*** NONTECHNICAL ABSTRACT *** This Faculty Early Career Award funds a project that will investigate novel light-matter interactions in low-dimensional graphitic materials. Such graphitic structures, including two-dimensional graphene and one-dimensional carbon nanotubes, have remarkable electrical, mechanical, and optical properties. This research project will advance our fundamental understanding of these novel carbon materials, the knowledge of which could enable new type of electronic and photonic devices. It also provides an active learning environment to train students with interdisciplinary skills. This CAREER project will take advantage of the diverse student body and education activities in UC Berkeley, including the Berkeley Edge program and the Cal-Teach platform, to enhance broad participation in science and technology.
This Faculty Early Career Award funds a project that will investigate novel light-matter interactions in graphene and carbon nanotubes. The remarkable physical properties of these low-dimensional graphitic systems have spurred a worldwide effort in their transport studies. The proposed research will advance our understanding of their photophysics using individual nanostructure spectroscopy. The CAREER project will focus on exploring Dirac fermion physics in gated graphene bilayers, which is expected to exhibit fascinating pseudo-spin phenomena and non-trivial Berry?s phases, and on probing ultrafast dynamics and quantum coherence in individual chirality-defined carbon nanotubes. This research will shed light on a range of important dynamical behavior of graphitic materials, including electron coherence and dephasing mechanisms and energy transfer processes. Situated at the interface of nanoscience and optical physics frontiers, the proposed research provides a truly interdisciplinary learning environment for graduate students as well as undergraduate students. Such education and outreach effort will be an integral part of this research project.
In his CAREER award, Wang has made several seminal contributions to understanding of light matter interaction in low dimensional materials, including (1) first discovery of indirect-bandgap to direct-bandgap transition in MoS2 monolayer, (2) mapping out one-to-one correspondence between chirality and optical transitions of carbon nanotubes, and (3) observing quantum coupled radial-breathing oscillation in double walled carbon nanotubes. In the MoS2 study, Wang observed for the first time an emerging photoluminescence when bulk MoS2 crystal is thinned to monolayer, revealing an indirect to direct bandgap transition in this d-electron system as a function of layer thickness. This discovery played a key role to ignite tremendous interests in optical property in MoS2 and related materials, and it has been cited by over 300 times since its publication (Splendiani et al, Nano Lett., 2010). In the second study, Wang established for the first time a one-to-one mapping between carbon nanotube atomic structure and its optical transitions by combining electron diffraction and Rayleigh scattering measurement on over 200 individual carbon nanotubes. This complete mapping between nanotube chiral index and optical transitions provides the ultimate reference for nanotube spectroscopic characterization, and enables systematic understanding of 1D many-body effects in carbon nanotube excited states (Liu et al, Nature Nanotechnology, 2012). In the third study, Wang first demonstrated that DWNT radial breathing oscillations are collective modes characterized by concerted inner- and outer-wall motions. These coupled RBM oscillations form novel quantum mechanical systems, which interact quantum mechanically with electronic excitations in both nanotube walls and vary strongly with DWNT structures (Liu et al, Nature Communications, 2013). Three additional papers (Liu et al, Phys. Rev. B, 2011; Hong et al,Optics Letter, 2012; Zhou et al, Carbon, 2012) were also supported by this CAREER award. Broader Impacts/Education: Graduate and undergraduate education is closely integrated in Wang’s research program. In the last four years, Wang has incorporated 9 undergraduate students in his NSF CAREER award research. Most of them have gone to top graduate program to continue pursuing research in physics or engineering.
