, I have always had the opportunity to learn even outside the lecture halls. This has made me realize that teaching goes well beyond the walls of a confined classroom. That being said, with effective strategies, a significant part of learning can be accomplished inside the classroom. You always get the best results when your thrive to excel is driven by curiosity. It is this idea which propels my research as well as teaching. Often the biggest challenge is getting students interested in the subject matter. Interactions and conversations help in infusing curiosity. I have always learnt more from conversations than lectures. Some key highlights of my curiosity driven teaching philosophy are highlighted in Figure 2.

I have been involved in teaching responsibilities in my graduate school as a teaching assistant (TA) for courses in the Department of Chemical and Biological Engineering like Engineering Thermodynamics and Chemical Reactor Design. In this position, I have delivered some lectures and review sessions organized doubt clearing sessions during office hours, graded assignments and examinations. I have had the opportunity to design questions for midterms. Additionally, I have also been involved as a TA in lab courses in Chemical Engineering. Here, I have worked with the students in ensuring they carry out their experiments responsibly and ethically keeping safety precautions in mind while asking them questions to stimulate their inquisitive mind. These experiences have prepared me for the challenges that come with the position, and I plan to discuss some challenges faced and lessons learned from these experiences.

I would be enthusiastic in teaching Transport Phenomena, Chemical Reactor Design, Engineering Thermodynamics and other courses in Chemical Engineering. A big thrust of my research is understanding the growth of 2D materials in a furnace. The growth process involves transport, heat transfer processes and the design and optimization of the reactor. As such, teaching these courses would directly complement my research. Additionally, the students might get to solve interesting real-life problems. I would also be interested in teaching electives related to “Growth of semiconductors”.