Dr Jun Li Research Laboratory
1. Nanomaterials Growth
Our nanomaterials synthesis work is focused on preparing high-aspect ratio nanowires (NWs). A major effort is on exploring new methods to grow nanowires deterministically on solid substrates with controlled diameter, length, and orientation (particularly in free-standing vertical orientation) for device applications. The nanowire materials include carbon nanotubes (CNTs), carbon nanofibers (CNFs), semiconducting inorganic crystalline nanowires (s-NWs), and metallic nanowires (m-NWs). The methods include thermal chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical deposition. Another effort is on the large-quantity synthesis of NWs with the hydrothermal method. NW materials such as ZnO, Bi2Te3, MnO2, etc. have been prepared for various applications.
2. Device Fabrication/Characterization
We employ conventional solid-state micro-/nano- fabrication techniques including lithography, CVD/PVD, plasma and wet chemical etching, sputtering, and chemical mechanical polishing. In addition, nonconventional methods such as soft-lithography, imprinting, templating, electrochemical etching/deposition, and chemical functionalization is investigated. Most fabrication processes employ a bottom-up method using massive arrays of vertically aligned CNTs and NWs on patterned substrates. The electronic, physical, and chemical properties and device performance are studied with electrochemistry, I-V measurements, optical spectroscopy, electron microscopy, and scanning probe microscopy. For biomaterials and biomedical devices, experiments involving molecular biochemistry, cell/tissue culture, and in-vivo animal experiments are carried in our lab or through collaborations.
3. Biosensor development
Inlaid CNF nanoelectrode arrays are employed as electronic sensors. The exposed tip of CNFs is selectively functionalized with oligo- nucleotides, antibodies, or peptides for the development of electrochemical or impedance-based sensors to detect nucleic acids, antigens, and kinase activities. In another configuration, the inlaid nanoelectrode array is fabricated in a microfluidic channel as highly effective dielectrophoresis (DEP) device for bioparticle trapping and sensing. An integrated biochip for bacteria detection is under development in collaboration with industrial partners.
4. Biomedical devices
Vertically aligned CNFs are used as a brush-like electrode to interface with tissues. A conductive polymer coated on the vertical CNF array is being explored as a multi-functional neural electrical interface to provide topographical, mechanical, chemical, and electrical support of the neural network. The modification of the surface with conductive polymers further improves the biocompatibility as investigated with neuronal cell culture. Electrical stimulation/recording with rat hippocampal slices has shown much-improved efficiency, indicating a more intimate neural electrical interface than planar microelectrode arrays.
5. Solid-state nanodevices
Novel integration and fabrication methods are developed for applications of CNTs, CNFs, and inorganic NWs as on-chip integrated circuit interconnects, thermal interface materials, transistors, and chemical/biochemical sensors. We are currently working on further evaluation and optimization of both materials properties and processes.
6. Energy conversion and storage
The large surface area of CNTs, CNFs, and nanowires are attractive for the development of new solar cells, supercapacitors, and lithium-ion batteries. Active energy materials such as TiO2, Si, MnO2, V2O5, etc. are deposited as a thin porous shell on the vertically aligned CNF array by MOCVD, ion sputtering and electrodeposition to form interesting core-shell structures which have been explored as novel vertical 3D architectures for dye-sensitized solar cells (DSSCs), lithium-ion batteries, supercapacitors and electrocatalyst supports. The fundamental understanding of energy conversion through materials and interface modification is being pursued with the support from NSF, NASA and DOE. These research projects are also a part of the large-scale collaboration involving researchers from all three major universities in Kansas, which was supported by the NSF EPSCoR program.