Advanced Functional Materials Research in Ramki Kalyanaraman's group

Advanced functional materials show new, improved or unusual behaviors either as a result of their structure, composition or size. A seen numerous times in history, new materials often lead to revolutionary changes and so the design the discovery of new materials is one the most important activities of our society.

CHALLENGES: As the sophistication of new functional materials increases, the technology to manufacture them also grows in complexity and cost. Therefore one of the key challenges in this area is to couple simple manufacturing approaches with materials discoveries. Our pathway to discovering new materials is by utilizing nanomanufacturing routes based on natural processes, such as self-organization. From an application perspective our research is on materials and devices for new and improved solar cells, magnetic applications, bio and chemical sensors, and electronics.

Oxide Resistant Nanoparticles for Plasmon Sensing New Nanostructures Oxide Nanowire Gas Sensor Anisotropic Nanomagnets

Oxide Resistant Nanoparticles for Plasmon Sensing

New Nanostructures

In this collaborative discovery-driven research with Prof. Khenner at WKU we are utilizing computer models to synthesize new types of nanostructures via self-organization. Over the last decade, core-shell nanostructures have been widely utilized to exploit the novel behavior of composite nanoparticles. One reason for the dominance of core-shell structures is the well developed solution chemistry route to fabricating such structures. However, new and improved functions could be achieved by alternate structures, such has horizontally and vertically stacked, embedded, etc. As shown in Fig. 1, recent modeling studies of bilayer self-organization predicted a number of new nanostructures may be accessible and we are pursuing experimental studies to verify if the models predictions are correct.

M. Khenner et al Phys. FL. 2012; R. Sachan et al Nanotechnology 2012

Oxide Nanowire Hydrogen Sensor

Anisotropic Nanomagnets

In this discovery-driven research with Dr. Ganagopadhyay and Prof Nussinov at WU we are utilizing nanosecond laser processing to control the magnetism in nanoparticles and nanowires. When the size of a magnetic material is decreased to a length scale comparable with the magnetic domain wall or exchange force distance, the material starts exhibiting unusual magnetic behaviors. For instance, well-studied ferromagnetic material like cobalt exhibits unique magnetic properties when it is in the form of nanoparticles (Fig. 1). For recording media application, perpendicular recording (using out-of-plane oriented data bit) has several advantages over parallel recording (in-plane), such as high density data storage, high stability, and short bit length. In order to make this technology possible, out-of-plane oriented magnetic data bit with large magnetic anisotropy and greater stability are desired. Similarly, nanowires with high length to width aspect ratio exhibit large coercivity, large anisotropy and high remanence due to the shape and crystalline anisotropy. Ferromagnetic nanowires have potential applications in magnetic MEMS (micro-electric-mechanical-system). Nanowires can also be utilized for sensing, manipulating and separating biological cells and these applications require high coercivities and stability at ambient conditions.

H. Krishna et al, J. Mag. Mag. Mat. 2011;H. Krishna et al J. Appl. Phys. 2008; N. Shirato et al SPIE 2010;N. Johnson et al, Phys. Rev. B, 2012

One extremely interesting magnetic state that has gained momentum in recent years is the skyrmionic state. It is characterized by a vortex where the edge magnetic moments point opposite to the core. Although skyrmions have many possible realizations, in practice, creating them in a laboratory is a difficult task to accomplish. In this work, different methods for skyrmion generation and customization are suggested. Skyrmionic behavior was numerically observed in minimally customized simulations of spheres, hemisphere, ellipsoids, and hemiellipsoids, for typical Cobalt parameters, in a range approximately 40–120 nm in diameter simply by applying a field. In. Fig. 4 a vector plot of the skyrmion state in a sphere of radius 59 nm is shown. The slice is along the equator of the sphere. Only a subset of local magnetic moments is shown for clarity.

N. Johnson et al, Phys. Rev. B, 2012.

Contact us for more information via email to ramki @ utk dot edu

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