Showing papers by "Xiaogang Liu published in 2003"

Nanopatterning of “Hard” Magnetic Nanostructures via Dip-Pen Nanolithography and a Sol-Based Ink

Abstract: A direct-write method for fabricating “hard” magnetic barium hexaferrite, BaFe12O19 (BaFe), nanostructures, based on dip-pen nanolithography and a sol−gel process, is presented. This method utilizes a conventional atomic force microscope tip, coated with the BaFe precursor solution, to generate patterns that can be post-treated at elevated temperature to generate magnetic features consisting of barium ferrite in its hexagonal magnetoplumbite (M-type) structure. Features ranging from several hundred nm down to below 100 nm were generated and studied using AFM, magnetic force microscopy, and X-ray photoelectron spectroscopy. The approach offers a new way for patterning functional inorganic nanostructures with deliberate control over feature size and shape, as well as interfeature distance and location.

Surface and Site‐Specific Ring‐Opening Metathesis Polymerization Initiated by Dip‐Pen Nanolithography

Abstract: Patterned polymeric structures have attracted significant interest for possible applications in the development of sensors, catalysis, and optical devices. Thus far, several strategies, based upon photolithography, electron beam lithography, and microcontact printing have been developed for generating polymer arrays. While useful for many applications, these methods do not allow one to control nanostructure composition in a site-specific manner and, therefore, do not allow one to fabricate complex multicomponent polymer arrays over the nanoto micrometer length scales. Having the capability to generate multicomponent arrays with nanoscopic features could afford one the opportunity to construct and study high-density combinatorial libraries of novel macromolecular systems. Herein, we report a novel approach, based upon dip-pen nanolithography (DPN) and ring-opening metathesis polymerization (ROMP), to the fabrication of polymer brush arrays on the nanometer length scale. The combined approach utilizes the attributes of DPN and ROMP for synthesizing high-density polymer brush arrays with control over feature size (on the nanometer length scale), shape, and interfeature distance. Furthermore, the capability of directly delivering monomers through a standard AFM microcantilever will allow one to generate small, but diverse, libraries of nanoscale polymer brushes that comprise large numbers of structurally distinct compounds by assembling many possible combinations of small building monomers containing desired active functionalities. To explore the potential of the combined approach and provide the basis for the studies leading to the design of combinatorial polymer libraries, two complementary routes have been developed for synthesizing arrays of the nanoscale polymer brushes based on DPN and ROMP. Route 1 is an approach based on growing polymers from a DPN-patterned template (Scheme 1). To test the viability of this route, 10(exo-5-norbornen-2-oxy)decane-1-thiol molecules were patterned on a gold substrate by bringing a tip coated with norbornenylthiol in contact with the substrate. The exo isomer rather than the corresponding endo isomer was used to optimize ROMP reactivity. Subsequently, the substrate

Patterning magnetic nanostructures

Abstract: A direct-write method for fabricating magnetic nanostructures, including hard magnetic nanostructures of barium hexaferrite, BaFe, based on nanolithographic printing and a sol-gel process. This method utilizes a conventional atomic force microscope tip, coated with a magnetic material precursor solution, to generate patterns that can be post-treated at elevated temperature to generate magnetic features consisting of barium ferrite in its hexagonal magnetoplumbite (M-type) structure. Features ranging from several hundred nm down to below 100 nm were generated and studied using AFM, magnetic force microscopy, and X-ray photoelectron spectroscopy. The approach offers a new way for patterning functional inorganic magnetic nanostructures with deliberate control over feature size and shape, as well as interfeature distance and location.

Single-Walled Carbon Nanotubes and C60 Encapsulated by a Molecular Macrocycle

Abstract: Computational simulations of macrocycle-encapsulated single-walled carbon nanotubes (SWNTs) and C60 are reported. A molecular mechanical force field method has been used to calculate the physical properties of these complexes. The calculation shows that the macrocycle-encapsulated SWNTs and C60 are more stable than free SWNTs and C60. When macrocycles are bound to SWNTs, energetically stable well regions have been observed. The energetic and dipolar changes of an armchair SWNT upon binding by a macrocycle are different from those of a zigzag SWNT. SWNTs with pentagon−heptagon defects are compared with normal SWNTs. Calculated large energetic stabilization in a water environment suggests that wrapping inorganic macrocycles around SWNTs can promote the solubility of SWNTs.

Structuration de nanostructures magnetiques

Abstract: L'invention concerne un procede d'ecriture directe permettant de fabriquer des nanostructures magnetiques, notamment des nanostructures magnetiques dures d'hexaferrite de baryum, BaFe, sur la base d'une impression nanolithographique et d'un procede sol-gel. Le procede met en oeuvre une pointe de microscope a force atomique classique, revetue d'une solution de precurseur de materiau magnetique, de maniere a produire des structures pouvant etre traitees par la suite a une temperature elevee aux fins de production de caracteristiques magnetiques sous la forme de ferrite de baryum dans sa structure hexagonale de magnetoplumbite (M-type). Des caracteristiques allant de plusieurs centaines de nm jusqu'au-dessous de 100 nm ont ete produites et etudiees au moyen de AFM (microscopie a force magnetique) et de la spectroscopie de photoelectrons induits par rayons X. L'approche propose une nouvelle maniere de structurer des nanostructures magnetiques inorganiques fonctionnelles avec une commande deliberee des dimensions et forme des caracteristiques, ainsi que de la distance et de l'emplacement de l'intercaracteristique.