About

Hongjie Dai's research lab at Stanford University

The research of our group interfaces with chemistry, physics, materials science and biological and medical sciences. Thus far, our group has made advances to the basic science of carbon nanotube and graphene and potential applications in the areas of nanoelectronics, nanobiotechnolgy, nanomedicine, energy storage and catalysis.

Our past research has focused on the science and technology of novel carbon based materials. Our recent research has branched into new materials including hybrid materials of various nanocrystals and nanoparticles with nano-carbon materials.

Materials chemistry, physics and nanoelectronics

Since 1997, we have developed the synthesis of self-oriented carbon nanotube arrays (or vertically aligned CNTs) [Fan, Science, 1999] and demonstrated that 1D nanomaterials can be synthesized in patterned and self-aligned fashions. We also developed the synthesis of high quality single-walled carbon nanotubes (SWNTs) by chemical vapor deposition (CVD) and their ordered, aligned growth [Kong, Nature, 1998]. This research has enabled deterministic synthesis of arrays of addressable electrical devices of individual nanotube quantum wires [Soh, Appl. Phys. Lett., 1999]. The approach has been used by many labs around the world for the synthesis of high quality SWNTs.

The high quality CVD SWNTs synthesized by our method are superior to other materials in terms of cleanness and high structural perfection desired for studying fundamental physics in one-dimensional systems. With high quality nanotubes, we and others have carried out electron transport measurements of ultra-clean nanotubes including the observation of ballistic transport in these 1D systems [Kong, Phys. Rev. Lett., 2001]. We have also carried out electromechanical investigations of single-walled nanotubes to uncover the influence of mechanical deformation to electron transport in these materials [Tombler, Nature, 2000; Cao, PRL, 2003].

In the nanoelectronics area, we have advanced carbon nanotube field effect transistors (FETs). High performance nanotube FETs with integrated high e gate dielectrics [Javey, Nature Materials, 2002] have been enabled to achieve ~ 70 mV/decade subthreshold swing. We have pushed the limit of nanotube FETs to the ballistic regime by developing ohmic contacts to ultrashort semiconducting nanotubes [Javey, Nature, 2003].

Our group has developed nanotube electronic sensors, based on our observation of molecular interactions with nanotubes drastically affecting the electrical properties of nanotubes [Kong, Science, 2000]. This has led to the exploration of nanosensors based on nanotubes and semiconductor nanowires.

We have developed a novel noncovalent functionalization method for carbon nanotubes by supramolecular p-p stacking. The original work published in JACS on pyrene p-stacking on nanotubes [R. Chen et al., 2001] has led to supramolecular functionalization chemistry for various graphitic nanomaterials.

Nanobiotechnology and Nanomedicine

Our group has developed biological and medical applications of carbon nanotubes [Liu, Nano Res., 2010] including drug delivery systems [Liu, Cancer Res. 2008] [Dhar et al., J. Am. Chem. Soc. 2008], in vitro and in vivo raman [Liu et al, JACS, 2008; Liu et al., Nano Res., 2010] and near-infrared (NIR) imaging (in the unusual but beneficial >1mm regime) [Welsher, Nature Nano, 2009] techniques, and novel protein microarrays based on nanotube SERS tags with femto-molar sensitivity [Chen et al., Nature Biotech, 2008]. We have also demonstrated photothermal tumor destruction using carbon nanotube near-infrared antennas in vitro and in vivo with mouse tumor models [Kam, PNAS, 2005][Robinson, Nano Res. 2010].

Novel Materials for Energy and Catalysis Research

This will be one of the most exciting research fronts in our group.

Recently, our group has developed several chemical methods to synthesize graphene sheets [Li, Nature Nano, 2008] and graphene nanoribbons [Li, Science, 2008][Jiao, Nature, 2009][Jiao, Nature Nano, 2010]. Graphene nanoribbons are considered a new allotrope of carbon materials due to distinct properties than the parent 2D graphene and nanotubes. We have demonstrated unzipping carbon nanotubes to form graphene nanoribbons that exhibit semiconducting characteristics due to quantum confinement effects.

We have developed the synthesis of various nanocrystals and nanoparticles on graphene, expanding our research into a wide range of material systems. For instances, Ni(OH)2 nanocrystals grown on graphene sheets with various degrees of oxidation are synthesized and investigated as advanced electrochemical pseudocapacitor materials for potential energy storage applications [Wang, JACS, 2010] [Wang, JACS, 2010 ]. We also developed the growth of Mn3O4 nanocrystal on graphene oxide (GO) to form a Mn3O4-reduced GO (RGO) hybrid material. The Mn3O4/RGO hybrid afforded an unprecedented high capacity of ~900mAh/g for Mn3O4 based anode [Wang, JACS, 2010].

We developed a direct synthesis of TiO2 nanocrystals on graphene oxide (GO) and demonstrated advanced photocatalytic properties of the resulting hybrid material. The resulting hybrid material showed superior photocatalytic degradation of rhodamine B and methylene blue over various other TiO2 materials [Liang, Nano Res. 2010], opening the possibilities of photocatalysis with novel hybrid materials.

Contact Info

Hongjie Dai

Department of Chemistry

Stanford University

William Keck Science Building rm 125

Stanford, CA 94305-5080

tel 650 723 4518

fax 650 725 9793

email hdai1@stanford.edu