In-Situ Characterization of Three-Dimensional Optical Matters by Light Diffraction

Three-dimensional optical matters are created by combining the single beam optical trapping with the conventional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one.Three-dimensional optical matters are created by combining the single beam optical trapping with the conven- tional Z-scan technique. Dynamic light diffraction is employed to evaluate the structure and quality of the optical matter formed at the optimum trapping power. The lattice constant of the optical matter is extracted based on the Bragg and Snell laws, showing that polystyrene spheres are nearly close-packed in the optical matter, confirmed by comparing the diffraction pattern of the optical matter with that of a colloidal photonic crystal fabricated by the self-assembled technique. The relatively broad diffraction peaks observed in the optical matter indicate that the density of disorders in it is higher than that in the photonic crystal. It is suggested that the optical matter possesses a random close-packed structure rather than a face centered cubic one.

Modification of the spontaneous emission of quantum dots near the surface of a three-dimensional colloidal photonic crystal

This paper demonstrates experimentally and numerically that a significant modification of spontaneous emission rate can be achieved near the surface of a three-dimensional photonic crystal. In experiments, semiconductor coreshell quantum dots are intentionally confined in a thin polymer film on which a three-dimensional colloidal photonic crystal is fabricated. The spontaneous emission rate of quantum dots is characterised by conventional and time-resolved photoluminescence （PL） measurements. The modification of the spontaneous emission rate, which is reflected in the change of spectral shape and PL lifetime, is clearly observed. While an obvious increase in the PL lifetime is found at most wavelengths in the band gap, a significant reduction in the PL lifetime by one order of magnitude is observed at the short-wavelength band edge. Numerical simulation reveals a periodic modulation of spontaneous emission rate with decreasing modulation strength when an emitter is moved away from the surface of the photonic crystal. It is supported by the fact that the modification of spontaneous emission rate is not pronounced for quantum dots distributed in a thick polymer film where both enhancement and suppression are present simultaneously. This finding provides a simple and effective way for improving the performance of light emitting devices.

Response of colloidal liquids containing magnetic holes of different volume densities to magnetic field characterized by transmission measurement

This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhancement in the transmission of such a colloidal liquid under a magnetic field exhibits a strong dependence on the volume density of magnetic holes. A linear increase in the maximum enhancement factor is observed when the volume density of magnetic holes is below a critical level at which a maximum enhancement factor of ~150 is achieved in the near infrared region. Once the volume density of magnetic holes exceeds the critical level, a sharp drop of the maximum enhancement factor to ~2 is observed. After that, the maximum enhancement factor increases gradually till a large volume density of ~9%. By monitoring the arrangement of magnetic holes under a magnetic field, it reveals that the colloidal liquids can be classified into three different phases, i.e., the gas-like, liquid-like and solid-like phases, depending on the volume density of magnetic holes. The response behaviour of colloidal liquids to magnetic field is determined by the interaction between magnetic holes which is governed mainly by their volume density. A phase transition, which is manifested in the dramatic reduction in the maximum enhancement factor, is clearly observed between the liquid-like and solid-like phases. The optical switching operations for colloidal liquids in different phases are compared and the underlying physical mechanisms are discussed.

软磁Ni_(80)Fe_(20)薄膜单元中磁涡旋结构的高分辨磁力显微观察

本文利用高分辨磁力显微技术对Ni80Fe20薄膜单元进行了直接观察,发现在双圆盘"花生形"单元中存在磁涡旋结构,并能够清晰地看到单元中心附近或亮或暗的涡旋核。实验结果表明,在包括针尖卷积效应的情况下,磁涡旋核中心轮廓线的直接测量宽度约为40 nm,这个分辨率远高于迄今为止报道的关于磁涡旋结构的MFM测量结果。

Octahedral distortion-driven electrical and vibrational properties of A_(2)ErTaO_(6)(A=Sr and Ca)double perovskite oxides

Rietveld refinement analysis indicates that A_(2)ErTaO_(6)(A=Sr^(+2),Ca^(+2)ceramics prepared by a solid-state route are crystallized in monoclinic perovskite phase with space group P21=n.Raman scattering and infrared spectroscopy are used to investigate the structure and phonon modes of the samples.Using Lorentzian lines,we have fitted the Raman spectra and the major Raman modes are assigned.Phonon vibrational frequency is modulated with the A-site cationic change.Impedance spectra of the samples over the frequency range of 100 Hz–1.1 MHz are investigated at different temperatures from 303 K to 573 K.Cole–Cole relaxation of dielectric constant is modified with the electrical conduction parameter to describe the temperature dependence of dielectric constant.The frequency-dependent conductivity spectra follow the double power-law.

Insulator-to-metal transition in RCoO_(3)(R=Pr,Nd)

We report a straightforward tool to investigate insulator-metal transition in RCoO_(3)(R=Pr,and Nd)nanoparticles prepared by a sol-gel technique.Thermogravimetric analysis(TGA)of the as-prepared gel is performed to get the lowest possible calcination temperature of RCoO_(3)nanoparticles.The Rietveld refinement of the powder X-ray diffraction(XRD)patterns for both samples shows that the samples crystallize in the orthorhombic(Pnma)phase at room temperature.The particle size of the sample is determined by scanning electron microscopy.Ac conductivity of the materials is analyzed in the temperature range from 303 K to 673 K and in the frequency range from 42 Hz to 1.1 MHz.The insulator-to-metal transition of PrCoO_(3)and NdCoO_(3)is analyzed by ac impedance spectroscopy.DC resistivity measurement is also done to cross check the insulator-metal transition in RCoO_(3)system.

Field-dependent spin waves in high-aspect-ratio singlecrystal ferromagnetic nanowires

We investigate the spin wave （SW） modes in high-aspect-ratio single-crystal ferromagnetic nanowires （FMNWs） using an all-optical time-resolved magnetooptical Kerr effect （TR-MOKE） microscope. The precessional magnetization dynamics in such FMNWs unveil the presence of uniform and quantized SW modes that can be tuned by varying the bias magnetic field （H）. The frequencies of the modes are observed to decrease systematically with a decreasing magnetic field, and the number of modes in the spectrum is reduced from four to three for H 〈 0.7 kOe. To understand these results, we perform micromagnetic simulations that reveal the presence of edge, standing wave, and uniform SW modes in the nanowires （NWs）. Our simulations clearly show how the standing wave and uniform SW modes coalesce to form a single mode with uniform precession over the entire NW for H 〈 0.7 kOe, reproducing the experimentally observed reduction in modes. Our study elucidates the possibility of manipulating the SW modes in magnetic nanostructures, which is useful for applications in magnonic and spintronic devices.