Z.Q. Xue

Ultrafast optical Kerr effect of Ag–BaO composite thin films

We report the ultrafast optical Kerr effect of Ag–BaO composite thin films by the femtosecond time-resolved pump-probe technique. The Ag–BaO thin films with Ag nanoparticles embedded into the BaO semiconductor matrix were prepared using a vacuum evaporation-deposition multimetallic layer method. The third-order nonlinear optical susceptibility of the thin films with the thickness of approximately 300 nm and the volume fraction of Ag nanoparticles in the thin films of about 25% was estimated to be 4.8×10−10 esu at the incident laser wavelength of 820 nm. The response time, i.e., the full width at half maximum of the Kerr signal, was as fast as 210 fs. The intrinsic third-order optical nonlinearity, or the optical Kerr effect of the thin films, can be attributed to the change of refractive index due to the intraband transition of electrons from the occupied state near the Fermi level to the unoccupied state in the Ag nanoparticles. Such nonlinearity is further enhanced by the local field effect that is pres...

Nanometer‐scale recording on an organic‐complex thin film with a scanning tunneling microscope

Nanometer‐scale recording on an organic‐complex thin film with a scanning tunneling microscope (STM) under ambient conditions is demonstrated. The recording marks are made by applying external voltage pulses between the tip and the highly ordered pyrolytic graphite substrate. A 30×30 nm2 STM image with recorded marks is given. The average recorded mark is 1.3 nm in diameter, which corresponds to a data storage density of about 1013 bits/cm2. The current–voltage characteristics measured by the STM show an insulator behavior for the unrecorded regions, and a conductor behavior for the recorded regions, which indicates that the data are recorded by local change of the electrical property of the films.

Data storage with 0.7 nm recording marks on a crystalline organic thin film by a scanning tunneling microscope

Ultrahigh density data storage on a novel organic thin film by scanning tunneling microscope (STM) under ambient conditions is demonstrated. The material, N-(3-nitrobenzylidene)p-phenylenediamine (NBPDA), is used for preparing thin film by vacuum evaporation method. Crystalline NBPDA films with electrical bistability are obtained by this method. Recording experiment on the films is made by applying voltage pulses between the STM tip and substrate. The recorded marks are 0.7 nm in size, corresponding to a storage density of 1014 bit/cm2. Current–voltage characteristic measurement shows that the resistance of the unrecorded region of the NBPDA films is much higher than that of the recorded region. The mechanism of recording is discussed.

2D fractal pattern in fullerene doped polymer

Abstract Fractals in C60 doped tetracyanoquinodimethane thin films are reported. The fractal patterns and their microscopic features have been characterized by transmission electron microscopy (TEM). The results indicate that the observed fractals can be compared to the cluster-diffusion-limited-aggregation model. The fractal dimension has been determined to be 1.69±0.04. In addition, the formation mechanism of the fractals is discussed.

Small Pt clusters supported on a graphite surface by scanning tunneling microscopy

Abstract In this experiment, the scanning tunneling microscope (STM) has been used to study some of the behavior of small Pt clusters on a graphite surface. The sample preparation was accomplished by controllable evaporation deposition from Wollaston wires at room temperature in uhv. Here we present a series of STM images of the ransformation process of small atomic clusters, which provide us with a better understanding on how substrate surfaces dominate this process. The transformation phenomena actually give rise to a complicated mechanism.

A new type of organometallic system for high density data storage by scanning tunneling microscopy

Abstract We report a new type of organometallic system, Ag-toluylene 2,4-dicarbamidonitrite (TDCN) composite thin film, for ultrahigh density data storage devices by scanning tunneling microscopy (STM). The Ag-TDCN thin film was prepared on a highly oriented pyrolytic graphite (HOPG) substrate using an ionized-cluster-beam (ICB) deposition method. Marks can be created on the thin film by employing a voltage pulse between the STM tip and surface of the HOPG substrate. The size of the created marks is about 50 nm and the corresponding data storage density is about 10 11 bits/cm 2 . The mechanism for the data storage can be attributed to the conductance transition in the complex system. This result shows a great potential for this new kind of organometallic composite system to find application in ultrahigh density data storage.

Large area dimer vacancy array on the Si(100) surface studied by scanning tunneling microscope

Abstract Large area dimer vacancy arrays can be formed on the Si(100) surface when Si atoms are deposited on the Si(100)-2×1 surface followed by quenching from 1200°C. The dimer vacancy lines (DVLs) of the dimer vacancy array run perpendicular to the dimer rows and the basic building cells of the DVLs are: (i) a cluster of two missing dimers; (ii) a complex of one missing dimer and a cluster of two missing dimers. Small isolated islands with DVLs like that of the Si(100) surface are observed on the surface. The precursors of the islands are investigated. The formation mechanism of the island is that the interaction between the stress field of the dimers on the Si(100) surface and that of the island causes the dimer vacancies in the dimer rows of the island and the attraction between the dimer vacancies in adjacent dimer rows aligns the dimer vacancies.

Diamond tips and nanometer-scale mechanical polishing

Abstract The major application of the scanning tunneling microscope (STM) is as a local surface topography and structure probe. The scanning tip usually is made of metal such as tungsten (W), platinum-iridium (Pt-Ir), gold (Au), etc., by electrochemical etching or mechanical cutting. STM has also recently demonstrated its potential application as a powerful tool for nanometer-scale surface modification. We made a kind of diamond STM tips by the MPCVD technique. The tips are quite stable, and hard enough to polish the metal film surface to produce relatively flat areas. Both SEM and STM were employed to check and analyze the tips and the results of polishing.

Spectral response of AgCsxO thin films

Abstract AgCs x O thin films, including AgOCs photocathodes, are useful for ultra-short laser pulse detection and high-speed photography. The long wavelength photoemission comes from small silver colloidal particles in the film. Its short wavelenth photoemission should come from silver granules, colloidal particles and host semiconductors. The explanation and formulae for the spectral responses of AgCs x O and the theoretical response curves for AgOCs photocathode are presented.

Study of C60-TDCN Nanometer Scale Thin Films

A novel polymer, toluylene 2, 4-dicarbamidonitrile (TDCN) with carbon-nitrogen conjugated backbones, has been synthesised in our Polymer Laboratory. The C60-TDCN thin films have been prepared by the ICB-TOFMS deposition system. The C60-TDCN thin films are very good crystalline and possess electric bistability.