Semiconductor nanoparticles are attractive for enhancing the color quality and efficiency of display and lighting applications. Synthetic techniques are currently unable to produce particles that are bright, that emit color pure, and that are stable without using materials that contain toxic heavy metals. This Scalable NanoManufacturing (SNM) research project is designed to produce application ready and heavy metal free nanoparticles suitable for applications in lighting and display technologies. Experimental methods and theoretical studies will be combined to improve our general understanding of the chemical and physical forces that control nanoparticle growth. Special chemical reactors that allow the researchers to study the molecular mechanisms of nanoparticle growth will be designed. Theoretical work using computer models of the nanoparticle surface and the molecules involved in growth will be used to complement these studies and gain a deeper understanding into the processes involved. By combining the experimental and theoretical results from these experiments, the researchers intend to develop a predictive model of nanoparticle growth that will insight into possible paths for the production of heavy metal free application ready nanoparticles. This understanding will allow the researchers to design synthetic methods to produce nanoparticles that meet the requirements for implementation in lighting and display applications and provide consumers with energy efficient displays with vibrant, rich colors. This research will impact national nanotechnology challenges through publishing, patenting, and industrial collaborations. Graduate students will be educated in synthesis and scalable manufacturing of quantum dots. Undergraduate research will be an integral part of the labs through the Undergraduate Research Opportunities Program at MIT. The impact of this fundamental research on science and technology will be disseminated to the K-12 educational audience through a series of video productions.
To be attractive for use in lighting and display technologies, fluorescent nanoparticles must be efficient and bright with narrow photoluminescence spectra. Currently, the only nanoparticles that are able to meet the specifications required for high impact applications in display technologies contain the heavy metal cadmium and are based on cadmium selenide. The most promising heavy metal free substitute for quantum dots for color downshifting applications is indium phosphide. However, it is not currently possible to make indium phosphide based materials with the narrow spectral linewidths required to meet the specifications of display applications. Preliminary mechanistic studies reveal that there are substantial challenges both in understanding the dynamics and mechanistics of nanoparticle growth at the earliest stages. This work will explore the earliest stages of nanoparticle growth by using stopped flow nuclear magnetic resonance (NMR) spectroscopy to study the evolution of the reagents just after mixing. Furthermore, continuous flow systems will be integrated with mass spectrometers in order to measure and quantify the evolution of species that form early in the reaction that are not well suited to NMR characterization. These experimental measurements will be complemented and informed by theoretical techniques that model the inorganic-organic interface at the nanoparticle surface, identify potential sources of surface poisoning and explore possible methods to mitigate this problem through techniques such as etching. A comprehensive model of the factors that control the dynamics of nanoparticle growth will be developed that includes the dynamics of never-before-characterized intermediate molecular species and their interaction with the nanoparticle surface. This model will be tested using a microfluidic reactor that allows rapid, reproducible scanning of growth conditions. As it is verified, the model will be used to predict the optimal conditions for control of nanoparticle size and size distribution. The continuous flow synthesis is both well suited for the fundamental study required to improve indium phosphide synthesis as well as inherently scalable for applications in lighting and consumer electronics.
