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Xu Research Group

Prof. Xu’s group carries out research in two main areas: (1) nanoscale energy transport, and (2) nano-optics and laser-based nano-optical engineering.

(1) Nanoscale energy transport

We investigate energy transport in nanoscale materials used for efficient energy conversion, including photovoltaic and thermoelectric energy conversion, and nanoscale materials for controlling - reducing or enhancing - thermal transport. At a microscopic level, energy transport and conversion is ultimately determined by the ultrafast dynamics of interactions among basic energy carriers such as electrons, phonons, and photons, which occur at a time scale of femtosecond (fs, 10^-15 s) to picosecond (ps, 10^-12 s). We develop advanced femtosecond (fs) laser based high temporal (~ 10 fs) and high spatial (~ 10's nm) resolution experimental techniques (e.g., coherent phonon spectroscopy) and molecular dynamics simulation techniques for the study of ultrafast energy transfer and conversion dynamics.

Current research projects in this area include (see details by following the links):

- Energy transport in thermoelectric materials for waste heat recovery from automobile exhaust gas

- Also see News Release: Technology uses auto exhaust heat to create electricity, boost mileage
		Purdue mechanical engineering doctoral student Yaguo Wang works with a high-speed laser at the Birck Nanotechnology Center to study thermoelectric generators. The devices harvest heat from an engine's exhaust to generate electricity, which could reduce a car's fuel consumption.

- Energy transport in nanoscale thermoelectric materials for power generation

- Coherent control of thermal transport

- Thermal transport in nanoscale thermal interface materials

- Energy transfer in nanoscale photovoltaic materials

(2) Nano-optics and laser-based nano-optical engineering

We are working on a broad range of topics related to nano-optics and nano-optical engineering. Our current effort is on laser-based nano-engineering using nanoscale optical antennas, which are developed in our laboratory. These antennas are capable of efficiently focusing light into a nanometer domain with intensity orders of magnitude higher than the incoming light intensity. Being able to concentrate light into a nanoscale domain with high intensity has numerous applications in nano-engineering, including nano-manufacturing, nanoscale imaging and diagnostics, and ultra-high density data storage. Our current research involves nano-optics theory (e.g., plasmonics), numerical design, micro/nano fabrication, experimental testing, instrumentation development, and applications in emerging engineering areas.

Current projects in this area include (see details by following the links):

- Parallel nanolithography using nanoscale optical antenna

-Also see Research.gov News Release: Engineers Make a New Low-cost Tool for Optical Nanomanufacturing
		The nanomanufacturing tool built at Purdue. The insert are the letters BNC (Birck Nanotechnology Center) written in parallel.

- Nanomaterials synthesis using nanoscale optical antenna and device development

- Near-field scanning optical microscopy

- Near-field radiation and nanostructures for efficient photovoltaic energy conversion

- High density data storage using nanoscale optical antenna

Keywords: Nanoscale heat transfer, thermoelectrics, photovoltaic, nano-optics, near-field optics, ultrafast laser, phonon spectroscopy, nano-manufacturing, nano-lithography, N/MEMS

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