The scientific goal of this CAREER project is two-fold: (1) to develop a general approach for making high-quality semiconductor nanocrystals doped with position-controlled impurities, and (2) to systematically study the physical consequences of position-controlled doping in various semiconductor nanocrystals. A three-step colloidal synthesis will be developed for doping semiconductor nanocrystals. In this synthesis, impurity doping only occurs in the nanocrystal growth stage, which allows for the easy control of doping levels and the radial positions of dopants in a spherical nanocrystal. The ability to control these material parameters will create a new opportunity to tailor the optical, electronic and magnetic properties of semiconductor nanocrystals. The successful application of this research will provide a new type of doping-based nanostructure for developing technological applications in biomedical diagnosis, photocatalysts, solar cells, LEDs, spintronic devices, etc. These nanocrystals will also provide unique, nanometer-scale semiconductor systems for systematically elucidating the fundamental interactions between quantum systems and position-tunable dopants. This advance will open a new direction to the rational design of functional nanomaterials, and it will further create new opportunities for nanocrystal-based applications. In the area of education, this CAREER project develops nanotechnology education for students at various levels: (1) undergraduate curriculum development for analytical chemistry, (2) a new graduate course on nanotechnology, and (3) nano-synthesis experiments for high-school students.
As one of the most exciting frontiers in modern science, nanoscience has created opportunities to profoundly impact technologies that run the gamut from labels for disease diagnosis to high-density data storage for computers and other consumer electronics. To produce such advanced technologies requires totally mastering the science of fabricating nanomaterials with new functions, which is the subject of this CAREER-development project. This project outlines three broad scientific tasks: (1) radial-position-controlled doping of semiconductor nanocrystals with magnetic impurities; (2) doping of semiconductor nanocrystals with conventional impurities; and (3) co-doping of semiconductor nanocrystals with magnetic and conventional impurities. The proposed research work will lead to a new type of doping-based nanostructure for developing technological applications such as highly sensitive biomedical diagnosis (for early-stage detection of cancer), more efficient solar cells, and spintronic devices for the next generation of computers. This CAREER project takes place in the field of nanotechnology at the intersection of chemistry, physics, and material sciences. The multi-disciplinary nature of this project makes it unique for educating students (at the high-school, undergraduate, and graduate levels) with the necessary knowledge, understanding, and skills to provide leadership in the emerging world of nanotechnology.
The research activities of this Career project focus on the studies of dopant-incorporation mechanism during nanocrystal doping, physical properties of nanocrystals arisen from radial position controlled dopants, as well as other fundamental questions related to doped nanocrystals. Thus far, the research activities have resulted in a number of important findings: (i) a comprehensive mechanism for doping semiconductor nanocrystals with Mn, in which dopant incorporation is determined by three activation-controlled processes: dopant adsorption, dopant replacement, and host-lattice growth; (ii) Mn-growth-induced size ripening of host particles with an activation energy; (iii) a surface-treatment procedure to eliminate nanocrystal surface traps and enhance nanocrystal photoluminescence; (iv) a detailed Mn radiative pathway of doped nanocrystals, where the efficiency of the emission from one Mn ion (?Mn) and energy-transfer efficiency (?ET); (v) excitation-intensity-dependent dual emissions from Mn-doped semiconductor nanocrystals; (vi) dopants-promoted nucleation for nanocrystal solid-state phase transitions; (vii) the identification of SeO2 as an ideal precursor in the synthesis for making monodispersed metal selenide nanocrystals; and (viii) the use of solvophobic interactions for making supercrystalline superparticles from monodispersed nanocrystals. These findings have been summarized in 16 publications in highly regarded journals such as the Journal of the American Chemical Society and Angewandte Chemie International Edition. Education activities include (1) research training of three graduate students and four postdocs, and (2) research outreach to host five high-school students for summer research, which is carried out with the support from the Center for Precollegiate Education and Training at the University of Florida (UF-CPET). To date, four postdocs and three graduate students have been involved in the project. They have received extensive training in the areas of colloidal nanocrystal synthesis and characterization. The materials characterization techniques include UV-Vis spectroscopy, fluorescence spectroscopy, Raman spectroscopy, inductively coupled plasma-atomic emission spectroscopy, X-ray powder diffraction, and transmission electron microscopy. In outreach activities, my group has been hosting high-school students for summer research for five years. These high-school students were trained to use our methods for making II-VI semiconductor colloidal nanocrystals from non-toxic precursors. After only a few weeks of training in our research lab, all these students have mastered the synthesis for making high-quality CdS and CdSe nanocrystals. Moreover, our findings have contributions out other disciplines: (i) our new doping model and our findings on dopant-position-dependent physical properties provide a general guideline for making doping-based nanostructures that are of great importance to applications such as biomedical diagnosis, photocatalysts, solar cells, light-emitting devices, and spintronic devices; (ii) our results on dopant-induced structural change in semiconductors at the nanometer scale is fundamentally important for the understanding of the physical behavior of semiconductors at the nanometer scale; (iii) our results regarding the metastable state in core/shell nanocrystals with and without dopants are important for understanding and building functional materials with well-defined mechanical properties using complex nanostructures; and (iv) our method for making supercrystalline superparticles from nanocrystal building blocks opens a new way for manufacturing functional materials from the bottom. Furthermore, the new findings resulted from this project have been patented by the University of Florida. A start-up company named Nanoalfa will develop commercial products based on the patented technology.
