News:

• A press release of our 3D printing work has been published on Optica, MSN, Phys.org, Science Daily, Purdue ME, 3dprinting.com and 3printr.com.
• Anwarul and Jason published their work in Optics Express!
• Mauricio published his work in Applied Physics Letters!
• Yikang and Mauricio published their work in Advanced Functional Materials!
• Shouyuan and Neil published their work in Nano Letters!

Check here for more group news.

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

(1) Nanoscale energy transport

We investigate energy transport in nanoscale materials used for efficient energy transfer and conversion, and for controlling - reducing or enhancing - thermal transport in modern electronic materials and devices. At a micro- and nano-scale, energy transport and conversion is ultimately determined by the 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) resolution experimental techniques (e.g., coherent phonon spectroscopy), Raman spectroscopy based thermometry, and high resolution (~ 10 nm) scanning probe based thermometry for the study of nanoscale energy transfer and conversion processes.

Current research projects include (details see Research Projects):

• Energy transport in 2D materials (very thin materials of a few atomic layers bonded by van der Waals forces which are used for new-generation electronic devices)

• Near field radiation (radiation between two very closed spaced surfaces) and radiation inside 2D materials

• Thermoelectric phenomena in 2D materials

• Applications: thermal management in electronic materials and devices, active thermal transport control, converting waste heat to power, photovoltaic for solar energy utilization

Thermal transport in the topological insulated surface state (TSS) in topological insulator (TI) thin films. The measured in-plane thermal conductivity indicates a large thermal conductivity and a large Lorenz number L of TSS.	Spatiotemporal response of a material after laser excitation. The high resolution of the pump-probe system allows for the direct measurement of the electrical thermal transport properties of a material.	Tunable thermoelectrics of a TI material using optical helicity (circular polarized light) and back gating, to enhance converting heat to power or enhance cooling of electronic devices.	Near-field radiative heat transfer between two closely spaced surfaces, which exceeds blackbody radiation by 18,000 times.

(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. One of our major effeorts is rapid 3D nanoscale printing. The main issue in 3D printing is its speed. We are developing various technologies for rapid, continuous 3D nanoscale printing. We also conduct research on laser-based nano-engineering utilizing nanoscale optical antennas 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 nanoscale with high intensity has numerous applications in nano-manufacturing, energy conversion, nanoscale imaging and diagnostixs, and ultra-high density data storage.

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

• Nanoscale rapid continuous 3D projection printing

• Parallel nanolithography and nanomaterials sythesis using nanoscale optical antenna and device development

• Near-field scanning optical microscopy with nanometer resolution

• High density data storage using nanoscale optical antenna

Ultrafast laser projection nanoscale printing for fabrication of arbitrary, complex 3D microstructures in a continuous manner at high volumetric print rates.