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Research

Graphene-based thin film electronic devices

A single sheet of graphite, or graphene, possesses extremely interesting properties arising from its unique energy dispersion. Graphene can be produced in large quantities and processed in a form of solution once appropriate chemical functionalization is applied. We have solution-processed graphene to fabricate a large area ultra-thin films which could be useful for macro-scale electronic devices such as photovoltaics, sensors, and thin film transistors. One of the major challenges of this work is the complete removal of functional groups from the starting graphene oxide solution (which are initially required for processability) to fully recover the intrinsic properties of graphene. Our aim is to optimize the opto-electronic properties of solution-processed graphene and incorporate it into large area thin film electronics.

Single walled carbon nanotubes-based thin film electronic devices

As-synthesized single walled carbon nanotubes (SWNTs) are heterogeneous containg metallic or semiconducting SWNTs. Due to averaging effect, when a random network (or thin films) of SWNTs is prepared, the material can behave as either metallic or semiconducting depending on the network density. SWNT thin films make great transparent conductors when metallic nature of SWNTs is exploited. On the other hand, high performance thin film transistors (TFTs) can be also fabricated from SWNT thin films in which semiconducting nature of SWNTs is utilized. We are currently investigating how the properties of SWNT thin films can be "tuned" for large area opto-electronic applications.

Dispersion of single walled carbon nanotubes and graphene

Single walled carbon nanoubes (SWNTs) are typically found in the form of bundles due to strong van der Waals forces between the tubes. Bundling of SWNTs is a major issue in studying SWNT based devices as it prevents access to the properties of individual SWNT. Bundles can be exfoliated in solution by various schemes, however, rebundling also takes place in many cases. We have been studying the dispersion and bundling dynamics using a simple optical technique. Dynamics associated with bundling helps understand the lack of irreproducibility in SWNT-based thin film devices. Similar studies are ongoing for graphene oxide and pure graphene dispersions.

Single walled carbon nanotube scaffolds for bone cell growth

The long term objective of this in-vitro study is to understand how carbon nanotube substrates affect and control osteoblastic cell behavior. In our wet chemistry laboratory, we prepare single walled carbon nanotube (SWNT) thin films that form a scaffold for cell growth. The matrix morphology (roughness and pore size) is easily controllable and thin films can be deposited on a wide range of materials to form a bio-inert coating. This layer can be also functionalized with desired proteins, ligands or calcium related (hydroxyapatite, a-tricalcium phosphate) formulations. Further evaluations of the engineered matrices take place in collaboration with nearby University of Medicine and Dentistry of New Jersey (UMDNJ) in the bio-physics laboratory of Prof. Federico Sesti (http://lifesci.rutgers.edu/~molbiosci/faculty/sesti.html). A variety of biochemical, fluorescent microscopy and optical techniques are commonly applied to record cellular behavior.

We are particularly interested in how the surface morphology of SWNT scaffolds impacts cell proliferation, differentiation, and calcification. Recent survey of the existing knowledge on the osteoblast cells response to carbon nanotubes reveals inconsistency. That is, reported biological studies describe nanotubes either as being toxic (Zhang et al. Nanotechnology 18 475102 (2007)) or enhancing cellular growth (Meng et al. J Biomed Mater Res Part A 79A 298 (2006)). By systematically studying osteoblastic cell development, we aim to reveal intrinsic interactions influencing tissue histogenesis.

Boron carbide nanowires

Boron carbide nanowires are important for their potential use in high performance armor and thermoelectric devices. We are exploring the role of boron/carbon ratio, temperature, inert gas pressure and dopants (Si) on the morphology, length and diameter of nanowires grown using a simple solid-liquid-solid (SLS) growth method. In addition, we are venturing into the growth parameters necessary for the Si doping of boron carbide nanowires which results in exotic structures ranging from nanowires and nanobelts to nano-cacti. The effect of doping on the conductivity is further evaluated and compared t pure boron carbide. The doped-B₄C nanowires are expected to have improved physical properties with the Hugoniot elastic limit (HEL) predicted to be above 40 GPa based on our calculations, the highest value ever found in solids.

Boron carbide thin films

Our research aims at understanding properties and capabilities of boron carbide-based materials for many potential applications such as hard coatings and ballistic impact shields. Although boron carbide possesses the highest dynamic elasticity among ceramic materials, it shows an anomalous glass-like behavior at high velocity impacts. The focus of our attention is to understand and adjust the mechanical response of boron carbide by investigating the chemistry, microstructure and morphology of boron carbide-based thin film.
Radio frequency magnetron sputtering is used for the deposition of boron carbide-based films. Electron microscopy, Raman spectroscopy, X-ray diffraction and nano-indentation are performed for a full chemical, structural and mechanical characterization of the films.