Research

Research  Overview

Understanding the structure–property relationships in materials to design, discover and deploy in technological applications.

Some Research Areas

We are interested in understanding and designing materials with novel properties for various applications based on computational methods such as Density Functional Theory (DFT). Moreover, we plan to go beyond standard DFT to include thermodynamics as well as relevant excited state properties. We provide synthesis routes to the experimental group. In addition, simulating device properties will be very useful for the device community. We 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. Here are some of the research areas we are working on:

Energy Storage Applications

Due to growing safety concerns 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. We have investigated the ion conduction mechanisms in bulk solid electrolytes. We have carried out extensive research on the crystal structure, contents (oxides, phosphides, sulfides), and their role in ion conduction and stability. There is a trade-off between ionic conductivity and electro-chemical stability [ref. Fig 2]. 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, the role of defects geometries in ionic conductivity, and so on. The electrode-electrolyte stability needs to be understood. Moreover, the mechanical stress and stability need to be addressed during the lithiation and de-lithiation process in the battery.  We have been looking into this and relevant problems to understand the electrode and electrolytes in solid -state batteries.

Electronic Device Applications

We study the surface and interfacial properties of them, in particular, III-V semiconductor and high dielectric constant oxide (high-κ) interface. Experimentally, due to the 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 [ref. Fig 1]. However, the details of the defect, oxidation of the surface,  and interface are not clearly understood yet. We have studied the stabilities of those materials and possible defect mechanisms. In addition, we  study the interfacial properties of Transition Metal Dichalcogenide (TMD) and high-κ dielectrics.

Materials for Functional Devices

Multiferroic materials possess two or more ferroic properties simultaneously and they have strong coupling between them [ref. Fig 3]. Due to such coupling, there is the possibility of making various kinds of functional devices such as non-volatile memory, spintronics, and another emerging 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,  this lab will investigate various functional materials especially optimizing properties of oxide materials using this approach. The interface properties between ferroelectric 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. We have investigated spin-lattice coupling in Bi-based perovskite oxides. We will plan to include more complex oxides and their interface properties with substrates.

Quantum Materials 

Recently, there has been tremendous interest in designing technology based on the laws of quantum mechanics. In order to develop such novel technology, we need to understand and be able to control individual atoms and spins in a quantum system. A detailed understanding and exploiting the physics of quantum materials is essential and critical. Density Functional Theory (DFT) and various other physics models will be very useful in understanding the behavior of materials in the regime of interest. Many novel materials are being actively considered for quantum information science and for realizing high-performance qubit operation at room temperature. For example, it is expected that deep defects in wide-bandgap semiconductors can facilitate spin states with long coherence times suitable for qubit operation. 

Modeling of Biomolecules

The radiation-induced damages in bio-molecules are ubiquitous processes in radiotherapy and radio-biology, and critical to space projects. We plan to study comprehensive bond dissociations and DNA damage mechanism and other biomolecules.