Yunjing Li

Third- and fifth-order optical nonlinearities in a new stilbazolium derivative

The third- and fifth-order optical nonlinear properties of a new stilbazolium derivative, trans-1-[p-(p-dimethylaminobenzyl-azo)-benzyl]-2-(N-methyl-4-pyridinium)-ethene iodide (DABAZO-PEI), were investigated with a Q-switched and mode-locked pulse laser with a duration of 35 ps at 1064 nm. Its linear optical properties were also discussed. DABAZO-PEI exhibits two-photon absorption and strong excited-state absorption induced by two-photon absorption. A positive third-order nonlinear refraction caused by bound electrons and negative excited-state refraction caused by the two-photon absorption-generated excited states were also observed. The magnitude and the sign of the real (refractive) and the imaginary (two-photon absorption) parts of the molecular third-order polarizability, and the excited-state absorption and refraction cross sections, were measured. A feature worth noting is the values of excited-state absorption and refraction cross sections. They are all as high as 10-17xa0cm2. Based on the excited-state absorption induced by the two-photon-absorption mechanism, a highly efficient optical-limiting behavior for incident fluence in the range of 0–10 J/cm2 was demonstrated in a 1-cm-path quartz cell containing DABAZO-PEI solution in dimethyl sulfoxide. The optical-limiting threshold was estimated to be as low as 5 mJ/cm2.

Growth mode of the SnO2 nanobelts synthesized by rapid oxidation

One-dimensional SnO2 nanobelts have been prepared in large scale via rapid oxidation of elemental tin at the temperature range from 1080 to 1250 degreesC. Transmission electron microscopic studies show that the as-synthesized SnO2 nanobelts appear to be single crystals but some of which are found to have steps at the surface of the nanobelts. Atomic imaging stretching over the belt width gives the trace that the growth might be associated with a layer-by-layer mode

Large-scale synthesis of β-SiC nanorods in the arc-discharge

Single crystals of Tb2Fe17 have been grown by Czochralski method cold crucible system. Good-quality crystals can be obtained by using the relative low growth rate and stoichiometrical composition. The single crystalline sample shows a pure hexagonal Th2Ni17 structure with lattice parameters of n=0.8368 +/- 0.0005nm, c=0.8331 +/- 0.0003nm. No detectable traces of Th2Zn17 phase can be found. A new phase diagram has been given based on the DTA results. Tb2Fe17 compound shows a congruent melting point of 1316 degreesC with 89.5 at % Fe and an eutectic point at 1301 degreesC With 92.5 at % Fe, which is different From the peritectic reacting published in some previous reports (see Dariel et al., J. Lesscommon Met. 35 (1976) 91). The magnetic measurements revealed a small difference in the magneto-crystalline anisotropy which could be measured in good crystal samples. Some growth conditions, such as high rate and non-stoichiometrical starting material, caused second-phase defects. Those defects are difficult to be observed by metallography. but can be indirectly found by measuring the magnetization behavior, type II first-order magnetization process (FOMP). Our results indicate that some defects might affect the rotation path of the magnetic victors in the FOMP

Growth of amorphous silicon nanowires

We have grown vertically aligned amorphous silicon nanowires on Au-Pd co-deposition silicon oxide substrate by thermal chemical vapor deposition using SiH4 gas at 800 degreesC. The diameter of silicon nanowires is in the range 10-50 nm and the length is about 1 mum. Transmission electron microscopy (TEM) observations show that the grown silicon nanowires are of an amorphous state and some of nanowires appear to bifurcate in the vertically growth process. The effect of Hz gas etchings on the catalytic size and the effect of catalytic size on the formation of the vertical growth nanowires are discussed

Catalytic synthesis of straight silicon nanowires over Fe containing silica gel substrates by chemical vapor deposition

We report a new method to synthesize very straight silicon nanowires using a porous iron/SiO2 gel as a template by thermal chemical vapor deposition at a temperature of about 500 degreesC. Scanning electron microscopy, transmission electron microscopy and Raman scattering spectroscopy were used to characterize the samples. The results show that a large amount of straight Si nanowires with diameters of about 30 nm and lengths of about 1 mum was obtained. High-resolution transmission electron microscopy observation shows that microtwin defects lie in the straight silicon nanowires. Raman scattering from the nanowires shows a larger line width (about 15 cm(-1)) and a down-shifted (about 9 cm(-1)) peak as compared to that of bulk crystalline silicon

The high fifth-order nonlinearity in a new stilbazolium derivative: trans-1-[p-(p-dimethylaminobenzyl-azo)-benzyl]-2-(N-methyl-4-pyridinium)-ethene iodide

The third- and fifth-order optical nonlinearities from the titled molecule were investigated using Z-scan technique. The titled molecule exhibits two-photon absorption (2PA) and 2PA-generated excited-state absorption (ESA). A very interesting feature is that the titled molecule shows a high fifth-order nonlinearity, being about one-order of magnitude larger than the reported organic molecules. Due to this strong ESA, a highly efficient optical limiting effect was observed.

Large optical power limiting induced by three-photon absorption of two stilbazolium-like dyes

Three-photon absorption (3PA) of two stilbazolium-like dyes containing conjugated triple bridge (abbreviated as APAI and PPAI) has been determined by using a Q-switched Nd:YAG laser pumped with 35 ps pulses at 1064 nm in DMSO. Nonlinear absorption coefficients alpha(3) derived from 3PA fitting curves are 4.3 and 3.2 x 10(-21) cm(3)/W-2, respectively. Large optical power limiting induced by 3PA has also been demonstrated for both dyes. When the maximum incident irradiance reaches to 400 GW/cm(2), the limiting nonlinear transmissions T-lim can reach to 13 and 17% with maximum transmitted radiances of 17 and 44 GW/cm(2), respectively

Three-photon absorption from six stilbazolium derivatives: application for optical limiting

Abstract Three-photon absorption (3PA) and subsequently induced optical limiting behavior of several stilbazolium derivatives were investigated by using a mode-locked/Q-switched Nd:YAG pulse with a duration of 35 ps and a repetition of 10 Hz at 1064 nm. The measured molecular 3PA cross-sections are in the order 10 −78 –10 −76 cm 6 s 2 at the intensity levels of 0–55 GW / cm 2 . It is observed that the 3PA cross-section as well as the optical limiting effect can be enhanced by increasing strength of electron-acceptor units of stilbazolium derivatives.

Growth of carbon nanofibers array under magnetic force by chemical vapor deposition

In this Letter, we report the growth of carbon nanofibers arrays by chemical vapor deposition in the presence of magnetic force. We find that when a magnet is applied carbon nanofibers arrays are grown and when the magnet is absent carbon nanotubes arrays are grown at the same experimental conditions. The nanofibers are worse in alignment and less in graphitization than those of the nanotubes grown at the same conditions. What is interesting is that two or three nanofibers can be connected together through a catalyst nanoparticle. These connections might be useful, especially in the fabrication of nanoelectronic devices.

Growth of carbon nanotube arrays using the existing array as a substrate and their Raman characterization

Abstract In this Letter, we report that after oxidation in air and reduction in hydrogen the existing carbon nanotube arrays can be used as a substrate to grow another nanotube array. The two arrays are connected through a thin catalyst layer. Micro-Raman study of these two nanotube arrays shows that they have different characteristic spectra. Besides the small shift in the peak frequencies of the two kinds of arrays in Micro-Raman spectra, we have observed changes in the relative intensities of D, G and D ′ lines and proposed the mechanism of this phenomenon.