Synthesis and Functionalization of Nanostructured Photonic Materials

The advent of nanotechnology created the need for developing efficient processes for producing nanostructured materials with precise control on their size, shape, atomic structure and composition. Our research aims to develop new synthetic routes and processes for producing II-VI semiconductor nanostructures, which are materials that exhibit size-dependent optoelectronic properties and have applications in biological imaging, sensors, high-density information storage, high-resolution displays, and solar cells. We employ liquid-phase and vapor-phase synthesis techniques to grow Zn-based nanocrystals (e.g., ZnSe, ZnS and ZnTe), core-shell structures (e.g., ZnSe/ZnS and ZnSe/ZnTe) and diluted magnetic nanocrystals (e.g., ZnSe:Mn and ZnSe:Fe). Microemulsions and liquid crystals formed by self-assembly of an amphiphilic block copolymer in the presence of a polar and a non-polar solvent have been used as templates for growing these nanostructures, in collaboration with the group of Prof. Paschalis Alexandridis (University at Buffalo). The templates enable precise control on size and shape, by isolating individual nanomaterials in the dispersed domains of the template, and easy scale up for commercial exploitation. Annealing of the nanostructures is performed to improve their crystalline quality and study the thermodynamic stability of core-shell and doped nanocrystals. Spectroscopic analysis of the nanocrystals is performed in collaboration with the group of Prof. Athos Petrou (University at Buffalo). Surface modification techniques are developed to enhance the stability of the nanocrystals and introduce functional units that enable applications in biological sensors and solar cells. Transport and kinetic processes during the synthesis of the nanostructures are studied using a combination of experiments, modeling and computer simulations to elucidate the underlying mechanisms and identify optimal operating conditions.

Novel Optical Biosensors based on ZnSe Nanocrystals

Our research aims to develop a new class of biosensors based on ZnSe nanocrystals that are conjugated with probe biomolecules, such as ssDNA, antibodies and other proteins. These probes are being used to detect the presence of target biomolecules in solution by measuring the changes in the fluorescence emission spectrum of the quantum dots upon binding of the probe to its intended target. Homogeneous (non-separation) assays are developed for rapid detection and quantitative analysis of biological targets in solution, including disease-relevant DNA mutations, antigens and antibodies. Multiplexed detection schemes and arrays for high-throughput screening are developed using nanocrystals that emit at different wavelengths. We are studying the performance of the biosensors using models of the transport phenomena and binding kinetics with the purpose of optimizing their performance and designing miniaturized instruments that can be used for point-of-care diagnostics. The ultimate objective of this work is the development of novel optical biosensors with high sensitivity, short response time, robustness, and wide range.

Metalorganic Vapor-Phase Epitaxy of Compound Semiconductors

We study the kinetics and transport phenomena during metalorganic vapor-phase epitaxy of thin films of compound semiconductors, such as III-V arsenides, phosphides and nitrides, using experiments and fundamental process models. The objective of this work is the design of thin-film deposition systems providing optimal growth conditions for multi-layer structures of compound semiconductors used in advanced electronic and photonic devices. Typical design objectives for the deposition reactors being studied include uniformity of film thickness and composition over large-area substrates, ability to grow atomically-abrupt heterojunctions, and maximization of reactant conversion into film.

Multi-scale Models of Reaction-Transport Processes

We study the transport and kinetic processes during the synthesis of nanostructured materials by liquid- and vapor-phase routes using stochastic mesoscopic simulations (e.g., lattice Monte Carlo) and macroscopic simulations (e.g., finite element descriptions of conservation equations). Ab initio quantum mechanical models are being used to understand doping mechanisms in semiconductor nanocrystals and to investigate the thermodynamic stability of core-shell structures, in collaboration with the group of Prof. Dimitrios Maroudas. We are also employing "equation-free" techniques to simulate the behavior of reacting systems in time and space using microscopic atomistic simulators in collaboration with the group of Prof. Ioannis Kevrekidis (Princeton University). The objective of this work is the development of robust multi-scale modeling approaches that can reveal the fundamental links between reactor-level operating conditions (temperature, pressure, flow rates, inlet concentrations of reactants) and particle-level properties (size, shape, crystallinity).

Gas-Particle Flows and Granular Flows

Transport processes involving granular materials are very common in the pharmaceutical and chemical industries. These materials can exhibit both fluid-like and solid-like behavior and the underlying physics are still not fully understood.We are interested in gas-particle flows that are related to fluidization, pneumatic transport, and gravity flow in standpipes that are vital particle transport links in many important industrial processes, e.g. in fluid catalytic cracking units. Standpipes are known to be pathogenic due to flow instabilities that lead to abrupt changes in the particle flow rate. We are interested in understanding the flow regimes and stability of granular flows in such systems to identify procedures for precisely controlling the particle flow rate. Design of fluidized-bed reactors for catalytic conversion of biomass to fuels and chemicals is being pursued using a combination of experiments, modeling and simulation, in collaboration with the groups of Prof. George Huber and Prof. Stephen de Bruyn Kops.