Solid State Phenomena Vols. 121-123

Abstract: The size effect of magnetocaloric effect (MCE) in CoCr2O4 has been investigated by comparing two samples with different crystal sizes. One is bulk CoCr2O4 sample (referred as A), and the other is a nanocrystalline CoCr2O4 sample (referred as B). It has been found that crystal size dramatically affects the magnetic properties and MCE for CoCr2O4, and that the nanocrystalline material is more favorable for application than the bulk material. The above results are explained in terms of the effect of small size and its distribution for sample B on the intrinsic magnetic properties and magnetic entropy change.

Abstract: To investigate the effect of magnification (M) on determination of particle size and shape by transmission electron microscopy (TEM) and image analysis. The calibration curve and its simulative equation of TEM magnification are obtained by measurement of a grating replica standard specimen at different magnifications. Based on the analysis of TEM images at a series of magnifications for a 350nm-sphere standard sample, It has been found that the two errors of its size measurement, caused by one pixel change of the pixel number per particle diameter (Np) and by one gray value change during thresholding, is smaller, and the shape of ‘circle’ particles are close to the standard one, while Np is larger than 35. It can be seen that the suitable TEM magnification is in inverse proportion to particle size and it can be calculated by given equation.

Abstract: At neutral pH value and room temperature, nanoporous silica has been prepared through self-organization of synthetic block copolypeptide Poly(ethyl glycol)-b-poly(L-phenylalanine) (MPEG44–b-Phe7) and silicane in the organic gel system. In this system, π－π interaction between anilino-methyl triethoxy silicane and block copolypeptide MPEG44–b-Phe7 effectively controlled the growth of the silica precursors. SEM images show that the size of silica is relatively uniform with the length ranging from 20~50 μm and the diameter ranging from 2~5 μm. FT-IR spectra reveals that there exists nanoporous structure in the calcined sample. N2 adsorption-desorption isotherms are consistent with the results of FT-IR spectra and show a type-IV isotherm with H1-type hysteresis loop, which means the presence of uniform nanoporous structure. This sample has a BET surface area of 171 m2.g-1 and a pore volume of 0.55 cm3.g-1. The average pore size calculated by BJH method is 10 nm. Our results suggest a new biomimetic avenue for synthesis of nanoporous inorganic materials templated by the self-organization of copolypeptide .

Abstract: La2/3(Ca0.6Ba0.4)1/3Mn1-xVxO3 (x=0, 0.03, 0.05, 0.07, 0.10, 0.15, 0.20) nanoparticles were synthesized using sol-gel technology. The experimental results reveal that, (1) the substitution of V for Mn in La2/3(Ca0.6Ba0.4)1/3Mn1-xVxO3 lowers the Curie temperature TC and the metal–insulator transition temperature TMI; (2) there exists the evident difference between the TC and the TMI for different V substitution ratio; (3) the low-temperature tunneling magnetoresistance and maximum magnetoresistance near Tc increase with the enhancement of V-doping content. Based on the tunneling magnetoresistance model and the percolation model near Curie temperature, the experimental results are explained well.

Abstract: Two types of individualized single-walled nanotubes (SWNTs) in aqueous surfactant suspensions have been studied by femtosecond two-color absorption spectroscopy. A careful selection of pump and probe wavelengths allows for the determination of the “intrinsic” lifetimes of the lowest excited states which depend on the diameter of the SWNTs. Furthermore, a fast decay component in the ps to sub-ps regime was also observed and tentatively attributed to bundle relaxation. Likewise, this experimental approach can also assess spectral regions with decays faster than 1 ps, which is of great interest for all-optical switching devices near the optical telecommunication wavelength.

Abstract: The determination of the spherical particle-sizes in colloidal suspension by Angular Light Scattering presents a lot of advantages, i.e.: the relative simplicity of the experimental installations, and its non-destructive character. The intensity of the scattered light is related with the radius of a particle by Mie Theory. However, the dynamic characteristic of the measurements establish a variations of the scattered intensity with the time which it has not considered. In the case of the particle suspended in water, the intensity of the scattered light measured in each angle θ is the superposition of the scattered intensity for each particle. In consequence, the intensity of the light scattered will be related with a particle-size distribution function, that in this work is assumed as a δ function. Then, the dependence of the scattered intensity with time is studied evaluating the variation of the center point of δ function with time taking account to the standard deviation of angular scattered intensity. The accuracy of the method is evaluated throw the deviation of the particle-size distribution taking in to account the standard deviation of the angular intensity scattered by calibrated particles of latex. A correct evaluation of the dynamic method is realized in terms of the static approach.

Abstract: The elastic deformation and piezoelectric field in GaN /AlN/ quantum dots have been investigated. The electronic levels of quantum dots have been given in this paper. The 3D strain field and piezoelectric potential are calculated based on and the effective mass theory and finite element method. The effect of spontaneous and piezoelectric polarization is taken into account in the calculation. The ground bound state and the several lowest excited states of quantum dots have been studied. It is found that the size of quantum dots controls the conduction band edge, electronic levels and more other optical properties. The calculation results are very helpful in designing high quality infrared photodetector and laser.

Abstract: Titanium containing carbon nitride (CNx) films are prepared by radio frequency magnetron sputtering method. The evolution of intrinsic stress within the nanocomposite films is monitored during growth by using an in situ bending-plate method. The effect of Ti-containing concentration on intrinsic stress is investigated. XRD data shows that TiN nanocrystals are synthesized to embed into the CNx matrix. The film intrinsic stress depends obviously on the content of Ti. We suggest that grain boundary effect is responsible to the intrinsic stress variation as a function of the content of Ti.

Abstract: ZnxCd1-xS (x = 0~1) nanoparticles were prepared in the channels of nanoporous VSB-5 (Versailles Santa Barbara-5) by introducing metal ions in the channels and followed by vulcanization. ZnxCd1-xS nanoparticles and VSB-n displayed their own spectra properties. However, ZnxCd1-xS nanoparticles demonstrate obvious blue-shift and tunable property in the UV-vis absorption spectra due to the quantum confinement effects.