Showing papers by "Hong-Jun Gao published in 2001"

Formation of Silver Nanoparticles and Self-Assembled Two-Dimensional Ordered Superlattice

Abstract: 1-Nonanethiol-capped silver nanoparticles of about 4.18 nm in diameter were prepared using a liquid−liquid two-phase method. Two-dimensional ordered superlattices of the nanoparticles were formed o...

Superlattices of silver nanoparticles passivated by mercaptan

Abstract: Two- and three-dimensional superlattices of passivated silver nanoparticles were formed on amorphous carbon films by the self-assembly technique. The x-ray diffraction (XRD) and x-ray photoelectron spectroscopy results demonstrated that the colloid system was composed of silver nanoparticles and, on the surface of the silver nanoparticles, the chemical bond was formed between the S of the 1-nonanethiol and the Ag of the particle. XRD and transmission electron microscopy also showed that the instability of the silver nanoparticles mainly resulted from the growth of the nanoparticles. Due to the relatively close-packed thiol layer on the surface of the nanoparticle, in the infrared spectra of the silver nanoparticles, absorption peaks of the terminal methyl group and methylene stretching modes were red shifted; meanwhile the transverse modes of the binding absorption disappeared.

Recording at the Nanometer Scale on p‐Nitrobenzonitrile Thin Films by Scanning Tunneling Microscopy

Abstract: A data storage density of at least 10(14) bits/cm(2) is possible using p-nitrobenzonitrile as the data storage medium and scanning tunneling microscopy (STM) as the recording method. This represents the smallest mark size among all the organic thin films studied by these authors. The figure shows a typical STM image of a recorded pattern.

The stability of self-organized 1-nonanethiol-capped gold nanoparticle monolayer

Abstract: 1-Nonanethiol-protected gold nanoparticles with the size of about 2 nm have been prepared by a wet chemical method through choosing a suitable ratio of Au:S (2.5:1). Size selective precipitation of nanoparticles has been used to narrow their size distribution, which facilitates the formation of an ordered nanoparticle close-packed structure. A Fourier transform infrared investigation provides the evidence of the encapsulation of Au nanoparticles by 1-nonanethiol while an ultraviolet-visible spectrum shows a broad absorption around 520 nm, corresponding to surface plasmon band of Au nanoparticles. X-ray photoelectron spectroscopy of the samples demonstrates the metallic state of the gold (Au0) and the existence of sulfur (S). The data from x-ray powder diffraction measurements confirm that the gold nanoparticles have the same face-centred cubic crystalline structure as the bulk gold phase. Finally, transmission electron microscopy (TEM) characterization indicates that the size of the monodisperse colloidal gold nanoparticles is about 2 nm and they can self-organize to form a two-dimensional hexagonal close-packed structure after evaporating a concentrated drop of nanoparticles-toluene solution on a carbon-coated TEM copper grid.

Two-dimensional self-organization of 1-nonanethiol-capped gold nanoparticles

Abstract: A two-dimensional (2D) ordered hexagonal close-packed structure, formed by 1-nonanethiol-capped gold nanoparticles, is reported. The structure was constructed only by dipping the gold nanoparticle colloidal solution on flat substrate. The gold nanoparticles were synthesized as follows: First, AuCl4−1was transferred from aqueous solution to toluene by the phase-transfer reagent of tetraoctylammonium bromide. Then it was reduced with aqueous sodium borohydride in the presence of a given amount of 1-nonanethiol molecules which was used to control the nucleation and growth of the gold nanoparticles for the desired size. The experimental techniques, such as UV-Vis, FT-IR, and X-ray photoelectron spectroscopy (XPS), were employed to characterize the obtained product. Transmission electron microscopy (TEM) measurement demonstrated the size of the gold nanoparticle and the formation of two-dimensional ordered hexagonal close-packed gold nanoparticle structure.

Structure studies of C3N4 thin films prepared by microwave plasma chemical vapour deposition

Abstract: Crystalline carbon nitride films have been synthesized on Si(100) substrates by a microwave plasma chemical vapour deposition technique, using a gas mixture containing nitrogen and methane at various ratios as precursors. Scanning electron microscopy shows that the films consisted of hexagonal crystalline rods, which are about 1-2 µm long and about 0.4 µm wide. X-ray diffraction and transition electron microscopy indicate that the films are mainly composed of α- and β-C3N4, and these results match more closely with the α-C3N4 than with the β-C3N4 phase. Fourier transform infrared absorption spectra of carbon nitride films support the existence of α- and β-C3N4.} \fnm{3}{Author to whom correspondence should be addressed.

Dynamics of the Thermohaline Circulation under Wind forcing

Abstract: The ocean thermohaline circulation, also called meridional overturning circulation, is caused by water density contrasts. This circulation has large capacity of carrying heat around the globe and it thus affects the energy budget and further affects the climate. We consider a thermohaline circulation model in the meridional plane under external wind forcing. We show that, when there is no wind forcing, the stream function and the density fluctuation (under appropriate metrics) tend to zero exponentially fast as time goes to infinity. With rapidly oscillating wind forcing, we obtain an averaging principle for the thermohaline circulation model. This averaging principle provides convergence results and comparison estimates between the original thermohaline circulation and the averaged thermohaline circulation, where the wind forcing is replaced by its time average. This establishes the validity for using the averaged thermohaline circulation model for numerical simulations at long time scales.

Ultrahigh data density storage with scanning tunneling microscopy

Abstract: Ultrahigh density data storage devices made by scanning probe techniques based on various recording media and their corresponding recording mechanisms, have attracted much attention recently, since they ensure a high data density in a non-volatile, erasable form in some kinds of ways. It is of particular interest to employ organic polymers with novel functional properties within a single molecule (or a single molecular complex) for fabricating electronic devices on a single molecular scale. Here, it is reported that a new process for ultrahigh density and erasable data storage, namely, molecular bistability on an organic charge transfer complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine (NBMN-pDA) switched by a scanning tunneling microscope (STM). Data density exceeds 10(13) bits/cm(2) with a writing time per bit of similar to1 mus. Current-voltage (I/V) measurements before and after the voltage pulse from the STM tip, together with optical absorption spectroscopy and macroscopic four-probe I/V measurements demonstrate that the writing mechanism is conductance transition in the organic complex. This mechanism offers an attractive combination of ultrahigh data density coupled with high speed. The ultimate bit density achievable appears to be limited only by the size of the organic complex, which is less than 1mn in our case, corresponding to 10(14) bits/cm(2). We believe that provided the lifetime can be improved, molecular bistability may represent a practical route for ultrahigh density data storage devices.