报告时间：2017年5月22日下午14:00

报告地点：科技创新大楼C501室

Synthesis and Applications of Novel Two-Dimensional Nanomaterials

ZHANG Hua（张华）

In this talk, I will summarize the recent research on synthesis, characterization and applications of two-dimensional nanomaterials in my group. I will introduce the synthesis and characterization of novel low dimensional nanomaterials, such as graphene-based composites including the first-time synthesized hexagonal-close packed (hcp) Au nanosheets (AuSSs) on graphene oxide, surface-induced phase transformation of AuSSs from hcp to face-centered cubic (fcc) structures, the synthesis of ultrathin fccAu@PtandAu@Pdrhombic nanoplates through the epitaxial growth of Pt and Pd on the hcp AuSSs, respectively, the first-time synthesis of 4H hexagonal phase Au nanoribbons (NRBs) and their phase transformation to fcc Au RNBs as well as the epitaxial growth of Ag, Pt and Pd on 4H Au NRBs to form the 4H/fccAu@Ag,Au@PtandAu@Pdcore–shell NRBs, and the epitaxial growth of metal and semiconductor nanostructures on solution-processable transition metal dichalcogenide (TMD) nanoshees at ambient conditions, single- or few-layer metal dichalcogenide nanosheets and hybrid nanomaterials, the large-amount, uniform, ultrathin metal sulfide and selenide nanocrystals, other 2D nanomaterials, nanodots prepared from 2D nanomaterials, and self-assembled 2D nanosheets and chiral nanofibers from ultrathin low-dimensional nanomaterials. Then I will demonstrate the applications of these novel nanomaterials in chemical and bio-sensors, solar cells, water splitting, hydrogen evolution reaction, electric devices, memory devices, conductive electrodes, other clean energy, etc.

Perovskite Materials: my research at NTU

WANG Junling （王峻岭）

Perovskite materials, including oxides and the recently developed hybrid lead halides, possess a wide spectrum of unique properties such as ferroelectricity, ferromagnetism, superconductivity and superior light absorbing properties. They have been extensively studied during the past decades for both funda-mental physics and applications.

In this talk, I will briefly introduce our recent work on the following topics:
(1) Photovoltaic effect in ferroelectric perovskite oxides. Ferroelectric oxides possess spontaneous polarization that can be switched by an external field. The spontaneous polarization generates an internal field that can be used to separate electron-hole pairs just like in a pn junction solar cell. Though the ferroelectric photovoltaic efficiency is generally low due to the large band gap, there are still interesting applications.
(2) Photovoltaic effect in hybrid lead halide perovskites. Efficiency of solar cells using the hybrid lead halide perovskites has increased dramatically during the last couple of years. However, the reason behind the long carrier lifetime and diffusion length is still under debate. We suggest that the polar nature of the A-site molecule is crucial.
(3) Ferroelectricity in 2D materials. If time permits, I will also introduce our recent discovery of ferroelectricity in a 2D material down to a few atomic layers.

References
1, “Non-volatile memory based on ferroelectric photovoltaic effect”, Rui Guo, Lu You, Yang Zhou, Zhi Shiuh Lim, Xi Zou, Lang Chen, R. Ramesh, Junling Wang*, Nature Communications, 4:1990 doi: 10.1038/ncomms2990 (2013)
2, “Oxygen Driven Anisotropic Transport in Ultra-thin Manganite Films”, Baomin Wang, Lu You, Peng Ren, Xinmao Yin, Yuan Peng, Bin Xia, Lan Wang, Xiaojiang Yu, Sock Mui Poh, Ping Yang, Guoliang Yuan, Lang Chen, Andrivo Rusydi* and Junling Wang*, Nature Communications, 4:2778 doi: 10.1038/ncomms3778 (2013).
3, “Giant Photostriction in Organic-Inorganic Lead Halide Perovskites”, Yang Zhou, Lu You, Shiwei Wang, Zhiliang Ku, Hongjin Fan, Daniel Schmidt, Andrivo Rusydi, Lei Chang, Le Wang, Peng Ren, Liufang Chen, Guoliang Yuan, Lang Chen and Junling Wang*, revised (2015).

Ag₂S QDs for Advanced In Vivo Imaging: Seeing is Believing

WANG Qiangbin（王强斌）

Fluorescent imaging in the second near-infrared window (NIR-II, 1.0~1.4 μm) is appealing in in vivo imaging due to minimal autofluorescence and negligible tissue scattering in this region, affording maximal penetration depth for deep tissue imaging with high feature fidelity. Herein, for the first time, we reported a new type of NIR-II QDs-Ag2S QDs and executed a series of in vivo imaging studies by using Ag2S QDs. The results show that, by using Ag2S QDs, the tissue penetration length can reach 1.5 cm, and the spatial and temporal resolution of the in vivo imaging can down to 25 µm and 50 ms, respectively, which are improved several to dozens of times in comparison with those using conventional fluorescence nanoprobes in the visible and the first near-infrared window (650-900 nm), offering in situ, real-time visualization of the biological events in vivo. With the advanced NIR-II fluorescence of Ag2S QDs, high signal to noise ratio imaging of tumor growth and angiogenesis, imaging-guided targeting drug-delivery and therapeutics, imaging-guided precision surgery of glioma, and stem cell tracking and regeneration in vivo, etc, have been achieved.