Department of Chemistry



H. Liu group

The H. Liu group takes a physical chemistry approach to study wetting phenomenon at the nanoscale. Part of their work is very fundamental in nature, aimed at understanding the most basic properties of nanomaterials. At the same time, his group also develops technologies that exploit wetting phenomena for material synthesis and nanofabrication. Intrinsic surface properties of graphitic carbon materialsCarbon material is one of the most important fuel sources and also extensively used in batteries, lubricants, and refractories. Surprisingly, recent work in the H. Liu group showed that many of the most fundamental properties of graphitic carbon (e.g., surface energy) have not been properly measured and understood. For example, it has long been established since the 1940s that graphite is hydrophobic. However, the H. Liu group discovered that a clean graphene and graphite is in fact mildly hydrophilic. The previously observed hydrophobicity was entirely due to unintentional contamination by airborne hydrocarbons (Figure 1, top). Their subsequent work showed that the currently accepted surface energy of graphite is also affected by the same contamination and is significantly lower than the intrinsic value. Based on their discovery, the group recently developed a novel method to disperse 2D materials in water without using any surfactant (Figure 1, bottom).Figure 1. Top: Airborne hydrocarbon contamination makes graphite more hydrophobic. Shown here are water contact angle measurements of freshly-cleaved and air-aged highly oriented pyrolytic graphite (HOPG) samples. Adapted from Nature Mater. 2013, 12, 925. Copyright 2013 Nature Publishing Group. Bottom: Karen showing off a vial of graphene dispersion. From left to right: graduate student Christopher J. Kurpiel, Professor Haitao Liu, and graduate student Karen B. Ricardo. DNA-mediated surface reactions and their applications in nanolithography Self-assembled DNA nanostructure (also known as DNA origami) is a very attractive template for bottom-up nanofabrication. However, due to its poor chemical stability, pattern transfer from DNA to inorganic substrates has been a long-standing challenge. The H. Liu group is developing chemistries that are compatible and responsive to the presence of DNA templates. For example, they discovered that the water adsorbed near a DNA nanostructure catalyzes the HF etching of SiO2 to transfer the shape of DNA to a SiO2 substrate. This catalytic effect is a very local one and can result in sub-10 nm patterns. This discovery opened the door to use DNA nanostructure as a general-purpose template for bottom-up nanofabrication. Following a similar concept, the group also developed chemical vapor deposition reactions that selectively deposit inorganic oxides onto a DNA template. Ongoing work in this area focuses on the fabrication of 3D nanostructures as well as using DNA nanostructure to modulate high temperature solid-state reactions.Figure 2. Top: A single strand of DNA can modulate the rate of HF etching of SiO2. Depending on the vapor pressure of water, the reaction results in either positive-tone or negative-tone pattern transfer. Adapted from J. Am. Chem. Soc. 2011, 133, 11868. Copyright 2011 American Chemical Society. Bottom: DNA nanotechnology sub-group. From left to right: H. Liu group (spring 2015). From left to right: Haitao Liu, Zhenbo Peng, Cheng Tian, Anqin Xu, Dong Wang, Mina Kim, Muhammad Salim, Karen Ricardo, Justin Hurst, HyoJeong Kim, Christopher Kurpiel, and Feng Zhou