Jun-Fu Liu

University of New Hampshire, Durham, NC, United States

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Publications (4)8.56 Total impact

  • Jun-Fu Liu, Glen P Miller
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    ABSTRACT: The tip-based nanofabrication method called field-assisted nanopatterning or FAN has now been extended to the transfer of metals, metal oxides and metal salts onto various receiving substrates including highly ordered pyrolytic graphite, passivated gold and indium-tin oxide. Standard atomic force microscope tips were first dip-coated using suspensions of inorganic compounds in solvent. The films prepared in this manner were non-uniform and contained inorganic nanoparticles. Tip-based nanopatterning on chosen substrates was conducted under high electric field conditions. The same tip was used for both nanofabrication and imaging. Arbitrary patterns were formed with dimensions that ranged from tens of microns to sub-20 nm and were controlled by tuning the tip bias during fabrication. Most tip-based nanopatterning techniques are limited in terms of the type of species that can be deposited and the type of substrates onto which the deposition occurs. With the successful deposition of inorganic species reported here, FAN is demonstrated to be a truly versatile tip-based nanofabrication technique that is useful for the deposition of a wide variety of both organic and inorganic species including small molecules, large molecules and polymers.
    Nanotechnology 03/2009; 20(5):055303. · 3.84 Impact Factor
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    ABSTRACT: We combine scanning tunneling microscopy (STM) measurements with ab initio calculations to study the self-assembly of long chain alkanes and related alcohol and carboxylic acid molecules on graphite. For each system, we identify the optimum adsorption geometry and explain the energetic origin of the domain formation observed in the STM images. Our results for the hierarchy of adsorbate-adsorbate and adsorbate-substrate interactions provide a quantitative basis to understand the ordering of long chain alkanes in self-assembled monolayers and ways to modify it using alcohol and acid functional groups.
    The Journal of Chemical Physics 04/2008; 128(12):124709. · 3.12 Impact Factor
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    ABSTRACT: Although related to conventional carbon nanotubes in both shape and construction, fullerene nanowhiskers and fullerene nanotubes have received far less attention. A modified liquid-liquid interfacial precipitation technique is described to produce relatively uniform batches of [60]fullerene nanotubes in high yield. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) reveal that the tubes possess approximately 100-nm inside diameters and 300-nm outside diameters. The [60]fullerene nanotubes degrade slowly at 180 degrees C, eventually collapsing into micron scale [60]fullerene discs and rods, as revealed by optical microscopy and AFM. Ultrasonic cavitation chops [60]fullerene nanotubes into smaller segments within seconds. Longer ultrasonic bathing leads to considerable structural damage in which the sidewalls rupture. Mechanical stress tests using an AFM microscope tip effectively dent and break [60]fullerene nanowhiskers, revealing a hollow interior.
    Microscopy Research and Technique 07/2007; 70(6):513-21. · 1.59 Impact Factor
  • Jun-Fu Liu, Glen P. Miller
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    ABSTRACT: A new atomic force microscopy (AFM)-based lithography method called field-assisted nanopatterning (FAN) has been demonstrated. Through the use of a conventional atomic force microscope with no alterations, FAN controllably patterns solid or liquid organic and inorganic molecules in the air under ambient conditions. In this manner, patterns can be produced with feature sizes that range from tens of microns to sub-20 nm. Examples include the high-resolution FAN of [60]fullerene, N-methylpyrrole, naphthalene, poly-3-octylthiophene, polyaniline, meso-tetraphenylporphyrin, and gold. These molecules have been patterned onto highly ordered pyrolytic graphite, indium−tin oxide, Au, and passivated Au. The molecules are first coated on a standard AFM tip and then are deposited onto the substrate when a threshold tip bias is achieved. The deposition process is a field-assisted transfer of the molecules from the tip to the substrate. Patterning is turned on or off by controlling tip bias, and the same tip is used for both patterning and imaging. Pattern dimensions are controlled by varying tip bias and fabrication (tip) speed.
    Journal of Physical Chemistry C - J PHYS CHEM C. 06/2007; 111(29).