Research Interest
One goal of modern condensed-matter science is to use constituents (mainly atoms and molecules) as the elementary bricks to build new materials. In this context, the field of clusters that concerns the aggregates of a few atoms to thousands of atoms (diameters between 1-100 nm) appears especially fascinating, since these systems are intermediate between of small molecules and bulk solids. On a fundamental level, they offer the opportunity to understand more precisely how atomic structure can lead to physical and chemical properties of macroscopic phases. Moreover, it is possible to produce in the form of clusters some atomic arrangements that do not normally exist in nature and may consequently exhibit specific properties that are not due only to the large number of surface atoms.
My research group can produce monodispersive nanoclusters with size range from 1 nm to 100 nm by our newly developed Sputtering-Gas-Aggregation (SGA) source. The unprecedented ability to assemble nanoclusters into new materials with unique or improved properties is thus creating a revolution in our ability to engineer condensed matter for desired utilization. These nanophase materials, assembled using nanoclusters as building blocks, can be synthesized to have a wide variety of controlled optical, electronic, magnetic, mechanical and chemical properties with attendant useful technological applications.
My research interests mainly include the following areas:
More details in my research area can be found below...
My research group can produce monodispersive nanoclusters with size range from 1 nm to 100 nm by our newly developed Sputtering-Gas-Aggregation (SGA) source. The unprecedented ability to assemble nanoclusters into new materials with unique or improved properties is thus creating a revolution in our ability to engineer condensed matter for desired utilization. These nanophase materials, assembled using nanoclusters as building blocks, can be synthesized to have a wide variety of controlled optical, electronic, magnetic, mechanical and chemical properties with attendant useful technological applications.
My research interests mainly include the following areas:
- Magnetic nanosorbents for industrial wastewater and spent nuclear waste treatment
- Irradiation effects on magnetic nanoclusters and applications
- Magnetic nanoclusters and cluster-assembled nanomaterials for energy and environmental applications,
- Magnetic and optical properties of ZnO and TiO2 based nanoclusters for spintronics and solar energy applications.
More details in my research area can be found below...
Magnetic Nanosorbents for Industrial Wastewater and Spent Nuclear Waste Treatment
With the development of magnetic separation nanotechnology, various engineered magnetic nanosorbents have been applied to a wide range of environmental applications, from contamination detection to water purification. Right now, the greater quantities of waste generation and the more stringent regulations for waste discharge call for a simpler, faster, cleaner, and more cost-effective separation process to overcome the drawbacks existing in the traditional methods. Therefore, in our group, we investigates the magnetic separation of heavy metal ions or actinides from aqueous solutions using magnetic nanosorbents which are surface functionalized magnetic nanoparticles (MNPs) conjugated with specific chelators (Che), MNP-Che conjugates for short . MNP-Che conjugates combines the Che’s excellent metal sorption capability and MNPs’ unique magnetic properties as well as their large specific surface area and high diffusivity. Therefore, after sorption, the sorbent-metal complexes can be easily and rapidly separated from aquesou solutions by applying an external magentic field.
In order to separate the heavy metal or radioactive waste from the aqueous stream, the MNP-Che conjugates are first added to the waste stream, which can either be in a tank or in situ. To maintain the conjugates’ suspension, the treatment stream can be mixed by mechanical stirring or other methods. The target species are then extracted onto the MNP-Che conjugates, usually taking less an hour to reach the equilibrium. The particles, now loaded with heavy metals or actinides, are magnetically collected and separated by a magnetic field gradient. The waste solution is decontaminated and can be released. The metal-loaded particles can then be stripped with a small amount of liquid (relative to the original waste stream) and magnetically separated from the resulting solution, allowing their reuse in the next waste treatment. Finally, the concentrated metal contaminants are ready to be treated for permanent waste disposal or for a recycle process. The challenge for magnetic separation of heavy metals or actinides is to synthesize the magnetic nanosorbents with sufficient magnetization, high stability, and dispersibility in an aqueous solution, as well as high surface density of reactive functional groups that contribute to the high efficiency for metal sorption. The sorption selectivity for different metal targets can be achieved by tailoring the surface functionality of the magnetic nanosorbents.
With the development of magnetic separation nanotechnology, various engineered magnetic nanosorbents have been applied to a wide range of environmental applications, from contamination detection to water purification. Right now, the greater quantities of waste generation and the more stringent regulations for waste discharge call for a simpler, faster, cleaner, and more cost-effective separation process to overcome the drawbacks existing in the traditional methods. Therefore, in our group, we investigates the magnetic separation of heavy metal ions or actinides from aqueous solutions using magnetic nanosorbents which are surface functionalized magnetic nanoparticles (MNPs) conjugated with specific chelators (Che), MNP-Che conjugates for short . MNP-Che conjugates combines the Che’s excellent metal sorption capability and MNPs’ unique magnetic properties as well as their large specific surface area and high diffusivity. Therefore, after sorption, the sorbent-metal complexes can be easily and rapidly separated from aquesou solutions by applying an external magentic field.
In order to separate the heavy metal or radioactive waste from the aqueous stream, the MNP-Che conjugates are first added to the waste stream, which can either be in a tank or in situ. To maintain the conjugates’ suspension, the treatment stream can be mixed by mechanical stirring or other methods. The target species are then extracted onto the MNP-Che conjugates, usually taking less an hour to reach the equilibrium. The particles, now loaded with heavy metals or actinides, are magnetically collected and separated by a magnetic field gradient. The waste solution is decontaminated and can be released. The metal-loaded particles can then be stripped with a small amount of liquid (relative to the original waste stream) and magnetically separated from the resulting solution, allowing their reuse in the next waste treatment. Finally, the concentrated metal contaminants are ready to be treated for permanent waste disposal or for a recycle process. The challenge for magnetic separation of heavy metals or actinides is to synthesize the magnetic nanosorbents with sufficient magnetization, high stability, and dispersibility in an aqueous solution, as well as high surface density of reactive functional groups that contribute to the high efficiency for metal sorption. The sorption selectivity for different metal targets can be achieved by tailoring the surface functionality of the magnetic nanosorbents.
Irradiation Effects on Magnetic Nanoclusters and Applications
Degradation of materials due to constant exposure of radiation and high temperatures has been a constant challenge for the current generation of nuclear reactors. Through Nano-Nuclear Technology, latest engineered-nano-materials are used for improving the nuclear power performances and safety. A significant contribution in the area of nano-nuclear technology could be a pivotal point in improving the safety of next generation nuclear reactors. This research focuses on studying the sensitivity and stability of nanomaterials under irradiation. With the aim of meeting the increasing demands on the understanding of irradiation-induced property changes in nuclear reactors, this research mainly focuses on addressing the role of interfaces, grains and grain boundaries in radiation resistance through the nanoparticle granular films and nanoparticle dispersed thin film matrices for resisting radiation, in order to develop a fundamental understanding of irradiation-induced interfacial-processes in nanoparticle-granular films and composites of metals and dispersed magnetic oxides, in particular.
The objective of this research is to understand the radiation resistant behavior of materials based on different interfaces, grains and grain boundaries by assessing the changes rendered to the magnetic, structural, electrical and mechanical properties of nanomaterials under irradiation. In its Research and Development Roadmap - Report to Congress dated April 2010, the Department of Energy’s (DOE) Office of Nuclear Energy clearly identified four research and development objectives, the top one being “Develop technologies and other solutions that can improve the reliability, sustain the safety, and extend the life of current nuclear reactors”. For these reasons, the Generation IV nuclear reactors, which are expected to be in commercial use soon after 2030, need enhanced safety. We are working through this project to achieve this goal by addressing the role of interfaces and grain boundaries in nanomaterials for radiation resistance by analyzing and studying the magnetic, structural, electrical and mechanical behaviors of nanomaterials under ion-irradiation, directly and indirectly.
Degradation of materials due to constant exposure of radiation and high temperatures has been a constant challenge for the current generation of nuclear reactors. Through Nano-Nuclear Technology, latest engineered-nano-materials are used for improving the nuclear power performances and safety. A significant contribution in the area of nano-nuclear technology could be a pivotal point in improving the safety of next generation nuclear reactors. This research focuses on studying the sensitivity and stability of nanomaterials under irradiation. With the aim of meeting the increasing demands on the understanding of irradiation-induced property changes in nuclear reactors, this research mainly focuses on addressing the role of interfaces, grains and grain boundaries in radiation resistance through the nanoparticle granular films and nanoparticle dispersed thin film matrices for resisting radiation, in order to develop a fundamental understanding of irradiation-induced interfacial-processes in nanoparticle-granular films and composites of metals and dispersed magnetic oxides, in particular.
The objective of this research is to understand the radiation resistant behavior of materials based on different interfaces, grains and grain boundaries by assessing the changes rendered to the magnetic, structural, electrical and mechanical properties of nanomaterials under irradiation. In its Research and Development Roadmap - Report to Congress dated April 2010, the Department of Energy’s (DOE) Office of Nuclear Energy clearly identified four research and development objectives, the top one being “Develop technologies and other solutions that can improve the reliability, sustain the safety, and extend the life of current nuclear reactors”. For these reasons, the Generation IV nuclear reactors, which are expected to be in commercial use soon after 2030, need enhanced safety. We are working through this project to achieve this goal by addressing the role of interfaces and grain boundaries in nanomaterials for radiation resistance by analyzing and studying the magnetic, structural, electrical and mechanical behaviors of nanomaterials under ion-irradiation, directly and indirectly.
Nano-magnetism in Biomedical and Environmental Applications
Since their introduction in the mid-1970s, magnetic particles (submicro- and microspheres and ferrofluids) are widely studied for their applications in various fields in biology and medicine such as magnetic targeting (drugs, genes, radio-pharmaceuticals), magnetic resonance imaging (MRI), diagnostics, immunoassays, RNA and DNA purification, cell separation and purification, as well as hyperthermia generation. These magnetic particles or beads are generally of core-shell type: biological species (cells, nucleic acids, proteins) are connected to the magnetic core through an organic or polymeric shell. Most magnetic particles used in biomedical applications are based on ferromagnetic iron oxides. Because magnetic particles and beads are large compared to the bio-objects, many bio-objects will attach to one magnetic particle. To manipulate and/or detect a single bio-object, such as a single cell, a molecule of DNA, an antibody, or another biomolecule, nano-sized magnetic particles are needed. My research goal will develop core technologies that will allow nanoscale magnetics to be integrated with single or a few biomolecules and cells. The objectives of our proposed work are to:
Since their introduction in the mid-1970s, magnetic particles (submicro- and microspheres and ferrofluids) are widely studied for their applications in various fields in biology and medicine such as magnetic targeting (drugs, genes, radio-pharmaceuticals), magnetic resonance imaging (MRI), diagnostics, immunoassays, RNA and DNA purification, cell separation and purification, as well as hyperthermia generation. These magnetic particles or beads are generally of core-shell type: biological species (cells, nucleic acids, proteins) are connected to the magnetic core through an organic or polymeric shell. Most magnetic particles used in biomedical applications are based on ferromagnetic iron oxides. Because magnetic particles and beads are large compared to the bio-objects, many bio-objects will attach to one magnetic particle. To manipulate and/or detect a single bio-object, such as a single cell, a molecule of DNA, an antibody, or another biomolecule, nano-sized magnetic particles are needed. My research goal will develop core technologies that will allow nanoscale magnetics to be integrated with single or a few biomolecules and cells. The objectives of our proposed work are to:
- Modify our prior methods for production of magnetic nanoparticles to produce very small magnetic nanoparticles that are readily reacted with biomolecules and therapeutic agents.
- Devise methods for attaching these molecules to our particles in a controlled (stoichiometric) manner. My longer-term goal is to develop technologies that will provide biologically active, nanoparticle-bimolecular conjugates as potential therapeutic agents for treatment of human disease.
Magneto-optical Properties of ZnO Based Spintronic Nanoclusters
Ferromagnetic semiconductors have emerged as important materials for spintronic devices. In quantum computing, the spin states are used to construct qubits, theoretically enabling the manipulation of huge amounts of data. For non-volatile memory storage applications, ferromagnetism is used to store data for long periods of time. The use of environmentally friendly materials in energy-efficient spintronic devices could have a significant positive impact. Zinc oxide (ZnO) is a leading candidate for such devices.
ZnO is a wide-bandgap semiconductor that has attracted tremendous interest as a blue light emitting material, a buffer layer for GaN-based devices, and a transparent conductor in solar cells. Unlike many other semiconductors, ZnO is environmentally friendly – in fact, a major use for ZnO is as a dietary supplement in animal feed. The stability of excitons in ZnO results in a very high quantum efficiency at temperatures of 300 K and higher, making it an ideal active material for the emission of blue to ultraviolet (UV) light in high-temperature environments. Theoretical work has predicted ferromagnetism above room temperature for Mn-doped ZnO, an important requirement for spintronic devices. Spurred by that prediction, research into ZnO bulk crystals and nanostructures for spintronic applications is an active area of experimental research. Fundamental optical and magnetic properties of ferromagnetic ZnO nanoclusters will be investigated in this proposed work.
Recent discoveries of ferromagnetic behavior in certain dilute magnetic semiconductors (DMSs) have led to increased interest in the development and studies of these materials. The development of room-temperature ferromagnetic materials will be essential for spintronics technology. Despite reports of ferromagnetic DMSs, including transition metal doped-ZnO thin films, little is understood about the origin of these ferromagnetic interactions. In addition, no work has been reported on ZnO DMS quantum nanoclusters. This work focuses on the synthesis of ZnO DMSs from a nanocluster deposition technique, and the investigation into their electronic structure and magnetic properties, magnetic Raman scattering and electron paramagnetic resonance (EPR) spectroscopies. These studies will give detailed insights into the strength and type of exchange interactions that occur, offering new information on the origins of ferromagnetism and other magneto-optical properties in oxide diluted magnetic semiconductor quantum nanoclusters.
My group has produced ferromagnetic ZnO nanoclusters with dopants of Co, Ni, Ti, V and Cu. Magnetic and UV optical properties has been measured by SQUID and PL. XPS and AFM and XRD measurements have been done. The average nanocrystallite size of the nanoclusters was ~7.5 nm. The 2% Co-doped ZnO nanocluster films exhibit significant ferromagnetism and UV photoluminescence (PL) at RT. The coercivity (Hc) doubled in the 2% Co-doped samples when compared to the 5% Co-doped samples. A strong UV-PL of ~3.33 eV was observed for the 2% Co-doped ZnO nanocluster film at RT. The 5% Co-doped ZnO nanocluster film showed a ferromagnetic behavior at RT but no UV luminescence.
Ferromagnetic semiconductors have emerged as important materials for spintronic devices. In quantum computing, the spin states are used to construct qubits, theoretically enabling the manipulation of huge amounts of data. For non-volatile memory storage applications, ferromagnetism is used to store data for long periods of time. The use of environmentally friendly materials in energy-efficient spintronic devices could have a significant positive impact. Zinc oxide (ZnO) is a leading candidate for such devices.
ZnO is a wide-bandgap semiconductor that has attracted tremendous interest as a blue light emitting material, a buffer layer for GaN-based devices, and a transparent conductor in solar cells. Unlike many other semiconductors, ZnO is environmentally friendly – in fact, a major use for ZnO is as a dietary supplement in animal feed. The stability of excitons in ZnO results in a very high quantum efficiency at temperatures of 300 K and higher, making it an ideal active material for the emission of blue to ultraviolet (UV) light in high-temperature environments. Theoretical work has predicted ferromagnetism above room temperature for Mn-doped ZnO, an important requirement for spintronic devices. Spurred by that prediction, research into ZnO bulk crystals and nanostructures for spintronic applications is an active area of experimental research. Fundamental optical and magnetic properties of ferromagnetic ZnO nanoclusters will be investigated in this proposed work.
Recent discoveries of ferromagnetic behavior in certain dilute magnetic semiconductors (DMSs) have led to increased interest in the development and studies of these materials. The development of room-temperature ferromagnetic materials will be essential for spintronics technology. Despite reports of ferromagnetic DMSs, including transition metal doped-ZnO thin films, little is understood about the origin of these ferromagnetic interactions. In addition, no work has been reported on ZnO DMS quantum nanoclusters. This work focuses on the synthesis of ZnO DMSs from a nanocluster deposition technique, and the investigation into their electronic structure and magnetic properties, magnetic Raman scattering and electron paramagnetic resonance (EPR) spectroscopies. These studies will give detailed insights into the strength and type of exchange interactions that occur, offering new information on the origins of ferromagnetism and other magneto-optical properties in oxide diluted magnetic semiconductor quantum nanoclusters.
My group has produced ferromagnetic ZnO nanoclusters with dopants of Co, Ni, Ti, V and Cu. Magnetic and UV optical properties has been measured by SQUID and PL. XPS and AFM and XRD measurements have been done. The average nanocrystallite size of the nanoclusters was ~7.5 nm. The 2% Co-doped ZnO nanocluster films exhibit significant ferromagnetism and UV photoluminescence (PL) at RT. The coercivity (Hc) doubled in the 2% Co-doped samples when compared to the 5% Co-doped samples. A strong UV-PL of ~3.33 eV was observed for the 2% Co-doped ZnO nanocluster film at RT. The 5% Co-doped ZnO nanocluster film showed a ferromagnetic behavior at RT but no UV luminescence.