Optical Performance and Nonlinear Scattering of Soluble Polystyrene Grafted Multi-Walled Carbon Nanotubes

Three soluble polystyrene grafted multi-walled carbon nanotube （MWNT） samples are synthesized, and their optical performance and nonlinear scattering properties are investigated by z-scan method using nanosecond pulses of 532 nm from a frequency-doubled Q-switched Nd： YLF laser. Analysis of the experimental results shows that other than nonlinear scattering, nonlinear absorption plays a major role in optical limiting performance of these stable and well-dispersed suspensions. These new synthesized materials which can be better dispersed in common organic solvents than MWNT itself can be considered as potential sources for further optical applications.

The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO2, UO3, and U2O3 molecules are systematically investigated using the density functional theory （DFT） with the method of generalized gradient approximation （GGA）. The bond lengths and the vibrational frequencies of the ground states of UO, UO2, and UO3 molecules are all in agreement with available experimental data. For U2O3 molecules, our calculations indicate that the ground state of the U203 molecule is an XTA1 state with Dah （trigonal bipyramid） symmetry （R1 （U O）=0.2113 nm, R2（U1 U2）=0.2921 nm, ZU1OU2 = 87.5° , dihedral angle O（U,O1,O2,O3）=62.40°）. The harmonic frequency, the IR intensity and the spin density of the U2Oa molecule are all obtained for the first time in theory. For the ground state of U203 molecules, the vibrational frequencies are 178.46 （Ai）, 276.79 （E1＇＇）, 310.77 （EL）, 396.63 （AS＇）, 579.15 （El）, and 614.98 （A1＇） cm-1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO3 and U203 molecules. Besides, the results of Gophinatan-Jng bond order indicate that UO, UO2, and UO3 molecules possess U=O double bonds and that the U203 molecule possesses U O single bonds and a U-U single bond.

High Heat Flux Tests of Small-scale Be/Cu Mock-ups for ITER

High temperature HIP joining technology of Be/CuCrZr alloy or DS-Cu has been applied by Europe and Japan for the frabrication of ITER first wall. At the first stage of our research, high temperature HIP joining of Be/CuCrZr alloy was investigated by referencing their successful experience and Ti was selected as interlayer. Since the first wall will receive high heat flux during ITER operation, the heat load resistance capabilities, in particular thermal fatigue property is a crucial criterion of FW mock-ups. In order to test the heat load resistance capabilities of Be/CuCrZr joints, an electron beam heat load facility with beryllium handling capability has been constructed and heat removal performances and thermal cycling tests of Be/CuCrZr joints were carried out.

Molecular dynamics simulations of point defects in plutonium grain boundaries

A modified analytic embedded atom method （MAEAM） potential is constructed for fcc 5-Pu. Molecular dynamics （MD） simulations with the potential are performed to investigate the interactions between two symmetrical tilt grain boundaries （GBs） and point defects such as He atom, vacancy and self-interstitial atom （SIA） in Pu. The calculated results show that point defect formation energies are on average lower than those in the lattice but variations from site to site along the GBs are very remarkable. Both substitutional and interstitial He atoms are trapped at GBs. Interstitial He atom is more strongly bound at the GB core than the substitutional He atom. The binding energy of SIA at GB core is higher than those of He atom and vacancy. GB core can bind many He atoms and SIAs due mainly to the fact that it contains many vacancies. Compared with He atom and SIA, the vacancy far from GB core is difficult to diffuse into the core. The GBs can act as sinks and sources of He atoms and SIAs, which may be a reason for the swelling of Pu after a period of self-irradiation because of the higher concentration of vacancy in the bulk.

Effect of Wafer Size on the Film Internal Stress Measurement by Wafer Curvature Method

Wafer curvature method has been applied to determine the internal stress in the films using Stoney＇s equation.During the film deposition,the wafer fixation on the sample holder will restrict the deformation of the rectangle-shaped wafer,which may result in the stress datum difference along length and width direction.In this paper,the effect of wafer size and the wafer fixation on the TiN film internal stress measured by wafer curvature method was discussed.The rectangle-shaped wafers with different length/width ratios（L/W=1：1,2：1,3：1 and 4：1） were fixed as a cantilever beam.After the TiN films deposition,the profiles of the film/wafer were measured using a stylus profilometer and then the internal stress was calculated using the Stoney equation in the film.The results showed that the fixed end of the wafers limited to some degree the curvature of the wafers along the width direction.For film internal stress measured by wafer curvature method,the wafer profile should be scanned along the length direction and the scan distance should be greater than or equal to half of wafer length.When the length/width ratio of the wafer reached 3：1,the wafer curvature and the calculated stress were basically the same at different positions along the length direction.For film internal stress measured by wafer curvature method,it was recommended that the length/width ratio of wafer should be considered to be greater than or equal to 3：1,and the deformed profile was scanned along the length direction.

Optical Limiting Properties of Two Soluble Polymer/Multi-Walled Carbon Nanotube Composites

Two soluble polymer grafted multi-walled carbon nanotubes （MWNTs）, including poly（N-vinylcarbazole）-MWNTs and poly（methyl methacrylate）-MWNTs, are synthesized. Their nonlinear optical properties and opticaJ limiting （OL） performances are investigated by z-scan method with 527nm nanosecond laser pulses. These grafted MWNTs dissolved in chloroform show much better optical limiting performance than those of MWNTs and C60 in toluene solution. Nonlinear absorption and nonlinear scattering mechanism are taken into consideration for explaining the observed results. The comparison of the experimental results shows that nonlinear absorption is the dominant mechanism for OL performance of these new samples.

Influence on electron energy loss spectroscopy of the niobium-substituted uranium atom:A density functional theory study

We present the electronic structure and electron energy loss spectroscopy (EELS) for uranium, niobium and U3Nb in which uranium is substituted by niobium. Comparing the electronic structures and optical properties for uranium, niobium and U3Nb, we found that when niobium atom replaces uranium atom in the center lattice, density of state (DOS) of U3Nb shifts downward to low energy. Niobium affects DOS for f and d electrons more than that for p and s electrons. U3Nb is similar to uranium for the electronic energy loss spectra.

Micro-Photoluminescence Confocal Mapping of Single V-Grooved GaAs Quantum Wire

We perform the micro-photoluminescence measurement at low temperatures and a scanning optical mapping with high spatial resolution of a single V-grooved GaAs quantum wire modified by the selective ion-implantation and rapid thermally annealing. While the mapping shows the luminescences respectively from the quantum wires and from quantum well areas between quantum wires in general, the micro-photoluminescence at liquid He temperatures reveals a plenty of spectral structures of the PL band for a single quantum wire. The spectral structures are attributed to the inhomogeneity and non-uniformity of both the space structure and compositions of real wires as well as the defects nearby the interface between quantum wire and surrounding quantum well structures. All these make the excitons farther localized in quasi-zero-dimensional quantum potential boxes related to these non-uniformity and/or defects. The results also demonstrate the ability of micro-photoluminescence measurement and mapping for the characterization of both opto-electronic and structural properties of real quantum wires.

Downward uniformity and optical properties of porous silicon layers

Porous silicon （PS） samples were fabricated by pulse current etching using different times. The down-ward uniformity and optical properties of the PS layers have been investigated using reflectance spectroscopy, photo- luminescence spectroscopy, and scanning electron microscopy （SEM）. The relationship between the refractive index and the optical thickness of PS samples and the etching depth has been analyzed in detail. As the etching depth increases, the average refractive index decreases, indicating that the porosity becomes higher, and the formation rate of the optical thickness decreases. Meanwhile, the reflectance spectra exhibit less intense interference oscillations, which mean the uniformity and interface smoothness of the PS layers become worse. In addition, the intensity of PL emission spectra is slightly increased.

Microstructure and mechanical properties of Cr films deposited with different peak powers by high-power impulse magnetron sputtering

For high-power impulse magnetron sputtering(HIPIMS),the peak power applied to the target is of great importance for regulating the ionization degree of the metal target and ion/atom flux ratio.In this work,chromium(Cr)films were deposited on 316-L stainless steel substrates and silicon(100) wafers with different peak powers by HIPIMS.The relationship between peak target power and properties of Cr films was explored in detail.The resulting structure and mechanical properties of deposited Cr films were characterized by X-ray diffraction(XRD),transmission electron microscope(TEM),atomic force microscopy(AFM),indentation hardness and scratch tester.The results indicate that the ionization degree of metal target and ion/atom flux ratio increase with the increase in peak power but without the loss of deposition rate at the same time.At low ionization degree,the deposited Cr film has low compressive residual stress and low hardness but good adhesion strength.When the ionization degree of target metal increases with increasing peak power,Cr film exhibits finer size and smoother surface with improved hardness but decreased adhesion strength.

Realignment of Slanted Fe Nanorods on Silicon Substrates by a Strong Magnetic Field

Slanted Fe nanorods prepared by glancing angle deposition on silicon substrates exhibited easy magnetization along their growth axis. By using a thin gold film on a silicon substrate as a buffer layer, slanted Fe nanorods can be realigned towards the substrate surface normal by a strong magnetic field. After realignment, the Fe nanorods retained the easy magnetization axis along their growth axis. The effects of the realignment by the strong magnetic field on the properties of the slanted Fe nanorods were also investigated. This study provides a possible way to fabricate magnetic nanostructures for perpendicular recording applications.

Computer Simulation of Helium Effects in Plutonium During the Aging Process of Self-Radiation Damage

Due to a radioactive decay Pu is vulnerable to aging.The behavior of He in Pu is the foundation for understanding Pu self-radiation damage aging.Molecular dynamics technique is performed to investigate the behavior of defects,the interaction between He and defects,the processes of initial nucleation and growth of He bubble and the dependence of He bubble on the macroscopical properties of Pu.Modified embedded atom method,Morse pair potential and the Lennard-Jones pair potential are used for describing the interactions of Pu-Pu,Pu-He and He-He,respectively.The main calculated results show that He atoms can combine with vacancies to form Hevacancy cluster(i.e.,the precursor of He bubble)during the process of self-radiation as a result of high binding energy of an interstitial He atom to vacancy;He bubble’s growth can be dominated by the mechanism of punching out of dislocation loop;the swelling induced by He bubble is very small;grain boundaries give rise to an energetically more favorable zone for the interstitial He atom and self-interstitial atom accumulation than for vacancy accumulation;the process of He release can be identified as the formation of release channel induced by the cracking of He bubble and surface structure.