Dr. Kartik GhoshCollege of Natural and Applied Sciences
Physics, Astronomy and Materials Science
I. Focus of Research
My current research focuses on multifunctional oxide semiconductor nanostructures for spintronic, renewable energy, and biomedical applications. Oxide semiconductor nanostructures and their heterostructures have been the subject of significant research in both academic as well as industrial laboratories worldwide because of wide range of applications such as high-temperature/ high-power electronics, visible to ultraviolet photo detectors, solar cells, non-volatile magnetic random access memories, drug delivery, and biosensors. Since I joined Missouri State University (MSU) in August 2000, I have been doing active research on synthesis, characterization, and fabrication of multifunctional inorganic and organic materials as well as their hetero-structures using pulsed laser deposition (PLD), scanning probe microscopy (SPM), scanning electron microscopy (SEM), and Raman-PL spectroscopy, and superconducting quantum interference device (SQUID) magnetometer primarily funded by National Science Foundation (NSF), Office of Naval Research (ONR), and National Institute of Health (NIH). At MSU, research projects participated by both undergraduate and graduate students resulted in over 90 peer-reviewed journal articles and 200presentations at professional meetings such as American Physical Society, Materials Research Society, and Missouri Academy of Science. The results of my research enhance the scientific understanding of nanostructured oxide semiconductors that will be used in future spintronics, optoelectronic, and biomedical devices.
II. Major Projects
- Magnetic Doped Oxide Semiconductors for Spintronics (2000 – 2012)
- Development of 2D Materials Graphene and Beyond (2012 – present)
- Nanoscale Investigation of Multiferroic Domian Dynamics Using Scanning Probe Microscopy (2010 – present)
- Inorganic-Organic Hetero-Junction Solar Cells (2004– present)
- Anti-Cancer RNA Nanoconjugates (2009 – present)
- Interaction between nanomaterials and biomolecules (2012 – present)
III. Future Directions of Research
At MSU, my research focuses on synthesis, characterization, and exploitation of oxide materials at the nanoscale- the scale of individual atoms for three major areas of spintronics, optoelectronics, and nanobiotechnology. We will continue on some of these projects next few years. A brief highlight of some research projects is given below.
Inorganic-Organic Hetero-Junction Solar Cells
In the 21st centuryone of the major problems that the world is facing, isthe scarcity of available energy resources, mainly in the form of fossil fuels. Fossil fuels are non-renewable sources of energy since it would take millions of years to completely restore the fossil fuels that have been consumed in just a few thousands. Furthermore, the use of these fossil fuels is not environment friendly. Hence the renewable energy comes in as an alternative solution for this global issue. Renewable energy appears in many commonly known forms such as solar, wind, and running water, and among them solar and hydro-energy show the greatest potential. A solar cell is basically a p-n junction or Schottky barrier/contact encapsulated between two electrodes, which directly converts solar energy into electricity in a clean process. However, there are two major issues: the efficiency and the cost of the cell. Theefficiency of a low cost solar cell can be improved through choosing proper low cost materials with innovative device structure that will have a smaller series and a larger shunt resistance of the device, a smaller reverse saturation current of the p-n junction, and a layer with higher absorption in the solar spectrum. These device parameters critically depend on optical transmittance, electrical conductivity, and work function of the electrodes; carrier concentration, carrier mobility, and band gap of semiconducting layers; carrier mobility and absorbance in the solar spectrum of the photo generator layer. The overall goal of this research project is to gain a better understanding of structural, electrical, and optical characteristics of oxide semiconductor-organic heterostructures in order to fabricate high efficiency solar cells. The main objectives of this research proposal are to: (1) improve electrical conductivity and transmittance of low cost bottom electrodes such as Al-doped ZnO (AZO) and reduced graphene oxide (RGO) through chemical doping and growth parameters; (2) control the electrical and optical properties of active layers and nanorods on AZO or RGO surfaces as well as surface properties of these layers to get better diode characteristics; (3) fabricate high quality nanoparticles embedded organic active layer with high mobility and improved exciton diffusion length (LD), with high absorption coefficient in the solar spectrum using matrix assisted pulsed laser evaporation (MAPLE) and spin coating techniques; (4) get optimum parameters such as carrier concentrations, mobility, absorbance, bandgap, thickness for all the layers of device through simulation; (5) integrate all these layers to architect a high efficient hybrid organic-inorganic photovoltaic cells having low series resistance, enhanced exciton diffusion length, high shunt resistance, and high photocurrent; (6) compare the efficiency of the device grown by both MAPLE and spin coating techniques; and (7) integrate research and educational opportunities for undergraduate and graduate students in the field of clean energy.
Nanoscale Investigation of Multiferroic Domian Dynamics Using Scanning Probe Microscopy
In recent years multiferroics have enjoyed a great interest because of promising magnetoelectronic device applications such as tunnel magneto resistance (TMR) sensors,non-volatile ferroelectric random access memories (NVFRAMs), and tunable microwave devices. This is mainly due to strong electromagnetic coupling between ferroelectricity and ferromagnetism. Experimental research has shown that ferroelectricity and ferromagnetism not only coexist in the same material but also couple so strongly that the magnetic degree of freedom can be manipulated by an electric field and the electric degree of freedom can be manipulated by a magnetic field. For example, a typical TMR device consists of two layers of ferromagnetic materials separated by a thin tunnel barrier (~2 nm) made of a multiferroic thin films. In such a device, spin transport across the barrier can be electrically tuned. In another configuration, a multiferroic layer can be used as the exchange bias pinning layer. If the antiferromagnetic spin orientations in the multiferroic pinning layer can be electrically tuned, then magnetoresistance of the device can be controlled by the applied electric field. Recently, there are many theoretical as well as experimental studies on multiferroic materials at bulk level. However, very few studies have focused on fundamental issues in multiferroic thin film capacitors, such as the exact nature of the complex domain structure in the polarizable/magnetizable layer and its dynamics under high-speed switching conditions such as electric and magnetic field. Thus, there is a need for a direct study of switching phenomena in such films. The polarization/magnetization state and its reversal are naturally linked to domain arrangements and their transformations. Direct imaging of domain structures and investigation of their behavior under an applied electric/magnetic field can provide a microscopic origin of switching phenomena and the role of domains in magneto-electric effect in multiferroic thin films. SPM is an useful technique for investigation of ferroelectric as well as ferromagnetic materials at nanoscale level, providing high-resolution visualization of ferroelectric/ferromagnetic domains. The overall research goal of this project is to better understand unusual electrical and magnetic properties of heterostructure of multiferroic thin films. The proposed research will focus on synthesis, characterization, and in particular on nanoscale investigation of multiferroic domain dynamics in multiferroics to better understand magneto-electric coupling on a single layer as well as a multilayer of multiferroic thin films. The main objectives of this research project are to: (1) grow high quality epitaxial single layer as well multilayer thin films of perovskite oxides such as BiFeO3, YFeO3, TbMnO3 and DyMnO3anddoped and undoped ferrites Fe3O4, (2) characterize bulk electrical and magnetic properties, and (3) investigate multiferroic domain dynamics under electric and magnetic using SPM.
Development of 2D Materials Graphene and Beyond
Immediately after its discovery, graphene was shown to be an excellent material for the fabrication of field effect devices. Due to its ballistic transport properties, very large mobilities can be achieved at least under optimum conditions. A graphene FET operating at GHz frequencies was reported by IBM researchers in 2008. Because graphene is a gapless semiconductor, it shows an ambipolar behavior. Therefore, researchers recently focus on other possible 2D materials which have a bandgap. Recently, other 2D layered transition-metal dichalcogenide (LTMD) materials MoS2, WSe2, and NbS2 have been the subject of significant research in both academic as well as industrial laboratories worldwide due to wide range of applications such as single molecule gas detection, ballistic transistors, optical modulators, and many others. Individual monolayers of LTMD can be isolated via micromechanical cleavage or the “Scotch tape method” used to obtain graphene from graphite. However, the majority of recent reports on MoS2, like the early literature on graphene, are based on samples prepared by mechanical exfoliatio. In order to fabricate and measure reliable devices properties, large area material with controlled layer count is required. In addition, the ultimate success of the devices critically depends on the improved electrical transport properties of the 2D materials. Our goal is to fabricate high quality thin films of 2D materials over a large area in a control manner using PLD and investigate detailed structural and electronic properties. The proposed research will focus on the growth and electronic transport properties of 2D materials primarily MoS2 grown using MOCVD and PLD technique. The overall goal of this research is to determine the electronic transport properties of MoS2 and heterostructures of 2D materials. Our objectives are to (1) grow high quality LTMD thin films over a large area having complete coverage in ultrathin films consisting of only few layers, (2) characterize magneto-transport properties of LTMD using temperature dependent resistivity and Hall effect; (3) understand the transport properties as we increase the number of layer, and 4)involve both undergraduate and graduate students actively in advanced electronics and renewable energy related research projects. Several students as well as my summer fellowships were supported by Air Force Office of Sponsor Research and NASA. Space Program.
Interaction between nanomaterials and biomolecules
The field of nanotechnology is growing at an exponential rate and engineered nanomaterials have been used into all aspects of life. Proposed uses for nanomaterials in medicine include: drug delivery, imaging, and the formation of bone composites. In particular, the nanoscale materials will be useful for military. The field of nanotechnology is growing at an exponential rate and engineered nanomaterials have been used into all aspects of life. Proposed uses for nanomaterials in medicine include: drug delivery, imaging, and the formation of bone composites. At MSU, there is a substantial activity currently centered on investigations of how various nanomaterials interact with biomolecules. In addition to a multitude of therapeutic and diagnostic applications for these bionanoconjugates, our group has been investigating their utility in the stabilization and delivery of protein, RNA and DNA. More recently we have begun extending our molecular cell biology experiments to nanomaterials derived of bio-elements contained naturally in cells and tissues, including zinc oxide (ZnO), manganese oxide (MnO) and cobalt. Via a similar approach we have shown that poly I:C RNA could be attached to MnO via polyamidoamine dendrimer “PAMAM”. Alternatively for proteins, we have seen ZnO nano-rods enhance the stability and activity of Luciferase enzyme. There is currently very little understanding of the mechanisms of interaction between bio-macromolecules and gold or these other nanomaterials. We have already begun applying absorbance, fluorescence, and Raman spectroscopy to probe these types of bio-nanoparticles. Recently, we have probed kinematics at molecular level between an energy biomolecule adenosine tri-phosphate (ATP), and hydrothermally synthesized ZnO nanostructures using micro-Raman spectroscopy, XRD and EM experiments. For the first time we have shown by Raman spectroscopy analysis that the ZnO nanostructures interact strongly with the nitrogen (N7) atom in the adenine ring of ATP biomolecule. Raman spectroscopy also confirms the importance of nucleotide base NH2 group hydrogen bonding with water molecules, phosphate group ionization and their pH dependence. Calculation of molecular bond force constants from Raman spectroscopy reinforces our experimental data. These data present convincing evidence of pH dependent interactions between ATP and zinc oxide nanomaterials. Significantly, Raman spectroscopy is able to probe such difficult to study and subtle nano-bio interactions and may be applied to elegantly elucidate the nano-bio interface more generally. This research will acquire the fundamental knowledge needed to improve understanding of nano-bio interaction mechanisms and provided in-depth analyses of corresponding effects on biological systems.
IV. Topics related to your research and of interest to the broad University Community, for which you are available for presentations and/or consultations.
- Development of Nanomaterials for Applications in Energy Technology
- Development of Nanomaterials for biotechnology
- Future of Nanoscience and Nanotechnology
- Fundamentals and Applications of Spintronics