I am interested in understanding and designing the materials with novel properties for various applications based on computational methods such as Density Functional Theory (DFT). Moreover, I go beyond standard DFT to include thermodynamics as well as relevant excited state properties. I provide synthesis routes to the experimental group. In addition, simulating device properties will be every useful for device community. I perform theoretical electronic structure calculations ( related to experimental ARPES), microscopy (STM imaging) and theoretical vibrational spectroscopy (Raman, IR, neutron experiments) in order to get better correlations between the structure and property. This will also greatly help to understand and explain the experimental findings. I have research experiences in the following areas:
Electronic Structure Methods for Electronic Device Applications
Since, Si-based Complementary Metal-Oxide-Semiconductor(CMOS) technology has reached the fundamental limitation of miniaturization, new materials or device architecture is needed to keep up with the advancement of semiconductor technology. III-V based semiconductors are being investigated as channel materials. I study the surface and interfacial properties of them, in particular, III-V semiconductor and high dielectric constant oxide (high-κ) interface. Experimentally, due to a large amount of interface defect states present at those interfaces, it is a challenge to realize a high-quality interface. Thus, identifying the origin of these defects and possible passivation mechanisms is highly demanding. Recently, two dimensional (2D) materials have also been investigated for semiconductor device applications as well as other applications due to their unique and tunable electronic properties. However, the details of the defect, oxidation of the surface and interface are not clearly understood yet. I have studied the stabilities of those materials and possible defect mechanisms. In addition, I also studied the interfacial properties of Transition Metal Dichalcogenide (TMD) and high-κ dielectrics.
Fig. : Atomic structure of a non -stoichiometric MoS2 : MoO3−x interface model. The pristine interface is suitable to use in tunnel field-effect device whereas the defective will be relevant as Ohomic contact in devices utilizing oxygen vacancies. Reference: Sci. Rep. , 6, 33562 (2016).
Energy Storage Applications
Due to growing safety concern and technological limitations of conventional organic liquid based electrolytes used in Li-ion batteries, inorganic solid electrolytes are being investigated for use in future thin film solid state Li-ion batteries. I have investigated the ion conduction mechanisms in bulk solid electrolytes. I have carried out extensive research on the crystal structure, contents (oxides, phosphites, sulfides) and their role in ion conduction and stability. There is a trade off between the ionic conductivity and the electro-chemical stability. There is some interesting research that has not been understood well such as the interface chemistry between the electrode and the electrolytes,mixed electrolytes systems, role of defects geometries in ionic conductivities and so on. The electrode-electrolyte stability need to be understood. Moreover, the mechanical stress and stability need to be addressed during lithiation and delithiation process in the battery. I have been looking into this and relevant problems to understand the electrode and electrolytes in solid state batteries.
Fig. : The current status of the various solid electrolytes in terms of electro-chemical stability and the ionic conductivity.
Materials for Functional Devices
Multiferroic materials possess two or more ferroic properties simultaneously and they have strong coupling between them. Due to such coupling, there is the possibility of making various kinds of functional devices such as non-volatile memory, spintronics and other emergence electronic phase utilizing the magnetoelectric effects. The well-defined order parameters like spin, charge, symmetry, and lattice can be manipulated to tune the material properties and optimize the devices. There is recent interest in interfacial engineering including strain, epitaxial growth with various substrates to stabilize different phases, polarization doping, and control of dimension to enhance properties of multiferroics. Exploring a wide range of chemical spaces within the materials genome initiatives framework will provide distinct materials structure-properties. This will be an important rational design strategy for creating novel materials properties for various applications. Thus, my group will investigate various functional materials especially optimizing properties of oxide materials using this approach. The interface properties between ferroelectic materials and other materials such as semiconductors or insulators will be important. Integrating the novel functionalities of complex oxides with traditional semiconducting materials is key to making emerging future devices. There are many opportunities to explore these areas where the properties can be tuned by substrate, strain, doping and application of fields. I have investigated spin-lattice coupling in Bi based perovskite oxides. I will plan to include more complex oxides and their interface properties with substrates.
Fig. Schematic of the interrelation between various ferroic phases such as ferromagnetic (FM), ferroelectric (FE), multi-ferroic (MF) and magnetoelectric (ME) materials. Reference: D. Khomskii, Physics 2 20 (2009).
- Complex Oxides, Layered Materials, Multiferroics, Energy storage. (2015-Present).
- 2D materials and their interfaces with dielectrics for semiconductor device applications. (2012-2015).
- Solid electrolytes, electrode-electrolyte interface for all solid state Li-ion battery application. (2010-2014).
- Ab-initio calculations of ground state properties of molecules. (2006-2007).
Electronic Structure Methods for Electronic Device Applications
Since, Si-based Complementary Metal-Oxide-Semiconductor(CMOS) technology has reached the fundamental limitation of miniaturization, new materials or device architecture is needed to keep up with the advancement of semiconductor technology. III-V based semiconductors are being investigated as channel materials. I study the surface and interfacial properties of them, in particular, III-V semiconductor and high dielectric constant oxide (high-κ) interface. Experimentally, due to a large amount of interface defect states present at those interfaces, it is a challenge to realize a high-quality interface. Thus, identifying the origin of these defects and possible passivation mechanisms is highly demanding. Recently, two dimensional (2D) materials have also been investigated for semiconductor device applications as well as other applications due to their unique and tunable electronic properties. However, the details of the defect, oxidation of the surface and interface are not clearly understood yet. I have studied the stabilities of those materials and possible defect mechanisms. In addition, I also studied the interfacial properties of Transition Metal Dichalcogenide (TMD) and high-κ dielectrics.
Energy Storage Applications
Due to growing safety concern and technological limitations of conventional organic liquid based electrolytes used in Li-ion batteries, inorganic solid electrolytes are being investigated for use in future thin film solid state Li-ion batteries. I have investigated the ion conduction mechanisms in bulk solid electrolytes. I have carried out extensive research on the crystal structure, contents (oxides, phosphites, sulfides) and their role in ion conduction and stability. There is a trade off between the ionic conductivity and the electro-chemical stability. There is some interesting research that has not been understood well such as the interface chemistry between the electrode and the electrolytes,mixed electrolytes systems, role of defects geometries in ionic conductivities and so on. The electrode-electrolyte stability need to be understood. Moreover, the mechanical stress and stability need to be addressed during lithiation and delithiation process in the battery. I have been looking into this and relevant problems to understand the electrode and electrolytes in solid state batteries.
Materials for Functional Devices
Multiferroic materials possess two or more ferroic properties simultaneously and they have strong coupling between them. Due to such coupling, there is the possibility of making various kinds of functional devices such as non-volatile memory, spintronics and other emergence electronic phase utilizing the magnetoelectric effects. The well-defined order parameters like spin, charge, symmetry, and lattice can be manipulated to tune the material properties and optimize the devices. There is recent interest in interfacial engineering including strain, epitaxial growth with various substrates to stabilize different phases, polarization doping, and control of dimension to enhance properties of multiferroics. Exploring a wide range of chemical spaces within the materials genome initiatives framework will provide distinct materials structure-properties. This will be an important rational design strategy for creating novel materials properties for various applications. Thus, my group will investigate various functional materials especially optimizing properties of oxide materials using this approach. The interface properties between ferroelectic materials and other materials such as semiconductors or insulators will be important. Integrating the novel functionalities of complex oxides with traditional semiconducting materials is key to making emerging future devices. There are many opportunities to explore these areas where the properties can be tuned by substrate, strain, doping and application of fields. I have investigated spin-lattice coupling in Bi based perovskite oxides. I will plan to include more complex oxides and their interface properties with substrates.
"We must not wait for things to come, believing that they are decided by irrescindable destiny. If we want it, we must do something about it."
- Erwin Schrodinger
- Erwin Schrodinger
