Haitao Liu

Research thrust I: Intrinsic properties of graphitic carbon materials

Graphite and other forms of graphitic carbon materials have found widespread applications in areas such as electrochemical energy storage, water purification, and catalyst support. Most of these applications involve a carbon surface in contact with either air or water, making the interfacial properties of graphitic materials an important topic of research.

Our work revealed a strong environmental influence on the surface properties of carbon materials. Unintentional surface contamination by the environment masks the intrinsic properties of carbon materials but has not been recognized by the community prior to our work. As such, our work has overturned a number of long-held views about graphitic materials. For example, it has been established since the 1940s that graphite is hydrophobic (i.e., it does not ‘like’ water). However, we discovered that clean graphite and graphene surfaces are in fact mildly hydrophilic. The previously observed hydrophobicity was entirely caused by unintentional contamination from airborne hydrocarbons; this contamination occurs within several minutes of exposing a graphitic surface to air and has been overlooked for the past 70 years! More importantly, this initial discovery suggests that many other surface properties of carbon materials (e.g., surface energy, double layer capacitance, and heterogeneous electron transfer rate) are likely impacted as well and that their literature values are likely not intrinsic.

Our ongoing work focuses on the study of electrochemical and chemical properties of clean graphene under mechanical or electrical stress. Our goal is to discover new catalytic properties not found in the ‘dirty’ carbon electrodes. In addition, we are also interested in developing the application of clean carbon materials in composite materials and air/water purification.

Research thrust II: DNA-based nanofabrication.

Self-assembled DNA nanostructure is an attractive template for ultra-high resolution (< 10 nm) and low-cost (< $10s/m2) nanofabrication. DNA nanostructures can be made into both 2D and 3D shapes with a resolution down to ca. 5 nm and size up to micrometer range.

 My research has been focused on the development of new pattern transfer methods for DNA-based nanofabrication. Due to the low chemical and mechanical stability of DNA templates, they are not compatible with most of the pattern transfer methods used in traditional lithography. Our early work discovered that DNA templates could change the amount of molecular catalyst or precursor that can be adsorbed by the substrate, which in turn changes the rate of etching or deposition reactions on the surface. This mechanism of pattern transfer is conceptually very different from that of the traditional lithography, which is based on physical masking. This fundamental research has resulted in a number of novel pattern transfer methods that can produce sub-20 nm resolution patterns on Si, self-assembled monolayers, and polymers.

Our ongoing work in this area focuses on two directions: (1) Scaling-up the DNA-based nanofabrication to allow patterning of large area substrates. (2) Fabrication of integrated nanoelectronics devices (transistors, memories) using DNA templates.

Postdoctoral, graduate research assistant, and undergraduate research assistant positions are available, please contact Prof. Haitao Liu (hliu@pitt.edu) for details. 

The Liu Group is currently accepting new graduate students.