Bingsuo Zou

Synthesis and characterization of functionalized silica-coated Fe3O4 superparamagnetic nanocrystals for biological applications

Superparamagnetic Fe3O4 nanocrystals were prepared by a chemical coprecipitation method with a thin thickness-adjustable silica layer coated on the surface by hydrolysis of tetraethyl orthosilicate. The silica-coated Fe3O4 nanocrystals were well dispersed and consisted of a 6-7 nm diameter magnetic core and a silica shell about 2 nm thick, according to transmission electron microscopy observations. Fourier transform infrared spectra revealed that amino (-NH2) groups were successfully covalently bonded to the silica-coated Fe3O4 and then carboxyl (-COOH) groups were functionalized to the surface through the reaction of -NH2 and glutaric anhydride. The synthesized nanocrystals have a cubic spinel structure as characterized by x-ray diffraction, electron diffraction and high-resolution transmission electron microscopy. Their magnetic properties were carefully investigated by a SQUID magnetometer. The results showed that the nanocrystals were superparamagnetic and the blocking temperature TB shifted from 131 K down to 92 K after they were coated with a thin nonmagnetic layer, since this layer can effectively suppress the magnetic dipolar interaction between particles; the chemically inert silica layer can limit the outside environment effect on the Fe3O4 cores quite well due to the excellent magnetic reproducibility of the coated nanocrystals after ageing for 7 months at room temperature. In addition, the dependence of their high-field specific magnetization on temperature has a T-2 relationship. These functionalized silica-coated Fe3O4 superparamagnetic nanocrystals have great potential in biomagnetic applications.

Ultraviolet lasing and time-resolved photoluminescence of well-aligned ZnO nanorod arrays

Well-aligned ZnO nanorod arrays were synthesized by thermal evaporation of ZnO powder on ZnO thin films. The nanorods are almost the same length of 5.5μm and well-oriented perpendicular to the substrates. The time-integrated and time-resolved photoluminescence spectra of the nanorod arrays revealed the existence of laser action with the excitation threshold of 130μJ∕cm2 and emission lifetime of less than 30 ps. At the excitation fluence a little below threshold, the decay fits well to a biexponential function with a fast component (∼80ps) and a slower component (∼360ps).

Structural characterization and optical properties of nanometer-sized SnO2 capped by stearic acid

Structure and optical properties of nanometer-sized SnO2 capped by a layer of stearic acid are investigated using TEM, XRD, ESR, UV-visible absorption spectrum, photoluminescence spectra, IR absorption spectra and Z-scan techniques. It is found that such capped SnO2 samples display new optical properties, which will enlarge their applications in nonlinear optics. The relationship between structure and optical properties of the SnO2 nanoparticles is also discussed.

Fabrication and photoluminescence of high-quality ternary CdSSe nanowires and nanoribbons

Ternary alloy CdSSe nanowires and nanoribbons were successfully grown through a one-step thermal evaporation route using Au as a catalyst. The nanostructures obtained are uniform in diameter, and have smooth surfaces. High-resolution transmission electron microscopy, energy dispersive x-ray spectra and x-ray diffraction showed that both the nanowires and the nanoribbons have high-quality single-crystalline nature, and their compositions can be determined as CdS(0.6)Se(0.4) and CdS(0.3)Se(0.7), respectively. The mechanisms of formation of these two different nanostructures were discussed. The photoluminescence measurements showed very strong band-edge emission for both samples, which further demonstrates the single-crystal nature of the as-obtained CdSSe alloys. This finding may be extended for fabricating other composition-tunable 1Dxa0ternary alloy nanostructures.

Size effect on the electron?phonon coupling in CuO nanocrystals

CuO is the prototype compound of cuprate superconductors, so understanding its electronic structures will facilitate the study of the pairing mechanism and miscellaneous states of high-temperature superconductors. We prepared uniform CuO nanocrystals (7-100xa0nm) and studied their size-dependent Raman scattering spectra. The relative variation between the two-phonon scattering band (2B(g)) and the one-phonon band (B(g)) indicates a decreasing electron-phonon coupling with reducing size, which unveils the dominant Fröhlich electron-phonon coupling, as indicated by Devreese, but not the small polaron in CuO. Moreover, the anomalous enhancement of the multi-phonon band at a critical size and 1D structure at room temperature is attributable to an enhanced electron-phonon coupling accompanied by phonon-plasmon coupling, i.e., the plasphon proposed by Alexandrov et al in 1981.

Phonon-assisted stimulated emission from single CdS nanoribbons at room temperature

We report room-temperature stimulated emission in single CdS nanoribbons obtained through Au-catalyzed physical evaporation route. These ribbons have single-crystal structures and uniform rectangular cross sections and grow along the [100] direction. The ribbons show good waveguide/cavity properties under local optical excitation. The stimulated emissions from the single ribbons were observed with both nanosecond and femtosecond laser pumpings. The results show that the CdS nanoribbons produce stimulated emission by bipolaronic excitons (two-longitudinal-optical phonon coupled free excitons) at room temperature.

The effects of different interfacial environments on the optical nonlinearity of nanometer-sized CdO organosol

The third-order optical nonlinearity χ(3) of nanometer-sized CdO with different interfacial environments has been measured using the Z-scan technique. The real and imaginary parts of χ(3) at 800 nm have been determined to be: −1.55×10−16u2009m2/W and 0.91 cm/GW for CdO–CTAB (cetyltrimethyl ammonium bromide) organosol, and −6.97×10−16u2009m2/W and 8.64 cm/GW for CdO–DBS (dodecylbenzene sulfonate) organosol. Origins of the optical nonlinearity and the effects of the interfacial conditions have been discussed. The optical Stark effect (OSE) and surface trapped states are the possible origins of the observed optical nonlinearity. The possible enhancement of optical nonlinearity of nanoparticles by intentional interfacial modification is suggested.

Time-resolved spectroscopic behavior of Fe2O3 and ZnFe2O4 nanocrystals

Using nanosecond (ns) and femtosecond (fs) time-resolved absorption spectroscopies (pump-probe technique), the carrier dynamics in transition metal oxide nanocrystals of alpha-Fe2O3 and ZnFe2O4 was studied during the photolysis process. For Fe2O3 and ZnFe2O4 nanocrystals, the fs measurements detect similar profiles of a positive nonlinear absorption in their capped nanocrystals, whereas much weak signals in the naked particles. In the nanosecond measurements Fe2O3 and ZnFe2O4 nanocrystals show obvious excitation-power dependent absorption properties and at the low pump power they show weak photobleaching, but at high pump power they produce positive nonlinear absorptions. For Fe2O3 nanocrystals, the threshold power of negative absorption (bleach) to positive absorption increases with reducing size, whereas for the ZnFe2O4 samples, the threshold powers reach minimum at a critical size of 11 nm, grow for both the bigger and the smaller nanocrystals. These results reflect the influences of their microscopic magnetic couplings and carrier correlation on biexciton absorption in Fe2O3 and ZnFe2O4 nanocrystals. All the results indicate that the time resolved photoabsorption techniques are useful to study the microscopic spin interactions and carrier correlations in transition metal oxide nanocrystals.

Electrical properties and phase transition of CoFe2O4 nanocrystals under pressure

The electric resistance CoFe2O4 nanocrystals of different sizes, obtained by the coprecipitation method was investigated under pressure up to 20 GPa in a diamond anvil cell at ambient temperature. The experimental results indicate that the phase transition (from the spinel to a tetragonal structure) takes place at 7.5 and 12.5 GPa for 6 and 80 nm, nanocrystals, respectively, in agreement with the prediction of scaling theory of the phase transition of nanocrystals. The relatively low transition pressure for CoFe2O4 is related to the high d-electron coupling between magnetic ions and to the small band gap in CoFe2O4 as compared to the other spinel ferrites. These results are discussed in terms of decreasing band gap with increasing pressure. The smaller the size of nanocrystals, the higher the phase transition pressure. The resistance of CoFe2O4 nanocrystal decreases exponentially under pressure, according to R∝exp(−CP), where C=0.7634u200aGPa−1 for large nanocrystals (80 nm) and C=0.5124u200aGPa−1 for CoFe2O4 of ...

Biphotonic self-diffraction in azo-doped polymer film

A new nonlinear optical phenomenon, biphotonic self-diffraction (BSD), is reported in azo dye doped in polymer matrix. The first-order and the second-order BSD signals are observed in the experiment. It is demonstrated that the dynamic behaviors of the BSD signals are dependent on the cis-trans isomerization of azo molecules by two color lights.