We report an ultrasound exfoliation of graphite in a weakly basic solution to produce multi-layer graphene dispersion. A unique feature of this process is that no surfactant was added to stabilize the exfoliated graphene in water. The concentration of the graphene dispersion prepared by this approach can be up to 0.02 mg mL(-1) and it was stable at room temperature for several months.

We report a mechanistic study of a DNA-mediated vapor phase HF etching of SiO 2 . The kinetics of SiO 2 etching was studied as a function of the reaction temperature, time, and partial pressures of H 2 O, HF, and 2-propanol. Our results show that DNA locally increases the etching rate of SiO 2 by promoting the adsorption of water and that the enhancement effect mostly originates from the organic components of DNA. On the basis of the mechanistic studies, we identified conditions for high-contrast (>10 nm deep), high-resolution (∼10 nm) pattern transfers to SiO 2 from DNA nanostructures as well as individual double-stranded DNA. These SiO 2 patterns were used as a hard mask for plasma etching of Si to produce even higher-contrast patterns that are comparable to those obtained by electron-beam lithography. ■ INTRODUCTIONIn recent years, research in DNA nanostructures has developed to a stage in which arbitrarily shaped and mechanically robust nanostructure can be constructed 1−8 with a theoretical precision of <5 nm at a cost as low as $6/m 2 . 9 The deposition of DNA nanostructures on the substrates has been demonstrated with precise control over their location and orientation, making them ideal templates for high-resolution, low-cost nanofabrication. 10−12 However, the pattern transfer from DNA nanostructures to inorganic substrates remains a bottleneck of this area of research. Tremendous efforts were dedicated to overcome the lack of chemical stability of DNA and the inadequate adhesion interaction between DNA and the substrate. 13 Metallization is the most widely used approach to DNAbased nanofabrication. Solution phase metallization of λ-DNA was first demonstrated by Sivan and co-workers. 14 Recently, the metallization of different metals, such as Ag, Cu, Ni, and Au, on DNA strands and DNA nanostructures has been demonstrated. 2,15−17 In addition to the deposition of metal onto the whole nanostructure, site-specific metallization was also made possible by modifying DNA nanostructure with binding sites that accept DNA-modified Au or Ag nanoparticles. 18−20 In addition to these solution phases approaches, vapor phase deposition of metals onto DNA has also been reported by the groups of Mao and Woolley. They used DNA to pattern vapor phase deposited metal, and the resulting metal film can be used as a hard mask for patterning the underlying substrate. 21−23 Our group recently showed that DNA nanostructures can modulate certain surface reactions to produce a faithful pattern transfer from the DNA nanostructures to an inorganic substrate. 24,25 In one of the studies, DNA was shown to have a local effect on the vapor phase HF etching, which resulted in direct negative-tone and positive-tone pattern transfers from DNA to SiO 2 . 24 The fact that DNA can be used to directly pattern SiO 2 carries significant technological significance because SiO 2 is one of the most important hard mask materials for semiconductor nanofabrication. 26 Although our early study established vapor phase HF etching as a promising appr...

DNA nanostructures are versatile templates for low cost, high resolution nanofabrication. However, due to the limited chemical stability of pure DNA structures, their applications in nanofabrication have long been limited to low temperature processes or solution phase reactions. Here, we demonstrate the use of DNA nanostructure as a template for high temperature, solid-state chemistries. We show that programmably shaped carbon nanostructures can be obtained by a shape-conserving carbonization of DNA nanostructures. The DNA nanostructures were first coated with a thin film of Al2O3 by atomic layer deposition (ALD), after which the DNA nanostructure was carbonized in low pressure H2 atmosphere at 800-1000 °C. Raman spectroscopy and atomic force microscopy (AFM) data showed that carbon nanostructures were produced and the shape of the DNA nanostructure was preserved. Conductive AFM measurement shows that the carbon nanostructures are electrically conductive.

Fluorescent organic dyes photobleach under intense light. Graphene has been shown to improve the photo-stability of organic dyes. In this paper, we investigated the Raman spectroscopy and photo-bleaching kinetics of dyes in the absence/presence of chemical vapor deposition (CVD)-grown graphene. We show that graphene enhances the Raman signal of a wide range of dyes. The photo-bleaching of the dyes was reduced when the dyes were in contact with graphene. In contrast, monolayer hexagonal boron nitride (h-BN) was much less effective in reducing the photo-bleaching rate of the dyes. We attribute the suppression of photo-bleaching to the energy or electron transfer from dye to graphene. The results highlight the potential of CVD graphene as a substrate for protecting and enhancing Raman response of organic dyes.

We report the deposition of DNA origami nanostructures on highly oriented pyrolytic graphite (HOPG). The DNA origami goes through a structural rearrangement and the DNA base is exposed to interact with the graphite surface. Exposure to ambient air, which is known to result in a hydrophilic-to-hydrophobic wetting transition of HOPG, does not significantly impact the deposition yield or the shape deformation of DNA nanostructures. The deposited DNA nanostructures maintain their morphology for at least a week and promote site-selective chemical vapor deposition of SiO. This process is potentially useful for a range of applications that include but are not limited to nanostructure fabrication, sensing, and electronic and surface engineering.