A direct-write "dip-pen" nanolithography (DPN) has been developed to deliver collections of molecules in a positive printing mode. An atomic force microscope (AFM) tip is used to write alkanethiols with 30-nanometer linewidth resolution on a gold thin film in a manner analogous to that of a dip pen. Molecules are delivered from the AFM tip to a solid substrate of interest via capillary transport, making DPN a potentially useful tool for creating and functionalizing nanoscale devices.

The formation of intricate nanostructures will require the ability to maintain surface registry during several patterning steps. A scanning probe method, dip-pen nanolithography (DPN), can be used to pattern monolayers of different organic molecules down to a 5-nanometer separation. An "overwriting" capability of DPN allows one nanostructure to be generated and the areas surrounding that nanostructure to be filled in with a second type of "ink."

Block polyelectrolytes P(Sm-6-VP"/CioD composed of polystyrene blocks (m = 54-480) and perdecylated poly(4-vinylpyridine) (n = 3-240) have been studied using the Langmuir film balance technique and the corresponding Langmuir-Blodgett films. The recently reported phenomenon of surface micelle formation1 has been found to be very general for those types of materials. Different morphologies, as visualized by transmission electron microscopy, arise, depending on the diblock composition. An unusual phase transition originates from one of the morphological units, i.e., small, circular starfish micelles, and is consistent with an ionic chain solubilization process induced by film compression. As the relative ionic block length is decreased, other morphologies are observed. The properties of surface rod aggregates are consistent with the rods being made up of two layers of the diblocks, with the PS blocks forming the core. Large planar aggregates also form, and appear to be one PS block thick and can extend up to several microns in width.Compressional hysteresis, temperature effects, and aggregation numbers have been used to provide a selfconsistent description of the surface micellization phenomenon.

No abstract

Hydrothermal reaction of (l)-N-(4'-cyanobenzy)-(S)-proline with CdCl2 as a Lewis acid catalyst and NaN3 gives colorless block compound 1, in which 1 displays a complicated 3D framework. Ferroelectric and dielectric property measurements reveal that 1 exhibits physical properties comparable to that of a typical ferroelectric compound with a dipole relaxation process and a dielectric constant of ca. 38.6 that makes it, by definition, a high dielectric material.

No abstract

A biocompatible, water-soluble, lower molecular weight chitosan has been used for, via a one-pot hightemperature refluxing strategy, the simultaneous synthesis and assembly of gold nanoparticles. Transmission electron microscopy (TEM) and ultraviolet-visible-near-infrared (UV-vis-NIR) extinction spectra allowed us to identify the existence of nanoparticle linear aggregates. Importantly, through such a preparation procedure, the chain length of the nanoparticle aggregates could be tuned by facile adjustment of the reaction reagent ratio. Further, the growth and assembly processes of gold nanoparticles were studied by quenching the intermediate reaction solutions with an ice-water bath. The structure evolution proceeded through a twostage process: initial generation of isolated nanoparticles, followed by the interconnection of nanoparticles into an aggregated morphology. A mechanism based on the nonuniform distribution of capping ligands is proposed to account for the one-dimensional chain structure formation.

A new noncovalent and nonorganic method has been utilized in dispersing single-walled carbon nanotubes (SWNTs) in water, up to single tube level. SWNTs, otherwise flocculated in aqueous solutions, were stabilized through the addition of highly charged nanoparticles. The dispersed SWNTs could be self-assembled into macroscopic materials in solutions by the application of external stimuli. By anchoring the solution SWNTs onto pyrene-modified Si/SiO 2 surfaces, discrete, individual nanotubes have been observed by atomic force microscopy (AFM). This new type of SWNT aqueous dispersions might open up new avenues in the fields of nanostructured materials, biological sensing, and nanotube electronics.