A Nobel Prize winner in Physics, Richard Feynman, predicted decades ago that, “When we get to the very very small world – say circuits of several atoms – we have a lot of new things that would happen that represent completely new opportunities for design. Atoms on a small scale behave like nothing on a large scale, for they satisfy the law of quantum mechanics.” With diameters often less than 2~5 nm, carbon nanotubes fall into the size range where quantum effects become important, and this, combined with their unusual symmetries, has led researchers to predict many remarkable electronic, magnetic, and lattice properties, which are quite different from those of their bulk counterparts.
Currently, there are several funded nanoscience and nanotechnology research projects underway in Dr. Jiao’s group:
Fabrication and Characterization of Wafer-Scale Chemical Vapor Deposition Graphene for Spintronics Applications
This project focuses on graphene as a material used for solid-state electronic devices and the development of these applications, specifically on the refinement of the growth processes of epitaxial CVD graphene and its characterization. Quality graphene—characterized by mono-layer, large crystalline size, and minimal defects—can be grown by controlling specific growth parameters including substrate material and crystal structure, temperature, ratio of ingredients, pressure and area of reaction chamber and using plasma to drive the reaction. To evaluate graphene quality, structural characterization is carried out through Raman Spectroscopy, AFM/STM, and TEM. The goal of the research is to develop optimized conditions for high-quality graphene growth. To characterize graphene spintronic properties, novel hybrid diffusion drift spin valve (HDDSV) arrays were designed and fabricated. The new device allows systematic investigations of graphene spin transport parameters including spin lifetime, spin diffusion length, and polarization injection efficiency by variations of device components and dimensions. Extracting parameters from non-local spin valves (NLSV), the most commonly employed device to study graphene spin transport, has resulted in experimental values that are orders of magnitude lower than those predicted by theory. To determine sources of this discrepancy, it is expected that the novel HDDSVs are capable of detecting nonlocal signals originating from a spin accumulation of spin polarized charge carriers, which occurs away from the influence of ferromagnetic (FM)/tunnel barrier (TB)/Graphene interfaces. Characterization of these devices will enable us to establish the device parameter and material effects.
Investigation of Low-Temperature Growth Parameters for Scalable Graphene Films Suitable for Graphene-Based Silicon–CMOS Applications
This project aims at developing a scalable technique for low-temperature (within 400°C~600°C) growth of graphene with controlled properties by a chemical vapor deposition (CVD) process. A systematic experimental investigation is carried out in three CVD systems (a traditional CVD, a plasma enhanced CVD, and inductively coupled plasma CVD) with varied functionality to implement different growth parameters. The results are comparatively analyzed. It is our intention to establish the correlations of the synergistic effects among the growth parameters. This will lead to the identification of optimal parameters for direct deposition of graphene films that could be readily integrated with the silicon and complementary-metal-oxide-semiconductor (CMOS) process for nanoscaled electronic fabrication and continued device scaling.
Activated Carbon Supported Pd-based Nanoparticles for Sustainable Groundwater Treatment
This research project aims to efficiently degrade volatile organic compounds in water, with a novel catalyst that combines the physical adsorption of carbon, and the chemical catalytic ability of palladium-based nanoparticle metals. The catalyst is being studied for optimum metal composition, stability and reaction kinetics. A variety of characterization techniques are employed for a better understanding of the catalyst, including SEM, FIB, HRTEM, and other microscopy and spectroscopy techniques. This project harmoniously integrates aspects of physics, chemistry and materials engineering. The scope of the project is currently limited to volatile organic compounds, but will systematically address other contaminants in groundwater for sustainable and efficient groundwater treatment.
Efficiency Enhancement of Photocatalytic Water Purification using 3D Optical Materials
Photocatalytic water purification is a scientific technique for the destruction of organic pollutants using light. This technology is based on the presence of a semiconductor that can be excited by light with an energy higher than its band gap, inducing the formation of energy-rich electron-hole pairs that can be involved in redox reactions. Recent progress has explored the chemical nature of nanoscale semiconductors with the object of improving their electronic and optical properties. This project aims to enhance the semiconductor’s photoresponse to visible light through the design and fabrication of 3D structures that optimize optical and electrical characteristics of the photocatalyst and reduce energy losses due to parasitic photon absorption and charge carrier recombination. 3D photocatalyst cartridges have been created using a chemical synthesis technique, and a continuous flow photoreactor has been designed and built as a means for testing the effectiveness of the material. In order to compare with other photocatalytic purifiers, quantification of the system's Electrical Energy per Order (EEO) is obtained by monitoring the change in concentration of pollutants with an in-line UV-Vis flow spectrometer as the water passes through the reactor. A patent is pending for this development.
Nanoparticulate Adjuvants and Delivery Systems Towards New Generation Vaccines
Vaccination has greatly impacted global public health by controlling and preventing infectious diseases and treating cancers. However, it remains difficult to generate sufficient immunity with vaccines containing insufficient immunogenic antigens. To amplify the interaction between antigens and the immune system, we recently reported that antigen coupled to alumina nanoparticles is 500 times more efficiently processed by dendritic cells for major histocompatibility complex (MHC) class I antigen presentation, and elicits strong cytotoxic T cell response against cancer in vivo (Nature Nanotechnology, 2011, 6,645-50). We now extend these studies to infectious disease, with the goal of utilizing alumina nanoparticles to elicit cytotoxic T cell response to defined pathogen antigens. Therapeutic cancer vaccination is an attractive strategy because it induces T cells of the immune system to recognize and kill tumor cells in cancer patients. However, it remains difficult to generate large numbers of T cells that can recognize the antigens on cancer cells using conventional vaccine carrier systems. We show that the alumina oxide (Al2O3), especially, the α-Al2O3 nanoparticles can act as an antigen carrier to reduce the amount of antigen required to activate T cells in vitro and in vivo. We found that α-Al2O3 nanoparticles delivered antigens to autophagosomes in dendritic cells, which then presented the antigens to T cells through autophagy. In collaborations with colleagues in local medical research institutions, immunization of mice with α-Al2O3 nanoparticles that are conjugated to either a model tumor antigen or autophagosomes derived from tumor cells resulted in tumor regression. These results suggest that α-Al2O3 nanoparticles may be a promising adjuvant in the development of therapeutic cancer vaccines. Our continued efforts are to functionalize the Al2O3 nanoparticles with different molecules and conjugate them with different proteins and understand the mechanism of activation of T-cells and analyze the immune response from different molecules to identify the molecules that are most effective at strengthening the immune response.
Surface Modification of Graphene with Various Metal and Metal oxide Nanocrystals for Renewable Energy Applications:
The principle of this project is to develop a very simple, scalable and environmentally benign process to hybridize high-crystalline graphene with various metal nanoparticles and their related alloys as well as metal oxide nanocrystals, which are suitable for clean and renewable energy applications. Three areas of research interests within the clean energy are: energy storage (supercapacitors), energy conversion (fuel cells), and energy production (water splitting). More specifically, the experiments have been carried out with surface decoration of conductive graphene with transition metal oxides, such as Fe3O4 and Mn3O4, for high-performance supercapacitor; Hybridization exfoliated graphene with Pt and Pt-based alloys as electrode materials for direct methanol fuel cells; Graphene supported TiO2 and N-doped TiO2 as efficient photocatalyst for water splitting. The project goal is to develop scalable manufacturing methods for mass production of high-performance graphene-based metal oxide hybrids for practical technological applications.
Optimization of Carbon Nanotube-Based Gas Sensors
The electronic transport properties of carbon nanotubes have been shown to be strongly dependent upon the constituent gases of the ambient environment. In order to improve the capabilities of these promising sensors, it is essential to completely understand the adsorption process and the nature of their interaction with gas molecules. Three principle techniques are used to further this understanding. Raman spectral mapping with sub-micron spatial resolution is used to structurally characterize the carbon nanotube channel and to quantify the number of lattice defects. A custom micro-environmental probe station system is used to measure the response of the electronic channel to ambient gas concentration, temperature and pressure, and to photonic stimulation (via a tunable infrared laser). In combination, these stimuli provide a great deal of information about the electronic state of the channel. These measurements are correlated to various ab initio computations, such as band structure and density of states, to provide a complete picture of how the ambient gas molecules influence the transport properties of the carbon nanotubes.