Assistant Professor
Ph.D Harvard University

Physical chemistry of nanomaterials and biomaterials

Group website

My research interests are centered on the physical chemistry of nanometer scaled materials and molecules. In particular, we aim to develop expertise in scanning force microscopy (SFM) and use this powerful and versatile tool to explore the physics, chemistry, and biology at the nanometer length scale.

AFM-based structural biology

In spite of the fast development in conventional structural biology methods such as X-ray crystallography and NMR, the structure of large complexes consist of multiple proteins and DNAs that have overall size on the order of a few to tens of nanometers remains highly challenging. In addition, some important biological questions are critically associated with the structure of intrinsically heterogeneous complexes, which conventional methods are inadequate to answer. AFM based single-molecule approach complements the conventional methods by studying the structure of each individual molecules and complexes. It measures global structural features of complexes on the order of nanometer to tens of nanometers although it is not capable of giving atomically resolved structures. Equipped with an up-to-date Asylum Research AFM, we will investigate both the AFM methodology and the structural biology of some specific systems such as DNA repair enzymes and plant extra-cellular matrix.

Organic nano-electronic materials

Organic electronics takes advantage of varieties in organic building blocks and versatility in molecular engineering methods to explore new and cheap applications that are orthogonal to conventional inorganic electronic materials. Promising applications include light-emitting diodes, thin-film transistors (TFTs) and photovoltaic devices; these devices can be integrated to make lightweight and flexible display and solar cells.

We are interested in studying fundamental questions using Electronic Force Microscopy (EFM) and Scanning Kelvin Probe Microscopy (SKPM). EFM and SKPM are variations of SFM that measure the electrostatic field gradient and electrostatic potential at the sample surface. By depositing very thin layers of nano-electronic materials on metallic or dielectric substrates, interfacial electronic structures and properties such as band bending and electronic level alignment at interfaces can be studied.

1. Liwei Chen, K.A. Haushalter, C.M. Lieber, and G.L. "Verdine Direct Visualization of a DNA Glycosylase" Searching for Damage Chemistry and Biology, 9, 345-350 (2002)
   
   
2. Liwei Chen, Chin Li Cheung, Paul Ashby and Charles Lieber "Single-Walled Carbon nanotube AFM Probes: Optimal Imaging Resolution of nanoclusters and Biomolecules in Ambient and Fluid Environments" Nano Letters, 4, 1725-1731 (2004)
   
   
3. Liwei Chen, R. Ludeke, Xiaodong Cui, Alejandro Schrott, Cherie Kagan, Louis E. Brus "Electrostatic field and Fermi level pinning at the pentacene-SiO2 interface" Journal of Physical Chemistry B, 2004, in press
   
   
4. Oksana Cherniavskaya, Liwei Chen, Mohammad A. Islam, and Louis Brus "hotoionization of Individual CdSe/CdS Core/Shell Nanocrystals on Silicon with 2-nm Oxide Depends on Surface Band Bending" "Nano Letters, 3, 497-501 (2003)
   
   
5. Oksana Cherniavskaya, Liwei Chen, Vivian Weng, Leonid Yuditsky, Louis E. Brus "Quantitative Non-contact Electrostatic Force Imaging of Nanocrystal Polarizability" Journal of Physical Chemistry B, 107,1525-1531, (2003)