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Chen, Jun

Publications and source records attributed to Chen, Jun.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Large scale and fast synthesis of multiferroic TbMn{sub 2}O{sub 5} single-crystalline nanorods

Graphical abstract: - Highlights: • Pure TbMn{sub 2}O{sub 5} phase was synthesized in a wide temperature range for a short time. • Smooth and uniform single-crystalline nanorods were obtained. • The element Mn in TbMn{sub 2}O{sub 5} exhibits a mix Mn{sup 3+/4+} valence state with an average value of 3.5+, and the element Tb exhibits Tb{sup 3+}. - Abstract: Crystalline multiferroic TbMn{sub 2}O{sub 5} nanorods were successfully synthesized by a facile and scalable molten salt synthesis with NaCl–Na{sub 2}SO{sub 4} eutectic salts used in the temperature range of 750–900 °C for only 2 h. The obtained TbMn{sub 2}O{sub 5} could be indexed to an orthorhombic phase by the results of XRD patterns. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), combined with high-resolution TEM (HRTEM), selected area electron diffraction (SAED), and EDS, have been employed to investigate the morphology, size, crystallinity, structure, and composition of the as-synthesized TbMn{sub 2}O{sub 5} nanorods. The TbMn{sub 2}O{sub 5} product exhibits smooth, uniform and crystalline nanorods with diameters of 30–70 nm, and length of varying from 3 to 6 μm. The results of X-ray photoelectron spectroscopy (XPS) analysis indicate that the elements Mn and Tb in TbMn{sub 2}O{sub 5} exhibit Mn{sup 3+/4+} and Tb{sup 3+}, respectively. The magnetic properties of the as-prepared TbMn{sub 2}O{sub 5} nanorods have been also characterized by physical properties measurement system (PPMS)

36 MATERIALS SCIENCE↗
DOE OSTI2014

Nuclear Data Sheets for A=85

Evaluated experimental data are presented for 13 known nuclides of mass 85 (Zn, Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo). Since the previous 1990 evaluation of A=85, {sup 85}Zn, {sup 85}Ga, {sup 85}Ge and {sup 85}nuclides are newly added here. Excited state data for {sup 85}Se, {sup 85}Zr have become available from radioactive decay and in–beam γ–ray studies. New and improved high–spin data are available for {sup 85}Br, {sup 85}Kr, {sup 85}Rb, {sup 85}Y, {sup 85}Nb and {sup 85}Mo. New direct and precise measurement of atomic masses of {sup 85}Ge, {sup 85}As, {sup 85}Se, {sup 85}Br, {sup 85}Rb, {sup 85}Zr, {sup 85}Nb and {sup 85}Mo have greatly improved the landscape of β decay–Q values and separation energies in this mass region. In spite of extensive experimental work on the isobaric nuclei of this mass chain several deficiencies remain. No excited states are known in {sup 85}Zn, {sup 85}Ga, {sup 85}As. Only a few excited state are assigned in {sup 85}Ge from {sup 85}Ga β– decay. From radioactivity studies, the decay schemes of {sup 85}Zn and {sup 85}Mo are not known, and those for {sup 85}Ga, {sup 85}Ge, {sup 85}As and 10.9–s isomer of {sup 85}Zr are incomplete. Level lifetimes are not known for excited states in {sup 85}Se, {sup 85}Br, {sup 85}Nb and {sup 85}Mo. The {sup 85}Tc nuclide has not been detected in fragmentation experiments at GANIL, alluding to its unbound nature for proton emission. The {sup 85}Kr, {sup 85}Rb, {sup 85}Sr, and {sup 85}Y nuclides remain the most extensively studied from many different reactions and decays. The evaluation of A=85 nuclides has been done after a span of 23 years, thus includes an extensive amount of new data for almost each nuclide. This work supersedes the data for A=85 nuclides presented in earlier full NDS publication by J. Tepel in 1980Te04 and a later one published in an update mode by H. Sievers in 1991Si01.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Quantum and quasi-classical dynamics of the OH + CO → H + CO{sub 2} reaction on a new permutationally invariant neural network potential energy surface

A permutationally invariant global potential energy surface for the HOCO system is reported by fitting a larger number of high-level ab initio points using the newly proposed permutation invariant polynomial-neural network method. The small fitting error (∼5 meV) indicates a faithful representation of the potential energy surface over a large configuration space. Full-dimensional quantum and quasi-classical trajectory studies of the title reaction were performed on this potential energy surface. While the results suggest that the differences between this and an earlier neural network fits are small, discrepancies with state-to-state experimental data remain significant.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

First-principles study on negative thermal expansion of PbTiO{sub 3}

It is well known that perovskite-type PbTiO{sub 3} behaves negative thermal expansion in a wide temperature range from room temperature to Curie temperature (763 K). The present study reports the first-principles study of the anisotropic thermal expansion of PbTiO{sub 3}, in the framework of the density-functional theory and the density-functional perturbation theory. The curve of temperature dependence of the unit cell volume is presented from 20 to 520 K through the calculation of the minimum of total free energy at each temperature point. The negative thermal expansion of PbTiO{sub 3} is calculated without empirical parameters. Furthermore, the distinctive thermodynamic act of PbTiO{sub 3} from expanding to contracting at tetragonal phase is reproduced. The ab-initio calculations reveal that this unique appearance depends on the phonon vibration. The dynamical contributions of various atoms are also calculated to account for the disparate role of Pb-O and Ti-O bond.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Silver nanocrystals of various morphologies deposited on silicon wafer and their applications in ultrasensitive surface-enhanced Raman scattering

Silver nanostructures with dendritic, flower-like and irregular morphologies were controllably deposited on a silicon substrate in an aqueous hydrogen fluoride solution at room temperature. The morphology of the Ag nanostructures changed from dendritic to urchin-like, flowerlike and pinecone-like with increasing the concentration of polyvinyl pyrrolidone (MW = 55,000) from 2 to 10 mM. The Ag nanostructures were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction. Through a series of time-dependent morphological evolution studies, the growth processes of Ag nanostructures have been systematically investigated and the corresponding growth mechanisms have been discussed. In addition, the morphology-dependent surface-enhanced Raman scattering of as-synthesized Ag nanostructures were investigated. The results indicated that flower-like Ag nanostructure had the highest activity than the other Ag nanostructures for Rhodamine 6G probe molecules. Highlights: • A simple method was developed to prepare dendritic and flower-like Ag nanostructures. • The flower-like Ag nanoparticles exhibit highest SERS activity. • The SERS substrate based on flower-like Ag particles can be used to detect melamine.

36 MATERIALS SCIENCE↗
DOE OSTI2013

An extended magnetostatic Born-Infeld model with a concave lower order term

This paper concerns an extended Born-Infeld model with a concave lower order term for the magnetostatic case. Three types of boundary value problems are considered: the boundary condition prescribing the tangential component of A, the natural boundary condition, and the boundary condition prescribing the tangential component of curl A. In each case we obtain existence and regularity of solutions for small boundary data.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Improvement of field emission properties of α-Fe{sub 2}O{sub 3} nanoflakes due to the lowered back contact barrier after high energy X-ray irradiation

Improvement in the field emission properties of α-Fe{sub 2}O{sub 3} nanoflakes is observed after high energy X-ray irradiation from synchrotron radiation. Field emission threshold field of α-Fe{sub 2}O{sub 3} nanoflakes is found to decrease from 10.1 to 7.8 MV/m after X-ray irradiation with the dose of 9.0 × 10{sup 14} phs/cm{sup 2}. Electrical measurement reveals that the potential barrier at the back contact between the α-Fe{sub 2}O{sub 3} layer and the iron substrate changes after X-ray irradiation. The observed threshold field decrease is well explained by the changes in potential barrier at the back contact of α-Fe{sub 2}O{sub 3} nanoflakes, which indicates the back contact plays an important role in controlling the field emission properties of α-Fe{sub 2}O{sub 3} nanoflakes. Our study shows that the α-Fe{sub 2}O{sub 3} nanoflakes are a promising material for the application as field emitter under X-ray environment.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis and characterization of Bi{sub 2}S{sub 3} composite nanoparticles with high X-ray absorption

Graphical abstract: - Highlights: • Uniform Bi{sub 2}S{sub 3} nanorods were prepared via a hot injection method. • Bi{sub 2}S{sub 3} nanorods were coated with TEOS and PEG for surface modification. • CT images of Bi{sub 2}S{sub 3}@SiO{sub 2}-PEG are much higher than clinical iobitridol when they have the same concentration. • Cellular toxicity of Bi{sub 2}S{sub 3}@SiO{sub 2}-PEG is low when the probes were directly in contact with tissue fluid. - Abstract: Owing to the high X-ray absorption, Bi{sub 2}S{sub 3} nanocrystals are widely used as CT contrast agents. Here, we prepared uniform Bi{sub 2}S{sub 3} nanorods via a hot injection method using bismuth (III) chloride, sulfur and oleyl amine. The resulting nanocrystals were coated with tetraethylorthosilicate (TEOS) and 2-[methoxy(polyethyleneoxy)propyl]yrimethoxysilane (PEG-silane) for the biological utility. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that the Bi{sub 2}S{sub 3} nanorods had an orthorhombic structure with the length of 14 nm and the diameter of 7 nm, respectively. Composite nanoparticles (0.0226 M) gave a CT number at 550 (HU), which was higher than that of the commercial available iobitridol CT contrast agent. Furthermore, cell experiments revealed that Bi{sub 2}S{sub 3} composite nanoparticles had a low cytotoxicity with a concentration up to 0.01 M of Bi for 24 h.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Growth and ferroelectric properties of sol–gel derived Bi(Mg 1/2 Zr 1/2 )O 3 –PbTiO 3 thin films

The electrical properties included temperature-dependent polarization of (1-x)Bi(Mg 1/2 Zr 1/2 )O 3 –xPbTiO 3 (BMZ–xPT) new ferroelectric films were investigated. The films with 220 nm thickness grown on Pt(111)/Ti/SiO 2 /Si substrates via sol–gel method were well crystallized with a phase-pure perovskite structure and homogeneous microstructure. Saturated polarization hysteresis loops are observed for all BMZ–xPT compounds, and BMZ–0.85PT films with high (100) orientation show a small leakage and remanent polarization of 36.1 μC cm -2 , which is comparable to the (100)-oriented BiScO 3 –PbTiO 3 thin films. The present films have high dielectric constants about 544-833. Furthermore, the polarization with elevated temperature slightly decreases, exhibiting stable ferroelectric properties and potentials for memory applications above room temperature such as non-volatile ferroelectric random access memories.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Temperature dependences of the ferroelectric and dielectric properties of high curie temperature PbTiO{sub 3}–BiScO{sub 3}–Bi(Zn{sub 1/2}Zr{sub 1/2})O{sub 3}

Highlights: ► Ceramics exhibit enhanced ferroelectric properties with the increase of temperature. ► A strong second harmonic generation effect was observed. ► Transmission electron microscopy results confirm the existence of MPB. - Abstract: The piezoelectric ceramics (1 − x − y)PbTiO{sub 3}–xBiScO{sub 3}–yBi(Zn{sub 1/2}Zr{sub 1/2})O{sub 3} exhibit greatly enhanced ferroelectric properties above room temperature, between 100 and 200 °C. A strong second harmonic generation (SHG) effect was observed below 200 °C. The highest remanent polarization (∼40 μC/cm{sup 2}) and lowest coercive field (∼10 kV/cm) were obtained at 200 °C. X-ray diffraction (XRD) analysis was used to investigate the morphotropic phase boundary (MPB) structure of (1 − x − y)PbTiO{sub 3}–xBiScO{sub 3}–yBi(Zn{sub 1/2}Zr{sub 1/2})O{sub 3} ceramics. Transmission electron microscopy (TEM) results confirm the existence of MPB, where the rhombohedral and tetragonal phases coexist. The results of thermal expansion analysis show a low thermal expansion and stability of this material. The optimal high temperature piezoelectric ceramic is obtained by the composition of 0.05BZZ–0.34BS–0.61PT.

36 MATERIALS SCIENCE↗