Search

In this paper, a microstrip resonator based on double split rings is used to build an electron spin resonance (ESR) measurement system. The resonator is optimized by the finite element electromagnetic simulation and the 3 dB bandwidth is 58.7 MHz. Due to the open structure of the resonator, large-size samples with high dielectric loss can be measured nondestructively. The ESR signal of 2,2-diphenyl-1-picrylhydrazyl (DPPH) powder with different quality is measured at room temperature, and the result indicated that the spin detection limit of this system can reach 9.66 ×1012 spins/Gs Hz1/2. It is demonstrated that the system can be used to characterize films deposited on different substrates such as silicon, glasses or ceramics regardless of its high frequency losses through the measurement of DPPH sample spin-coated on silicon and zerodur. Our system provides a convenient approach to research the defect of thin films and to characterize their performances within microwave frequency.

ABSTRACT: Using sequential RAFT polymerization, single monomer insertion, and “click” chemistry, a series of triblock copolymers, poly(ethylene oxide)‐b‐polystyrene‐b‐poly(ethylene oxide), PEO‐b‐PS‐b‐PEO, were synthesized, where one of the two junction points is a UV cleavable ortho‐nitrobenzyl (ONB). Ordered patterns of PEO‐b‐PS‐b‐PEO were produced by solvent vapor annealing. Upon exposure to ultraviolet (UV) light, the PEO‐b‐PS‐b‐PEO was converted into a mixture of a PEO homopolymer and a PS‐b‐PEO diblock copolymer. It was found that the microdomain spacing could be tuned by adjusting the UV exposure time, due to the change in the copolymer architecture and the swelling of the PEO microdomain by the PEO homopolymer produced. By selective area exposure of the PEO‐b‐PS‐b‐PEO thin films, the domain spacing was changed over selected locations across the film, generating patterns of different microdomain sizes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 355–361. [ABSTRACT FROM AUTHOR]

Abstract: M-type barium ferrite thin films were deposited onto sapphire (00l) substrates by radio frequency magnetron sputtering. Columnar grains were formed on the surface of the films under lower sputter pressure with bubble magnetic domains, which is originated from high magnetocrystalline anisotropy of the film. Magnetic hysteresis loops agree with the change of the morphology, where in-plane and out-of-plane loops are quite different of the samples prepared under high sputtering pressures, while they are almost identical under low pressures. The influence of the sputtering pressure was understood by that with the increase of the pressure, resputtering of the film is hindered. Nucleation with c-axis normal to the film plane was enhanced. Thus samples prepared under low pressure have more acicular crystallites which have c-axis parallel to the film plane. [Copyright &y& Elsevier]

Abstract: Hexagonal barium ferrite thin films were fabricated by spin coating of precursors obtained by sol-gel methods onto sapphire (00l) faces. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used to tune the morphology of the films. The films show texture with c-axis normal to the film plane as shown by the strong x-ray diffractions from the (001) plane with full width at half maximum of the rocking curves about 0.4°. The [100] direction of the film is parallel to the [110] direction of the sapphire. With the increase of the citric acid, the percentage of the acicular crystallites increased. EDTA can be used to produce films with the best texture where faceted grains were obtained. The maximum coercive force obtained was about 302 kA/m. [Copyright &y& Elsevier]