Strain dependence of bonding and hybridization across the metal-insulator transition of VO 2
Not Available
Laverock, J.↗
Engineering topics
Lu, J
Publications and source records attributed to Lu, J.
Soft X-ray Spectroscopic Study of the Ferromagnetic Insulator V0.82Cr0.18O2
The chromium-vanadium oxide system V{sub 1-x}Cr{sub x}O{sub 2} (0.1 < x < 0.2) displays both insulating character in the rutile phase and room-temperature ferromagnetism. A combination of x-ray photoemission spectroscopy, resonant inelastic x-ray scattering, and resonant x-ray emission spectroscopy of the V L{sub 3,2}, O K, and Cr L{sub 3,2} edges was used to study the electronic structure near the Fermi level of V{sub 0.82}Cr{sub 0.12}O{sub 2}. Our results show that the chromium enters as Cr{sup 3+} with the d{sup 3} configuration, resulting in the formation of Cr{sup 3+}-V{sup 5+} ion pairs, in contrast to the simple Cr{sup 4+} substitution expected from the end members VO{sub 2} and CrO{sub 2}. The occupied Cr 3d orbital is located -2 eV below the Fermi level. Comparison with the parent material VO{sub 2} reveals significant changes in the O 2p bandwidth and increased O 2p-V 3d hybridization in V{sub 0.82}Cr{sub 0.12}O{sub 2}, which are attributed to the reduced atomic spacing upon doping. Two energy loss features due to d-d* transitions are observed at 0.95 and 1.75 eV in the V L{sub 3}-edge x-ray scattering spectra and are explained in terms of the splitting of the t{sub 2g}-derived {pi} band.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Increased Stability Toward Oxygen Reduction Products for Lithium-Air Batteries with Oligoether-Functionalized Silane Electrolytes
The successful development of Li-air batteries would significantly increase the possibility of extending the range of electric vehicles. There is much evidence that typical organic carbonate based electrolytes used in lithium ion batteries form lithium carbonates from reaction with oxygen reduction products during discharge in lithium-air cells so more stable electrolytes need to be found. This combined experimental and computational study of an electrolyte based on a tri(ethylene glycol)-substituted trimethylsilane (1NM3) provides evidence that the ethers are more stable toward oxygen reduction discharge species. X-ray photoelectron spectroscopy (XPS) and FTIR experiments show that only lithium oxides and no carbonates are formed when 1NM3 electrolyte is used. In contrast XPS shows that propylene carbonate (PC) in the same cell configuration decomposes to form lithium carbonates during discharge. Density functional calculations of probable decomposition reaction pathways involving solvated oxygen reduction species confirm that oligoether substituted silanes, as well as other ethers, are more stable to the oxygen reduction products than propylene carbonate. These results indicate that the choice of electrolyte plays a key role in the performance of Li-air batteries.
Environmental Molecular Sciences Laboratory↗
Atomic-Scale Structural Evolution and Stability of Supercooled Liquid of a Zr-Based Bulk Metallic Glass
In this Letter, direct experimental evidence is provided for understanding the thermal stability with respect to crystallization in the Zr{sub 41.2}Ti{sub 13.8}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5} glass-forming liquid. Through high-resolution transmission electron microscopy, the atomic-structure evolution in the glass-forming liquid during the isothermal annealing process is clearly revealed. In contrast with the existing theoretical models, our results reveal that, prior to nanocrystallization, there exists a metastable state prone to forming icosahedralike atomic clusters, which impede the subsequent crystallization and hence stabilize the supercooled liquid. The outcome of the current research underpins the topological origin for the excellent thermal stability displayed by the Zr-based bulk metallic glass.
36 MATERIALS SCIENCE↗
Alumina over-coating on Pd nanoparticle catalysts by atomic layer deposition : enhanced stability and reactivity.
ALD Alumina was utilized as a protective layer to inhibit the sintering of supported nano-sized ALD Pd catalysts in the methanol decomposition reaction carried out at elevated temperatures. The protective ALD alumina layers were synthesized on Pd nanoparticles (1-2 nm) supported on high surface area alumina substrates. Up to a certain over-coat thickness, the alumina protective layers preserved or even slightly enhanced the catalytic activity and prevented sintering of the Pd nanoparticles up to 500 C.
10 SYNTHETIC FUELS↗
Ohmic contact properties of magnetron sputtered Ti{sub 3}SiC{sub 2} on n- and p-type 4H-silicon carbide
Epitaxial Ti{sub 3}SiC{sub 2} (0001) thin film contacts were grown on doped 4H-SiC (0001) using magnetron sputtering in an ultra high vacuum system. The specific contact resistance was investigated using linear transmission line measurements. Rapid thermal annealing at 950 deg. C for 1 min of as-deposited films yielded ohmic contacts to n-type SiC with contact resistances in the order of 10{sup -4} {Omega} cm{sup 2}. Transmission electron microscopy shows that the interface between Ti{sub 3}SiC{sub 2} and n-type SiC is atomically sharp with evidence of interfacial ordering after annealing.
36 MATERIALS SCIENCE↗
Origin of ferromagnetism in self-assembled Ga{sub 1-x}Mn{sub x}As quantum dots grown on Si
Self-assembled Ga{sub 1-x}Mn{sub x}As magnetic semiconductor quantum dots have been grown on Si (001) substrates using droplet epitaxy by molecular-beam epitaxy. Structural characterization reveals that these dots possess a zinc-blende lattice. The Ga{sub 1-x}Mn{sub x}As quantum dots with 8% Mn content are ferromagnetically soft and slightly anisotropic at low temperature, and show the superparamagnetic behavior with a blocking temperature of 20 K in the in-plane direction. Moreover, the results of x-ray absorption near edge structure provide direct evidences for the substitutional Mn{sup 2+} ion with a half-filled d{sup 5} configuration for the Ga site, suggesting the hole-mediated ferromagnetism in zero-dimensional Ga{sub 1-x}Mn{sub x}As quantum dots.
36 MATERIALS SCIENCE↗
N. meningitidis 1681 is a member of the FinO family of RNA chaperones.
The conjugative transfer of F-like plasmids between bacteria is regulated by the plasmid-encoded RNA chaperone, FinO, which facilitates sense - antisense RNA interactions to regulate plasmid gene expression. FinO was thought to adopt a unique structure, however many putative homologs have been identified in microbial genomes and are considered members of the FinO-conjugation-repressor superfamily. We were interested in determining whether other members were also able to bind RNA and promote duplex formation, suggesting that this motif does indeed identify a putative RNA chaperone. We determined the crystal structure of the N. meningitidis MC58 protein NMB1681. It revealed striking similarity to FinO, with a conserved fold and a large, positively charged surface that could function in RNA interactions. Using assays developed to study FinO-FinP sRNA interactions, NMB1681, like FinO, bound tightly to FinP RNA stem-loops with short 5-foot and 3-foot single-stranded tails but not to ssRNA. It also was able to catalyze strand exchange between an RNA duplex and a complementary single-strand, and facilitated duplexing between complementary RNA hairpins. Finally, NMB1681 was able to rescue a finO deficiency and repress F plasmid conjugation. This study strongly suggests that NMB1681 is a FinO-like RNA chaperone that likely regulates gene expression through RNA-based mechanisms in N. meningitidis.
59 BASIC BIOLOGICAL SCIENCES↗
Magnetic anisotropies of laterally confined structures of epitaxial Fe films on GaAs (001)
We have investigated magnetic properties of laterally confined structures of epitaxial Fe films on GaAs (001). Fe films with different thicknesses were grown by molecular-beam epitaxy and patterned into regular arrays of rectangles with varying aspect ratios. In-plane magnetic anisotropy was observed in all of the patterned Fe films both at 15 and 300 K. We have demonstrated that the coercive fields can be tuned by varying the aspect ratios of the structures. The magnitudes of the corresponding anisotropy constants have been determined and the shape anisotropy constant is found to be enhanced as the aspect ratio is increased.
36 MATERIALS SCIENCE↗
Laser-induced damage threshold of silicon in millisecond, nanosecond, and picosecond regimes
Millisecond, nanosecond, and picosecond laser pulse induced damage thresholds on single-crystal are investigated in this study. The thresholds of laser-induced damage on silicon are calculated theoretically for three pulse widths based on the thermal damage model. An axisymmetric mathematical model is established for the transient temperature field of the silicon. Experiments are performed to test the damage thresholds of silicon at various pulse widths. The results indicate that the damage thresholds obviously increase with the increasing of laser pulse width. Additionally, the experimental results agree well with theoretical calculations and numerical simulation results.
36 MATERIALS SCIENCE↗
A SIMPLE HETERODYNE TEMPORAL SPECKLE-PATTERN INTERFEROMETER
A common light path design of heterodyne speckle pattern interferometer based on temporal speckle pattern interferometry is proposed for non-contact, full-field and real-time continuous displacement measurement. Double frequency laser is produced by rotating a half wave plate. An experiment was carried out to measure the dynamic displacement of a cantilever plate for testing the proposed common path heterodyne speckle pattern interferometer. The accuracy of displacement measurement was checked by measuring the motion at the mid-point of the plate with a point displacement sensor.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗