My current and future research interests can be divided into two broad thrusts areas, that are linked by my expertise in the areas of synthesis/processing, characterization, and properties measurement:
- Structural ceramics, and their composites and coatings, for mechanical, thermal, and optical applications.
- Functional nanomaterials (1-D and 2-D) and devices for study of nanoscale phenomena in oxides and hybrids.
Following are some of my specific projects, which are in collaboration with a wide network of researchers in academia, industry and national laboratories, both in the US and abroad.
1. Structural Ceramics, Composites and Coatings
1.1. Thermal Barrier Coatings (TBCs). These are coatings of low thermal-conductivity ceramics, applied to metallic components used in the hot-section of gas-turbine engines (power-generation, aircraft). My research focuses on understanding the failure of TBCs, and developing and understanding new TBCs deposited using novel thermal spray methods. The microstructures and attributes of the new TBCs are rationally designed to enhance their performance in increasingly demanding high-temperature environments of gas-turbine engines.
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Figure 1.1. Thermal barrier coatings for gas-turbine engine applications. |
1.2. Infrared (IR) Transparent Ceramic Nanocomposites. This involves the study and development of high-strength ceramic nanocomposites for use as IR transparent windows domes in military applications, such as protection for optical detectors and sensors. Typically, IR windows are made from single-crystal ceramics. However, these are inherently difficult to form into complex shapes, and they are prohibitively expensive. Also, although single-crystal windows have excellent optical properties, they cannot withstand the mechanical demands of some applications, leading to catastrophic failures. Here we are using ceramic nanocomposites approaches in making IR transparent windows that are mechanically robust. We are also developing novel processing methods which will allow the fabrication of complex-shaped IR-transparent windows and domes with relative ease and at low cost.
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Figure 1.2. Infrared transparent ceramic dome. (Surmet Corp.) |
1.3. Ceramic/Single-Wall Carbon Nanotubes (SWNTs) Composites. These composites have one of the most unusual interface structures, where bundles of SWNTs have been found segregate at the ceramic grain boundaries. The hierarchical grain-boundary structure has been described as a 3-D network of 2-D mats made up of random 1-D SWNTs, which can be potentially engineered. These unprecedented grain-boundary structures are giving rise to some unusual contact-mechanical and high-temperature creep properties, which can be tailored.
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Figure 1.3. Alumina/SWNT composites. (Vasiliev et al., Scripta Mat., 2007) |
1.4. Contact-Damage Resistant Ceramics. This effort is directed towards innovative processing of contact-damage resistant ceramics with tailored micro- and nano-structures. The key role played by these structures in determining the unusual contact-mechanical behavior (indentation, sliding-wear) observed in these ceramics is being investigated and modeled.
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Figure 1.4. Wear-resistant nanoceramics. (Wang et al., Acta. Mat., 2004) |
2. Functional Nanomaterials (1-D and 2-D)
2.1. Engineered Nanowires and Devices. Here we have demonstrated the feasibility of generic methods for the synthesis of high-definition metal—oxide—metal (MOM) heterojunction nanowires, where a nanoscale segment of a functional oxide is sandwiched axially between two noble-metal nanowires. These MOM nanowires have distinct advantages over all-oxide nanowires (where the entire nanowire is an oxide), in terms of the true nanoscale nature of the oxide (both radially and axially), integral high-quality electrical contacts, ease of assembly, and low losses. These MOM nanowires have been integrated into circuits with macroscopic contacts. This nanowire architecture provides an unique opportunity to study fundamental nanoscale size-effects in functional oxides, without the dominating effect of the substrate, in the context of chemical-sensing, ferroelectric, piezoelectric, and magentoresistance properties. These nanowires could also be used as 1-D building blocks in the “bottom up” approach to multifunctional nanoelectronics.
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2.2. Oxide Thin Films. This effort is directed towards the use of low-temperature chemical methods for the synthesis of transparent conducting oxide thin films, and patterned functional-oxide thin films using anodic titanium oxide templates.
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Figure 2.2. Nano-tubes patterned functional thin films. |
2.3. Hybrid Nanostructures for Novel Photovoltaics. This project is aimed at integrating novel ordered oxide nanostructures with novel light-harvesting molecules and organic hole conductors, in creating solar cells with expanded spectral absorption.
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Figure 2.3. SEM cross-sectional image of ordered TiO2 nanotubes on ITO coated glass substrate. |
2.4. Graphene-Based Devices. Over the past 4 years graphene (2-D carbon sheets) has been shown to possess some highly unusual electronic properties, which could lead to devices such as high-frequency field-effect transistors, single-electron transistors, chemical sensors, and magneto-electronics. This project is aimed at developing a new method for making high-throughput graphene-based devices.